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Saving for a Rainy Day Suppose you earned extra money by having a part-time job. At first, you might be tempted to spend all of the money, but then you decide to open a bank account. 1. What are the benefits of having a bank account? 2. What do you have to do if you need some of this money? 3. What might your body do when it has more energy than it needs to

carry out its activities? 4. What does your body do when it needs energy?

Section 8-1

Interest Grabber

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8–1 Energy and Life A. Autotrophs and Heterotrophs B. Chemical Energy and ATP

1. Storing Energy 2. Releasing Energy

C. Using Biochemical Energy

Section 8-1

Section Outline

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Autotrophs • All living things need and use energy. • Living things get this energy from food, but the energy in the food ultimately comes from the sun. • Plants and some other types of organisms are able to use light energy from the sun to produce food. • Organisms that can make their own food are called Autotrophs.

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Heterotrophs

• Organisms, such as animals, can not directly use the sun’s energy. • Organisms that obtain energy from the food they consume are called heterotrophs.

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Chemical Energy in ATP

•  Living things use chemical fuels. •  The principal chemical

compound that cells use to store and release energy is adenosine triphosphate (ATP).

•  ATP is made up of 3 main parts: 1.  Adenine 2.  5-carbon sugar (ribose) 3.  3 phosphate groups

•  The phosphate groups are the key to ATP’s ability to store and release energy.

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Adenine Ribose 3 Phosphate groups

Section 8-1

ATP

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Storing Energy

• When an organism has extra energy, it can store small amounts of it by adding a phosphate group to adenosine diphosphate (ADP) to make ATP.

–  ADP only has 2 phosphate groups. • ATP is like a fully charged battery ready for use.

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ADP ATP

Energy

Energy Adenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)

Partially charged battery

Fully charged battery

Section 8-1

Figure 8-3 Comparison of ADP and ATP to a Battery

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ADP ATP

Energy

Energy Adenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)

Partially charged battery

Fully charged battery

Section 8-1

Figure 8-3 Comparison of ADP and ATP to a Battery

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Releasing Energy

• How do cells get energy from ATP? • The cell simply breaks the bond between the second and third phosphate groups. • The energy released can power active transport, protein synthesis, and muscle contractions. • The characteristics of ATP make it exceptionally useful as the basic energy source of all cells.

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Trapping Energy

Have you ever used a solar-powered calculator? No matter where you go, as long as you have a light source, the calculator works. You never have to put batteries in it.

Section 8-2

Interest Grabber

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1. A solar-powered calculator uses solar cells that are found in rows along the top of the calculator. Into what kind of energy is the light energy converted so that the calculator works?

2. Recall that plants use light energy from the sun to make food. Into what kind of energy is the light energy converted by plants?

3. Most plants, no matter what size or shape they are, have some parts that are green. Which parts of a plant are usually green?

4. What does the green color have to do with the plant’s ability to convert light energy into the energy found in the food it makes?

Section 8-2

Interest Grabber continued

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8–2 Photosynthesis: An Overview A. Investigating Photosynthesis

1. Van Helmont’s Experiment 2. Priestley’s Experiment 3. Jan Ingenhousz

B. The Photosynthesis Equation C. Light and Pigments

Section 8-2

Section Outline

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The Photosynthesis Equation

• Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen. • The equation is:

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Light Energy

Chloroplast

CO2 + H2O Sugars + O2

Section 8-2

Photosynthesis: Reactants and Products

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Light and Pigment • How do plants use energy from the sun? • Energy from the sun travels to Earth in the form a light. • You perceive the light as white, but it is made up of a spectrum of colors. • Plants gather the sun’s energy with light-absorbing molecules called pigments. • The main pigment in plants is chlorophyll. • Chlorophyll absorbs blue-violet and red light very well, but not green. Green light is reflected by leaves which is why they appear green. • The energy absorbed by chlorophyll is transferred directly to electrons raising the energy level of those electrons.

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Absorption of Light by Chlorophyll a and Chlorophyll b

V B G Y O R

Chlorophyll b

Chlorophyll a

Section 8-2

Figure 8-5 Chlorophyll Light Absorption

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A Look Into the Future

It is 100 years in the future and you are a research scientist. An enormous volcanic eruption has recently sent huge quantities of dust and ash into the atmosphere. Working with a partner, make a list of how this event will affect each of the following:

1. photosynthesis 2. plant life 3. animal life 4. human societies

Section 8-3

Interest Grabber

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8–3 The Reactions of Photosynthesis A. Inside a Chloroplast B. Electron Carriers C. Light-Dependent Reactions D. The Calvin Cycle E. Factors Affecting Photosynthesis

Section 8-3

Section Outline

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Inside a Chloroplast

• Chloroplasts contain saclike photosynthetic membranes called thylakoids. • Thylakoids are arranged in stacks called grana. • Proteins in the thylakoid membrane organize chlorophyll into clusters called photosystems which collect the light from the sun.

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Electron Carriers •  When light excites electrons

to make a high energy electrons, they require a special carrier.

