rubisco

Question 1

what is rubisco?

Answer 1

rubisco is a key enzyme of the light independent stage of photosynthesis.

Question 2

what are the varied functions of rubisco?

Answer 2

can bind to co2 and facilitate more reactoions in photosynthesis process, or it can bind to o2 and initiate a wasteful process called photorespiration

Question 3

what is rubsico responsible for in the independent stage?

Answer 3

responsible for initial changes to carbon dioxide at the beginning of the calvin cycle. basically responsible for carbon fixation

Question 4

what does rubisco use to produce the fixed carbon used in the calvin cycle?

Answer 4

rubisco uses 3 CO2 molecules and 3 five carbon molecules called (RuBp) to produce 6 three-carbon molecules (3-PGA)

Question 5

equation for the process of rubisco?

Answer 5

3CO2 + 3RUBP –> 6 x 3-PGA

Question 6

what happens to the 6 x 3 - PGA so it can be used in light independent reaction

Answer 6

the 6 x 3 - PGA is converted by ATP and NADPH from light dependent reactions to make 6-three carbon molecules (G3P)

Question 7

how does this conversion between 6x3PGA to G3P happen? and what is the similarity between both of them?

Answer 7

the conversion happens via ATP and NADPH from the light dependent reactions. The similairty is that they both have 3 carbon atoms

Question 8

what is the reasoning behind glucose having 6 carbon molecules?

Answer 8

because one of the G3P molecules leaves the cycle to assist in other reactions to help make glucose. to replace that G3P molecule, 3CO2 molecules are required. And, as 2 G3P molecules are required to make 1 glucose molecule, it explains why 6CO2 molecules exist in glucose.

Question 9

what happens to the remaining 5 x G3P molecules?

Answer 9

they are recycled with the help of ATP to regenerate the 3 x RUBP we had at the start of the cycle, beginning it again.

Question 10

how many times does the cycle turn to produce one glucose molecule?

Answer 10

twice

Question 11

why does all of this cycling of carbon molecules happen?

Answer 11

to produce glucose from CO2, NADPH and ATP.

Question 12

what is special about this cycle?

Answer 12

it serves as a way of conserving energy as plants converting CO2 into glucose is too energy consuming.

Question 13

what can the role/function of rubisco be summarised as (in terms of specificity)?

Answer 13

responsible for initial changes to carbon dioxide at the beginning of the calvin cycle. rubisco binds to CO2 and fixes the carbon into organic 3-PGA, thus initiating the calvin cycle.

Question 14

what is the problem with rubisco? and why is it a problem?

Answer 14

rubisco uses O2 as a substrate to bind to, rather than using CO2 as a substrate. This is known is photorespiration, a wasteful process, and it is a problem as it limits photosynthesis.

Question 15

what is rubisco responsible for in photosynthesis? What might happen if it doesn’t bind to CO2?

Answer 15

Rubisco is responsible for catalysing photosynthesis. without its binding to CO2, photosynthesis cannot occur.

Question 16

how are plants affected when there is less photosynthesis due to rubisco binding to O2?

Answer 16

less glucose is produced, which sustains plants, and when combined with wasted energy used in the photorespiration pathway, it negatively impacts a plants ability to grow, survive and reproduce. it explains why photorespiration is unwanted and a wasteful process in plants.

Question 17

what are the 2 factors that influence whether Rubisco binds to CO2 or O2?

Answer 17

Substrate concentration and temperature.

Question 18

how does substrate concentration affect photosynthesis?

Answer 18

as there are 2 pathways for rubisco (photosynthesis or photorespiration), the higher the concentration of substrate (O2 OR CO2) , the higher the chance of rubisco binding to that substrate to undergo a reaction

Question 19

how is rubisco introduced to a high concentration of CO2?

Answer 19

stomata of plant leaves open to allow CO2 to enter the plant from the environment, while O2 and water vapour simultaneously diffuse out of the plant.

Question 20

how is rubisco introduced to a high concentration of O2?

Answer 20

stomata of plant leaves may close when it needs to conserve water, which causes a build up of O2 produced during the light-independent stage in the cells, which leads to photorespiration.

Question 21

in what temperatures is rubisco’s affinity for CO2 greater?

