Unit 2 - alternative mechanisms of carbon fixation

Question 1

Leaf stucture

Answer 1

1) waxy cuticle
2) spongy mesophyll tissue
3) stoma
4) guard cells
5) air spaces
6) palisade mesophyll tissue

Question 2

waxy cuticle

Answer 2

a protectice layer that reduces water loss from the leaf whole still allowing light through

Question 3

spongy mesophyll tissue

Answer 3

contains large air space to allow gases to diffuse efficiently through the leaf

Question 4

stoma

Answer 4

plural: stomata
small openings that allow gases to diffuse into and out of the leaf

Question 5

guard cells

Answer 5

a pair of cells that control the opening and closing of the stomata

Question 6

air spaces

Answer 6

allow O2 and CO2 to diffuse through the leaf

Question 7

Palisade mesophyll tissue

Answer 7

contains many chloroplasts to absorb light for photosynthesis

Question 8

prevent water loss

Answer 8

waxy cuticle = pwl through evaporation
stomata = small pores in the surface of a leaf that can be opened or closed to control gases between atmosphere and leaf interior

Question 9

open and closed

Answer 9

open during the day to allow co2 to enter
closed at night to prevent wl

Question 10

during high temp or water shortage

Answer 10

stomata can close or shrink even during the day to conserve water

Question 11

Problem w Rubisco

Answer 11

v slow enzyme, catalyzing the cixation of only about 3 mols of CO3 per second. its slow rate of catalysis is countered by its abundance within the cells

Question 12

when rubisco sites bind w oxygen gas instead of carbon dioxide

Answer 12

it forms a product that plants do not need (2 phosphoglycolate) that then needs to be converted back to a useful product. this process is long and needs peroxisome and the use of the mitochondria along w the chloroplast. + consumes ATP and releases CO2

Question 13

Photorespiration

Answer 13

the catalysis of O2 instead of Co2 by rubisco into RuBP which slows the Calvin cycle consumes Atp and results in release of carbon

Question 14

Calvin Cycle vs. Photorespiration

Answer 14

• binding w CO2 will occur abt 80x faster then binding with O2
• atmosphere contains significantly more O2 (21%) than CO2 (0.04%)
• 25% of the time Co2 is released rather than fixed (cell still maintains its normal demand for energy-rich carbs)

Question 15

Plants in Hot Dry Environments (stomata open vs close and heat factors)

Answer 15

• terrestrial plants in hot dry environments face problems w photorespiration and water loss
• stomata open = more co2
  -stomata shut = conserve water
• increased heat also decreases solubility of O2 an CO2

Question 16

C4 Plants

Answer 16

• some plants in hot climates have structures that minimize photorespiration
• Calvin cycle r performed by bundle-sheath cells, which surround the leaf veins

Question 17

Bundle-sheath cells

Answer 17

r surrounded by mesophyll cells that sperate them from the air spaces within the lead
- reduces exposure of rubisco containing BSC to O2

Question 18

C4 Cycle

Answer 18

operate a 2nd carbon fixation pathway
-CO2 combines w a 3c mol (PEP) to make 4c ocaloacetate

Question 19

C4 cycle Oxaloacetate

Answer 19

is reduced to malate by ET from NADPH

Question 20

C4 cycle malate

Answer 20

diffuses into the BSC where it enters chloroplast and is oxidized to pyruvate releasing co2e

Question 21

enzyme used in C4 Cycle

Answer 21

PEP carboxylase has a higher affinity for CO2 than rubisco
ie. many tropical plants as well as crops like corn

Question 22

Disadvantes of C4

Answer 22

need extra energy
- 6 ATP for every G3P from the calvin cycle

Question 23

advantages of C4

Answer 23

• hot climates often have more sun increasing light dependent rxn (extra ATP)
• C4 plants do not open stoma as much, can live in arid environments
• need 6x less rubisco (less nitrogen + can live in poor soil)

Question 24

Florida vs Manitoba C4 plants

Answer 24

F = 70% of native species r C4 plants
M= no C4 plants

Question 25

CAM plants (crassulacean acid metabolism)

Answer 25

a metabolic pathway used mostly by succulent plants in which the Calvin cycle and the C4 cycle are separated in time for better efficiency of Co2 fixation

Question 26

Cam plants

Answer 26

live in hot dry environments during the day and cool at night ie. cacti need low surface volume w less stomate

Question 27

cam plants during the night

Answer 27

Stomata r only open at night
-O2 is release and CO2 enters
-CO2 is fixed via C4 pathway into malate stored in vacuoles as mali acid

Question 28

cam plants during the day

Answer 28

stomata closed and malic acid moved to the cyotosol
- malate is then oxidized to pyruvate
- large amounts of co2 r release

Question 29

C3 C4 and CAM

Answer 29

C3
no separation
stomata open during day
cool wet environments
C4
separation between mesophyll bundle sheath cells
stomata open during the day
Hot, sunny environments
CAM
separation between night and day
stomata open at night
v hot, dry environments