LECTURE 7: PHOTOSYNTHESIS

I. How Organisms Obtain Food.

A. Autotrophs.

B. Heterotrophs.

C. Photosynthesis.

1. Used by autotrophs to make their own food.

2. Process that converts sunlight energy into chemical energy.

II. Photosynthesis: Structures. (Figure 7.3)

A. Takes place in chloroplasts of plant cells.

B. Leaf structure.

1. Stomata.

2. Mesophyll.

C. Chloroplast structure.

1. Stroma.

2. Grana.

3. Thylakoids.

III. Photosynthesis: The Reactions.

A. The general equation.

1. "Waste products" from respiration (CO2 and H2O) are the ingredients.

2. Products of photosynthesis (glucose and O2) are used in aerobic respiration.

B. Photosynthesis: the light reactions and the Calvin cycle (Figure 7.4).

IV. The Light Reactions.

A. Require sunlight.

B. Photophosphorylation.

C. Splitting water and producing O2.

D. ATP and NADPH produced.

E. Occur in the thylakoids.

E. Water-splitting photosystem.

1. Water split, oxygen release, 2 electrons "energized."

2. Electrons passed down electron transport chain — ATP produced.

F. NADPH-producing photosystem.

1. Connect to water-splitting system by electron transport chain.

2. Light-excited electrons used to make NADPH from NADP+.

G. Figure 7.10.

H. Summary.

1. Water molecules split and oxygen has been released.

2. ATP and NADPH produced.

V. The Calvin Cycle.

A. Reactions do not require sunlight to occur.

B. Reactions take place in the stroma of chloroplasts.

C. CO2 fixation.

1. CO2 removed from atmosphere.

2. ATP and NADPH used to produce the glucose precursor G3P.

D. Figure 7.13.

E. What happens to the G3P.

a. glucose -- "food."

b. polysaccharides -- e.g. starch, cellulose.

c. amino acids, lipids, nucleotides.

 

VI. Miscellaneous Points.

A. Photosynthesis has a 30% efficiency rate.

B. 18 ATP and 12 NADPH needed to make 1 glucose (2-G3P).

C. Chemosynthesis — other pathways used by autotrophs.

D. Earth’s early atmosphere.

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