Briefly describe how the proton gradient is related to ATP synthesis. For each o

ID: 74390 • Letter: B

Question

Briefly describe how the proton gradient is related to ATP synthesis.

For each of the factors below, choose how the rate of photosynthesis will be affected:

a.increase the rate of photosynthesis

b.decrease the rate of photosynthesis

1)decreased CO2

2)increased CO2

3)decreased temp

4)increased temp

5)decreased light

6)increased light

7)increased red and blue light

8)giving the plant only green light

Define carbon fixation. What enzyme is required in order to allow for carbon fixation of carbon dioxide molecules?

Which molecule represents the source of energy driving Calvin cycle reactions?

How many carbon dioxide molecules are required to produce one glucose molecule?

Which types of plants undergo C3, C4, and CAM mechanisms? Briefly describe the major difference between these mechanisms.

Explanation / Answer

(1)- According to the Chemo-osmotic model proposed by Peter Mitchell, the electrochemical energy inherent in difference in proton concentration & separation of charge across inner mitochondrial membrane drives synthesis of ATP.

The electron-accepting coenzymes donate the electrons to oxygen via the electron transport chain in the inner mitochondrial membrane- hence an electrochemical gradient is formed across the inner mitochondrial membrane.

As the proton concentration increases in the intermembrane space, the Proton-motive force pumps the protons from the membrane to the matrix through the ATP synthase complex and their potential energy is used to synthesize ATP from ADP and inorganic phosphate (Pi) in a process known as oxidative phosphorylation.

(2)- a.increase the rate of photosynthesis

b.decrease the rate of photosynthesis

1) decreased CO2 – (b) as CO2 is converted to sugar.

2) increased CO2 – (a) to a certain extent, then no change as CO2 concentration further increases.

3) decreased temp- lower than optimum (below 15oC) then (b) as enzymes participating in photosynthesis depends on temp & are not functional at low temp.

4) increased temp- greater than optimum temp (higher than 38oC), then (b) as enzymes participating in photosynthesis depends on temp & are denatured at high temp.

5) decreased light- (b)

6) increased light- (a) to a certain extent, beyond which (b)- due to photobleaching.

7) increased red and blue light- (a) as the photosystems are activated at such spectrum of light.

8) giving the plant only green light- (b)

(3)- Carbon fixation is defined as the process during the dark phase of photosynthesis (Calvin’s cycle) in green plants where the carbon of the carbon-dioxide of the atmosphere is incorporated in organic compounds (mainly glucose).

Carbon fixation is catalyzed by RuBisCO: Ribulose 1,5-bisphosphate carboxylaseoxygenase

(4)- 3-Phosphoglyceraldehyde represents the source of energy driving Calvin cycle reactions. Out of 12 PGAld molecules, two are used to synthesize 1 molecule of glucose & the rest 10 are used to regenerate RUBP (Ribulose 1,5-bisphosphate).

(5)- 6 molecules of CO2 are required to produce one glucose molecule.

(6)- The major differences between the Photosynthetic mechanisms in C3 & C4 plants are:

C3 plants

C4 plants

1-Fixation of CO2

Directly in RUBP

Indirectly, first fixed in RUBP (Ribulose 1,5-bisphosphate), then in PEP (Phosphoenol Pyruvate)

2- Kranz anatomy

absent

Present

3- RUBISCO location

Present in mesophyll tissue

Present in bundle-sheath tissue

4- Photorespiration

Occurs at a greater rate

Doesn’t occur at a high rate

5- Photosynthetic efficiency

Lower

Comparatively higher

CAM plants are C4 plants but instead of segregating the C4 and C3 pathways in different parts of the leaf, they separate them in time instead. CAM stands for crassulacean acid metabolism because it was first studied in members of the plant family Crassulaceae.