Physiology of C3 and C4 plants

24 important questions on Physiology of C3 and C4 plants

What are the most important photosynthesis reactions?

- Light reaction
- 'Dark reaction'

What happens in the light reaction?

- Light harvest by PSII
- Electron transport
- Light harvest by PSI

What happens in the 'dark' reaciton?

C- fixation metabolism under influence of ATP and NADPH
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What does excist in C3 species?

Photorespiration

Why is C4 afvantageous?

- Thick-walled bundle sheath cells are rarely in contact with intercellulair space
- Initial carbocylation occurs in mesophyll cells, convreting HC03- into C4 acids by phospoenolpyruvate carboxylase
- C4 acids are decarboxylated in bundle sheath cells into CO2 which will be re-carboxylated but by rubisco

To what is a typical humble solar energy conversion efficiency (ca 1%) by annual crops mainly due to?

- actual crop production not at its potential level
- incomplete energy interception during both estabishment and senescence periods
- loss during conversion to, and maintenance of, biomass

What happens during the light independent reactions (calvin cycle)?

- Carbon dioxide from the air is fixated
- Electrons and hydrogen delivered by NADPH, powered by ATP.
- Carbon dioxide, H+ and electrons are rearranged in to glucose with high energy bonds

What do different wavelengths of light do?

Carry different amount of energy

What happens with a shorter wavelength?

Higher energy

What happens when sunlight hits the plant?

The energy is aborped by the pigment. Different pigments aborb different wavelengths, if not absorbed the wavelength is reflected

What is the major photsynthetic pigment?

Chlorophyll. It is absorbing some wavelengths, but reflecting greens

What are diffrences between phyotsytem 1 and 2?

Differences between wavelength

What happens during the non-cyclic pathway?

Light strikes photosystem 2 (p680) and electrons bounce around. It reaches the reaction centre and will be picked up by electron acceptor. The electron is delevired to the electron transport chain. At the end the electron is low in energy and goes to p700 (and goes to the cyclic pathway).

What is the source of electrons in p680?

By water, photolysis hapens which produces electrons and H+

What are the two sources of H+?

The pumping action of the electron transport chain
The splitting of water

What are the costs of using the stomata?

Water loss; this becomes a problem at hot areas

How do plants reduce water loss?

Close the stomate at night and under heat stress

What happens when the stomata close?

Composition of the air inside the leaf changes; less CO2, more O2. Photoresporation will happen. will decrease the rate of photosynthesis

What is the C4 pathway?

Uses an unique anatomical difference to ensure optimal carbon fixation

What happens in the C4 pathway?

Carbon gets fixed twice; in the mesophyll cells and then in the bundle sheath cells. This way it keeps O2 away from RuBP; this is not used. It uses PEP.

What is the CAM pathway?

- These plants keep the stomata closed during the day to reduce water loss
- During the night CO2 is collected
- During the daytime photosynthesis is happening

Where does phyotosynthesis take place?

In stroma of chloroplast

How can you pass the barriers?

- Cell wall mesohyl cel
- Chloroplast envelope

Why is leaf nitrogen important?

Because more N means darker leaves, means more light absoption, more reflection of green light

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