CHAPTER 2 Cell Structure and Function

CHAPTER 2 LESSON 4

Cell Structure and Function

Key Concepts

? How does a cell obtain energy?

? How do some cells make food molecules?

Cells and Energy

What do you think? Read the two statements below and decide

whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you've read this lesson, reread the statements to see if you have changed your mind.

Before

Statement

After

7. ATP is the only form of energy found in cells.

8. Cellular respiration occurs only in lung cells.

3TUDY#OACH

Use an Outline As you read, make an outline to summarize the information in the lesson. Use the main headings in the lesson as the main headings in the outline. Complete the outline with the information under each heading.

Visual Check 1. Locate Circle where sugar breaks down in the cell during glycolysis.

Cellular Respiration

All living organisms need energy to survive. Cells use energy from food and make an energy-storing compound, ATP. Cellular respiration is a series of chemical reactions that convert the energy in food into a usable form of energy called ATP. Cellular respiration takes place in the cytoplasm and in the mitochondria of a cell.

Reactions in the Cytoplasm

The first step of cellular respiration is called glycolysis. It

takes place in the cytoplasm of all cells. Glycolysis is a process

by which a sugar called glucose is broken down into smaller molecules.

Glycolysis produces some ATP molecules. It also uses energy

from other ATP molecules.

More ATP is made during the second step of cellular respiration than during glycolysis.

ATP Glucose

(sugar)

Cytoplasm

Chemical reactions

Smaller

ATP

molecules

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34 Cell Structure and Function

Reading Essentials

Reactions in the Mitochondria

The second step in cellular respiration, shown below, takes place in the mitochondria of eukaryotic cells. This step uses oxygen. The smaller molecules made during glycolysis are broken down. Many ATP molecules are made. Cells use ATP molecules to power all cellular processes. Two waste products, water and carbon dioxide (CO2), are given off during this step of cellular respiration. The CO2 released by cells as a waste product is used by plants and some unicellular organisms in a process called photosynthesis.

Step 1

Glycolysis

Smaller molecules

The products of glycolysis are used in step 2.

Oxygen (O2)

Reactions in the mitochondria convert oxygen and small molecules into energy, water, and carbon dioxide.

Step 2

Mitochondrion

ATP (Energy)

Water (H2O)

Carbon dioxide (CO2)

Fermentation

Sometimes, as you exercise, there is not enough oxygen in your cells to make ATP molecules through cellular respiration. When this happens, cells use a process called fermentation to obtain chemical energy. Fermentation is a reaction that eukaryotic and prokaryotic cells use to obtain energy from food when oxygen levels are low. Because no oxygen is used, fermentation makes less ATP than cellular respiration does. Fermentation takes place in a cell's cytoplasm, not in mitochondria.

Types of Fermentation

There are several types of fermentation. One type occurs when glucose is changed into ATP and a waste product called lactic acid.

Lactic-Acid Fermentation Some bacteria and fungi help produce cheese, yogurt, and sour cream using lactic-acid fermentation. The muscle cells in animals, including humans, can release energy during exercise using lactic-acid fermentation.

Make a half-book to record information about the different types of energy production.

Cellular Respiration

Fermentation

Visual Check

2. Compare the reactions

in mitochondria with glycolysis.

Key Concept Check 3. Explain how a cell obtains energy.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Reading Essentials

Cell Structure and Function 35

Reading Check

4. Compare lactic-acid

fermentation and alcohol fermentation.

Alcohol Fermentation Some types of bacteria and yeast make ATP through a process called alcohol fermentation. Alcohol fermentation produces an alcohol, called ethanol, and carbon dioxide. Many types of bread are made using yeast. The carbon dioxide produced by yeast during alcohol fermentation makes bread dough rise. Lactic-acid fermentation and alcohol fermentation are shown below.

Lactic-Acid Fermentation

Visual Check

5. Identify the products of

both lactic-acid fermentation and alcohol fermentation.

Muscle cells

Yeast cells

Glucose (C6H12O6)

ATP + Lactic acid (Energy)

Glucose (C6H12O6)

Alcohol Fermentation

ATP + Carbon dioxide + Alcohol

(Energy)

(CO2)

Key Concept Check 6. Explain how some cells make food molecules.

Photosynthesis

Plants and some unicellular organisms obtain energy from light. They use photosynthesis. Photosynthesis is a series of chemical reactions that convert light energy, water, and carbon dioxide into the food-energy molecule glucose and the waste product oxygen.

Light and Pigments

Photosynthesis uses light energy. In plants, pigments such as chlorophyll absorb light energy. As chlorophyll absorbs light, it absorbs all the colors in it except green.

The green light is reflected as the green color that you see in leaves and stems. Plants might also contain pigments that reflect other colors, such as red, yellow, or orange light.

Reactions in Chloroplasts

The chlorophyll that absorbs light energy for photosynthesis is in chloroplasts. Chloroplasts are organelles in plant cells that convert light energy to chemical energy in food. During photosynthesis, light energy, water, and carbon dioxide combine and make sugars. Photosynthesis also produces oxygen, which is released into the atmosphere.

