PACKET #31CHAPTER #10

Photorespiration

Introduction

Plants that use the Calvin Cycle to fix carbon, in the molecule sugar, are called C3 plants.

During photorespiration, C3 plants consume oxygen and generate CO2 but do not produce ATP Conserving water and preventing passage of CO2 into the

leafPhotorespiration is said to be an evolutionary

relic and lowers the efficiency of photosynthesis by removing carbon molecules from the Calvin Cycle. Photorespiration reduces the rate of photosynthesis.

Introduction II

Photorespiration reduces the rate of photosynthesis in plants in three ways Carbon dioxide is released Energy (ATP) is diverted from photosynthetic

reactions to photorespiratory reactions. Competition between oxygen and carbon dioxide

reduces the efficiency of the important photosynthetic enzyme ribulose-bisphosphate (RuBP) carboxylase.

Photorespiration in C3 Plants

On dry, hot days in the presence of light C3 plants close their stomata.

This causes the plant to use of oxygen, similar to aerobic cellular respiration, and produce CO2 and H2O.

C4 and CAM Plants

C4 & CAM Plants Introduction

C4 and CAM plants have devised mechanisms that prevent/reduce the impact of photorespiration.

C4 Plants

Photorespiration & C4 Plants

Photorespiration is negligible in C4 plants because the concentration of carbon dioxide is always high in the bundle sheath cells.

Photorespiration & C4 Plants II

In C4 plants, during hot dry periods, oxygen molecules in the chloroplast bind with Rubisco and prevent carbon fixation.

RuBP and oxygen combine, and the intermediates in the Calvin Cycle degrade to form CO2 and water.

Pathway in C4 Plants

C4 Plants

Developed a technique to reduce the occurrence of photorespiration

PEP carboxylase binds CO2 Even at low concentrations

CO2 is fixed into oxaloacetate

Oxaloacetate is converted to malate Malate moves into a bundle

sheath cell while CO2 is removed

CO2 enters the Calvin Cycle

CAM Plants

CAM Plants

CAM is an acronym for crassulacean acid metabolism.

Examples Succulent plants {family

Crassulaceae} Family Cactaceae Family Lilaceae Family Orchidaceae Many others in 25 families.

Plants exhibit a pathway similar to C4 plants and allow them to live in highly xeric conditions.

CAM Plants

PEP carboxylase fixes carbon at night in the mesophyll cells Stomata are open at

night Minimizes water loss

and allows the entry of CO2

Calvin Cycle occurs during the daytime

Homework Assignment

What are some of the similarities, and differences, between C4 and CAM plants?