MDCAT Biology chapter 2: Biology · Bioenergetics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
35 exam-style questions on Biology · Bioenergetics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Biology · Bioenergetics questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Three similar plants are grown for two weeks under red, blue and green light of the same intensity. The plant under green light grows least because
A
chlorophyll reflects or transmits most green light, so little is absorbed
B
green light carries too much energy and damages the chlorophyll
C
chlorophyll absorbs green light strongly but cannot use it in photolysis
D
green light is absorbed only by carotenoids, which cannot pass energy on
Show answer
Answer: A. Only light that is absorbed can drive photosynthesis. Chlorophyll absorbs red and blue light strongly but little green; most green light is reflected or passes through the leaf, which is also why leaves look green.
2. Which pigment forms the reaction centre of both photosystem I and photosystem II?
A
chlorophyll a
B
chlorophyll b
C
β-carotene
D
xanthophyll
Show answer
Answer: A. The reaction centre of each photosystem is chlorophyll a: P700 in photosystem I and P680 in photosystem II. Chlorophyll b and the carotenoids are accessory pigments that pass the energy they absorb to the reaction centre.
3. A mouse breathes air in which the oxygen is labelled with the isotope 18O. In which product of its aerobic respiration does the labelled oxygen first appear?
A
carbon dioxide
B
pyruvic acid
C
glucose
D
water
Show answer
Answer: D. Oxygen is the final electron acceptor of the respiratory chain, where it combines with electrons and H+ to form water. The CO2 released in the link reaction and Krebs cycle gets its oxygen from the respiratory substrate and water, not from the oxygen breathed in.
4. Which sequence shows the correct order in which electrons from NADH pass along the respiratory chain?
A
cytochromes → coenzyme Q → oxygen
B
oxygen → cytochromes → coenzyme Q
C
coenzyme Q → cytochromes → oxygen
D
coenzyme Q → oxygen → cytochromes
Show answer
Answer: C. Electrons from NADH pass through a flavoprotein to coenzyme Q, then along the cytochromes (ending with cytochrome oxidase), and finally to oxygen, which is reduced to water. Oxygen must come last because it is the final electron acceptor.
5. When fat is respired, its fatty acids are broken into 2-carbon units that enter the Krebs cycle as
A
pyruvic acid
B
glyceraldehyde phosphate
C
acetyl CoA
D
oxaloacetic acid
Show answer
Answer: C. Fatty acids are split into 2-carbon pieces (β-oxidation) that combine with coenzyme A to form acetyl CoA. It is the glycerol part of the fat that enters glycolysis as glyceraldehyde phosphate.
6. In autumn the leaves of many trees turn yellow or orange before they fall. The main reason is that
A
chlorophyll a is converted into yellow-green chlorophyll b
B
iron replaces the magnesium atom in each chlorophyll molecule
C
chlorophyll breaks down, unmasking the carotenoids already present
D
the leaves begin to absorb green light instead of red
Show answer
Answer: C. Carotenoids (yellow xanthophylls and orange carotenes) are present in the chloroplasts all year but are normally masked by the green chlorophyll. When the chlorophyll is broken down, their colours show.
7. RuBisCO, thought to be the most abundant protein on Earth, is the enzyme that
A
joins carbon dioxide to ribulose bisphosphate
B
splits water molecules in photosystem II
C
makes ATP as protons cross the thylakoid membrane
D
reduces NADP+ at the end of the electron chain
Show answer
Answer: A. RuBisCO (ribulose bisphosphate carboxylase) fixes CO2 onto the 5-carbon RuBP in the stroma, the first step of the Calvin cycle. ATP is made by ATP synthase, and NADP+ is reduced by NADP reductase.
8. In glycolysis of one glucose molecule, how many ATP molecules are used in the early steps, and how many are made in the later steps?
A
2 used and 4 made
B
2 used and 2 made
C
4 used and 2 made
D
1 used and 4 made
Show answer
Answer: A. Two ATP are used to phosphorylate the sugar, and four ATP are made as the two 3-carbon molecules are oxidised to pyruvic acid: a net gain of 2 ATP. "2 made" confuses the net gain with the total made.
9. Which of these stages in the breakdown of glucose releases no carbon dioxide?
A
the link reaction
B
glycolysis
C
the Krebs cycle
D
alcoholic fermentation
Show answer
Answer: B. Glycolysis splits glucose into two pyruvic acids without removing any carbon. CO2 is released whenever pyruvic acid or a Krebs cycle acid is decarboxylated: in the link reaction, in the Krebs cycle, and when yeast converts pyruvic acid to acetaldehyde.
10. Each FADH2 yields fewer ATP than each NADH in the electron transport chain because FADH2
A
hands its electrons to a later carrier, so one ATP-forming step is missed
B
gives its electrons straight to oxygen without using the chain
C
carries only one electron, while NADH carries two
D
is made in the cytoplasm and must first be carried into the mitochondrion
Show answer
Answer: A. NADH passes its electrons to the start of the chain, but FADH2 passes them to coenzyme Q, beyond the first site of ATP formation. Both carry two electrons, and FADH2 is made in the matrix during the Krebs cycle.
35, each with the answer and a short explanation, across 2 topics: Photosynthesis, Cellular respiration. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 2 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
