Biol 221 Lec 11 MCQs

At the molecular level, how is a proton gradient generated by the quinone loop?

• Light causes the quinone to “flip” a proton to the outside of the membrane.

• The quinone donates 2 protons to O₂ to make water, which leaves the cell.

• The quinone donates both H⁺ and electrons, but FeS proteins only accept electrons.

• The quinone, which is located in the periplasm, accepts H⁺ from the cytoplasm.

• Electrons in the quinone are excited by light, and end up in NADH, which creates the PMF.

Compared to mitochondrial ETS (electron transport systems), bacterial ETS . . .

• use far fewer quinones

• use a much greater variety of terminal electron acceptors

• do not have cytochromes

• always generate much less of a PMF

• typically involve 6 electron transport components rather than 5

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NGSS.HS-LS2-3

In oxygenic photosynthesis, as practiced in bacteria . . .

• the electrons that are excited by light return to the same photosystem

• the main photosynthetic reaction pigment is bacteriochlorophyll

• the electrons have such low energy that they must be energized twice

• oxygen is the terminal electron acceptor

• there are two electron transport chains

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Why are purple sulfur bacteria considered metabolically unique?

• They use H₂S as an electron donor.

• They must perform reverse electron transport to make NADH.

• They use only one photosynthetic reaction center.

• They produce a PMF from photosynthetic electron transport.

• They make oxygen as a byproduct of photosynthesis.

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NGSS.HS-LS2-3

How are respiratory and photosynthetic electron transport chains similar?

• Both use the same electron donor.

• Both use the same terminal electron acceptor.

• Both use heme-containing electron carriers.

• Both are used to generate reducing power for the cell.

• Both involve adding external energy to electrons.

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Purple sulfur bacteria (PSB) must use reverse electron transport, but green sulfur bacteria (GSB) do not. Why is there a difference?

• GSB use noncyclic photosynthesis, whereas PSB use cyclic.

• PSB do not make a PMF with their electron transport chain.

• GSB use a bacteriochlorophyll with enough energy to donate its electrons directly to ferredoxin.

• GSB use two photosystems, thereby boosting electrons to higher energy levels.

• Making the sulfur granules in PSB requires electrons from reverse electron transport.

Which of the following is true for all electron carriers?

• They must be capable of being oxidized and reduced.

• They must be able to accept both H+ and electrons.

• They must be able to accept O2.

• They are proteins with metal ions at the center.

• In bacteria, they are only found in the cytoplasm.

During oxygenic photosynthesis, the terminal electron acceptor for the electron transport chain involving photosystem II and plastoquinone is . . .

• oxygen

• NADP+

• the reaction center of photosystem I

• H2O

• ATP

Which of the following is similar in all three photosynthetic mechanisms we discussed?

• the way reducing power is formed

• the use of water as an electron donor

• the way ATP is formed

• the photosynthetic reaction center chlorophyll

• the electrons return to the reaction center from which they were oxidized

Which of the following statements correctly describes the molecule at right?

• it can only be reduced, not oxidized

• it carries only electrons, not H+

• it carries only H^+, not electrons

• it carries both electrons and H+

• it carries electrons from glycolysis to the TCA cycle

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NGSS.HS-LS1-7

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NGSS.HS-PS1-2