Responses to all questions in the Reading Essentials for Biology textbook.

Chapter 1: The Study of Life

Section 1.1: What is Biology?

Before You Read

Topics I think I will learn about as I study biology:

In biology, I expect to learn about living things, including plants, animals, humans, cells, genes, ecosystems, diseases, and how organisms grow, survive, and interact with their environments.

Reading Check

1. What is biology?

Biology is the study of life. It is the science that studies living things and how they interact with each other and with their environment.

2. What is a species?

A species is a group of organisms that share similar characteristics and can reproduce with one another to produce offspring.

3. Name three or more things that make up the environment.

The environment includes things such as water, air, temperature, soil, sunlight, plants, animals, and other organisms.

Think It Over

4. Some trees drop their leaves in the fall in response to which choice?

Correct choice: b. lower temperatures

Some trees drop their leaves in the fall because lower temperatures and seasonal changes act as signals that winter is coming.

After You Read

1. Write a sentence for each word: adaptation, evolution, and homeostasis.

Adaptation: An adaptation is a trait or behavior that helps an organism survive in its environment.

Evolution: Evolution is the gradual change in a species over time.

Homeostasis: Homeostasis is the ability of an organism to keep its internal conditions stable, even when the outside environment changes.

2. List four characteristics biologists use to recognize living things.

1. Living things are organized.

2. Living things reproduce.

3. Living things grow and develop.

4. Living things respond and adapt to their environment.

3. Give two examples of ways in which humans depend on other living things.

Humans depend on plants and animals for food. Humans also depend on plants for oxygen, wood, cotton, and some medicines.

Section 1.2: The Methods of Biology

Before You Read

Question I might test with an experiment:

Do plants grow taller when they are given fertilizer?

Reading Check

1. What is a hypothesis?

A hypothesis is a possible explanation or answer to a scientific question that can be tested.

2. What are the two groups in a controlled experiment?

The two groups in a controlled experiment are the control group and the experimental group.

3. Who is responsible for making sure that safety procedures are followed when conducting an experiment?

The scientist or person conducting the experiment is responsible for following safety procedures and making sure the experiment is done safely.

After You Read

1. Write a sentence using at least two Mini Glossary terms.

A scientist may form a hypothesis and then conduct an experiment to test whether the hypothesis is supported by the data.

2. Arrange the steps used in scientific research in the order they usually take place.

1. c. Observe and identify a problem to solve

2. b. Form a hypothesis

3. a. Conduct experiments

4. d. Study results data to see if hypothesis is supported

3. Choose one question heading and answer it.

Question: What is a controlled experiment?

Answer: A controlled experiment is an experiment that compares a control group with an experimental group. The control group is used as the standard for comparison, while the experimental group receives the factor being tested.

Section 1.3: The Nature of Biology

Before You Read

Examples of important discoveries in biology:

Important discoveries in biology include the discovery of cells, DNA, vaccines, antibiotics, heredity, and how diseases spread. These discoveries help scientists understand living things and improve human health.

Reading Check

1. What are the two main types of scientific research?

The two main types of scientific research are quantitative research and qualitative research.

After You Read

1. Write the definitions of both terms in your own words.

Ethics: Ethics are rules or values that help people decide what is right and wrong.

Technology: Technology is the use of scientific knowledge to create tools, machines, or methods that help solve problems.

2. Fill in the outline about scientific research.

I. Scientific Research

A. Quantitative Research

1. What is it? Research that uses numbers, measurements, and data that can be counted.

2. Give an example: Measuring the temperature at which ice melts or recording how tall plants grow each day.

B. Qualitative Research

1. What is it? Research that uses descriptions or observations instead of numbers.

2. Give an example: Describing the color, shape, or behavior of an organism.

3. Give an example of how technology has helped human life and the world around us.

Technology has helped human life by allowing scientists and doctors to create medical tools, vaccines, and treatments for disease. It has also helped the world by improving farming, reducing pollution, and allowing scientists to study the environment more carefully.

Chapter 2: Principles of Ecology

Section 2.1: Organisms and Their Environment

Before You Read

Organisms I come into contact with during a typical week:

I come into contact with humans, pets, insects, birds, trees, grass, flowers, bacteria, fungi, and many tiny organisms that cannot be seen without a microscope.

Think It Over

1. What animals share your world?

Animals that share my world include pets such as dogs and cats, insects such as ants and flies, birds, squirrels, fish, and other animals that live near homes, parks, or schools.

Reading Check

2. What do ecologists study?

Ecologists study the relationships between organisms and their environment.

3. What is the biosphere?

The biosphere is the part of Earth that supports living things. It includes the air, land, and water where organisms can be found.

4. Name four examples of abiotic factors.

Four examples of abiotic factors are:

1. Temperature

2. Moisture

3. Light

4. Soil

5. What is an ecosystem made of?

An ecosystem is made of all the different populations in a biological community and the abiotic factors in the community’s physical surroundings.

6. What is a habitat?

A habitat is the place where an organism lives out its life.

Think It Over

7. Which of the following does a polar bear use to survive in its habitat?

Correct choice: b. thick coat to protect it from the cold

A polar bear’s thick coat is an adaptation that helps it survive in a cold environment.

Reading Check

8. What is the name of the relationship in which both species benefit?

The relationship in which both species benefit is called mutualism.

After You Read

1. Circle the three terms that identify specific types of relationships between organisms that live in the same ecosystem. Give an example of each.

The three terms are:

Mutualism: Both organisms benefit.
Example: Ants and an acacia tree. The ants get food and shelter, and the tree is protected by the ants.

Commensalism: One organism benefits, and the other is not helped or harmed.
Example: Moss growing on a tree. The moss gets a place to live, but the tree is not affected.

Parasitism: One organism benefits while the other is harmed.
Example: A tick living on a dog. The tick gets food, but the dog may be harmed.

2. List the four levels that ecologists have organized the living world into, from least complex to most complex.

1. Organism

2. Population

3. Community

4. Ecosystem

3. Match each new concept with the correct example.

1. abiotic factor — c. rain

2. habitat — b. a rain forest

3. predator-prey relationship — a. an owl eating a mouse

4. biological community — e. millipedes, centipedes, insects, slugs, and earthworms under a log

5. parasitism — d. a tick on a cat

Section 2.2: Nutrition and Energy Flow

Before You Read

How might a pet’s food be different if it had to live in the wild and get its own food?

A pet living in the wild would have to find or catch its own food instead of being fed by humans. For example, a pet dog or cat might hunt small animals, eat plants, or search for leftovers instead of eating prepared pet food.

Reading Check

1. What do decomposers do?

Decomposers break down the complex compounds of dead and decaying plants and animals. They change these materials into simpler forms that can be used again.

Think It Over

2. When energy is transferred between trophic levels, what is always given off to the environment?

Correct choice: b. heat

At each energy transfer, some energy is given off to the environment as heat.

Reading Check

3. What type of organisms appear at the bottom of the ecological pyramid?

Autotrophs, or producers, appear at the bottom of the ecological pyramid.

4. What is biomass?

Biomass is the total mass or weight of living matter in a given area or at each trophic level.

5. What type of organisms change nitrogen in the air into a form plants can better use?

Bacteria change nitrogen from the air into a form that plants can better use.

After You Read

1. Define autotrophs and heterotrophs in your own words. Give an example of each.

Autotrophs are organisms that make their own food using energy from the sun or from chemical compounds.
Example: grass, trees, algae, or other green plants.

Heterotrophs are organisms that cannot make their own food, so they must eat other organisms for energy and nutrients.
Example: rabbits, wolves, bears, humans, or fungi.

2. Food chain table: Grass → Rabbit → Wolf

Grass

• Performs photosynthesis

• Autotroph

• On lowest trophic level

Rabbit

• Heterotroph

• Eats autotrophs

• Provides energy for other heterotrophs

Wolf

• Heterotroph

• Eats other heterotrophs

• On highest trophic level

3. Mark each statement T for true or F for false.

a. Although 78 percent of air is nitrogen, plants cannot use this form well.
T

b. Heterotrophs can get the energy they need directly from the sun.
F

c. During part of its cycle, phosphorus falls back to Earth as rain, ice, or snow.
F

d. All life on Earth is based on carbon.
T

Chapter 3: Communities and Biomes

Section 3.1: Communities

Before You Read

Plants and animals in my community:

In my community, I might see grass, trees, flowers, weeds, birds, squirrels, insects, worms, dogs, cats, and bacteria. An organism that might have trouble surviving where I live is a polar bear, because it needs a very cold habitat with ice and snow.

Reading Check

1. Anything that limits an organism’s ability to live in an environment is called a ________.

Anything that limits an organism’s ability to live in an environment is called a limiting factor.

2. What is succession?

Succession is the gradual, natural change and replacement of species in the communities of an ecosystem over time.

Think It Over

3. After a flood destroys everything growing on the land, which type of succession is most likely?

Correct choice: b. secondary

Secondary succession is most likely because the land already had life before the flood, and soil is usually still present after the disturbance.

After You Read

1. Highlight the three terms that deal with changes in an ecosystem. Then circle the term that refers to a situation in which there are few or no changes.

The three terms that deal with changes in an ecosystem are:

1. Primary succession

2. Secondary succession

3. Succession

The term that refers to a situation with few or no changes is:

Climax community

2. Fill in the flowchart about what takes place after a volcanic eruption.

Volcanic eruption occurs → Lava cools and new land forms → Pioneer species begin to live on the new land

A good answer for the blank box is:

Pioneer species, such as lichens, begin to grow on the new land.

3. Match each concept with the correct example.

1. limiting factors — d. cold temperatures and high winds that prevent tree growth in mountain areas

2. pioneer species — a. the first organisms to grow on a new patch of cooled, hardened lava

3. tolerance — c. ability of mosquitoes to survive in very different conditions all over the world

4. climax community — e. an old forest that has not had any fire damage in over 200 years

5. secondary succession — b. weeds and wildflowers beginning to grow in a field after a corn crop is harvested

Section 3.2: Biomes

Before You Read

Important idea about biomes:

Different biomes have different climates, plants, animals, and conditions for survival. For example, deserts are dry and have little plant life, while rain forests are warm, wet, and full of many different organisms.

Reading Check

1. What is an estuary?

An estuary is a coastal body of water that is partly surrounded by land and forms where a river meets the ocean. In an estuary, freshwater and salt water mix.

2. Why are plankton important?

Plankton are important because they form the base of the entire aquatic food chain. Many aquatic animals either eat plankton or eat animals that depend on plankton.

3. What five abiotic factors does climate include?

Climate includes these five abiotic factors:

1. Wind

2. Cloud cover

3. Temperature

4. Humidity

5. Amount of rain and snow

Think It Over

4. Because of the many types of grains that can grow in these areas, they are called the breadbaskets of the world.

Correct choice: b. grasslands

Grasslands are called the breadbaskets of the world because many grains grow well there.

Reading Check

5. What are the two types of rain forests?

The two types of rain forests are:

1. Temperate rain forests

2. Tropical rain forests

After You Read

1. Use one Mini Glossary term that describes a biome in a complete sentence.

The desert is the driest biome and has little rainfall, so plants and animals there must be adapted to conserve water.

2. Fill in the blanks with the words: desert, tundra, plankton, photic zone, rain forest.

a. The rain forest biome is home to more types of life than any other biome.

b. The tundra is so cold that very little life exists there.

c. The driest biome is the desert biome.

d. The part of the marine biome that is shallow enough for sunlight to penetrate is called the photic zone.

e. The base of the entire marine biome food chain is formed by plankton.

Chapter 4: Population Biology

Section 4.1: Population Dynamics

Before You Read

What populations of living things can you observe where you live? Have those populations ever increased or decreased? Why?

Near where I live, I might observe populations of people, birds, insects, squirrels, grass, trees, flowers, and bacteria. These populations can increase or decrease depending on food, space, weather, disease, predators, and human activity. For example, insects may increase in warm weather when there is more food, but decrease during cold weather or after pesticide use.

Reading Check

1. What limits a population’s growth?

A population’s growth is limited by limiting factors. These can include food, space, disease, predators, parasites, competition, temperature, storms, floods, drought, chemical pesticides, and habitat disruption.

Think It Over

2. What type of body size do rapid life-history organisms have?

Correct choice: a. small

Rapid life-history organisms usually have a small body size, a short life span, reproduce early, and produce many offspring in a short time.

Reading Check

3. Name five density-dependent factors.

Five density-dependent factors are:

1. Disease

2. Competition

3. Predators

4. Parasites

5. Food availability

Think It Over

4. An example of a density-independent factor is:

Correct choice: a. a frost that destroys tomato plants

A frost affects a population no matter how many organisms are in the population. A fungus spreading from plant to plant is density-dependent because it spreads more easily when organisms are close together.

Reading Check

5. Why did the brown tree snake population on Guam increase unchecked?

The brown tree snake population on Guam increased unchecked because the snakes had no natural predators on the island. Without predators to limit them, their population grew rapidly and greatly reduced bird populations.

After You Read

1. Choose a Mini Glossary term and write a sentence describing how it relates to population dynamics.

Carrying capacity relates to population dynamics because it is the maximum number of organisms an environment can support for a long time.

