UNIT A: Cell Biology

Chapter 2: The Molecules of Cells

Chapter 3: Cell Structure and Function

Chapter 4: DNA Structure and Gene Expression

Chapter 5: Metabolism: Energy and Enzymes

Chapter 6: Cellular Respiration

Chapter 7: Photosynthesis: Section 7.1

In this chapter you will learn how certain pigments, like the ones that give leaves their particular colours, trap energy from the Sun and use it for photosynthesis.

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Chapter 7: Photosynthesis

Which pigments provide the maximum efficiency for a plant as it conducts photosynthesis?

Why do leaves appear green in the spring and summer and then turn to red or yellow in the fall?

7.1 Overview of PhotosynthesisPhotosynthesis is a process of

converting solar energy into chemical energy in the form of carbohydrate.•Organisms that can carry out photosynthesis are called autotrophs because they can produce their own food. Plants, algae, and cyanobacteria are autotrophs.•Autotrophs not only feed themselves but also supply food for consumers, which must take in organic molecules. Consumers are heterotrophs.

Figure 7.1c Photosynthetic organisms

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Overview of Photosynthesis

Pigments allow photosynthetic organisms to capture solar energy.•Most photosynthetic organisms contain chlorophyll, a pigment that gives them a green colour •Some contain carotenoids, which give them a yellow to red colour

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Figure 7.1a and b Photosynthetic organisms.

Flowering Plants as Photosynthesizers

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Portions of flowering plants, especially the leaves, contain pigments that enable them to carry out photosynthesis.•Leaves contain mesophyll tissue, which contains cells specialized for photosynthesis•Plant roots absorb water, which moves up to the leaves, and carbon dioxide in the air enters the leaves through stomata•Water and carbon dioxide diffuse into cells in the leaves and enter chloroplasts, the organelles that carry out photosynthesis

Flowering Plants as Photosynthesizers

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Figure 7.2a Leaves and photosynthesis. The raw materials for photosynthesis are carbon dioxide and water. Water, which enters a leaf by way of leaf veins, and carbon dioxide, which enters by way of the stomata, diffuse into the cells and enter the chloroplasts.

Flowering Plants as Photosynthesizers

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• Chloroplasts have a double membrane that surrounds the fluid-filled interior, called the stroma.

• Within the stroma are flattened sacs, called thylakoids. The space within thylakoids is called the thylakoid space.

• In some places thylakoids are stacked into grana (sing. granum).

• Chlorophyll and other pigments that absorb solar energy for photosynthesis are part of the thylakoid membrane.

• The stroma is where carbon dioxide first attaches to an organic molecule that eventually produces carbohydrate.

Flowering Plants as Photosynthesizers

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Figure 7.2b, c, and d Leaves and photosynthesis. b. Chloroplasts have two major parts. c. The grana are made up of thylakoids, membranous disks that contain photosynthetic pigments such as chlorophylls a and b. These pigments absorb solar energy. d. The stroma, as indicated in this micrograph, is a fluid-filled space where carbon dioxide is enzymatically reduced to carbohydrate.

Photosynthetic Reaction

The overall equation for photosynthesis is often represented as

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• Oxygen given off by photosynthesis is

from water.• Carbon dioxide is reduced and becomes a carbohydrate; the energy for this is provided by the Sun.

• Plants provide us with food in the form of carbohydrate, as well as much of the oxygen we breathe.

• The light reactions (light-dependent reactions) release O2 and produce molecules used in the second set of reactions.

• The Calvin cycle reactions (light-independent reactions) reduce CO2 to carbohydrate.

• NADP+ (nicotinamideadenine dinucleotide phosphate) is a coenzyme.

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Chapter 7: Photosynthesis

Two Sets of Reactions

Figure 7.3 Overview of photosynthesis.

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Chapter 7: Photosynthesis

Check Your Progress

1. Identify the primary source of energy for carbohydrate production in plants.

2. Describe the structure of a chloroplast.

3. Identify the overall equation for photosynthesis.

4. Describe the two sets of reactions involved in photosynthesis.

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Chapter 7: Photosynthesis

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Chapter 7: Photosynthesis