Answer 21

rubisco’s affinity for CO2 is greater at lower temperatures

Question 22

in what temperatures is rubisco’s affinity for O2 greater?

Answer 22

rubisco’s affinity for O2 is greater at higher temperatures

Question 22

what are some features of adaptivity against photorespiration in C3 plants?

Answer 22

-doesn’t restrict photorespiration
-no seperation of initial CO2 fixation and remainer of calvin cycle.
-stomata opens in the day.

Question 22

an advantage of C3 plants adaptivity against photorespiration in C3 plants?

Answer 22

doesn’t consume extra energy

Question 23

a disadvantage of C3 plants adaptivity against photorespiration in C3 plants?

Answer 23

susceptible to photorespiration initiation

Question 24

what are C3 plants best adapted to in terms of environment?

Answer 24

moderate, cool and wet environments.

Question 25

example of plants that are C3?

Answer 25

most plants including wheat, rice and all trees.

Question 26

how are C4 plants adapted against photorespiration?

Answer 26

initial carbon fixation occurs in a mesophyll cell, however remaining calvin cycle occurs in specialised bundle sheet cells.

Question 27

Comparison of C4 plants and C3 plants in photosynthesis?

Answer 27

-it has an additional biochemical pathway when compared to C3 photosynthesis
-requires more energy to undertake photosynthesis compared to C3 plants

Question 28

what is carbon fixation?

Answer 28

Carbon fixation – which refers to the conversion of CO2 and RuBP into 3-PGA. Here, we say that the carbon from the inorganic CO2 is ‘fixed’ into an organic compound.

Question 29

what does the pumping of CO2 in the form of malate into the bundle sheath cells do?

Answer 29

allows for a higher concentration of CO2 for rubisco to bind with instead of oxygen.

Question 29

what do the mesophyll cells do in C4 plants?

Answer 29

pump a source of CO2 in the form of malate into the bundle sheath cells

Question 29

similarities between C3 and C4 plants?

Answer 29

the light dependent stage occurs in the same way

Question 30

how is photorespiration minimised in C4 plants?

Answer 30

With the mesophyll cells constantly pumping a source of CO2 (in the form of malate) into the bundle-sheath cells, there is always a higher concentration of CO2 present for Rubisco rather than O2. As a result, photorespiration is minimised and photosynthesis is maximised.

Question 31

why do C4 plants require extra energy compared to C3 plants?

Answer 31

ATP is required to convert pyruvate to PEP for the initial carbon fixation.

Question 32

some features of C4 plants?

Answer 32

-stomata opens in the day
-minimises photorespiration
-consumes extra energy
-best adapted to hot sunny habitats. in such conditions, benefits of reduced photorespiration outweigh the cost of using ATP in C4 photosynthesis.

Question 33

types of C4 plants?

Answer 33

corn, sugarcane, switchgrass

Question 34

process of CAM plants minimising photorespiration?

Answer 34

in CAM photosynthesis, steps in calvin cycle are seperated over time, by opening their stomata to bring in CO2. the CO2 is fixed into an organic molecule such as malate through multiple processes. the malate is stored inside vacoules within mesophyll cell until the daytime. CAM plants don’t open their stomata during daytime to prevent waterloss. they can still photosynthesise during the day as the malate (or other) molecule is transported out of the vacoule and broken down to release CO2. The CO2 is then free to enter the calvin cycle in the same way as C3 and C4 plants, leading to glucose production.

Question 35

how do CAM plants minimise photorespiration (summarised)

Answer 35

controlled release of molecules out of the vacoules ensures a high concentration of CO2 is maintained near rubisco, maximising photosynthesis and minimising photorespiration.

Question 35

similarities between CAM plants and C3 plants?

Answer 35

same light dependent reaction

Question 36

disadvantage of CAM plants?

Answer 36

consumes extra energy

Question 37

where are CAM plants most adapted to?

Answer 37

very hot, dry habitats

Question 38

similarity between C4 AND C3 plants (stomata)

Answer 38

both open in the day

Question 39

when does the stomata of CAM plants open?

Answer 39

at night

Question 40

what types of plants are classified as CAM plants

Answer 40

cacti, pineapples and orchids.