Copyri

ght

© G

lenco

e/M

cGra

w-H

ill,

a d

ivis

ion o

f T

he

McG

raw

-Hil

l C

om

pan

ies,

Inc.

Materials for Plant ProcessesFood, water, and oxygen are three things you need to

survive. Some of your organ systems process these materials. Other systems transport them throughout your body. Like you, plants need food, water, and oxygen to survive. Unlike you, plants do not take in food. Most plants make their own food.

Moving Materials Inside PlantsXylem (ZI lum) and phloem (FLOH em) are the vascular

tissue in most plants. These tissues transport materials throughout a plant.

After water enters a plant’s roots, it moves into xylem. Water then flows inside xylem to all parts of a plant. Without enough water, plant cells wilt.

Most plants make their own food—a liquid sugar. The liquid sugar moves out of food-making cells, enters phloem, and flows to all plant cells. Cells break down the sugar and release energy. Some plant cells can store food.

Plants require oxygen and carbon dioxide to make food. Like you, plants produce water vapor as a waste product. Carbon dioxide, oxygen, and water vapor pass into and out of a plant through tiny openings in leaves.

What do you think? Read the three 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

1. Plants do not carry on cellular respiration.

2. Plants are the only organisms that carry on photosynthesis.

3. Plants make food in their underground roots.

Key Concepts • How do materials move

inside plants?• How do plants perform

photosynthesis?• What is cellular respiration?• How are photosynthesis

and cellular respiration alike, and how are they different?

Key Concept Check1. Determine How do materials move through plants?

Make an Outline Summarizethe information in the lesson in an outline. Use the main headings in the lesson as the main headings in your outline. Use your outline to review the lesson.

Plant Processes and ReproductionEnergy Processing in Plants

LESSON 1

CHAPTER 8

Reading Essentials Plant Processes and Reproduction 125

C225_001_006_RE_L1_889406.indd 1C225_001_006_RE_L1_889406.indd 1 2/25/10 4:09:11 PM2/25/10 4:09:11 PM

Copyrig

ht ©

Glen

coe/M

cGraw

-Hill, a d

ivisio

n o

f The M

cGraw

-Hill C

om

pan

ies, Inc.

PhotosynthesisPlants make their own food through a process called

photosynthesis (foh toh SIHN thuh sus). Photosynthesis is a series of chemical reactions that convert light energy, water, and carbon dioxide into the food-energy molecule glucose and give off oxygen.

Leaves are the major food-producing organs of plants. This means that photosynthesis takes place in the plant’s leaves. The structure of a leaf is well-suited to its role in photosynthesis.

Leaves and PhotosynthesisThe figure below shows the many types of cells in a leaf.

The epidermal (eh puh DUR mul) cells make up the upper and lower layers of the leaf. Epidermal cells are flat and irregularly shaped. The bottom epidermal layer of most leaves has small openings called stomata (STOH muh tuh). Carbon dioxide, water vapor, and oxygen pass through stomata. Epidermal cells can produce a waxy covering called the cuticle.

Most photosynthesis occurs in two types of mesophyll (ME zuh fil) cells inside a leaf. Mesophyll cells contain chloroplasts, which are the organelles where photosynthesis occurs. The palisade mesophyll cells are near the top surface of the leaf. They are packed close together. This arrangement exposes the most cells to light. Spongy mesophyll cells are below the palisade mesophyll cells. They have open spaces between them. Gases needed for photosynthesis flow through the spaces between the spongy mesophyll cells.

Visual Check2. Locate Which layer of cells contains vascular tissue?

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

Make a shutterfold book and label it as shown to use as a diagram of leaf structure.

Upper Epidermis

Lower Epidermis

Mesophyll Cells

Chloroplast

Inner membrane

Outer membrane

Upperepidermal cells

CuticlePalisademesophyll cells

Spongymesophyll cells

StomaLowerepidermal cells

Vasculartissue

Cross Section of a Leaf

126 Plant Processes and Reproduction Reading Essentials

C225_001_006_RE_L1_889406.indd 2C225_001_006_RE_L1_889406.indd 2 2/25/10 4:09:25 PM2/25/10 4:09:25 PM

Copyri

ght

© G

lenco

e/M

cGra

w-H

ill,

a d

ivis

ion o

f T

he

McG

raw

-Hil

l C

om

pan

ies,

Inc.

Capturing Light EnergyPhotosynthesis is a complex chemical process. It consists

of two basic steps: capturing light energy and using that energy to make sugars. Look at the figure below as you read about these steps to help you understand the process.

In the first step, chloroplasts capture the energy in light. Chloroplasts contain plant pigments. Pigments are chemicals that can absorb and reflect light. Chlorophyll is the most common plant pigment. It is necessary for photosynthesis. Most plants appear green because chlorophyll reflects green light. Chlorophyll absorbs other colors of light. This light energy is used during photosynthesis.

Chlorophyll traps and stores light energy. Then this energy can be transferred to other molecules. During photosynthesis, water molecules are split apart. The oxygen from the water molecules is released into the atmosphere, as shown below. The hydrogen atoms in the water are used to make sugars in the second step of photosynthesis.

Making SugarsIn the second step of photosynthesis, sugars are made

from the light energy. In chloroplasts, carbon dioxide from the air is converted into sugars by using the energy stored and trapped by chlorophyll. Carbon dioxide combines with hydrogen atoms from the splitting of water molecules and forms sugar molecules. Plants can use this sugar as an energy source. Plants can also store the sugar for later use. Potatoes and carrots are examples of plant structures where plants store excess sugar.

Reading Check3. Identify How do plants capture light energy?

Key Concept Check4. Name What are the two steps of photosynthesis?

Visual Check5. Describe Use the figure to explain to a partner the first step of photosynthesis. Then have your partner use the figure to explain the second step of photosynthesis.