2. Write two examples of each factor that affects population growth.

Life-History Patterns

1. Rapid life-history pattern

2. Slow life-history pattern

Density-Dependent Factors

1. Disease

2. Competition

Density-Independent Factors

1. Drought

2. Floods

Section 4.2: Human Population

Before You Read

What words come to mind when you hear the term human population? Do population concepts apply to humans?

When I hear the term human population, I think of people living in cities, countries, and the world. I also think of birthrate, death rate, population growth, resources, food, water, space, and health care. Population concepts do apply to humans because human populations can increase, decrease, move, and be affected by resources and the environment.

Reading Check

1. How are humans different from other populations?

Humans are different from other populations because they can consciously change their environment. Humans can grow resources by farming and raising animals, and they can use medicine to control some diseases.

Think It Over

2. If the population growth rate is positive, it means there are:

Correct choice: a. more births than deaths

A positive growth rate means the population is growing. This happens when the birthrate is greater than the death rate.

Think It Over

3. In the age structure graph, which country has the smallest percentage of people in the 80+ age group?

Correct choice: b. rapid growth country

The rapid growth country has a wide base with many young people and a very narrow top, meaning it has the smallest percentage of people in the oldest age groups.

After You Read

1. Circle the four key terms that scientists use to gather important information about a population.

The four key terms are:

1. Age structure

2. Birthrate

3. Death rate

4. Demography

2. Place each characteristic under the correct heading.

Increasing Population

• Positive growth rate

• More children than adults

• Will have doubling time

Decreasing Population

• Negative growth rate

• More adults than children

• Will not have doubling time**

Chapter 5: Biological Diversity and Conservation

Section 5.1: Vanishing Species

Before You Read

Name one animal and one plant that would change the way you live if they became extinct. Explain why each is important.

One animal that would change the way people live if it became extinct is the honeybee. Honeybees help pollinate many plants, including crops people eat. Without bees, many fruits, vegetables, and nuts would be harder to grow.

One plant that would change the way people live if it became extinct is corn. Corn is used as food for people and animals, and it is also used in many products. Losing corn would affect food supplies and farming.

Reading Check

1. Where is the most biodiversity found?

The most biodiversity is found in warm, tropical places near the equator. Examples include rain forests, coral reefs, and tropical lakes.

2. What does it mean to say that all living things are interdependent?

It means that all living things depend on other living things to survive. For example, animals may depend on plants for food, and some plants depend on animals to move pollen from one flower to another.

3. What is habitat fragmentation?

Habitat fragmentation is the separation of wilderness areas from other wilderness areas. It happens when large habitats are divided into smaller, disconnected pieces, such as when roads, farms, or buildings split a forest.

Think It Over

4. Which diagram demonstrates habitat fragmentation?

Correct choice: a.

Diagram a shows two populations separated by a barrier, which represents habitat fragmentation. The populations are cut off from each other and may no longer be able to interact or breed.

Reading Check

5. Why do more ultraviolet waves reach Earth today?

More ultraviolet waves reach Earth today because pollution has damaged the ozone layer. The ozone layer normally absorbs some ultraviolet waves before they reach Earth.

Think It Over

6. Which of the following does not threaten biodiversity?

Correct choice: b. rain forests

Rain forests do not threaten biodiversity. They usually have high biodiversity. Acid rain and exotic species can threaten biodiversity.

After You Read

1. Circle the terms that refer to things that pose a threat to the biodiversity of an area.

The terms that refer to threats to biodiversity are:

1. Acid precipitation

2. Habitat degradation

3. Habitat fragmentation

4. Exotic species

2. Fill in the outline.

I. Biological Diversity

A. What is it?
Biological diversity, or biodiversity, is the variety of species in a particular area.

B. How is it measured?
It is commonly measured by counting the number of different species in a certain area.

C. Where is the highest biodiversity?
The highest biodiversity is found in warm, tropical places near the equator, such as rain forests, coral reefs, and tropical lakes.

II. Importance of Biodiversity

A. What is true of all living things?
All living things are interdependent, meaning they depend on other living things to survive.

B. What can biodiversity bring to an ecosystem?
Biodiversity can bring stability to an ecosystem.

C. What benefit might preserving biodiversity bring humans in the future?
Preserving biodiversity may help humans by keeping a supply of living things that could provide food, resources, and possible medicines, such as future drugs to treat diseases.

III. Loss of Biodiversity

A. Extinction can occur.
B. Species can become endangered or threatened.

IV. Threats to Biodiversity

A. Habitat fragmentation
B. Habitat degradation

3. Match each new concept with the correct example.

1. habitat fragmentation — d. a road splitting a forest in half

2. biodiversity — a. all the species in an area of rain forest

3. extinct species — e. triceratops dinosaurs

4. land pollution — b. DDT

5. habitat degradation — c. acid precipitation

Section 5.2: Conservation of Biodiversity

Before You Read

List things you do to keep a favorite plant or animal safe and healthy.

To keep a favorite plant or animal safe and healthy, I would provide clean water, enough food, shelter, space, and protection from harm. I would also keep its habitat clean and avoid using harmful chemicals nearby.

Reading Check

1. What is conservation biology?

Conservation biology is the study and carrying out of ways to protect biodiversity. It develops ways to conserve species and natural resources.

2. What are reintroduction programs?

Reintroduction programs take members of an endangered species, breed and raise them in protected habitats, and then release them back into the area where they would naturally live.

After You Read

1. Use one Mini Glossary term in a sentence that supports conservation efforts in your community.

Habitat corridors can support conservation efforts in my community by giving animals safe paths to move between natural areas.

2. Fill in the conservation biology diagram.

Top two boxes: Methods used to protect natural resources

Endangered and Threatened Species
Laws can protect endangered and threatened species so their numbers do not continue to decrease.

Habitats
Habitats can be protected through natural preserves and national parks so species have safe places to live.

Bottom three boxes: What the methods attempt to accomplish

Habitat Corridors
Habitat corridors connect separated wilderness areas so plants and animals can move between habitats and reproduce.

Sustainable Use
Sustainable use allows people to use natural resources in ways that benefit people while still maintaining the ecosystem.

Reintroduction Programs
Reintroduction programs help save endangered species by raising them in protected areas and returning them to their natural habitats.

Chapter 6: The Chemistry of Life

Section 6.1: Atoms and Their Interactions

Before You Read

What do living and nonliving things have in common?

Living and nonliving things are both made of matter. Matter is made of atoms and elements, so both living things, such as plants and animals, and nonliving things, such as rocks and water, are made from the same basic building blocks.

Reading Check

1. What is an element?

An element is a substance that cannot be broken down into simpler chemical substances.

2. What are the two types of charged particles in an atom?

The two charged particles in an atom are:

1. Protons, which have a positive charge

2. Electrons, which have a negative charge

3. What is a compound?

A compound is a substance made of atoms of two or more elements that are chemically combined.

4. What is a group of atoms held together by covalent bonds called?

A group of atoms held together by covalent bonds is called a molecule.

Think It Over

5. What does a covalent bond do that an ionic bond does not?

Correct choice: a. shares electrons

A covalent bond forms when atoms share electrons. An ionic bond forms when electrons are gained or lost, creating charged ions that attract each other.

Reading Check

6. What is metabolism?

Metabolism is all of the chemical reactions that occur within an organism.

7. What is the difference between reactants and products?

Reactants are the substances that are present before a chemical reaction takes place. Products are the substances that are formed as a result of the chemical reaction.

Think It Over

8. Pouring milk over cereal creates a solution.

Correct choice: b. False

Pouring milk over cereal creates a mixture, not a solution. The cereal and milk are together, but the cereal does not dissolve evenly throughout the milk.

Reading Check

9. What is the pH of a neutral substance?

A neutral substance has a pH of 7.

After You Read

1. Choose two related Mini Glossary terms and explain how they are related.

Term 1: acid
Term 2: pH

These terms are related because pH measures how acidic or basic a solution is. An acid has a pH below 7 and forms hydrogen ions in water.

2. Match each term in Column A to the best explanation in Column B.

1. compound — j. table salt

2. element — i. gold

3. covalent bond — e. what holds hydrogen and oxygen together in a water molecule

4. chemical reactions — b. an organism’s metabolism

5. mixture — g. sugar and sand stirred in a bowl

6. solution — f. drink mix dissolved in water

7. acid — d. forms hydrogen ions in water

8. neutral — a. substance with a pH of 7

9. base — c. forms hydroxide ions in water

10. ionic bond — h. what holds sodium and chloride together in table salt

Section 6.2: Water and Diffusion

Before You Read

How is water important in your life?

Water is important because I need it to drink, stay healthy, digest food, remove wastes, and keep my body temperature stable. I also use water for washing, cooking, growing plants, and many daily activities.

Reading Check

1. What allows water to dissolve salt and sugar?

Water can dissolve salt and sugar because it is a polar molecule. Its positive and negative ends attract ions and other polar molecules.

Think It Over

2. Which will diffuse more quickly?

Correct choice: b. concentrated orange juice in warm water

Diffusion happens faster in warm water because higher temperature makes particles move more quickly.

Reading Check

3. Why do cells use diffusion?

Cells use diffusion to move substances into and out of the cell. Diffusion helps materials move from areas of higher concentration to areas of lower concentration.

After You Read

1. Select one term and define it in your own words.

Term: diffusion

Definition in my own words: Diffusion is the movement of particles from an area where there are more particles to an area where there are fewer particles.

2. Complete the sentences about water and diffusion.

a. Water is a polar molecule.

b. Water can creep up thin tubes in plants.

c. Water resists temperature changes.

d. Water expands when it freezes.

e. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

f. The three factors that affect the rate of diffusion are concentration, temperature, and pressure.

g. Diffusion allows cells to move substances in and out of the cell.

Section 6.3: Life Substances

Before You Read

What substances do you think make up your body?

My body is made of water, proteins, fats, carbohydrates, minerals, vitamins, DNA, RNA, and many other molecules. These substances help build cells, store energy, carry information, and keep my body working.

Reading Check

1. What three elements are carbohydrates made of?

Carbohydrates are made of:

1. Carbon

2. Hydrogen

3. Oxygen

Think It Over

2. DNA is an example of a:

Correct choice: d. all of the above

DNA is a nucleic acid, a biomolecule, and a carbon compound.

After You Read

1. Choose two related Mini Glossary terms and explain how they are related.

Term 1: nucleic acid
Term 2: nucleotides

These terms are related because nucleic acids, such as DNA and RNA, are made of smaller units called nucleotides. Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base.

2. Complete the biomolecules diagram.

I. Biomolecules

A. Carbohydrates
B. Lipids
C. Proteins
D. Nucleic acids

Under Nucleic acids:

1. DNA

2. RNA

Chapter 7: A View of the Cell

Section 7.1. The Discovery of Cells

Reading Check

1. What are the three main ideas of cell theory?

The three main ideas of cell theory are:

1. All living things are made of one or more cells.

2. Cells are the basic units of structure and function in living things.

3. All cells come from other cells.

Think It Over

2. Compare: Which cells are more complex?

Eukaryotic cells are more complex than prokaryotic cells.

Eukaryotic cells have a nucleus and membrane-bound organelles, which allow different cell activities to happen in separate parts of the cell. Prokaryotic cells do not have a nucleus or membrane-bound organelles, so they are simpler.

Reading Check

3. What does a nucleus do?

The nucleus controls the cell’s activities and contains the cell’s DNA.

After You Read

1. Circle two terms from the Mini Glossary above that are related to each other. On the lines below, tell how these terms are related.

Two related terms are nucleus and eukaryote.

These terms are related because eukaryotic cells have a nucleus. The nucleus controls the cell’s activities and contains DNA.

2. Use the Venn diagram below to help you review what you have read. List what makes prokaryotic and eukaryotic cells different. Then list their common characteristics in the middle.

Prokaryotic Cells

• Do not have a nucleus

• Do not have membrane-bound organelles

• Usually unicellular

• Bacteria are examples

• DNA is not inside a nucleus

Both Types of Cells

• Are cells

• Have DNA

• Have cell membranes

• Carry out life processes

• Are basic units of living things

Eukaryotic Cells

• Have a nucleus

• Have membrane-bound organelles

• Can be unicellular or multicellular

• Plants, animals, fungi, and many protists are examples

• More complex than prokaryotic cells

3. Write the three main ideas of the cell theory in the spaces below.

The Cell Theory

1. All living things are made of one or more cells.

2. Cells are the basic units of structure and function in living things.

3. All cells come from other cells.

Section 7.2. The Plasma Membrane

Reading Check

1. What is the function of the plasma membrane?

The plasma membrane separates the cell from its surroundings. It helps maintain homeostasis by controlling what enters and leaves the cell.

Think It Over

2. Which part of a phospholipid molecule contains the phosphate group? Which is nonpolar?

The head of a phospholipid contains the phosphate group and is polar.

The tails are made of fatty acid chains and are nonpolar.

For the Think It Over question, the worksheet asks:

“Which part of a phospholipid molecule contains the phosphate group? Which is nonpolar?”

A phospholipid has two main parts: a head and two tails.

The head contains the phosphate group. Because of the phosphate group, the head is polar, which means it has an uneven electrical charge. Polar molecules are attracted to water, so the head is also called hydrophilic, meaning “water-loving.”

