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)

Absorbance Spectrum of Plant Leaf Pigments

Data from AP Biology Class

April 03-04

-0.200

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

380

400

420

440

460

480

500

520

540

560

580

600

620

640

660

680

700

720

Wavelegnths in nm

Abso

rban

ce

Chlorophyll b

Chlorophyll a

Xantophyll

Carotenes

Fitness of light

High energy photons

Visible light Low energy photons

Drive electrons out of atoms--break bonds

Excite electrons to higher energy levels

Increase molecule vibrations

Screened out by ozone and O2 in atmosphere

Able to penetrate earth’s atmosphere

Screened out by H2O vapor and CO2 in atmosphere

Structure of chlorophyll (Fig. 10.8)

Harvesting light with a

photosystem (Fig. 10.10)

Photoexcitation of isolated chlorophyll (Fig. 10.9)

Noncyclic electron flow (Fig. 10.11)

Mechanical analogy for

the light reaction

(Fig. 10.12)

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 Buffer 1 mL 1 mL 1 mL 1 mL 1 mL

Distilled Water 4 mL 3 mL 3 mL 3 mL3 mL +

3 drops

DPIP dye

(replaces NADP+)___ 1 mL 1 mL 1 mL 1 mL

Unboiled Chloroplasts

3 drops 3 drops 3 drops ___ ___

Boiled Chloroplasts

___ ___ ___ 3 drops ___

% Transmission

Chemiosmosis in

mitochondria and

chloroplasts (Fig. 10.14)

Tentative model for thylakoid membrane

(Fig. 10.15)

Cyclic electron flow (Fig. 10-13)

Calvin cycle (Fig. 10.16)

Photorespiration

• In stroma of chloroplasts:

RuBP + O2 glycolic acid + G3P

• In mitochondria and peroxisomes (in presence of light):

glycolic acid + O2 CO2 + H2O

• Drains away up to 50% of carbon fixed by the Calvin cycle in C3 plants.

PEP carboxylase: the enzyme for hot, dry, and bright conditions• PEP carboxylase

binds CO2 at low concentrations.

• Plants keep stomata closed most of the time to save water.

• PEP carboxylase does not bind O2 leading to photorespiration.

• RuBP carboxylase does not bind CO2 at low concentrations.

• Plants must keep stomata open to get enough CO2.

• RuBP carboxylase does bind O2 leading to photorespiration.

C4 anatomy and pathway (Fig. 10.17)

C4 Photosynthesis

In mesophyll cells:• PEP carboxylase adds

CO2 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

CO2 + PEP (3C).

• PEP transported back to mesophyll cells.

• RuBP carboxylase adds CO2 to RuBP to begin Calvin cycle.

C4 vs. CAM Photosynthesis

C4 Photosynthesis

1. CO2 incorported into 4C organic acids in mesophyll cells using PEP carboxylase.

2. 4C organic acids release CO2 to Calvin cycle in bundle-sheath cells.

CAM Photosynthesis

1. CO2 incorported into 4C organic acids at night when stomata are open.

2. 4C organic acids release CO2 to Calvin cycle during the day when stomata closed.

Review of photosynthesis (Fig. 10.19)