Two stages of photosynthesis
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Two Stages of Photosynthesis. Light Reaction aka light dependent rxn. Calvin Cycle aka light independent reaction. Transforming light photons into ATP and the electron carrier NADPH. Use ATP/NADPH to make glucose. The Calvin Cycle : C 3 carbon fixation . In stroma of chloroplast.

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Two Stages of Photosynthesis

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Two stages of photosynthesis

Two Stages of Photosynthesis

Light Reaction

aka light dependent

rxn

Calvin Cycle aka light independent reaction

Transforming light photons into ATP and the electron carrier NADPH

Use ATP/NADPH to make glucose


The calvin cycle c 3 carbon fixation

The Calvin Cycle : C3 carbon fixation

In stroma of chloroplast

Inputs

CO2 ATP NADPH

from air

from light rxn

e

Output

G3P: a 3C organic molecule used to make glucose,

fructose, starch, cellulose…


The calvin cycle c 3 carbon fixation1

The Calvin Cycle : C3 carbon fixation

3 turns

of the cycle

Rubisco enzyme

RuBP

ATP

ATP

Energy input

Most G3P used to regenerate

RuBP

e-

G3P

one ‘extra’

G3P

Energy stored


Two stages of photosynthesis

Calvin Cycle Accounting

Per turn 3 turn 6 turns

Consume CO2 1 3 6

Consume ATP 3 9 18

Consume NADPH 2 6 12

Produces G3P 1 2

Produces Glucose 1


Two stages of photosynthesis

http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

http://faculty.nl.edu/jste/calvin_cycle.htm

http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html

http://www.blinkx.com/watch-video/photosynthesis-bioflix-animation/zWVQ8TsGQEG7FGsd2MWPTw

http://www.wiley.com/college/boyer/0470003790/animations/photosynthesis/photosynthesis.htm


Two stages of photosynthesis

This version of photosynthesis is used by 85% of plants - the C3 plantsC3 plants include grains, soy, legumes, cotton, most trees, and more

Selection produces functional adaptations, but not necessarily at optimal efficiency

What about the other 15%?

i.e. the C4 and CAM plants


In hot dry conditions plant will undergo photorespiration

In hot, dry conditions, plant will undergo Photorespiration

• to conserve water, leaf stomata close, preventing CO2 intake and O2 release.

• as CO2 concentration in the chloroplasts drops,

Rubisco fixes oxygeninstead of CO2.

• Photorespiration wastes radiant energy

no glucose is made, no ATP is made

What’s a plant to do?


C 4 plants separate c fixation and the calvin cycle into different cells

C4 Plantsseparate C-fixation and the Calvin cycle into different cells

CO2 uptake in mesophyll cells

Light reaction occurs

O2 produced stays here

4C molecule – PEP - made

PEP shuttles CO2 to

bundle-sheath cells

4C 3C + CO2 used in Calvin cycle

Therefore can keep stomata closed


C 4 plants corn sugarcane

C4 Plantscorn, sugarcane

In mesophyll:

H20 input

light rxn

O2 , PEP fixes C

PEP yields CO2

In bundle-sheath cells:

Calvin cycle

G3P sugar


Cam plants c fixation and calvin at different times of the day

CAM Plants C-fixation and Calvin at different times of the day

Avoiding evaporative loss

  • Stomates open at night

  • CO2 is converted to an

    acid and stored

hottest, driest conditions

• During the day, the acid is broken down

• CO2 released to RUBISCO for photosynthesis

CAM plants can ‘idle’ a while


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