The tails are made of fatty acid chains. These tails are nonpolar, meaning they do not have charged ends. Because they are nonpolar, they avoid water and are called hydrophobic, meaning “water-fearing.”

This difference is very important in the plasma membrane. Since cells are surrounded by watery fluid, the polar heads face outward toward the water, while the nonpolar tails point inward away from the water. This arrangement forms the phospholipid bilayer, which is the basic structure of the plasma membrane.

So the answer is:

The phosphate group is in the head of the phospholipid. The fatty acid tails are nonpolar.

Reading Check

3. Name three elements that float in the plasma membrane.

Three things that float in the plasma membrane are:

1. Phospholipids

2. Proteins

3. Cholesterol

After You Read

1. Choose one key term from the Mini Glossary. Then write the definition in your own words.

Key term: selective permeability

Definition in my own words: Selective permeability means that the plasma membrane allows some substances to pass through, but blocks others. This helps the cell keep the right balance inside.

2. Fill in the missing information in the outline.

I. Parts of a phospholipid molecule

A. 2 fatty acids
B. 1 glycerol
C. 1 phosphate group

II. Fluid mosaic model of plasma membrane

A. Called fluid because the phospholipids and proteins can move around within the membrane.
B. Called mosaic because the surface has a pattern made by different molecules, such as proteins, floating among the phospholipids.

3. Choose one heading from the Read to Learn section. Turn the heading into a question. Then write your answer.

Question: How does the plasma membrane help maintain a balance?

Answer: The plasma membrane helps maintain balance by using selective permeability. It lets some molecules enter or leave the cell, keeps some substances out, and allows others through only at certain times or in limited amounts. This helps the cell maintain homeostasis.

Section 7.3. Eukaryotic Cell Structure

Reading Check

1. Which organelle in the nucleus makes ribosomes?

The nucleolus makes ribosomes inside the nucleus.

2. What are the two types of endoplasmic reticulum?

The two types of endoplasmic reticulum are:

1. Rough endoplasmic reticulum

2. Smooth endoplasmic reticulum

The rough ER has ribosomes attached to it, while the smooth ER does not.

3. What do chloroplasts do?

Chloroplasts capture light energy from the sun and change it into chemical energy. They are found in green plants and some protists. Chloroplasts also contain chlorophyll, the green pigment that gives plants their color.

4. What is the job of microtubules and microfilaments?

Microtubules and microfilaments are parts of the cytoskeleton. They support the cell’s organelles, help materials move around inside the cell, and help the cell keep or change its shape.

After You Read

1. Highlight the name of an organelle that is found in plants but not animals. Then explain what the organelle does.

Organelle: chloroplast

What it does: Chloroplasts are found in plants but not animals. They capture light energy from the sun and convert it into chemical energy that the plant can use. They also contain chlorophyll, which gives plants their green color.

2. Choose two structures that work closely together in the cell. Describe what they do and how they work together.

Two structures that work closely together are the nucleus and ribosomes.

The nucleus contains DNA, which gives directions for making proteins. Ribosomes use those directions to build proteins. The nucleolus inside the nucleus makes ribosomes, and then the ribosomes move into the cytoplasm, where they help make proteins for the cell.

Chlorophyll is not a cell structure or organelle. It is a green pigment, which means it is a molecule that gives plants their green color.

The chloroplast is the structure/organelle. Chlorophyll is found inside chloroplasts and helps trap light energy so the plant can make food through photosynthesis.

So:

Structure/organelle: chloroplast
Substance/pigment inside it: chlorophyll

Chapter 8: Cellular Transport and the Cell Cycle

Section 8.1. Cellular Transport

Reading Check

1. What is the term for the flow of water across the plasma membrane?

The flow of water across the plasma membrane is called osmosis.

2. What is the movement called when a cell does not use energy to move particles across the cell’s membrane?

When a cell does not use energy to move particles across the cell’s membrane, the movement is called passive transport.

After You Read

1. Highlight two terms in the Mini Glossary that identify specific types of active transport.

Two specific types of active transport are:

1. Endocytosis

2. Exocytosis

2. Venn Diagram: Facilitated Diffusion and Active Transport

Characteristics of Facilitated Diffusion

• Does not require energy from the cell

• Is a type of passive transport

• Uses transport proteins to help particles move across the membrane

• Moves particles from higher concentration to lower concentration

• Moves particles with the concentration gradient

Characteristics of Both

• Move materials across the plasma membrane

• Help the cell maintain homeostasis

• May involve proteins in the plasma membrane

• Help control what enters or leaves the cell

Characteristics of Active Transport

• Requires energy from the cell

• Moves particles against the concentration gradient

• Moves particles from lower concentration to higher concentration

• Uses carrier proteins for many substances

• Includes processes such as endocytosis and exocytosis

3. Choose one main heading and turn it into a question. Then answer it.

Question: How does osmosis affect cells?

Answer: Osmosis affects cells by causing water to move into or out of them. In an isotonic solution, water moves in and out at the same rate, so the cell keeps its normal shape. In a hypotonic solution, more water enters the cell than leaves, causing the cell to swell. In a hypertonic solution, water leaves the cell, causing it to shrink.

Section 8.2. The Cell Growth and Reproduction

Reading Check

1. What structures appear in the nucleus shortly before cell division?

Short, stringy structures called chromosomes appear in the nucleus shortly before cell division.

2. What do tissues organize to form?

Tissues organize together to form organs.

After You Read

1. Circle the terms from the Mini Glossary that identify the phases of mitosis. Then list them in the order they occur.

The four phases of mitosis, in order, are:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

2. Cell Cycle Diagram: Give two facts for each period.

Interphase

1. The cell grows in size, carries on metabolism, and performs normal cell activities.

2. The cell duplicates its chromosomes and prepares for division.

Mitosis

1. The nucleus divides to form two daughter nuclei.

2. The duplicated chromosomes separate so each daughter cell receives a complete set of chromosomes.

3. Fill in the blanks with the following terms: tissues, sister chromatids, cell cycle, mitosis, and chromosomes.

a. Two identical halves of a duplicated parent chromosome are called sister chromatids.

b. The process of cell division is called mitosis.

c. Chromosomes are the carriers of genetic material that is copied and passed from generation to generation.

d. The cell cycle is the period of growth and division of a cell.

e. Tissues are groups of cells that work together to perform specific functions.

Section 8.3. Control of the Cell Cycle

Reading Check

1. What occurs when uncontrolled cell division takes place?

When uncontrolled cell division takes place, cancer occurs. Cells divide when they should not, and cancerous cells can form masses of tissue called tumors.

Think It Over

2. Infer: Which snack is more healthful?

An apple is more healthful than a chocolate candy bar.

An apple is a better choice because fruits are low in fat and high in fiber. The article says that fruits, vegetables, and grain products are good food choices that may help reduce the risk of some cancers.

After You Read

1. Write a sentence using both terms from the Mini Glossary.

A change in a gene can cause the cell cycle to lose control, which may lead to cancer.

2. Place the events in the appropriate box based on the order in which they occur.

1. Environmental factors or viral infections damage genes.

2. Uncontrolled cell division occurs.

3. Cancer occurs.

4. Cancerous cells form tumors that deprive normal cells of nutrients.

Chapter 9: Energy in a Cell

Section 9.1. The Need for Energy

Reading Check

1. What does ATP do?

ATP stores energy and provides quick energy for cells when they need it. Cells use ATP to power cell processes such as making molecules, moving materials, and maintaining homeostasis.

Think It Over

2. Analyze: A cell’s internal environment is kept stable through which choice?

The correct choice is:

b. homeostasis

Homeostasis means keeping the cell’s internal environment stable and balanced.

After You Read

1. Tell how the two terms in the Mini Glossary are related.

ATP and ADP are related because they are part of the same energy cycle in cells. ATP stores energy in its phosphate bonds. When ATP releases one phosphate group, energy is released and ATP becomes ADP. Then ADP can add another phosphate group to become ATP again.

2. Fill in the diagram to show the complete formation and breakdown cycle of ATP.

You can fill the diagram like this:

Left box

ADP adds a phosphate group and stores energy.

This changes ADP into ATP.

Right box

ATP releases a phosphate group and energy.

This changes ATP into ADP.

3. Fill in the missing numbers.

ATP contains 3 phosphate group(s).

1 phosphate group(s) is released.

ADP contains 2 phosphate group(s).

ADP adds 1 phosphate group(s) to become ATP.

Section 9.2. Photosynthesis-Trapping the Sun’s Energy

1. What are the two parts of photosynthesis?

The two parts of photosynthesis are:

1. Light-dependent reactions

2. Light-independent reactions

2. What happens during the Calvin cycle?

During the Calvin cycle, carbon dioxide is used to form simple sugars. The sugars store energy that the plant can use later.

After You Read

1. Choose one key term and define it in your own words.

Key term: photosynthesis

Definition in my own words: Photosynthesis is the process plants use to capture energy from sunlight and change it into chemical energy stored in sugars.

2. Select one question heading and answer it.

Question: Where does photosynthesis take place?

Answer: Photosynthesis takes place in the chloroplasts of plant cells. Chloroplasts contain pigments, such as chlorophyll, that absorb sunlight so the plant can make sugars.

3. Complete the concept diagram using the terms provided.

Phases of Photosynthesis

Left box: light-dependent reactions
Right box: light-independent reactions

Light-dependent reactions side

Light energy transfers to chlorophyll,
which passes the energy through the electron transport chain.

Lost energy is:

• used to form ATP

• stored as NADPH

Light-independent reactions side

Light-independent reactions use carbon dioxide to form sugars that are stored as energy in the Calvin cycle.

Section 9.3. Getting Energy to Make ATP

1. What are the three stages of cellular respiration?

The three stages of cellular respiration are:

1. Glycolysis

2. Citric acid cycle

3. Electron transport chain

2. When might your body perform fermentation processes?

Your body might perform fermentation when your cells do not get oxygen for a short time, such as during heavy exercise.

3. List two ways photosynthesis and cellular respiration are similar.

Two ways photosynthesis and cellular respiration are similar are:

1. Both use electron carriers and a cycle of chemical reactions.

2. Both use electron transport chains in their processes.

After You Read

1. List two terms that are anaerobic chemical reactions.

Two anaerobic chemical reactions are:

1. Alcoholic fermentation

2. Lactic acid fermentation

2. Fill in the outline about cellular respiration.

I. Glycolysis

A. Chemical reactions break down glucose.
B. Pyruvic acid is formed.

II. Citric acid cycle

A. Series of chemical reactions.
B. The molecule used in the first reaction is also available at the end of the cycle.
C. Also called the Krebs cycle.

III. Electron transport chain

A. Electrons are passed from protein to protein.
B. Electrons lose energy.
C. ATP formed.

Chapter 10: Mendel and Meiosis

Section 10.1. Mendel’s Law’s Heredity

Reading Check

1. What is the difference between self-pollination and cross-pollination?

Self-pollination happens when pollen from a flower pollinates the female sex cells in the same flower.

Cross-pollination happens when pollen from one plant pollinates the female reproductive organ of a different plant.

2. What is a monohybrid?

A monohybrid is an offspring whose parents have different forms of one trait. For example, if one parent plant is tall and the other is short, their offspring are monohybrids because height is the one trait being studied.

3. List the abbreviations for each generation and tell what they stand for.

P generation means the parent generation.

F₁ generation means the first filial generation, or the offspring of the parent generation.

F₂ generation means the second filial generation, or the offspring of the F₁ generation.

4. If a plant has a dominant allele for height and a recessive allele for height, which allele will determine the height of the plant?

The dominant allele will determine the height of the plant.

For example, if the plant has one allele for tallness and one allele for shortness, the plant will be tall because the tall allele is dominant.

5. Explain the difference between phenotype and genotype.

A phenotype is the way an organism looks or behaves, such as being tall or short.

A genotype is the organism’s allele combination, such as TT, Tt, or tt.

6. Explain the difference between homozygous and heterozygous.

Homozygous means an organism has two of the same alleles for a trait, such as TT or tt.

Heterozygous means an organism has two different alleles for a trait, such as Tt.

7. What does the law of independent assortment state?

The law of independent assortment states that genes for different traits are inherited independently of each other.

This means one trait, such as seed shape, does not have to be inherited together with another trait, such as seed color.

After You Read

1. Write a sentence using at least two terms from the Mini Glossary.

A dominant allele can hide, or mask, a recessive allele in an organism’s phenotype.

2. Arrange the steps Mendel used in his first experiment with pea plants.

The correct order is:

1. c. Find true breeders for a single trait

2. a. Cross-pollinate P₁ generation to grow monohybrids

3. d. Allow F₁ generation to self-pollinate

4. b. Observe results in F₂ generation

3. Cause and Effect Diagram: Mendel’s Two Laws

Cause: Law of Segregation

Effect: Each organism has two alleles for each gene, but each gamete receives only one allele. During fertilization, alleles randomly pair to produce different combinations.

Cause: Law of Independent Assortment

Effect: Genes for different traits are inherited independently of each other, so traits can appear in different combinations in offspring.

Section 10.2. Meiosis

Reading Check

1. What do you call a cell with two of each kind of chromosome?

A cell with two of each kind of chromosome is called a diploid cell.

2. What do you call a cell with one of each kind of chromosome?

A cell with one of each kind of chromosome is called a haploid cell.

