CLEP Biology Cellular Respiration and Photosynthesis 5

Question 1

What is the primary reason why the theoretical ATP yield from glucose oxidation is never achieved in living cells?

Accepted Answer

Proton leakage, variable P/O ratios, and energy costs of membrane transport reduce efficiency

Answer

Real ATP yields are lower than theoretical maxima because protons leak across the inner membrane, P/O ratios vary, and ATP/ADP transport across the mitochondrial membrane consumes some proton-motive force.

Question 2

In the context of the Calvin cycle, what does the term 'regeneration of RuBP' refer to?

Accepted Answer

The ATP-dependent conversion of Calvin cycle intermediates back into ribulose-1,5-bisphosphate

Answer

Regeneration of RuBP is the third stage of the Calvin cycle, where ATP is used to convert 5-carbon intermediates (ribulose-5-phosphate) back into RuBP so CO2 fixation can continue.

Question 3

Which regulatory molecule activates phosphofructokinase-1 (PFK-1), signaling that the cell needs more energy?

Accepted Answer

AMP (adenosine monophosphate)

Answer

AMP activates PFK-1, the key regulatory enzyme of glycolysis, signaling low energy charge and stimulating glucose breakdown to generate more ATP.

Question 4

What structural feature of the inner mitochondrial membrane dramatically increases its surface area for ATP synthesis?

Accepted Answer

Cristae (infoldings of the inner membrane)

Answer

Cristae are extensive infoldings of the inner mitochondrial membrane that greatly increase its surface area, accommodating more ETC complexes and ATP synthase molecules.

Question 5

What is the fate of the G3P (glyceraldehyde-3-phosphate) molecules produced in the Calvin cycle?

Accepted Answer

About 5/6 of G3P is used to regenerate RuBP, and 1/6 exits to form glucose or other organic molecules

Answer

For every 6 G3P produced (from 3 turns of the Calvin cycle), 5 are used to regenerate RuBP and only 1 net G3P exits to be used for glucose synthesis or other biosynthesis.

CLEP Practice Test

CLEP Practice Test

CLEP Biology Cellular Respiration and Photosynthesis 5