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36 Cell Structure and Function

Reading Essentials

Importance of Photosynthesis

Photosynthesis uses light energy and carbon dioxide to make food energy. Oxygen is released during this process. This food energy is stored as glucose. When an organism eats plant material, such as fruit, it takes in food energy. The cells of the organism will then go through cellular respiration. They will use the oxygen released during photosynthesis and convert the food energy into ATP. These organisms then release carbon dioxide into the atmosphere. The relationship between cellular respiration and photosynthesis is shown in the diagram below.

WORD ORIGIN

photosynthesis from Greek photo, means "light," and synthesis, means "composition'

Light energy

Chloroplast

Carbon dioxide (CO2) Water (H2O)

Mitochondrion

Glucose (C6H12O6) Oxygen (O2)

Visual Check

7. Explain the relationship

between cellular respiration and photosynthesis.

ATP

C6H12O6 + 6O2

6CO2 + 6H2O +

ATP (Energy)

Cellular respiration

6CO2 + 6H2O

C6H12O6 + 6O2

Photosynthesis

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Reading Essentials

Cell Structure and Function 37

Mini Glossary

cellular respiration: a series of chemical reactions that convert the energy in food molecules into a usable form of energy called ATP

fermentation: a reaction that eukaryotic and prokaryotic cells use to obtain energy from food when oxygen levels are low

glycolosis: a process by which glucose, a sugar, is broken down into smaller molecules

photosynthesis: a series of chemical reactions that converts light energy, water, and carbon dioxide into the food-energy molecule glucose and gives off oxygen

1. Review the terms and their definitions in the Mini Glossary. Explain, using complete sentences, how photosynthesis and respiration are related.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

2. Fill in the table below to identify what is needed by each chemical reaction and what is produced by each chemical reaction.

What is needed?

Photosynthesis 1. 2. 3.

Respiration 1. 2.

Fermentation 1. glucose molecules

1.

1.

1.

What is

2.

2.

2.

produced?

3.

3. As chlorophyll in plants absorbs light, it absorbs all the colors except one color. Which color is that?

What do you think

Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?

38 Cell Structure and Function

ConnectED

Log on to ConnectED.mcgraw- and access your textbook to find this lesson's resources.

END OF LESSON

Reading Essentials

Name

Date

Class

Content Vocabulary

LESSON 4

Cells and Energy

Directions: In this word search puzzle, find and circle the four terms listed below. Then write each term on the line before its definition.

cellular respiration

fermentation

glycolysis

photosynthesis

F HG L X R L X POB J K A L F CMX E R R S P A Y I KMU Y G I Q Y B P Q R C Y F KQN I Y SNS V F V YDHN M A R WW G K U B E J S W C R A O O L E G Y U L I C WW T J T E Z J S O T C N V L X F D BWQ Y S B Z K V E J O L T E E YCXHVS BVHE KXZOS F A J F X CWUDN I N Z P Z O E C Y I T D H UWO A V A G C H F P V A J N E I NA FM I L Z K Z F F BAHUF TG OQGOR B S Y P A V F B B KN I HC NO I T AR I P S E R RA L U L L E C KQOE PGK VG I Y SO L U S I S B VZAYUPP EQBS J I EVBT I O UQ E S HWE UD K Y R GWNGM S Y

1. Cells use oxygen in this process to convert food energy into ATP.

2. This is a reaction used by cells to obtain energy from food when oxygen levels are low.

3. This process breaks apart glucose. 4. This process converts light energy into glucose and

releases oxygen.

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Cell Structure and Function

67

Name

Date

Class

Lesson Outline

LESSON 4

Cells and Energy

A. Cellular Respiration

1. All

things need energy to survive.

2.

is a series of chemical reactions that convert the energy

in food molecules into a usable form of energy called ATP.

3. The first step of cellular respiration, called glycolysis, occurs in the

of all cells.

4. During glycolysis molecules.

, a sugar, is broken into smaller

5. The second step of cellular respiration occurs in the

of

eukaryotic cells. This step requires

.

6. During the second step of cellular respiration, the smaller molecules made during

are broken down. Large amounts of usable energy,

called

, are produced.

7.

and carbon dioxide (CO2) are two waste products that

are given off during the second step of cellular respiration.

B. Fermentation

1. Eukaryotic and prokaryotic cells use fermentation to obtain energy from food when

levels are low.

2. Fermentation occurs in a cell's

.

3. Lactic-acid fermentation converts product called lactic acid.

into ATP and a waste

4. Some types of bacteria and yeasts make ATP during

fermentation. This process produces C. Photosynthesis

and CO2.

1. Plants and some unicellular organisms obtain energy

from

.

2. Photosynthesis is a series of chemical reactions that convert light energy, water, and

CO2 into

and

3. In plants, light energy is absorbed by chlorophyll.

. such as

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

68

Cell Structure and Function

Name

Date

Class

Lesson Outline continued

4. The chemical reactions of photosynthesis occur in organelles in plant cells that convert light energy into food.

, the

5. Photosynthesis uses CO2 that is released during

to

make food energy and release oxygen.

6. When an organism eats plant material, it takes in

energy. An organism's cells use photosynthesis.

released during

Copyright ? Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Cell Structure and Function

69

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