Chapter 10 Photosynthesis AP Biology Mr. Orndorff April 2004

Site of photosynthesis in a plant (Fig. 10.2)

Overview of photosynthesis (Fig. 10.4)

Electromagnetic spectrum (Fig. 10.5)

Interaction of light with matter in a chloroplast (Fig. 10.6)

Absorption and action spectra for photosynthesis (Fig. 10.7)

Fitness of light High energy photons Visible lightLow energy photons Drive electrons out of atoms-- break bonds Excite electrons to higher energy levels Increase molecule vibrations Screened out by ozone and O 2 in atmosphere Able to penetrate earth’s atmosphere Screened out by H 2 O vapor and CO 2 in atmosphere

Structure of chlorophyll (Fig. 10.8)

Harvesting light with a photosystem (Fig )

Photoexcitation of isolated chlorophyll (Fig. 10.9)

Noncyclic electron flow (Fig )

Mechanical analogy for the light reaction (Fig )

Dye-reduction technique for measuring rate of photosynthesis Blank (1) Unboiled Chloroplasts Dark (2) Unboiled Chloroplasts Light (3) Boiled Chloroplasts Light (4) No Chloroplasts (5) Phosphate Buffer1 mL Distilled Water4 mL3 mL 3 mL + 3 drops DPIP dye (replaces NADP + ) ___1 mL Unboiled Chloroplasts 3 drops ___ Boiled Chloroplasts ___ 3 drops___ % Transmission

Chemiosmosis in mitochondria and chloroplasts (Fig )

Tentative model for thylakoid membrane (Fig )

Cyclic electron flow (Fig )

Calvin cycle (Fig )

Photorespiration In stroma of chloroplasts: RuBP + O 2  glycolic acid + G3P In mitochondria and peroxisomes (in presence of light): glycolic acid + O 2  CO 2 + H 2 O Drains away up to 50% of carbon fixed by the Calvin cycle in C 3 plants.

PEP carboxylase: the enzyme for hot, dry, and bright conditions PEP carboxylase binds CO 2 at low concentrations. Plants keep stomata closed most of the time to save water. PEP carboxylase does not bind O 2 leading to photorespiration. RuBP carboxylase does not bind CO 2 at low concentrations. Plants must keep stomata open to get enough CO 2. RuBP carboxylase does bind O 2 leading to photorespiration.

C 4 anatomy and pathway (Fig )

C 4 Photosynthesis In mesophyll cells: PEP carboxylase adds CO 2 to PEP (3C) to make oxaloacetate and malate (both 4C acids). 4C acids transported to bundle-sheath cells via plasmodesmata. In bundle-sheath cells: 4C acids + ATP make CO 2 + PEP (3C). PEP transported back to mesophyll cells. RuBP carboxylase adds CO 2 to RuBP to begin Calvin cycle.

C 4 vs. CAM Photosynthesis C 4 Photosynthesis 1.CO 2 incorported into 4C organic acids in mesophyll cells using PEP carboxylase. 2.4C organic acids release CO 2 to Calvin cycle in bundle- sheath cells. CAM Photosynthesis 1.CO 2 incorported into 4C organic acids at night when stomata are open. 2.4C organic acids release CO 2 to Calvin cycle during the day when stomata closed.

Review of photosynthesis (Fig )