3. What does meiosis produce?

Meiosis produces haploid cells, or gametes, such as sperm and eggs. These cells have half the number of chromosomes as the parent body cell.

4. What happens during crossing over?

During crossing over, parts of homologous chromosomes exchange pieces of genetic material. This creates new combinations of alleles and increases genetic variation.

5. How does meiosis provide for genetic variation?

Meiosis provides genetic variation by creating many possible gene combinations. This happens through crossing over and the reassortment of genetic information during meiosis.

6. What is nondisjunction?

Nondisjunction is the failure of chromosomes to separate correctly during meiosis. This can cause gametes to have too many or too few chromosomes.

After You Read

1. List four terms that have to do with genetic variation.

Four terms related to genetic variation are:

1. Crossing over

2. Genetic recombination

3. Meiosis

4. Homologous chromosomes

2. Fill in the boxes explaining how each topic relates to meiosis.

Genetic Variation

Meiosis creates genetic variation by producing many possible gene combinations. Crossing over and genetic recombination help offspring have different traits from their parents.

Mendel’s Results

Mendel’s results can be explained by the way chromosomes separate and are distributed during meiosis. Meiosis helps explain how traits are passed from parents to offspring.

Sexual Reproduction

Meiosis produces haploid sex cells, such as sperm and eggs. During sexual reproduction, these haploid cells unite to form a diploid zygote.

Nondisjunction

Nondisjunction can happen during meiosis when chromosomes do not separate correctly. This can produce gametes with too many or too few chromosomes.

Cell Division

Meiosis is a type of cell division that reduces the chromosome number by half. One diploid cell divides to produce four haploid cells.

3. Match each new concept with the correct example.

1. meiosis — c. one diploid cell produces four haploid cells

2. nondisjunction — d. the failure of chromosomes to separate properly during meiosis

3. crossing over — b. exchange of genetic material

4. Mendel’s results — a. explained by the distribution of chromosomes during meiosis

Chapter 11: DNA and Genes

Section 11.1. DNA: The Molecule of Heridity

Reading Check

1. What three items form a nucleotide?

A nucleotide is made of three parts:

1. A simple sugar

2. A phosphate group

3. A nitrogenous base

2. What is the purpose of DNA replication?

The purpose of DNA replication is to make a copy of DNA before a cell divides. This allows each new cell to receive the same genetic information as the original cell.

Think It Over

3. When one DNA molecule replicates, how many new DNA molecules are formed?

The correct answer is:

b. two

When one DNA molecule replicates, it produces two DNA molecules. Each new DNA molecule has one original strand and one newly made strand.

After You Read

1. Use each Mini Glossary term in a sentence.

DNA replication: DNA replication happens before cell division so each new cell receives a complete copy of the DNA.

Double helix: A DNA molecule has the shape of a double helix, which looks like a twisted ladder or spiral staircase.

Nitrogenous base: A nitrogenous base is one part of a nucleotide, and the bases pair together to help form the “rungs” of the DNA ladder.

2. Fill in the missing bases on the DNA strand.

Use the base-pairing rules:

• A pairs with T

• T pairs with A

• C pairs with G

• G pairs with C

From left to right, the missing bottom-strand bases should be:

C, A, G, T, T, A

So the completed base pairs would include:

• G pairs with C

• T pairs with A

• C pairs with G

• A pairs with T

• A pairs with T

• T pairs with A

3. Circle the correct statement.

The correct statement is:

b. The illustration above is of a DNA strand replicating.

The picture shows bases being added to form a matching strand, which means DNA replication is taking place.

Section 11.2. From DNA to Protein

Reading Check

1. What are the three types of RNA?

The three types of RNA are:

1. Messenger RNA, or mRNA

2. Ribosomal RNA, or rRNA

3. Transfer RNA, or tRNA

2. What is a codon?

A codon is a group of three nitrogenous bases in mRNA that codes for one amino acid.

Think It Over

3. What is the difference between transcription and translation?

Transcription is the process of copying information from part of a DNA strand into mRNA. It happens in the nucleus.

Translation is the process of using the information in mRNA to build a protein. It happens at the ribosome in the cytoplasm.

4. Sequence: The pathway of information flows from which choice?

The correct choice is:

a. DNA to mRNA to protein

This is called the central dogma. Genetic information in DNA is copied into mRNA, and then mRNA is used to make a protein.

After You Read

1. Define transcription and translation in your own words.

Transcription is when a cell makes an mRNA copy of part of DNA’s instructions.

Translation is when the ribosome reads the mRNA message and uses tRNA to bring amino acids together to make a protein.

Section 11.3. Genetic Changes

Before You Read

Why do you think the technician protects you from X rays but does not protect the part of your body being X-rayed?

The technician protects the rest of my body because X rays can damage DNA and may cause mutations. The part of the body being X-rayed has to be exposed so the image can be taken, but the rest of the body is covered with a lead shield to limit unnecessary exposure.

Reading Check

1. When is a mutation helpful?

A mutation is helpful when it gives an organism a trait that helps it survive better in its environment. If the mutation happens in a reproductive cell, it can be passed on to offspring.

2. Why is a mutation in a body cell not passed on to offspring?

A mutation in a body cell is not passed on to offspring because body cells are not used in reproduction. Only mutations in sex cells, such as sperm or egg cells, can be inherited by offspring.

3. Are chromosomal mutations more common in plants or animals?

Chromosomal mutations are more common in plants than in animals.

4. What is a mutagen?

A mutagen is any outside agent that can cause a change in DNA. Examples include radiation, chemicals, high temperatures, X rays, and ultraviolet light.

5. In what ways could you limit your exposure to mutagens?

You could limit your exposure to mutagens by avoiding too much sunlight or UV radiation, wearing sunscreen and protective clothing, avoiding cigarette smoke and harmful chemicals, and only getting X rays when medically needed.

After You Read

1. Why is a frameshift mutation usually more harmful than a point mutation?

A frameshift mutation is usually more harmful because it changes the way the genetic code is read from the mutation point forward. Since bases are read in groups of three, adding or deleting one base shifts all the codons after it. This can cause many wrong amino acids to be added to a protein. A point mutation usually changes only one base pair, so it may affect only one amino acid.

2. Fill in the outline.

I. Mutations occur

A. In reproductive cells
B. In body cells

II. Types of Mutations

A. Point mutations
B. Frameshift mutations
C. Chromosomal mutations

III. Causes of Mutations

A. Just happens = spontaneous
B. Environmental factor = mutagen

Chapter 12: Patterns of Heredity and Human Genetics

Section 12.1: Mendelian Inheritance of Human Traits

Before You Read

Two important facts about how diseases are passed from generation to generation:

Some genetic diseases are caused by recessive alleles, so both parents may need to pass on the recessive allele for a child to have the disease.

A pedigree can help show whether a trait or genetic disease has been passed through a family and whether a person may be a carrier.

Reading Check

1. What is a pedigree?

A pedigree is a visual diagram of genetic inheritance. Geneticists use pedigrees to map traits and study how traits are passed through families.

2. What symbols represent males and females in a pedigree?

In a pedigree, squares represent males and circles represent females.

Think It Over

3. Which alleles cause genetic disorders such as PKU?

Correct choice: a. recessive

Most genetic disorders, including PKU, are caused by recessive alleles. For an offspring to inherit a recessive disorder, both parents must carry or have the recessive allele.

After You Read

1. Use the words pedigree and carrier in a sentence.

A pedigree can show whether a family member is a carrier for a recessive allele that may be passed to future children.

2. Fill in the diagram about genetic disorders caused by recessive alleles.

The center box should say:

Simple Recessive Heredity

Examples of genetic disorders caused by recessive alleles include:

1. Tay-Sachs disease

2. Cystic fibrosis

3. Phenylketonuria, or PKU

3. Pedigree Symbols

You can fill in the box with these symbols and definitions:

Square: male
Circle: female
Shaded square: affected male
Shaded circle: affected female
Half-shaded square or circle: carrier, or known heterozygote for a recessive allele
Horizontal line between a square and circle: mating or parents
Vertical line from parents to offspring: children or offspring
Line connecting offspring: siblings
Symbol with a slash through it: death

Section 12.2: When Heredity Follows Different Rules

Before You Read

How many different combinations of colors are there in plant and animal life?

There are many different color combinations in plants and animals. Examples include red, pink, white, yellow, blue, brown, black, gray, spotted, striped, and blended colors. These differences can happen because traits may be inherited through incomplete dominance, codominance, multiple alleles, polygenic inheritance, or environmental influences.

Reading Check

1. What is the term that describes when both alleles show up equally?

The term is codominant inheritance.

In codominance, both alleles are expressed equally in the heterozygous offspring.

Think It Over

2. Which of the following is the best description of codominance?

Correct choice: c. Phenotypes of both parents are expressed equally.

Codominance means both traits show at the same time instead of one hiding the other.

Reading Check

3. What is the 23rd pair of chromosomes called?

The 23rd pair of chromosomes is called the sex chromosomes.

Think It Over

4. Height in humans is an example of which choice?

Correct choice: a. polygenic inheritance

Height is controlled by more than one gene, so it is an example of polygenic inheritance.

After You Read

1. Circle two terms that are related to each other. Tell how they are related.

Two related terms are sex chromosomes and sex-linked traits.

They are related because sex-linked traits are traits controlled by genes located on the sex chromosomes.

2. Fill in the outline.

I. Sex of an individual

A. Determined by sex chromosomes
B. Females are represented by the letter X
C. Males are represented by the letter Y

II. Sex-linked traits

A. First discovered by Thomas Hunt Morgan
B. Genes are located on sex chromosomes

Section 12.3: Complex Inheritance of Human Traits

Before You Read

Ways family members may resemble each other:

Family members may resemble each other in eye color, hair color, skin tone, height, facial features, blood type, dimples, freckles, hair texture, and some inherited health traits.

Think It Over

1. Which term describes when the phenotypes of both parents are expressed equally?

Correct choice: b. codominance

Codominance means the traits from both parents are expressed equally in the offspring.

Think It Over

2. If a mother has type O blood and a father has type A blood, their child can have which blood types?

Correct choices: a. A and b. O

A mother with type O blood has the genotype OO. A father with type A blood could be AA or AO. If the father is AA, the child will have type A blood. If the father is AO, the child could have type A or type O blood.

Reading Check

3. What is hemophilia?

Hemophilia is an X-linked disorder that keeps blood from clotting quickly. A person with hemophilia may bleed for a long time after a cut and may also have internal bleeding from bruises.

Reading Check

4. List two examples of polygenic inheritance.

Two examples of polygenic inheritance are:

1. Eye color

2. Skin color

Reading Check

5. What is one example of an abnormal number of chromosomes in humans?

One example of an abnormal number of chromosomes in humans is Down syndrome.

Another example would be an abnormal number of sex chromosomes, such as XO, XXX, XXY, or XYY.

After You Read

1. Use the word karyotype correctly in a sentence.

A karyotype can help scientists identify whether a person has an abnormal number of chromosomes.

2. Match each concept with the correct fact.

1. sickle-cell disease — b. an example of codominance

2. A, B, AB, O — a. human blood types

3. sex-linked traits — d. mostly located on the X chromosome

4. 47 chromosomes — c. abnormal number of chromosomes 

Chapter 13: Genetic Technology

Section 13.1: Applied Genetics

Before You Read

Two important facts about applied genetics:

Applied genetics uses knowledge of heredity to help humans choose or change traits in organisms.

Selective breeding can increase the frequency of desired traits in a population, but it may take several generations for the desired trait to become common.

Think It Over

1. How does selective breeding influence the frequency of desired traits in a population?

Correct choice: a. increases the frequency

Selective breeding increases the frequency of desired traits because breeders choose parents that already have those traits. Over time, more offspring inherit the desired traits.

Reading Check

2. What is a hybrid?

A hybrid is the offspring of parents that have different forms of a trait.

For example, if breeders cross one type of rose with another type of rose to combine traits, the offspring is a hybrid.

Reading Check

3. What is a test cross?

A test cross is a cross between an individual with an unknown genotype and an individual with a known genotype. It helps breeders determine the unknown genotype of a parent.

After You Read

1. Write a sentence for each Mini Glossary term.

Inbreeding: Inbreeding is mating closely related individuals so that offspring are more likely to have the desired traits, although harmful recessive traits may also appear.

Test cross: A test cross helps breeders determine an unknown genotype by crossing an organism with another organism of known genotype.

2. Place the information under the correct heading.

Selective Breeding

b. Produces hybrids that are usually bigger and better
c. Uses inbreeding

Determining Genotypes

a. Uses test crosses
d. Works best if known individual is homozygous recessive

3. Write a paragraph explaining how applied genetics has helped improve human life.

Applied genetics has helped improve human life by allowing people to breed plants and animals for useful traits. Farmers can produce crops with better yields, stronger disease resistance, or better nutrition. Breeders can also produce animals that give more milk, grow faster, or have other helpful traits. By using selective breeding and test crosses, humans can increase the chances that desired traits will appear in future generations.

Section 13.2: Recombinant DNA Technology

Before You Read

Examples of useful changes to an organism that could be made through DNA technology:

DNA technology could be used to create crops that resist insects, plants that grow in dry conditions, bacteria that produce medicines, or animals that grow healthier and stronger. One useful change would be a crop plant that makes its own natural insect protection, because that could reduce the need for chemical pesticides.

