1 Review Summarize what happens during the light dependant reactions

2 Explain How do each of the three primary factors affect the rate of photosynthesis

3 Review What are the different ways that plants cope with water shortages

CH 8 PHOTOSYNTHESIS8.3 The Process of Photosynthesis

Why do chloroplasts contain so many membranes? Membranes are the key to capturing light energy.

Light Dependant Reactions: Generating ATP and NADPH

Photosystems Series of proteins in the thylakoid that absorb sunlight

and make high-energy electrons.

Electron Transport Chain

Series of electron carriers that shuttle high-energy electrons during ATP-generating reactions

Electron Transport Chain (ETC).

Photosystem II Light energy is

absorbed by electrons High energy electrons

move through the ETC.

Photosystem II Thylakoid provides new

electrons from water Water breaks up into 2

electrons, 2 H+ ions, and 1 oxygen atom.

Photosystem II 2 electrons replace the

high-energy electrons that have been lost to ETC

H+ ions released inside thylakoid

Oxygen is released into the air.

Photosystem II Energy from electrons

is used by proteins in ETC to pump H+ ions from the stroma into the thylakoid space.

Photosystem II The ETC gives electrons

to Photosystem I.

Photosystem I

Electrons used energy to pump H+ ions so have less energy

Photosystem I uses energy from light to reenergize the electrons.

Photosystem I

After 2nd ETC, NADP+ molecules in the stroma pick up high-energy electrons and H+ ions at the outer surface of the thylakoid membrane to become NADPH.

Hydrogen Ion Movement and ATP Formation

H+ ions accumulate within the thylakoid space from splitting water and pumping them across.

Hydrogen Ion Movement and ATP Formation

Gradient of H+ ions Charge and concentrations.

Hydrogen Ion Movement and ATP Formation

H+ ions cannot directly cross membane ATP synthase

Protein that allows H+ ions to pass through Causes it to rotate and bind ADP and a phosphate.

Hydrogen Ion Movement and ATP Formation

Produces NADPH and ATP.

The Light-Independent Reactions: Producing Sugars

Called the Calvin Cycle Plants use ATP and NADPH to build stable high-

energy carbohydrate compounds that can be stored for a long time.

Carbon Dioxide Enters the Cycle

Carbon dioxide molecules enter the Calvin cycle from the atmosphere

Combine CO2 with 5-carbon compounds 6 CO2 enter, twelve 3-carbon compounds are

produced.

Enzymes convert the 3-carbon compounds into higher-energy forms using ATP and NADPH.

Sugar Production Two of the 3-carbon

molecules are removed to make sugar.

Sugar Production Remaining ten 3-

carbon molecules are converted back into six 5-carbon molecules

Combine with the new CO2 to start the next cycle.

ATP

ADP

Summary of the Calvin Cycle Uses 6 molecules of

carbon dioxide to produce a single 6-carbon sugar.

ATP

ADP

Energy for the reactions is supplied by compounds produced in the light-dependent reactions.

ATP

ADP

Sugars are used by the plant for energy needs and to build other macromolecules for growth and development.

ATP

ADP

Factors Affecting Photosynthesis

Temperature Light intensity Water availability.

Temperature

Enzymes work best between 0°C and 35°C Lower temps slow enzymes Higher temps denature enzymes.

Light Intensity

High light intensity increases the rate of photosynthesis

There is a maximum to light intensity increasing photosynthesis.

Water Availability

Water is needed in the reaction Water shortage can stop reaction Certain plants have special adaptations

C4 plants CAM plants.

C4 Photosynthesis

Very good and getting CO2 Uses a 4 carbon molecule Requires added energy Corn, sugar cane, and sorghum.

CAM Plants

Open their leaves at night and trap CO2

Seal leaves shut during day to conserve water and use trapped CO2

Pineapple trees and many desert cacti.