Calvin Cycle(Kreb Cycle)

Calvin Cycle(Kreb Cycle)

Occurs in the stroma

CO2 enters from the air and is put inside the sugar

Spends ATP as an energy source and consumes NADPH as reducing power (gaining electrons) to make sugar

1.Phase 1 Carbon Fixation (catalysed by RuBisCO)

2.Phase 2 Reduction

3.Phase 3 Regeneration of the CO2 acceptor (RuBP)

RuBisCO is an important enzyme and is the world's most abundant protein

In order to net on G3P the cycle must go through 3 rotations and fix three CO2

Provides a Short-Lived Intermediate by the RuBisCo using the Ribulose Bisphosphate (RuBP) and that eventually turns into 3-Phospholyglycerate. This then goes trunks into 1,3 Bisphophosglycaerate. This turns into Glyceraldehyde 3- phosphate(G3P) (The output is 1 G3P). It produces 6 G3P which 5 of them turn into ADP and goes back to the RuBP.

For 3CO2 molecules (1 enters at a time) 9 ATP is needed 6NADPH is needed and 1 G3P is produced.

CO2 enters the leaf through the stomata

Water exits the same pores

On hot, dry days C3 plants produce less sugar because stomata are closed to conserve water

No CO2 uptake and the levels decline

C3 plants problems

In most plants initial fixation of carbon occurs via the enzyme RuBisco(Calvin cycle)

These are called C3 plants because the first organic plant takes 3CO2 to produce 1 G3P

RuBisCO can bind to O2 in place of CO2

Causes oxidation or breakdown of RuBP

Results in loss of energy and loss of carbon for the plant

This process is called photorespiration

This can drain away as much as 50% of the carbon fixed

Two adaptations to reduce phosphorespiration

C4 plants

The stomata are closed in the hotter days and time 

Sugar is continued to be made through 2 types of cells: Bundle-Sheat cells and Mesophyll cells

CO2 is added to PEP(3C) to form oxaloacetate(4C)

Uses different enzyme (PEP carboxylase)

Carbon is fixed

Mesophyll cells export the 4C to the bundle sheath cells

Oxaloacetate is broken down releasing CO2

Co2 enters the Calvin Cycle

Keeps CO2 levels high and avoid photorespiration

Cam Plants

During the day Stomata is closed to prevent excessive water loss

Prevents CO2 intake 

During the night stomata open, and CO2 is fixed into organic acids and stored in vacuole ins mesophyll cells

Next Day stomata closes and plant cells release the stored CO 2 and proceed with photosynthesis.

All the plants use the Calvin Cycle

Different methods of getting to the cycle

C4 and CAM photosynthesis first transform CO2 into an organic intermediate before it enters the Calvin Cycle

C4 and CAM create organic acids

CAM uses bundle sheath cells while the C4 uses that and mesophyll cells

Plants reflect green light

Plants absorb blue and violet because it is an adaptation TikTok of the Calvin Cycle