Reading Check

1. What advantages does genetic engineering have over selective breeding?

Genetic engineering is faster and more reliable than selective breeding. Instead of waiting for several generations, scientists can directly insert a desired gene into an organism.

Reading Check

2. What is a vector?

A vector is the means by which DNA from another species can be carried into a host cell. Examples of biological vectors include viruses and plasmids.

Reading Check

3. Why do scientists want to clone animals?

Scientists want to clone animals so farmers and ranchers may someday be able to copy the most productive, healthy animals. This could help increase and improve the food supply.

Reading Check

4. Which three areas will most likely benefit from DNA technology?

The three areas most likely to benefit from DNA technology are:

1. Industry

2. Medicine

3. Agriculture

After You Read

1. Circle two related terms and explain how they are related.

Two related terms are plasmid and vector.

They are related because a plasmid can be used as a vector. A plasmid is a small ring of DNA found in bacteria, and scientists can use it to carry DNA from another organism into a host cell.

2. List the steps for producing a transgenic organism.

Step 1: Cut the DNA fragment out of one organism using restriction enzymes.

Step 2: Connect the DNA fragment to a carrier, such as a plasmid vector.

Step 3: Insert the DNA fragment and its carrier into a new organism.

Section 13.3: The Human Genome

Before You Read

Example of another important scientific achievement and how the world might be different without it:

One important scientific achievement is the discovery of antibiotics. Without antibiotics, many bacterial infections would be much harder to treat, and more people might die from infections that doctors can now cure or control.

Reading Check

1. What is the Human Genome Project?

The Human Genome Project is an international effort to completely map and sequence the human genome. Its goal is to identify and organize the thousands of genes found on the 46 human chromosomes.

Reading Check

2. What is gene therapy?

Gene therapy is the insertion of normal genes into human cells to correct genetic disorders.

Reading Check

3. Why does DNA fingerprinting work?

DNA fingerprinting works because no two individuals, except identical twins, have the same DNA sequences. Also, almost all cells in one person have the same DNA, except for gametes.

After You Read

1. Write a sentence using at least two Mini Glossary terms.

A linkage map created from the human genome can help scientists locate genes and learn more about genetic disorders.

2. Fill in the applications diagram.

Application 1: Diagnosing genetic disorders
Example: Doctors can diagnose genetic disorders before birth by analyzing fetal DNA.

Application 2: Gene therapy
Example: Treat patients with cystic fibrosis.

Application 3: DNA fingerprinting
Example: Law enforcement can compare DNA from a crime scene with DNA from a suspect.

3. Circle T or F for each sentence.

1. Humans have more than 75,000 genes located on 48 chromosomes.
F

Humans have about 35,000 to 40,000 genes located on 46 chromosomes.

2. A linkage map shows the exact location of a gene on a chromosome.
F

A linkage map shows the relative location of genes, not their exact location.

3. Using polymerase chain reaction, or PCR, millions of copies of DNA fragments can be cloned in a day.
T

PCR can make many copies of DNA fragments quickly.

4. Gene therapy is the insertion of abnormal genes into human cells to correct genetic disorders.
F

Gene therapy is the insertion of normal genes into human cells to correct genetic disorders.

Chapter 14: The History of Life

Section 14.1: The Record of Life

Before You Read

What evidence do you think rocks provide about life?

Rocks can provide evidence about life because they may contain fossils. Fossils can show what organisms lived long ago, what they looked like, where they lived, and sometimes how they moved or what they ate. Layers of rock can also help scientists understand the order in which different life-forms appeared on Earth.

Reading Check

1. Why can scientists not be sure how Earth was formed?

Scientists cannot be completely sure how Earth was formed because rocks from Earth’s earliest history have been destroyed and new rocks have formed. The oldest rocks found on Earth are about 3.9 billion years old, so the earliest evidence is missing.

Think It Over

2. How might fossil teeth reveal an animal’s diet?

Fossil teeth can show what an animal ate because different types of teeth are suited for different foods. Sharp teeth may suggest the animal ate meat, while flat grinding teeth may suggest the animal ate plants. The size, shape, and wear on teeth can give scientists clues about the animal’s diet.

Reading Check

3. Explain relative dating of fossils.

Relative dating is a way to estimate the age of fossils by comparing the rock layers where they are found. Fossils in lower rock layers are usually older than fossils in higher layers. Relative dating does not give an exact age, but it shows whether one fossil is older or younger than another.

4. List the two most common radioactive isotopes used by scientists to date rocks and fossils.

The two most common radioactive isotopes used are:

1. Potassium-40

2. Carbon-14

5. What is a mass extinction?

A mass extinction is an event in which many organisms disappear from the fossil record at about the same time.

6. What is the “explosion” paleontologists refer to?

The “explosion” refers to the Cambrian explosion, a time during the Paleozoic era when many new types of living things appeared. Many kinds of animals, including worms, sea stars, arthropods, and fishes, appeared in the oceans.

After You Read

1. Select one Mini Glossary term and create a drawing to help remember its definition.

Term: fossil

Drawing idea: Draw a rock with the outline of a fish bone or leaf pressed inside it.

Explanation: This drawing would show that a fossil is physical evidence of an organism that lived long ago. Fossils may be found in rocks, amber, or ice.

3. Fill in the blanks using the terms: sedimentary, radiometric, plate tectonics, Cenozoic.

a. Humans and large mammals appeared in the Cenozoic Era.

b. The theory of plate tectonics explains how continents move.

c. Most fossils are found in sedimentary rocks.

d. Scientists use radiometric dating to determine the age of rocks and fossils.

Section 14.2: The Origin of Life

Before You Read

Something in biology I would like to learn more about and an experiment that could help me learn about it:

I would like to learn more about how early cells may have formed. An experiment could test whether simple organic molecules can form under conditions similar to early Earth, such as heat, water vapor, gases, and electrical energy.

Reading Check

1. What did Francesco Redi’s experiment prove?

Francesco Redi’s experiment showed that maggots do not come from decaying meat by spontaneous generation. Instead, flies lay eggs on meat, and those eggs develop into maggots.

Think It Over

2. How did Pasteur develop the concept of biogenesis?

Pasteur designed an experiment using a special glass bottle that allowed air to enter but kept microorganisms out. As long as microorganisms were kept out, the broth stayed clear. His experiment showed that microorganisms come from other microorganisms, which supported the idea of biogenesis: living things come only from other living things.

Reading Check

3. What two things had to happen before life could appear on Earth?

Two things had to happen before life could appear:

1. Organic molecules, or carbon-containing molecules, had to form.

2. Organic molecules had to join together to form more complex molecules, such as proteins, carbohydrates, and nucleic acids.

Think It Over

4. What happens when amino acids are heated?

Correct choice: b. They become proteins.

When amino acids are heated, they can join together to form proteins.

Reading Check

5. What were two results of oxygen in the atmosphere?

Two results of oxygen in the atmosphere were:

1. Organisms that use oxygen began to develop.

2. Oxygen helped form the ozone layer, which protected organisms from harmful ultraviolet radiation and allowed more complex organisms to evolve.

After You Read

1. Highlight the two key terms that describe ideas about the origin of living things. Explain which idea came first and why it was replaced.

The two key terms are:

1. Spontaneous generation

2. Biogenesis

Spontaneous generation came first. It was the mistaken idea that living things could come from nonliving materials. It was replaced by biogenesis because experiments by Redi and Pasteur showed that living things come from other living things.

2. Place the events in order on the timeline.

The correct order is:

1. Oceans contain organic molecules

2. Complex organic molecules form

3. Protocells develop

4. Prokaryotes appear

5. Organisms use chemosynthesis

6. Organisms use photosynthesis

7. Ozone layer develops

8. Eukaryotes develop

3. Select one timeline event and explain its importance in three sentences.

Event: Ozone layer develops

The ozone layer was important because it helped shield Earth from harmful ultraviolet radiation. This protection made it possible for more complex organisms to survive and evolve. Without the ozone layer, life on land and many complex life-forms would have been much harder to develop.

Chapter 15: The Theory of Evolution

Section 15.1: Natural Selection and the Evidence for Evolution

Before You Read

Three important facts about Charles Darwin:

Charles Darwin was an English naturalist who studied plants and animals.

Darwin spent five years on a research voyage around the world, including time in the Galápagos Islands.

Darwin developed the idea that natural selection helps explain how species change over time.

Reading Check

1. What forms the basis of modern evolutionary theory?

The ideas of Charles Darwin form the basis of modern evolutionary theory.

Reading Check

2. What is the process in which organisms with favorable traits tend to survive and pass on these traits to their offspring?

This process is called natural selection.

Think It Over

3. Which of the following is an example of mimicry?

Correct choice: a. A harmless fly looks like a wasp.

This is mimicry because one species resembles another species. The harmless fly may be protected because predators might mistake it for a wasp.

Reading Check

4. What is the term for structural features that have a common evolutionary origin?

Structural features that have a common evolutionary origin are called homologous structures.

Think It Over

5. What is the difference between analogous and vestigial structures?

Analogous structures are body parts that are similar in function but do not have a common evolutionary origin. For example, bird wings and insect wings both help with flight, but they evolved separately.

Vestigial structures are body parts that no longer serve their original purpose in a modern organism. For example, mole rats still have eyes, but the eyes are no longer used for sight.

After You Read

1. Choose a term that describes a type of structural adaptation. Write a sentence using the term.

Term: camouflage

Sentence: Camouflage is a structural adaptation that helps an organism blend in with its surroundings so predators have a harder time finding it.

Section 15.2: Mechanisms of Evolution

Before You Read

What barriers might divide a population?

Barriers that might divide a population include rivers, mountains, roads, deserts, oceans, canyons, glaciers, lava flows, or human-made structures. These barriers can separate groups so they no longer interact or mate with each other.

Think It Over

1. Which of the following is an example of genetic equilibrium?

Correct choice: a. Generation after generation of a population of roses are red.

This is genetic equilibrium because the allele frequency stays the same over generations.

Think It Over

2. On what population would genetic drift most likely have the greatest impact?

Correct choice: a. a population of twelve turtles on a small, isolated island

Genetic drift has the greatest effect on small, isolated populations because chance events can change allele frequencies more strongly in small groups.

Reading Check

3. What is one way that reproductive isolation can occur?

Reproductive isolation can occur when populations become so genetically different that fertilization cannot happen. It can also occur when similar populations have different mating seasons.

Reading Check

4. What features do unrelated species that develop similar traits in different parts of the world demonstrate?

They demonstrate convergent evolution.

Convergent evolution happens when unrelated species live in similar environments and develop similar traits because they face similar environmental pressures.

After You Read

1. Circle the two terms that refer to different ideas about the rate in which speciation occurs. Then use one in a sentence.

The two terms are:

Gradualism

Punctuated equilibrium

Sentence: Punctuated equilibrium is the idea that speciation can happen quickly in rapid bursts, followed by long periods with little change.

2. Fill in the results of each type of isolation.

Cause: Geographic Isolation

Effect: A barrier divides a population, so members of the same species can no longer mate because they cannot reach each other.

Cause: Reproductive Isolation

Effect: The genetic material of the populations becomes so different that fertilization cannot occur, or the populations have different mating seasons.

3. Fill in the blanks using the terms: punctuated equilibrium, speciation, genetic equilibrium, polyploid, mutation.

1. When the frequency of alleles for a specific trait remains the same for generations, it is called genetic equilibrium.

2. One of the factors that can interrupt genetic equilibrium is mutation.

3. Speciation occurs when members of similar populations can no longer interbreed to produce fertile offspring within their natural environment.

4. The idea that a sudden environmental change can cause rapid changes in a population’s gene pool is called punctuated equilibrium.

5. A polyploid is an individual with a multiple of the normal set of chromosomes.

Chapter 16: Primate Evolution

Section 16.1: Primate Adaptation and Evolution

Before You Read

Compare human behaviors with behaviors you have observed in non-human primates.

Humans and non-human primates have some similar behaviors. Both can live in social groups, care for their young, use their hands to hold objects, communicate with others, and learn from experience. Humans, however, use more complex language, create advanced tools, build communities, and use technology in ways other primates do not.

Reading Check

1. Where do strepsirrhines live?

Strepsirrhines live in the tropical forests of Africa and Southeast Asia.

2. List the three divisions of the anthropoid group.

The three divisions of the anthropoid group are:

1. Hominoids

2. Old World monkeys

3. New World monkeys

3. What unusual feature do many New World monkeys have?

Many New World monkeys have a prehensile tail. This is a long, muscular tail that can be used like an arm or leg to grasp and wrap around tree branches.

Think It Over

4. On which continent would you not expect to see an Old World monkey?

Correct choice: c. North America

Old World monkeys live in places such as Africa and Asia. New World monkeys live in South and Central America, so North America would not be a place where you would expect to find Old World monkeys naturally.

Reading Check

5. Which two hominoids were the last to evolve?

The two hominoids that were the last to evolve were African apes and humans.

After You Read

1. Highlight the key terms that apply to humans. Then choose one of the highlighted words and write a sentence using the word.

