AP Biology - Environmental Adaptions for Plants

plants who use CO2 to make a 3-C compound as the 1st step of the Calvin Cycle

C3 plants

occurs in C3 plants
As oxygen builds up from the closing of the stomata, rubisco will cheat and add oxygen instead of CO2
the product will split and a two carbon piece will be exported out of the chloroplast
Mitochondria and Peroxisomes will breath the 2 carbon compound into CO2
Oxygen and energy are used, but no sugar is produced

photorespiration

rubisco probably evolved when. . .

there was little oxygen in the atmosphere and did not compete for the enzyme

plants in hot, dry climates will conserve water by

closing their stomata

Have an alternate pathway for making sugars
Some plants in hot, arid climates use this process to minimize photorespiration
Important in agriculture (about 19 species) including corn, sugarcane, and grasses
Must have a unique leaf anatomy

C4 plants

net effect of the normal calvin cycle

gain 6 fixed carbon atoms and 1 glucose

net effect of photorespiration

-lose 3 fixed carbon atoms
-no glucose
-not enough carbon atoms to regenerate 6 RuBP

RuBP

rubisco

C4 plants have these two types of photosynthetic cells in the leaves

bundle-sheath
mesophyll

C3 plants only have __ cells that are capable of photosynthesis

mesophyll

tightly packed around veins, dark reactions

bundle-sheath cells

tightly packed and organized around bundle-sheath cells

mesophyll cells

having 2 photosynthetic cells hides oxygen in the ___ cells from rubisco so it can't cheat

mesophyll

special enzyme in the mesophyll cells that will fix CO2 into PEP (3-C) to make a 4-C compound

PEP carboxylase

4-C compound made by PEP carboxylase

oxaloacetate

PEP carboxylase has a higher affinity for ___ and therefore will not cheat, even when O2 levels are higher

CO2

Oxaloacetate is shuttled through the plasmodesmata and is broken down into pyruvate (3-C) and CO2, which is given off into rubisco
The 3-C leftover is recycled into PEP by use of

ATP

In C4 plants, sugar will be made like all other dark reactions, just. . .

in a different location

another adaptation to arid conditions
Only open their stomata at night

CAM plants

At night, CAM plants take up CO2 and use PEP carboxylase to fix it into an

organic acid molecule

CAM plants store excess organic acids in their ____ in mesophyll cells

vacuoles

CAM plants usually have

waxy, thick leaves

separating light and dark reactions by night and day

temporal separation

Sugar is made like all other reactions, it is just started at

night

During the day when the light reactions can make ATP and NADPH to power the ______, the organic acids will release CO2 absorbed in the night to be used in

the Calvin Cycle

only about ___ of the organic material made in photosynthesis is used for cell respiration
the rest of the plant depends on products made by the "green cells"

50%

leaves transport the carbohydrates (usually in sucrose) to other areas via

veins

excess sugar is stored in. . .

roots, tubers, seeds, fruits

On a global scale, photosynthesis accounts for ___ metric tons of carbohydrates per year

160 billion