Ecosystems - CO2 Effects on Plants

Question 1

What types of effects does CO2 have on plants?

Answer 1

Direct, CO2 itself
Indirect, climate change

Question 2

Photorespiration

Answer 2

This is a reverse process in plants of intake of oxygen and release of CO2

Question 3

What is the general effect of CO2 on C3 plants?

Answer 3

Increased CO2 concentration gradients, thus increasing uptake with increasing leaf concentraiton, increasing photosynthesis

Question 4

CO2 Saturation Point

Answer 4

This is where increased biomass and plant growth from enhanced RUBISCO activity reaches a plateua

Question 5

What is the general pathway or RUBISCO?

Answer 5

RuBP carboxylation with CO2 production and 3-PG formation

Question 6

Why do light reactiosn requrie ATP and NADPH?

Answer 6

They are energetically unfvaourable.

Question 7

What is the oxygenic activity of RUBISCO?

Answer 7

Photorespiration where on 3-PGA and one 2-Phosphoglycolyate

Question 8

What is the process of RUBISCO oxygenation?

Answer 8

O2 binds active site forming a highly reactive intermediate reacting with RuBP leading to glycolate and 3-PGA

Question 9

Why does RUBISCO exhibit oxygenic activity?

Answer 9

Higher affinity for O2 when CO2 concentration is low

Question 10

Why does oxygenation require more energy than carboxylation?

Answer 10

Highly unfavourable intermediate called 2-carboxy-3-ketoarabinitol-1,5-biphosphate, rapidly converting to 3PG and 2PG

Question 11

How may plants decrease carbon loss?

Answer 11

Limiting photorespiration and increasing gradient for CO2 uptake

Question 12

What are examples of decreasing photorespiration?

Answer 12

CO2 Concentration Mechanisms
Rubisco Activase
Photorespiration Inhibitors

Question 13

How are CCM mediated in the C4 pathway?

Answer 13

CO2 fixed into malate acid in mesophyll cells, then decarboxylated with CO2 release after transport into bundle sheath cells, CO2 used by RUBISCO.

Question 14

What does RUBISCO activase do?

Answer 14

Regulates RUBISCO by releasing inhibitory molecules by binding and facilitating hydrolyiss, allowing further CO2 fixation

Question 15

What are the specialized cells in C4 plants?

Answer 15

Mesophyll and Bundle sheath cells

Question 16

Whay do mesophyll cells contain?

Answer 16

Phospho-Enol-Pyruvate Carboxylase which fxates CO2 into oxaloacetate then malate, transported to BSC.

Question 17

What happens in bundle sheath cells?

Answer 17

Malate is dexarboxylated, releasing CO2

Question 18

Why is mesophyll and BSC seperation important?

Answer 18

Photoseperation is decreased thus CO2 fixation enhanced however CO2 only optimal at low concentration

Question 19

Why does PEPC have higher CO2 affinity?

Answer 19

It is an anaplerotic enzyme thus replenishes intermediates in the metabolic pathway, thus fixation continues at low CO2 conce
More negative charge at the active site

Question 20

What is photorespiraiton repressed in C4?

Answer 20

O2 concentration decreased around RUBISCO as cells are seperated

Question 21

What is an example of indirect effects on plants?

Answer 21

Temperature increases photosynthetic rate with increased enzyme activity rate like RUBISCO

Question 22

Why do temperatue increase C4 photosnythesis more-so?

Answer 22

CCM, increased CO2/o2 ratio at RUBISCO active site in C3 plants from increased temperature

Question 23

How does RUBISCO CO2 affinity relate to temperature?

Answer 23

Affinity for CO2 decreases within increasing temperatures in C3 despite increased carboxylation reacting rate.

Question 24

Why does CO2/O2 ratio increase with temperatsure?

Answer 24

Temperature dependence on solubility, where CO2 solubility decreases at a rate more-so than oxygen

Question 25

How does increasing photorespriation with temperature effect plants?

Answer 25

Consumption of energy in photorespiration negatively affect crop producitvity