Key terms that apply to humans include:

• Primate

• Anthropoid

• Opposable thumb

Sentence: Humans are primates because they share traits such as large, complex brains, forward-facing eyes, and opposable thumbs.

2. In each box, write one important fact about the primate group named in that box.

Primates:
Primates are mammals that include lemurs, monkeys, apes, and humans.

Strepsirrhines:
Strepsirrhines are small primates that usually have large eyes, are active at night, and live in tropical forests.

Haplorhines:
Haplorhines include tarsiers and anthropoids.

Anthropoids:
Anthropoids are humanlike primates that include hominoids, Old World monkeys, and New World monkeys.

Old World monkeys:
Old World monkeys are generally larger than New World monkeys and live in Africa and Asia.

Hominoids:
Hominoids include apes and humans.

New World monkeys:
New World monkeys live in South and Central America, and many have prehensile tails.

Section 16.2: Human Ancestry

Before You Read

List some things humans can do that other animals cannot do.

Humans can use complex spoken and written language, create advanced tools, build cities, develop science and technology, record history, make art and music, farm crops, and solve complex problems. Humans can also pass large amounts of knowledge from one generation to the next.

Reading Check

1. What was different about the skull Raymond Dart discovered?

The skull Raymond Dart discovered had mostly apelike features, but the opening for the spinal cord was in the same place as it is in a human skull. This suggested that the organism walked upright.

Reading Check

2. Who is “Lucy”?

“Lucy” is the most famous fossil of the species Australopithecus afarensis. Donald Johanson discovered Lucy’s skeleton in 1974, and she lived about 3.2 million years ago.

Think It Over

3. What is the significance of tool making?

Tool making is significant because it shows problem-solving ability and more advanced behavior. The use of tools suggests that early hominids could plan, use their hands skillfully, and adapt to their environment more successfully.

Reading Check

4. What two species appeared before Homo sapiens?

The two species thought to have appeared before Homo sapiens were:

1. Homo antecessor

2. Homo heidelbergensis

After You Read

1. Circle the three key terms that identify particular early hominid species.

The three key terms are:

1. Australopithecine

2. Neandertal

3. Cro-Magnon

2. List the characteristics of each hominid species.

Australopithecines

3 to 4 million years ago

Characteristics:
Australopithecines were early African hominids with both apelike and humanlike features. They had small brains like apes, but their pelvis and body structure suggest that they could walk upright on two legs.

Homo habilis and Homo erectus

1.5 to 2 million years ago

Characteristics:
Homo habilis had a larger brain than australopithecines and was the earliest known hominid to make and use stone tools. Homo erectus means “upright human.” Homo erectus had a more humanlike face, used fire, made stone axes, lived in caves, and migrated from Africa into Asia and possibly Europe.

Neandertals

35,000 to 100,000 years ago

Characteristics:
Neandertals were an early Homo species that lived in Europe, Asia, and the Middle East. They had thick bones, large faces, prominent noses, and brains at least as large as modern humans. Evidence suggests they used tools and may have communicated with spoken language.

Cro-Magnons

35,000 to 40,000 years ago

Characteristics:
Cro-Magnons were a species of Homo sapiens and were very similar to modern humans in height, skull structure, tooth structure, and brain size. They were toolmakers and artists, and they may have used language.

Chapter 17: Organizing Life’s Diversity

Section 17.1: Classification

Before You Read

Describe the advantages of being organized.

Being organized makes things easier to find, compare, and understand. For example, organizing clothes, books, or music into groups helps you know where everything belongs. In biology, organization helps scientists compare organisms and understand how they are related.

Reading Check

1. What is taxonomy?

Taxonomy is the branch of biology that groups and names organisms based on their characteristics.

Reading Check

2. In the species name Homo sapiens, what is the genus? What is the specific epithet?

In the species name Homo sapiens, Homo is the genus.

sapiens is the specific epithet.

Together, the genus and specific epithet form the scientific name of modern humans.

Think It Over

3. For which of the following could taxonomy be used?

Correct choice: c. both a and b

Taxonomy could be used to determine whether a plant is safe to be planted in a school yard. It could also be used to help find a new source for a medicine that comes from plants.

Reading Check

4. Which taxonomic group is a group of similar families?

A group of similar families is called an order.

After You Read

1. Find two terms from the Mini Glossary that make up the two-word naming system called binomial nomenclature.

The two terms are:

1. Genus

2. Specific epithet

These two parts together make up a scientific name. For example, in Homo sapiens, Homo is the genus and sapiens is the specific epithet.

2. Fill in the triangle to show the taxonomic classification system.

From broadest to most specific, the taxonomic groups are:

1. Kingdom

2. Phylum

3. Class

4. Order

5. Family

6. Genus

7. Species

A helpful memory phrase is: King Philip Came Over For Good Soup.

Section 17.2: The Six Kingdoms

Before You Read

List characteristics you would use to identify members of the same family.

To identify members of the same family, I might compare physical traits such as eye color, hair color, face shape, height, body shape, and skin tone. I might also look at shared behaviors, language, family history, and genetic relationships.

Reading Check

1. What are the five characteristics used to determine evolutionary relationships?

The five characteristics are:

1. Structural similarities

2. Breeding behavior

3. Geographical distribution

4. Chromosome similarity

5. Biochemistry, such as DNA and protein similarities

Think It Over

2. Finding that two species have similar DNA is an example of studying which characteristic to determine evolutionary relationships?

Correct choice: a. biochemistry

DNA is a biochemical molecule. If two species have similar DNA sequences, scientists may infer that they are closely related.

Think It Over

3. Using the figure, decide which species are most closely related.

Correct choice: b. ferns and conifers

In the fanlike diagram, ferns and conifers are close together, which means they are probably more closely related than the other choices.

Reading Check

4. List two ways fungi and plants are different.

Two ways fungi and plants are different are:

1. Plants are autotrophs, meaning they make their own food through photosynthesis. Fungi are heterotrophs, meaning they absorb nutrients from organic material.

2. Plants can have tissues and structures for photosynthesis, while fungi do not photosynthesize and are mostly stationary absorbers.

Another acceptable difference is that plants are always multicellular, while fungi can be unicellular or multicellular.

After You Read

1. Explain how the terms cladistics, cladogram, and phylogeny are related.

Phylogeny is the evolutionary history of a species or group.

Cladistics is a classification method that uses shared inherited traits to study phylogeny.

A cladogram is a branching diagram made through cladistics that shows probable evolutionary relationships.

In other words, scientists use cladistics to study phylogeny, and they show those relationships with a cladogram.

2. List the six kingdoms of organisms. Next to each kingdom, write one fact about that kingdom.

1. Eubacteria — These are prokaryotes with strong cell walls; some are autotrophs and some are heterotrophs.

2. Archaebacteria — These are prokaryotes that often live in extreme environments, such as hot vents, swamps, or very salty water.

3. Protists — These are mostly simple eukaryotes that may be unicellular or multicellular; some are autotrophs and some are heterotrophs.

4. Fungi — These are heterotrophs that absorb nutrients from organic material; they can be unicellular or multicellular.

5. Plants — These are multicellular autotrophs with cell walls; they make food through photosynthesis.

6. Animals — These are multicellular heterotrophs; most can move from place to place and do not have cell walls.

Chapter 18: Viruses and Bacteria

Section 18.1: Viruses

Before You Read

Examples of health problems caused by viruses:

Viruses can cause many health problems, including colds, the flu, chicken pox, cold sores, hepatitis B, HIV/AIDS, and some plant diseases such as tobacco mosaic virus.

Reading Check

1. What is the cell in which a virus reproduces called?

The cell in which a virus reproduces is called a host cell.

Think It Over

2. Another layer around some large viruses is called the:

Correct choice: b. envelope

Some large viruses have an outer layer called an envelope outside the capsid.

Reading Check

3. Although there are two ways that viruses get into a cell, both ways result in the virus releasing its nucleic acid into the cell.

Correct choice: a. True

Whether the virus injects its nucleic acid or enters through a vacuole, the result is that the virus releases its nucleic acid into the host cell.

Reading Check

4. What is the cycle called during which the virus does not destroy the host cell?

The cycle is called the lysogenic cycle.

In this cycle, the viral DNA becomes part of the host cell’s chromosome and can be copied each time the host cell reproduces.

Reading Check

5. What is the name for viral DNA that is integrated into the host cell’s chromosome?

Viral DNA that is integrated into the host cell’s chromosome is called a provirus.

Think It Over

6. Why is the presence of the enzyme reverse transcriptase a sign of infection by a retrovirus?

Reverse transcriptase is a sign of infection by a retrovirus because retroviruses carry this enzyme inside their capsid. The enzyme changes viral RNA into viral DNA. If reverse transcriptase is found in a person, it suggests that a retrovirus is present.

Think It Over

7. Which of the following is an example of a viroid?

Correct choice: b. a plant disease

Viroids are virus-like infectious agents made of a single circular strand of RNA with no protein coat. They cause infectious diseases in plants.

After You Read

1. Write a sentence for each term: provirus and virus.

Provirus: A provirus is viral DNA that becomes part of a host cell’s chromosome and is copied when the host cell reproduces.

Virus: A virus is a nonliving, disease-causing particle made of nucleic acid inside a protein coat that can reproduce only inside a host cell.

2. Choose one question heading and answer it.

Question: What is a retrovirus?

Answer: A retrovirus is an RNA virus with a complex replication cycle. It uses an enzyme called reverse transcriptase to make DNA from its RNA. The viral DNA can then become part of the host cell’s chromosome as a provirus.

3. Arrange the steps in the replication process of the retrovirus in the correct order.

The correct order is:

1. b. Virus enters cell

2. a. DNA is made from viral RNA

3. d. Viral DNA, or provirus, integrates into host cell’s chromosomes

4. c. Host cell and provirus reproduce; new virus forms

Section 18.2: Archaebacteria and Eubacteria

Before You Read

What I think about when I hear the word bacteria:

When I hear the word bacteria, I often think of germs and disease. However, some bacteria are helpful because they help with digestion, recycle nutrients, make foods such as yogurt and cheese, and help plants get usable nitrogen.

Reading Check

1. What are the three environments where archaebacteria live?

The three environments where archaebacteria live are:

1. Oxygen-free environments, such as marshes, lake bottoms, and digestive tracts

2. Very salty water, such as the Great Salt Lake or the Dead Sea

3. Hot, acidic waters, such as sulfur springs and deep ocean vents

Reading Check

2. Identify the process that bacteria use to make food from the breakdown of inorganic compounds.

The process is called chemosynthesis.

Chemosynthetic bacteria break down inorganic compounds containing sulfur and nitrogen to release energy and make food.

Think It Over

3. List the two ways bacteria can reproduce. Circle the method that produces genetically identical cells.

The two ways bacteria can reproduce are:

1. Binary fission

2. Conjugation

The method that produces genetically identical cells is binary fission.

Reading Check

4. What type of bacteria must have oxygen in order to survive?

Bacteria that must have oxygen in order to survive are called obligate aerobes.

Reading Check

5. How do bacteria help plants?

Bacteria help plants by converting nitrogen from the air into forms plants can use. This process is called nitrogen fixation. Without these bacteria, plants would not be able to use nitrogen from the air directly.

Think It Over

6. If someone tells you that bacteria are bad, how would you respond?

I would explain that some bacteria can cause disease, but many bacteria are helpful or even necessary for life. Bacteria help recycle nutrients, help plants get usable nitrogen, produce oxygen as a byproduct of making food, help digest food in our intestines, and are used to make foods such as yogurt, cheese, pickles, and sauerkraut.

After You Read

1. Circle the two words that describe how bacteria reproduce. Underline the word that describes the type of reproduction that results in bacteria with new genetic material. Then describe how that might be useful to bacteria.

The two words that describe how bacteria reproduce are:

1. Binary fission

2. Conjugation

The word that describes reproduction resulting in new genetic material is:

Conjugation

Conjugation can be useful to bacteria because it creates new genetic combinations. This may help bacteria survive changes in their environment, such as new conditions or exposure to antibiotics.

3. Bacteria come in three different shapes. Write their scientific names below each figure.

1. Spheres: coccus

2. Rods: bacillus

3. Spirals: spirillum

Chapter 19: Protists

Section 19.1: The World of Protists

Before You Read

Name the six kingdoms.

The six kingdoms are:

1. Archaebacteria

2. Eubacteria

3. Protists

4. Fungi

5. Plants

6. Animals

Reading Check

1. What are protozoans?

Protozoans are unicellular, animal-like protists. They are heterotrophs, which means they feed on other organisms or dead organic matter.

2. How are protozoans grouped?

Protozoans are grouped into four groups:

1. Amoebas

2. Flagellates

3. Ciliates

4. Sporozoans

Amoebas, flagellates, and ciliates are grouped by how they move. Sporozoans are grouped together because they are parasites.

Think It Over

3. Name the two ways that paramecia can reproduce.

Paramecia can reproduce in two ways:

1. Asexually, by dividing into two cells

2. Sexually, through conjugation, when two paramecia exchange genetic material

After You Read

1. Circle the key terms that identify three of the four groups that protozoans are divided into. Write the name of the missing group.