Sugar

C6H12O6

Oxygen

O2

Carbon dioxide

CO2

Water

H2O

Light

energy

PhotosynthesisCarbon dioxide + Water Sugar + Oxygen

6CO2+ 6H2O C6H12O6+ 6O2

Light energy

Chlorophyll

Photosynthesis

Reading Essentials Plant Processes and Reproduction 127

C225_001_006_RE_L1_889406.indd 3C225_001_006_RE_L1_889406.indd 3 2/25/10 4:09:33 PM2/25/10 4:09:33 PM

Copyrig

ht ©

Glen

coe/M

cGraw

-Hill, a d

ivisio

n o

f The M

cGraw

-Hill C

om

pan

ies, Inc.

Why is photosynthesis important?Try to imagine a world without plants. The world would

certainly look different, and its atmosphere would also be different. How would humans or other animals get the oxygen they need?

Plants help maintain the atmosphere you breathe. Photosynthesis produces as much as 90 percent of the oxygen in the atmosphere. Without green plants, humans would not have enough oxygen to breathe.

Cellular RespirationAll organisms require energy to survive. Energy is in the

chemical bonds in food molecules. A process called cellular respiration releases energy. Cellular respiration is a series of chemical reactions that convert the energy in food molecules into a usable form of energy called ATP.

Releasing Energy from SugarsGlucose is the sugar produced by photosynthesis. Glucose

molecules break down during cellular respiration. Much of the energy released during this process is used to make ATP. ATP is an energy storage molecule.

Cellular respiration occurs in the cytoplasm and mitochondria of cells. This process requires oxygen and produces water and carbon dioxide as waste products.

Why is cellular respiration important?If your body did not break down the food you eat, you

would not have energy to do anything. All organisms must break down their food to produce energy. Plants produce their own food—glucose—during photosynthesis. Without cellular respiration, plants could not grow, reproduce, or repair tissues.

Comparing Photosynthesis and Cellular Respiration

Photosynthesis requires light energy and the reactants carbon dioxide and water. Reactants are substances that react with one another during the process.

Oxygen and glucose are the products, or end substances, of photosynthesis. Glucose is a molecule of stored energy. Most plants, some protists, and some bacteria carry on photosynthesis.

Key Concept Check7. Explain What is cellular respiration?

Reading Check6. Name Which cellular process converts food energy into usable energy?

ACADEMIC VOCABULARYenergy(noun) usable power

128 Plant Processes and Reproduction Reading Essentials

C225_001_006_RE_L1_889406.indd 4C225_001_006_RE_L1_889406.indd 4 2/25/10 4:09:57 PM2/25/10 4:09:57 PM

Copyri

ght

© G

lenco

e/M

cGra

w-H

ill,

a d

ivis

ion o

f T

he

McG

raw

-Hil

l C

om

pan

ies,

Inc.

Chemical Equation for Photosynthesis Look at the chemical equation for photosynthesis on the right in the figure above. Notice that photosynthesis requires carbon dioxide (CO2) and water (H2O) molecules. These molecules react with light energy and produce glucose (C6H12O6) and oxygen (O2).

Chemical Equation for Cellular Respiration The chemical equation for cellular respiration is on the left in the figure above. The reactants are glucose (C6H12O6) and oxygen (O2). It produces carbon dioxide (CO2) and water (H2O) molecules. Cellular respiration releases energy in the form of ATP.

Most organisms carry on cellular respiration. The connection between photosynthesis and cellular respiration is shown in the table below. Life on Earth depends on a balance of these two processes.

Visual Check8. Distinguish Refer to the figure above and the table below. What are the reactants of cellular respiration? What are the products?

Comparing Photosynthesis and Cellular Respiration

Process Photosynthesis Cellular Respiration

Reactants light energy, CO2, H2O glucose (sugar), O2

Products glucose, O2 CO2, H2O, ATP

Organelle in which it occurs chloroplasts mitochondria

Type of organismphotosynthetic

organisms including plants and algae

most organisms, including plants and

animals

Key Concept Check9. Compare How are photosynthesis and cellular respiration alike, and how are they different?

Lightenergy

ATP

Chloroplast

Mitochondrion

Glucose (C6H

12O

6)

Oxygen (O2)

Carbon dioxide (CO2)

Water (H2O)

Photosynthesis

6CO2+ 6H2O C6H12O6+ 6O2

Light energy

Chlorophyll

Cellular respiration

C6H12O6+ 6O2 6CO2+ 6H2O+(Energy)

ATP

Photosynthesis and Cellular Respiration Work Together

Reading Essentials Plant Processes and Reproduction 129

C225_001_006_RE_L1_889406.indd 5C225_001_006_RE_L1_889406.indd 5 2/25/10 4:10:17 PM2/25/10 4:10:17 PM

Copyrig

ht ©

Glen

coe/M

cGraw

-Hill, a d

ivisio

n o

f The M

cGraw

-Hill C

om

pan

ies, Inc.

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

photosynthesis (foh toh SIHN thuh sus): a series of

chemical reactions that convert light energy, water, and

carbon dioxide into the food-energy molecule glucose and

give off oxygen

1. Review the terms and their definitions in the Mini Glossary. Write a sentence describing how cellular respiration depends upon photosynthesis.

2. Use what you have learned about photosynthesis and cellular respiration to complete the graphic organizer below.

requires

requires

produces

Photosynthesisoccurs in chloroplasts

Cellular Respirationoccurs in mitochondria

produces

130 Plant Processes and Reproduction Reading Essentials

C225_001_006_RE_L1_889406.indd 6C225_001_006_RE_L1_889406.indd 6 2/25/10 4:10:30 PM2/25/10 4:10:30 PM