Photorespiration and C3, C4, and CAM plants

photosynthesizers, specifically photoautotrops…

nourish the living world by using light energy to produce organic compounds (food)

Nourish heterotrophs

organisms which must consume food

Plants balance uptake and water loss through…

stomata

stomata

small openings in leaf formed by guard cells

open stomata

CO2 enters, O2 exits; 95% water loss from plants through stomata

by regulating the stomata…

plants can control water loss

water limited

guard cells are flaccid and stomata are closed

water not limited

guard cells are turgid, stomata are open

closed stomata can lead to…

Photorespiration, which is when O2 interferes with carbon fixation in the Calvin cycle

Rubisco can…

fix O2 to RuBP when O2 is high and Co2 is low

photorespiration

interferes with carbon fixation, drains away carbon, requires ATP.

it might have been an evolutionary holdover due to ancient atmosphere having low O2, and it may help get rid of excess oxygen

C4 plants

avoid photorespiration by maintaining high localized concentrations of CO2 in cells where Calvin cycle occurs.

1. extra cycle before Calvin. PEP carboxylase fix CO2 into a 4-C molecule in mesophyll, requires ATP

2. release CO2 from 4-C molecule into a specialized cell in bundle sheath cells

achieve high CO2 in the same place that Rubisco operates

CAM plants

also fixes CO2 into 4-C, but they store CO2 in 4C compounds overnight.

1. open stomata at night to reduce evaporative water loss during the day. fix CO2 into 4c to store at night

2. during the day, 4C is transformed back into 3C + CO2 and CO2 enters Calvin

Common for hot/dry environments

C3 plants

no separation of CO2 intake and Calvin cycle photorespiration