The three key terms in the Mini Glossary are:

1. Ciliates

2. Flagellates

3. Sporozoans

The missing group is:

Amoebas

2. Fill in the numbered boxes to complete the chart.

Under Protozoans, the four boxes should be:

1. Amoebas

2. Flagellates

3. Ciliates

4. Sporozoans

3. Write a fact for each numbered box.

1. Amoebas: Amoebas move and feed using pseudopodia, which are extensions of the plasma membrane.

2. Flagellates: Flagellates move using one or more whip-like structures called flagella.

3. Ciliates: Ciliates move using short hairlike structures called cilia.

4. Sporozoans: Sporozoans are parasitic protozoans that reproduce by producing spores.

Section 19.2: Algae: Plantlike Protists

Before You Read

Additional uses for diatomite:

Because diatomite is absorbent, sparkling, and abrasive, it could be used to absorb oil spills, clean dirty surfaces, polish metals, filter liquids, or help soak up moisture. It might also be useful in garden products or cleaning powders.

Reading Check

1. What do scientists call unicellular photosynthesizing algae?

Scientists call unicellular photosynthesizing algae phytoplankton.

2. How does storing food as oil help diatoms?

Storing food as oil helps diatoms float near the surface of the water, where more sunlight is available for photosynthesis.

Think It Over

3. Describe the food chain that leads from dinoflagellates to humans.

Dinoflagellates may be eaten by shellfish, such as clams or mussels. If the dinoflagellates are toxic, the shellfish can store the toxins. Humans may then become poisoned if they eat those contaminated shellfish.

Reading Check

4. What do red algae have that allows them to survive in deep water?

Red algae have photosynthetic pigments that absorb green, violet, and blue light. These wavelengths of light can penetrate deeper water, allowing red algae to photosynthesize where many other algae cannot.

5. What is one method of asexual reproduction in green algae?

One method of asexual reproduction in green algae is fragmentation. During fragmentation, an individual breaks into pieces, and each piece can grow into a new organism.

6. What is the name of the life cycle of green algae?

The life cycle of green algae is called alternation of generations.

After You Read

1. Circle the three words that relate to the life cycle of green algae. Then describe the process in your own words.

The three words are:

1. Alternation of generations

2. Gametophyte

3. Sporophyte

Description: In alternation of generations, green algae alternate between two life stages. The gametophyte is the haploid stage that produces gametes. When gametes join, they form a zygote that grows into the diploid sporophyte stage. The sporophyte produces spores, and those spores grow into new gametophytes.

2. Place the six phyla of algae in the appropriate column. One algae will be used twice.

One-celled

• Euglenoids

• Diatoms

• Dinoflagellates

• Green algae

Multicellular

• Red algae

• Brown algae

• Green algae

Green algae are used twice because they can be unicellular or multicellular.

Section 19.3: Slime Molds, Water Molds, and Downy Mildews

Before You Read

Where are molds and mildew most often found? What conditions help them grow?

Molds and mildew are often found in damp bathrooms, basements, kitchens, old food, wet leaves, rotting logs, soil, and other moist places. They grow best in environments that are moist, cool, and rich in decaying organic material.

Reading Check

1. Name the two different types of slime mold.

The two different types of slime mold are:

1. Plasmodial slime molds

2. Cellular slime molds

2. How do cellular slime molds differ from plasmodial slime molds?

Cellular slime molds are made of many individual cells, each with its own cell membrane. Plasmodial slime molds form one large mass of cytoplasm with many nuclei but no separate cell walls or membranes.

Think It Over

3. How are water molds and downy mildews different from slime molds?

Water molds and downy mildews are different from slime molds because they live in water or very moist places and grow and feed more like fungi. Some are plant parasites. Slime molds are more animal-like during much of their life cycle because they move and engulf food like amoebas.

Reading Check

4. What evidence suggests that ancient green algae was the ancestor of modern plants?

Evidence from RNA analysis suggests that ancient green algae were probably the ancestors of modern plants.

After You Read

1. Write a sentence using the term plasmodium.

A plasmodium is a large mass of cytoplasm in a plasmodial slime mold that contains many diploid nuclei but has no separate cell walls or membranes.

2a. How are plasmodial slime molds and cellular slime molds different?

Plasmodial slime molds form one large feeding mass with many nuclei and no cell walls or membranes between them. Cellular slime molds are made of many separate amoeba-like cells that can gather together into a multicellular mass before reproducing.

2b. How are some funguslike protists harmful to plants?

Some funguslike protists are harmful because they are plant parasites. For example, downy mildew can attack crops such as potatoes and destroy large amounts of food.

Chapter 20: Fungi

Section 20.1: What is a Fungus?

Before You Read

What do places where mushrooms grow have in common? Were they hot, dry, cool, or damp? Did the mushrooms appear suddenly or grow slowly over time?

Mushrooms usually grow in places that are damp, moist, and shaded. They often appear after rain or in areas with decaying leaves, wood, or soil. Mushrooms may seem to appear suddenly, but the fungus has usually been growing slowly underground or inside the food source before the mushroom becomes visible.

Reading Check

1. Identify the fungal group that has a symbiotic relationship.

Fungi that have a symbiotic relationship include fungi that form mycorrhizae and lichens.

In these relationships, the fungus lives closely with another organism. In a mycorrhiza, the fungus lives with plant roots. In a lichen, the fungus lives with algae or cyanobacteria.

2. In what type of fungi does budding occur?

Budding occurs in yeasts, which are unicellular fungi.

During budding, mitosis occurs and a new individual pinches off from the parent.

3. What is a sporangium?

A sporangium is a sac or case where spores are produced.

In fungi, sporangia are often located at the tips of specialized hyphae.

After You Read

1. Circle one key term and write the definition in your own words.

Key term: mycelium

Definition in my own words: A mycelium is a network of branching hyphae that makes up much of the body of a fungus. It helps the fungus grow through its food source and absorb nutrients.

2. Write facts you have learned about fungi to complete the web diagram.

Structures

• Fungi have cell walls made of chitin.

• Most multicellular fungi are made of threadlike filaments called hyphae.

• Many hyphae branch together to form a network called a mycelium.

• Some hyphae have walls called septa that divide them into cells.

Sources of Food

• Fungi are heterotrophs, so they cannot make their own food.

• They digest food outside their bodies and then absorb the smaller molecules.

• Some fungi are saprophytes that feed on dead or decaying matter.

• Some fungi are parasites that absorb nutrients from living hosts.

• Some fungi have symbiotic relationships with other organisms.

Methods of Reproduction

• Fungi can reproduce by fragmentation.

• Yeasts can reproduce by budding.

• Most fungi reproduce by making spores.

• Some fungi can produce spores by mitosis or meiosis during different parts of their life cycles.

Section 20.2: The Diversity of Fungi

Before You Read

Think about the methods by which fungi spread their spores.

Fungi can spread their spores in several ways. Some spores are light and can be carried by the wind. Others may be spread by water, animals, or insects. Some fungi shoot spores into the air, while others use strong smells to attract animals that help spread the spores.

Reading Check

1. What is the function of rhizoids?

Rhizoids penetrate the food source and anchor the mycelium. They also secrete enzymes for extracellular digestion, which helps break down food into smaller molecules that the fungus can absorb.

Think It Over

2. What adaptive advantages are evident in a zygospore?

A zygospore has a thick wall that helps it survive unfavorable conditions, such as dryness, cold, or heat. It can remain dormant for a long time until conditions become favorable again. This helps the fungus survive when the environment is not good for growth.

Reading Check

3. What ascomycete might you encounter every day?

An ascomycete you might encounter every day is yeast.

Yeasts are used in bread making because they produce carbon dioxide, which causes bread dough to rise. They are also used to make products such as wine and beer.

4. What are the two types of symbiotic relationships that fungi share with other organisms?

The two types of symbiotic relationships are:

1. Mycorrhizae

2. Lichens

5. What percent of plants have a mycorrhizal relationship?

About 80 to 90 percent of plants have a mycorrhizal relationship.

6. Why are fossils of fungi so rare?

Fossils of fungi are rare because fungi are made mostly of soft materials, which usually do not preserve well as fossils.

After You Read

1. Circle the two terms that have to do with symbiotic relationships and mutualism. Use those terms in a sentence.

The two terms are:

1. Mycorrhiza

2. Lichen

Sentence: A mycorrhiza and a lichen are both examples of symbiotic relationships in which a fungus lives closely with another organism, and at least one partner benefits from the relationship.

2. Fill in the numbered boxes to complete the chart.

Bread mold consists of:

1. Hyphae

Called:

2. Stolons

3. Rhizoids

That grow upward and end in:

4. Sporangia

That grow horizontally and produce a:

5. Mycelium

3. When you transplant flowers, shrubs, or trees, why should you not disturb the soil around a plant’s roots?

You should avoid disturbing the soil around a plant’s roots because many plants have helpful fungi called mycorrhizae living near or around their roots. These fungi help the plant absorb water and minerals from the soil. If the soil is disturbed too much, the fungal hyphae may be damaged, and the plant may lose some of the benefits of that relationship.

Chapter 21: What is a Plant?

Section 21.1: Adapting to Life on Land

Before You Read

What are some other things that plants provide?

Plants provide many useful materials besides food, oxygen, and medicine. They provide wood for building, paper, cotton for clothing, rubber, oils, spices, fibers, shade, habitats for animals, and materials used in furniture and tools. Plants also help prevent soil erosion and make environments more beautiful.

Reading Check

1. What are the main characteristics of plants?

Plants are multicellular eukaryotes. Their cells have a true nucleus and membrane-bound organelles. Plants also have cell walls made of cellulose, most have a waxy cuticle, and most can make their own food through photosynthesis.

2. What is the purpose of the cuticle?

The cuticle is a waxy covering on the stems and leaves of many plants. Its purpose is to help reduce water loss by keeping water from evaporating from the plant’s tissues.

3. What is vascular tissue?

Vascular tissue is tissue made of tubelike, long cells that transport materials through a plant. It moves water, nutrients, food, and other materials from one part of the plant to another.

After You Read

1. Explain how the development of the cuticle and seeds were adaptations to life on land.

The development of the cuticle helped plants live on land because it reduced water loss. Land plants are exposed to air, wind, and sunlight, so they can dry out more easily than plants or algae living in water. A waxy cuticle helps protect the plant by keeping water inside its tissues.

The development of seeds also helped plants adapt to land. A seed contains an embryo, a food supply, and a protective coat. This protects the young plant from drying out and gives it stored food so it can survive until conditions are good for growth.

2. Choose one question heading and answer it.

Question: What are the basic plant organs?

Answer: The basic plant organs are leaves, roots, and stems. Leaves are usually where photosynthesis takes place. Roots absorb water and nutrients from the soil and anchor the plant. Stems support the plant and move water, food, and other materials between the roots and leaves.

Section 21.2: Survey of the Plant Kingdom

Before You Read

If you were to place plants into divisions, what characteristics would you use?

I would classify plants by whether they have vascular tissue, whether they produce seeds, whether they have flowers or cones, and whether they reproduce using spores. I would also look at structures such as roots, stems, leaves, fronds, cones, flowers, and fruits.

Reading Check

1. What are the highlights of plant evolution?

The highlights of plant evolution include:

1. The origin of plants from green algae

2. The production of a waxy cuticle

3. The development of vascular tissue and roots

4. The production of seeds

2. What do studies suggest about liverworts?

Some studies suggest that liverworts may be the ancestors of all plants.

3. What do all seed plants have in common?

All seed plants produce seeds and have vascular tissue.

4. How many different species are in the ginkgophyta division?

There is only one living species in the ginkgophyta division: Ginkgo biloba.

After You Read

1. Use each Mini Glossary term in a sentence.

Cones: Cones are scaly structures in some seed plants that support male or female reproductive structures and are sites of seed production.

Frond: A frond is a fern leaf, and fronds can vary greatly in size.

2. Sort each statement into the correct box: Non-seed or Seed.

Non-seed Plants

a. There are seven divisions of these plants.
c. These plants release reproductive cells called spores.
e. These plants may be either vascular or nonvascular.

Seed Plants

b. These plants release seeds.
d. There are five divisions of these plants.
f. These plants contain a plant organ made up of an embryonic plant and a food supply covered by a hard protective coat.
g. All of these plants are vascular.

Chapter 22: The Diversity of Plants

Section 22.1: Nonvascular Plants

Before You Read

How might a habitat benefit by pioneer species such as moss?

A habitat can benefit from pioneer species such as moss because moss can be one of the first plants to grow after a disturbance. Moss helps hold soil in place, reduces erosion, traps moisture, and begins adding organic material to the area. This can make the habitat better for other plants and animals later.

Reading Check

1. What are the two classifications of liverworts?

The two classifications of liverworts are:

1. Thallose liverworts

2. Leafy liverworts

2. What kind of body do hornworts have?

Hornworts have a thallose body, similar to some liverworts.

3. What do scientists hypothesize were the first land plants?

Scientists hypothesize that liverworts were the first land plants.

After You Read

1. Tell how the two key terms are related.

The two terms are antheridium and archegonium.

They are related because both are reproductive structures in nonvascular plants. The antheridium is the male reproductive structure where sperm develop, while the archegonium is the female reproductive structure where eggs develop.

Section 22.2: Non-Seed Vascular Plants

Before You Read

What did you miss most about not having plumbing?

