Use this pathway schematic to answer questions a through d.
a. Which enzyme carries out a redox reaction? In this reaction, what is being reduced and what is being oxidized?
b. Which enzyme would be the most likely to be regulated by feedback inhibition?
c. What is the end product of this pathway?
d. Which enzyme carries out substrate-level phosphorylation?

Which substance in the following reaction is being reduced?

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a. acetaldehyde

b. NADH

c. ethanol

d. NAD⁺

In the sulfur cycle, microbes degrade organic sulfur compounds, such as (a) _________________, to release H₂S, which can be oxidized by Acidithiobacillus to (b) _________________. This ion can be assimilated into amino acids by (c) _________________ or reduced by Desulfovibrio to (d) _________________. H₂S is used by photoautotrophic bacteria as an electron donor to synthesize (e) _________________. The sulfur-containing by-product of this metabolism is (f) _________________.

Which of the following reactions is an oxidation carried out by A. ferrooxidans?

a. Fe²⁺ → Fe³⁺

b. Fe³⁺ → Fe²⁺

c. CuS→ CuSO₄

d. Fe⁰ → Cu⁰

e. none of the above

Label each reactant and product in the reactions as reduced or oxidized (X is a theoretical molecule or atom).

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All cells require a source of ___________ for redox reactions.

Most oxidation reactions in bacteria involve the _______.

a. removal of hydrogen ions and electrons

b. removal of oxygen

c. addition of hydrogen ions and electrons

d. addition of hydrogen ions

Redox reactions ______.

a. transfer energy

b. transfer electrons

c. involve oxidation and reduction

d. are involved in all of the above

A reduced molecule ______.

a. has gained electrons

b. has become more positive in charge

c. has lost electrons

d. is an electron donor