5B - Rubisco in C3, C4, and CAM Photosynthesis

Question 1

overview of light dependent stage

Answer 1

where light energy splits water molecules to produce
ATP, NADPH, and oxygen. This stage occurs in the thylakoid membranes of the grana.

Question 2

overview of light independent stage

Answer 2

where carbon dioxide is converted into organic
molecules using ATP and NADPH, and more water is produced. This stage occurs in the stroma, and is also known as the Calvin cycle

Question 3

rubisco

Answer 3

a pivotal enzyme
involved in initial carbon fixation during the light-independent
stage of photosynthesis

Question 4

overall steps of the chemical processes
involved in the light-independent stage

Answer 4

1 Carbon fixation –conversion of CO2
and RuBP into 3-PGA.
- carbon from the inorganic CO2 is ‘fixed’ into an organic compound.
Rubisco is responsible for taking carbon from an inorganic, gaseous form (CO2) and incorporating it into an organic compound (3-PGA)
2 Reduction – NADPH donates electrons to an intermediate three-carbon
molecule in the cycle to produce G3P
3 Regeneration – the RuBP molecules needed to start the cycle again are reproduced.

Question 5

photorespiration

Answer 5

a wasteful
process in plants initiated by Rubisco binding to O2 rather than CO2, that limits photosynthesis

• energy is wasted in reactions
• no photosynthesis – no glucose is produced
• plant survival and growth can suffer

Question 6

how does substrate concentration affect photoresperation

Answer 6

more substrate = greater chance it can
bind to an enzyme and undergo a reaction.
- normally stomata of the plant leaves open to allow CO2 to enter the plant, while O2 and water vapour simultaneously diffuse out of the plant.
- plant needs to conserve water = close stomata = O2
build up in cells
- greater concentration of oxygen = photorespiration.

Question 7

how does temp affect photoresperation

Answer 7

low/reg temp = rubisco greater affinity for CO2
- higher temp = greater affinity for O2
- leading to Rubisco
binding oxygen more often.

Question 8

C3 plants 

Answer 8

plants with no
evolved adaptation to
minimise photorespiration

Question 9

C4 plants 

Answer 9

plants that minimise
photorespiration by separating initial carbon fixation and the remainder of the Calvin cycle over space
In C4 plants, initial carbon fixation occurs in a mesophyll cell, however, the remaining
Calvin cycle occurs in specialised cells called bundle-sheath cells.

Question 10

C4 photosynthesis gets its name

Answer 10

from the first four-carbon molecule produced in
the initial carbon fixation.