Without plumbing, I would miss having easy access to clean water and a simple way to remove waste. Plumbing helps move water where it is needed and carries waste away. In a similar way, vascular tissue helps plants move water, nutrients, and other substances throughout the plant.

Think It Over

1. What might a drought do to the long-term survival of non-seed vascular plants?

A drought could hurt the long-term survival of non-seed vascular plants because they need water for reproduction. Their sperm must swim through a thin film of water to reach the egg. Without enough moisture, reproduction would be harder, and fewer new plants would grow.

Reading Check

2. Where do most horsetails grow?

Most horsetails grow in damp soil, in places such as shallow ponds, marshes, and stream banks.

Think It Over

3. Why are non-seed vascular plants smaller and less widespread than their prehistoric ancestors?

Non-seed vascular plants are smaller and less widespread today because Earth’s climate became cooler and drier over time. Their reproduction still depends on water, so they are limited to moist habitats. Many of their large prehistoric relatives died out when conditions changed.

After You Read

1. Write a sentence using at least two Mini Glossary terms.

A fern’s prothallus is the gametophyte stage, while its rhizome is a thick underground stem that stores food.

3. Explain why most non-seed vascular plants live in moist habitats.

Most non-seed vascular plants live in moist habitats because they need water for reproduction. Their sperm must swim through water to reach the egg. Moist habitats also help these plants avoid drying out.

Section 22.3: Seed Plants

Before You Read

List products that originate from seeds.

Products that originate from seeds include corn, wheat, oats, rice, beans, peas, nuts, apples, oranges, olives, figs, strawberries, grapes, sunflower seeds, popcorn, flour, cereal, cooking oil, and many fruits and vegetables.

Reading Check

1. What do you call plants that produce seeds protected by fruit?

Plants that produce seeds protected by fruit are called angiosperms.

Think It Over

2. What two divisions of plants have male and female reproductive structures on separate plants?

The two divisions are:

1. Cycadophyta

2. Ginkgophyta

Reading Check

3. How does dropping leaves help keep a plant from losing water?

Plants lose most of their water through their leaves. When water is scarce, dropping leaves helps a plant reduce water loss and survive by becoming dormant until conditions improve.

Reading Check

4. How can you identify if a seed plant is a monocot or a dicot?

You can identify a monocot or dicot by looking at the seed leaves and leaf veins.

A monocot has one cotyledon and usually has parallel leaf veins.

A dicot has two cotyledons and usually has netlike or branching leaf veins.

Reading Check

5. What is the name for plants that have a life span of more than two years?

Plants that have a life span of more than two years are called perennials.

Think It Over

6. Which best describes the order in which plants likely appeared on Earth?

Correct choice: b. conifers then anthophytes

Conifers appeared before anthophytes. Anthophytes, or flowering plants, appeared later.

After You Read

1. Circle the three terms that categorize plants by their life spans. Write the terms and provide two examples for each category.

Annuals: plants that live for one year or less
Examples: corn and peas

Biennials: plants that live for two years
Examples: carrots and beets

Perennials: plants that live for several years
Examples: strawberries and asparagus

2. Complete the diagram by writing in seven adaptations of seed plants.

Seven adaptations of seed plants are:

1. Seeds that protect the embryo

2. Stored food inside the seed for the young plant

3. Tough protective seed coat

4. Pollen grains that allow fertilization without a continuous film of water

5. Ovules that develop into seeds after fertilization

6. Fruits that protect seeds and help with seed dispersal

7. Cotyledons that store or absorb food for the developing embryo

Chapter 23: Plant Structure and Function

Section 23.1: Plant Cells and Tissues

Before You Read

Prediction: What might happen if you place freshly cut celery stalks in colored water?

The celery stalks will probably begin to change color. The food coloring will move upward through the celery’s vascular tissue, especially the xylem, which transports water. After a few hours, the veins or edges of the celery may show the color.

Reading Check

1. How are fibers useful to people?

Fibers are useful because they can be used to make materials such as linen, rope, and clothing. Fibers provide strength because they are long, thick-walled cells.

2. What is the function of the stomata?

Stomata are small openings in leaves and stems that allow gases to move in and out of the plant. They also allow water vapor to leave the plant during transpiration.

3. What is transported by xylem?

Xylem transports water and dissolved minerals from the roots to the stems and leaves.

4. What are the functions of ground tissue?

Ground tissue helps with storage, support, and photosynthesis. In leaves, ground tissue contains chloroplasts that make food. In stems and roots, it may store water, starch, oils, or other materials.

After You Read

1. Explain how the terms stomata and guard cells are related.

Stomata are tiny openings in a leaf or stem that allow gases and water vapor to pass in and out. Guard cells are the cells that surround each stoma. Guard cells control whether the stomata open or close, which helps the plant regulate gas exchange and water loss.

2. Venn Diagram: Xylem and Phloem

Xylem

• Transports water

• Transports dissolved minerals

• Moves materials mostly upward from roots to stems and leaves

• Made of tracheids and vessel elements

• Cells are dead when fully mature

Both

• Are vascular tissues

• Transport materials through the plant

• Are found in roots, stems, and leaves

• Help connect different parts of the plant

• Are made of specialized plant cells

Phloem

• Transports sugars

• Transports organic compounds

• Moves food from where it is made to where it is needed or stored

• Made of sieve tube members and companion cells

• Contains living cells

Section 23.2: Roots, Stems, and Leaves

Before You Read

List examples of foods that come from roots, stems, and leaves.

Roots: carrots, radishes, beets, turnips, sweet potatoes

Stems: potatoes, asparagus, celery, sugarcane

Leaves: lettuce, spinach, cabbage, kale, herbs

Reading Check

1. How does bark protect a plant?

Bark protects a plant by forming a tough outer covering around woody stems and roots. It helps prevent water loss and protects the plant from insects, disease, and injury.

2. Does primary growth lengthen or thicken a stem?

Primary growth lengthens a stem.

Secondary growth is what thickens stems and roots.

3. What regulates transpiration?

Stomata and guard cells regulate transpiration. Guard cells open and close the stomata, controlling how much water vapor leaves the plant.

After You Read

1. Choose three leaf-related terms and explain how they relate to leaves.

Cuticle: The cuticle is a waxy covering on the outside of leaves that helps prevent water loss.

Mesophyll: Mesophyll is the inner tissue of a leaf where most photosynthesis takes place.

Stomata: Stomata are openings in the leaf that allow carbon dioxide to enter and oxygen and water vapor to leave.

Together, these structures help leaves carry out photosynthesis while also controlling water loss.

Section 23.3: Plant Responses

Before You Read

How do plants respond to light and touch?

Plants respond to light by growing toward it. This helps leaves receive more sunlight for photosynthesis. Plants can also respond to touch. For example, vines may curl around supports, and some leaves may close when touched.

Think It Over

1. Why might a florist need to use gibberellins?

A florist might use gibberellins to help flower buds open or to make plant stems grow taller. Gibberellins affect plant growth and can help control flowering and stem length.

Think It Over

2. How might placing ripe fruit in a brown paper bag with unripe fruit cause the unripe fruit to ripen?

Ripe fruit releases ethylene, a plant hormone that speeds up ripening. When ripe fruit is placed in a closed paper bag with unripe fruit, ethylene builds up in the bag and causes the unripe fruit to ripen faster.

Reading Check

3. Why are tropisms not reversible?

Tropisms are not reversible because they involve growth. Once a plant stem or root grows in a certain direction, that growth cannot be undone. However, if the direction of the stimulus changes, new growth can begin in a different direction.

After You Read

1. Explain how auxins and tropism relate to each other.

Auxins are plant hormones that cause cells to elongate. Tropism is a change in plant growth in response to a stimulus. Auxins help cause tropisms by making cells on one side of a stem or root grow longer than cells on the other side, which causes the plant part to bend or grow in a certain direction.

2. Match each concept with the correct example.

1. plant hormones — c. affect plant growth and functions

2. tropisms — a. growth responses to external stimuli

3. nastic movement — b. sometimes caused by changes in cell pressure

4. phototropism — e. growth of plant toward light

5. thigmotropism — d. growth response to touch

Chapter 24: Reproduction in Plants

Section 24.1: Life Cycles of Mosses, Ferns, and Conifers

Before You Read

Questions I have about alternation of generations:

How are the gametophyte and sporophyte generations different?

Why is one generation dominant in some plants but not in others?

How do mosses, ferns, and conifers reproduce differently?

Reading Check

1. Is the gametophyte or the sporophyte the dominant generation in most plant species?

In most plant species, the sporophyte is the dominant generation.

The sporophyte is usually the larger, more visible plant form.

2. How do moss gametophytes reproduce by vegetative reproduction?

Moss gametophytes can reproduce by vegetative reproduction when they become dry and brittle and break into pieces. When moisture returns, each piece can grow into a protonema and then develop into a new gametophyte.

Think It Over

3. What are the differences between male and female reproductive cones?

Male cones are usually smaller and produce microspores, which develop into male gametophytes, or pollen grains.

Female cones are usually larger and contain ovules. Inside the ovules, megaspores develop into female gametophytes that contain eggs.

After You Read

1. Write a brief paragraph describing vegetative reproduction.

Vegetative reproduction is a type of asexual reproduction in plants. A new plant grows from an existing plant part, such as a stem, root, leaf, or piece of plant tissue. In mosses, a dry gametophyte can break apart, and each piece can grow into a protonema and then a new gametophyte when moisture returns. This allows plants to reproduce without seeds or fertilization.

2. Fill in the table about mosses, ferns, and conifers.

3. Explain why mosses and ferns need a moist environment for sexual reproduction.

Mosses and ferns need a moist environment because their sperm must swim through a film of water to reach the egg. Without water, fertilization cannot easily occur, so these plants usually reproduce sexually in damp or moist habitats.

Section 24.2: Flowers and Flowering

Before You Read

Flowers I associate with seasons or days of the year:

I associate tulips and daffodils with spring because they often bloom when the weather begins to warm. I associate sunflowers with summer because they grow well in bright sunlight. I associate poinsettias with winter and the holiday season because they are commonly used as decorations during that time.

Think It Over

1. Which controls flowering?

Correct choice: b. length of darkness

Scientists once thought flowering was controlled mainly by daylight, but the article explains that the length of darkness controls flowering.

Reading Check

2. What are the four different categories of flowering plants within photoperiodism?

The four categories are:

1. Short-day plants

2. Long-day plants

3. Day-neutral plants

4. Intermediate-day plants

3. How does photoperiodism ensure pollination?

Photoperiodism helps all the plants of a species flower at the same time. This ensures that many flowers are available at once and that there is a large population of pollinators when pollination needs to occur.

After You Read

1. Highlight four terms that deal with photoperiodism. Then circle the terms for the four organs that make up flowers.

Four terms that deal with photoperiodism are:

1. Photoperiodism

2. Short-day plant

3. Long-day plant

4. Day-neutral plants

The four organs that make up flowers are:

1. Sepals

2. Petals

3. Stamens

4. Pistils

2. List the organs and structures of a flower in the diagram.

Flower

• Pistil — female organ

  • Stigma

  • Style

  • Ovary

• Petals

• Sepals

• Stamen — male organ

  • Anther

  • Filament

Section 24.3: The Life Cycle of a Flowering Plant

Before You Read

Why might a potato or onion grow leaves or roots in a pantry or refrigerator?

A potato or onion may grow leaves or roots because it contains stored food and living plant tissue. If conditions become favorable, such as enough moisture, warmth, and time, buds can begin to grow into new shoots or roots. This is a form of plant growth from existing plant parts.

Reading Check

1. What are the three ways that pollen is carried to the stigma?

Pollen can be carried to the stigma by:

1. Wind

2. Water

3. Animals

2. Why do animal-pollinated plants produce less pollen than wind-pollinated plants?

Animal-pollinated plants produce less pollen because animals usually carry pollen directly from one flower to another. Wind-pollinated plants must produce large amounts of pollen because much of it may be lost and never reach the correct flower.

3. What is double fertilization?

Double fertilization is a process in flowering plants where one sperm fertilizes the egg cell to form a diploid zygote, and the other sperm joins with the central cell to form a triploid endosperm.

4. What are the functions of the seed coat?

The seed coat protects the embryo inside the seed. It also helps the seed survive harsh conditions and can help with seed dispersal.

Think It Over

5. How might a plant benefit from producing seeds that can remain dormant for long periods?

A plant benefits because dormant seeds can survive unfavorable conditions, such as drought, cold, or lack of light. The seeds can wait until conditions are better for growth. This increases the chance that the next generation will survive.

Reading Check

6. When does photosynthesis begin in a new plant?

Photosynthesis begins when the young plant’s leaves turn green and are exposed to sunlight. At that point, the plant can begin making its own food.

7. Producing a new plant from part of another plant is called:

Correct choice: b. vegetative reproduction

Vegetative reproduction produces a new plant from roots, stems, leaves, or other plant parts.

After You Read

1. Circle two terms that are related to each other. Tell how these terms are related.

Two related terms are dormancy and germination.

They are related because dormancy is the period when a seed is inactive, and germination begins when dormancy ends. During germination, the embryo starts developing into a new plant.

2. Place check marks to indicate whether each organ or structure is involved in each activity.

Chapter 25: What Is an Animal?