Take this Quiz: AP Biology Units 3–4 — energy and signalling | Zestly

Question 1

An experiment tests an enzyme's reaction rate at varying substrate concentrations in the presence of a molecule X. As the substrate concentration increases, the reaction rate eventually reaches the same maximum velocity ($V_{max}$) as the control group without X. Which conclusion is most accurate?

Accepted Answer

Molecule X is a competitive inhibitor that binds to the active site

Answer

Molecule X is a non-competitive inhibitor that binds to an allosteric site

Answer

Molecule X is a co-factor that increases the enzyme's affinity for the substrate

Answer

Molecule X is an irreversible inhibitor that permanently denatures the enzyme

Question 2

If a chemical uncoupler is added to mitochondria, it creates pores in the inner membrane that allow protons to leak back into the matrix. What is the immediate physiological consequence?

Accepted Answer

ATP synthesis decreases because the proton motive force is dissipated

Answer

The electron transport chain stops because oxygen is no longer reduced

Answer

Glycolysis rate increases to compensate for the lack of NADH

Answer

The pH of the intermembrane space increases significantly

Question 3

In photosynthesis, how do the light-dependent reactions and the Calvin cycle differ in their requirements and outputs?

Accepted Answer

Light reactions produce ATP and NADPH; Calvin cycle uses them to fix CO$_2$

Answer

Light reactions produce glucose; Calvin cycle produces ATP

Answer

Light reactions occur in the stroma; Calvin cycle occurs in the thylakoid

Answer

Light reactions require CO$_2$; Calvin cycle requires H$_2$O

Question 4

Which statement best contrasts cellular respiration with photosynthesis, beyond saying that one is the reverse of the other?

Answer

Photosynthesis releases energy overall, while respiration consumes it.

Answer

Respiration oxidises glucose to carbon dioxide; photosynthesis reduces carbon dioxide to sugar.

Answer

Respiration uses an electron transport chain and photosynthesis does not.

Answer

Respiration happens only in animals and photosynthesis only in plants.

Question 5

A signal molecule binds to a G-protein coupled receptor, triggering a phosphorylation cascade. Why is a cascade more effective than a single-step response?

Answer

It ensures the signal is sent to the nucleus immediately

Answer

It prevents the signal from being degraded by enzymes

Answer

It amplifies the signal, allowing a small stimulus to produce a large response

Answer

It allows the cell to bypass the need for secondary messengers