chapter 10 cell structure and function · cell structure and function cells and energy lesson 4...

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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 CytoplasmThe 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.

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.

Key Concepts • How does a cell obtain

energy?• How do some cells make

food molecules?

Visual Check1. Locate Circle where sugar breaks down in the cell during glycolysis.

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.

Chemical

reactions

Cytoplasm

Smaller

molecules

Glucose

(sugar)

ATP

ATP

Cell Structure and Function

Cells and Energy

LESSON 4

CHAPTER 10

178 Cell Structure and Function Reading Essentials

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Reactions in the MitochondriaThe 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.

Key Concept Check3. Explain how a cell obtains energy.

Visual Check2. Compare the reactions in mitochondria with glycolysis.

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

CellularRespiration Fermentation

Glycolysis

Step 1

Step 2

(Energy)

Water(H2O)

Carbondioxide(CO2)

Oxygen (O2)Smaller

molecules

The products of glycolysis are used in step 2.

ATP

Mitochondrion

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

FermentationSometimes, 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 FermentationThere 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.

Reading Essentials Cell Structure and Function 179


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Reading Check4. Compare lactic-acid fermentation and alcohol fermentation.

Visual Check 5. Identify the products of both lactic-acid fermentation and alcohol fermentation.

ATP

ATP

Lactic-Acid Fermentation

Alcohol Fermentation

Glucose

(C6H12O6)+ Alcohol

(Energy)

(Energy)

Glucose

(C6H12O6)+ Lactic acid

+

Muscle

cells

Yeast

cells

Carbon dioxide

(CO2)ATP

ATP

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

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.

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 PigmentsPhotosynthesis 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 ChloroplastsThe 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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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.

Visual Check 7. Explain the relationship between cellular respiration and photosynthesis.

Lightenergy Chloroplast

Mitochondrion

Photosynthesis

6CO2+ 6H2O C6H12O6+ 6O2

Carbon dioxide (CO2)Water (H2O)

Glucose (C6H12O6)Oxygen (O2)

Cellular respiration

C6H12O6+ 6O2 6CO2+ 6H2O+ ATP

ATP

(Energy)

WORD ORIGINphotosynthesisfrom Greek photo, means “light,” and synthesis, means “composition’

Reading Essentials Cell Structure and Function 181


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Mini Glossary

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?

What do you think

END OF LESSON

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

ConnectED

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.

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

Photosynthesis Respiration Fermentation

What is needed?

1.

2.

3.

1.

2.

1. glucose molecules

What is produced?

1.

2.

1.

2.

1.

2.

3.

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



chapter 10 cell structure and function · cell structure and function cells and energy lesson 4...

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