8-3 The Reactions of Photosynthesis - District 186

[Pages:22]8-3 The Reactions of Photosynthesis

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8-3 The Reactions of Photosynthesis Inside a Chloroplast

Inside a Chloroplast

In plants, photosynthesis takes place inside chloroplasts.

Plant

Chloroplast

Plant cells

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8-3 The Reactions of Photosynthesis Inside a Chloroplast

Chloroplasts contain thylakoids--saclike photosynthetic membranes.

Single thylakoid

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Chloroplast

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8-3 The Reactions of Photosynthesis Inside a Chloroplast

Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.

Granum

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Chloroplast

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8-3 The Reactions of Photosynthesis Inside a Chloroplast

Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast.

Photosystems

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Chloroplast

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8-3 The Reactions of Photosynthesis Inside a Chloroplast

The reactions of photosystems include: the lightdependent reactions and the light-independent reactions, or Calvin cycle. The light-dependent reactions take place within the thylakoid membranes. The Calvin cycle takes place in the stroma, which is the region outside the thylakoid membranes.

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8-3 The Reactions of Photosynthesis Inside a Chloroplast

H2O Light

CO2

NADP+

ADP + P

Lightdependent reactions

CCalavlivnin Cyccylcele

Chloroplast

O2

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Sugars

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8-3 The Reactions of Photosynthesis Electron Carriers

Electron Carriers

When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy. Cells use electron carriers to transport these highenergy electrons from chlorophyll to other molecules.

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8-3 The Reactions of Photosynthesis Electron Carriers

One carrier molecule is NADP+. Electron carriers, such as NADP+, transport electrons. NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+). This converts the NADP+ into NADPH.

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8-3 The Reactions of Photosynthesis Electron Carriers

The conversion of NADP+ into NADPH is one way some of the energy of sunlight can be trapped in chemical form. The NADPH carries high-energy electrons to chemical reactions elsewhere in the cell. These high-energy electrons are used to help build a variety of molecules the cell needs, including carbohydrates like glucose.

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8-3 The Reactions of Photosynthesis Light-Dependent Reactions

What happens in the light-dependent reactions?

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8-3 The Reactions of Photosynthesis Light-Dependent Reactions

Light-Dependent Reactions

The light-dependent reactions require light. The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.

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8-3 The Reactions of Photosynthesis Light-Dependent Reactions

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8-3 The Reactions of Photosynthesis Light-Dependent Reactions

Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level.

Photosystem II

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8-3 The Reactions of Photosynthesis Light-Dependent Reactions

These high-energy electrons are passed on to the electron transport chain.

Photosystem II

High-energy electron

Electron carriers

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8-3 The Reactions of Photosynthesis Light-Dependent Reactions

Enzymes on the thylakoid membrane break water molecules into:

Photosystem II

2H2O

High-energy electron

Electron carriers

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