•  Cells use a carrier molecule that will accept a pair of high-energy electrons and transfer them to other molecules.

•  This is called electron transport.

•  Photosynthesis uses a molecule called NADP+.

•  NADP+ accepts 2 electrons and a hydrogen ion to form a NADPH molecule.

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Light-Dependent Reactions •  The light-dependent reactions produce oxygen gas and convert ADP and NADP

+ into the energy carriers ATP and NADPH. •  Here’s the process.

1.  Photosynthesis begins in Photosystem II. The light energy absorbed excites electrons to a higher energy level and then are passed on the electron transport chain. The Thylakoid membrane breaks down water into 2 electrons, 2 hydrogen ions, and one oxygen molecule.

2.  The high-energy electrons travel to Photosystem I. These electrons are used to transport hydrogen ions from the stroma into the inner thylakoid space.

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Light-Dependent Reactions

3.  Photosystem I absorbs more light to reenergize the electrons. NADP+ picks up the electrons and a hydrogen ion to form NADPH.

4.  The remaining hydrogen ions pass through a protein called ATP synthase. As the ion passes through, the protein rotates and binds a phosphate group to ADP to form ATP.

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Hydrogen Ion Movement Photosystem II

Inner Thylakoid Space

Thylakoid Membrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Section 8-3

Figure 8-10 Light-Dependent Reactions

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The Calvin Cycle

• The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. • These reaction are also known as the light-independent reactions, because they don’t require light.

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Steps of the Calvin Cycle

1.  Six carbon dioxide molecules enter the cycle and combine with six 5-carbon molecules resulting in 12 3-carbon molecules.

2.  Energy from ATP and NADPH convert the 12 3-carbon molecules into higher-energy forms.

3.  2 of the 12 molecules are removed to produce sugars, lipids, amino acids, and other compounds.

4.  The remain 3-carbon molecules are converted back to the six 5-carbon molecules.

End result - 6 carbon dioxide molecules are formed into a 6-carbon sugar.

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ChloropIast

CO2 Enters the Cycle

Energy Input

5-Carbon Molecules Regenerated

Sugars and other compounds

6-Carbon Sugar Produced

Section 8-3

Figure 8-11 Calvin Cycle

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Photosynthesis

includes

of

take place in takes place in uses

to produce to produce

use

Light- dependent reactions

Calvin cycle

Thylakoid membranes Stroma NADPH ATP Energy from

sunlight

ATP NADPH O2 Chloroplasts High-energy sugars

Section 8-3

Concept Map

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Chloroplast Light

O2 Sugars

CO2

Light- Dependent Reactions

Calvin Cycle

NADPH ATP

ADP + P NADP+ Chloroplast

Section 8-3

Figure 8-7 Photosynthesis: An Overview

Video Contents

Videos

Click a hyperlink to choose a video. ATP Formation Photosynthesis Light-Dependent Reactions, Part 1 Light-Dependent Reactions, Part 2 Calvin Cycle

Video 1

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Video 1

ATP Formation

Video 2

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Video 2

Photosynthesis

Video 3

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Video 3

Light-Dependent Reactions, Part 1

Video 4

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Video 4

Light-Dependent Reactions, Part 2

Video 5

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Video 5

Calvin Cycle

Internet

ATP activity Interactive test For links on Calvin cycle, go to www.SciLinks.org and enter the Web Code as follows: cbn-3082. For links on photosynthesis, go to www.SciLinks.org and enter the Web Code as follows: cbn-3083.

Go Online

Section 1 Answers

Interest Grabber Answers

1. What are the benefits of having a bank account? To save money and earn interest.

2. What do you have to do if you need some of this money? Go to the bank and take out the money you need.

3. What might your body do when it has more energy than it needs to carry out its activities? Students will likely say that the body stores the energy.

4. What does your body do when it needs energy? Student answers may include that energy is gotten from food.

Section 2 Answers

Interest Grabber Answers

1. A solar-powered calculator uses solar cells that are found in rows along the top of the calculator. Into what kind of energy is the light energy converted so that the calculator works? They convert light energy into electrical energy.

2. Recall that plants use light energy from the sun to make food. Into what kind of energy is the light energy converted by plants? Plants convert light energy into chemical energy.

3. Most plants, no matter what size or shape they are, have some parts that are green. Which parts of a plant are usually green? Leaves are green, as are some stems.

4. What does the green color have to do with the plant’s ability to convert light energy into the energy found in the food it makes? The green color is the pigment chlorophyll, which absorbs light energy from the sun and converts it to chemical energy in the process of photosynthesis.

Section 3 Answers

Interest Grabber Answers

Working with a partner, make a list of how this event will affect each of the following:

1. photosynthesis The rate of photosynthesis will decrease due to reduced sunlight. 2. plant life Plants will grow more slowly or die off due to decreased rate of photosynthesis. 3. animal life Animal populations will decrease after a while due to fewer plants for herbivores to eat. Fewer herbivores will eventually result in fewer carnivores. Also, less oxygen will be available. 4. human societies Human societies will have to adjust their eating habits as some food species die out.

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