Biology Questions and Answers

Answer: A

The belief that the earth was only a few thousand years old did not help Darwin - it hindered him.

Natural selection needs immense stretches of time, and Lyell's geology, which showed the earth to be far older than the biblical reckoning, was what made the theory possible.

Answer: A

Water supplies the electrons for the light reactions.

Chlorophyll loses an electron when it absorbs a photon, and replaces it by splitting water:

\[ \mathrm{2H_2O \rightarrow 4H^+ + 4e^- + O_2} \]

The oxygen released is the by-product, and every molecule of it in the atmosphere came from this reaction.

Answer: A

DDT reduced bird numbers because many of the eggs laid did not hatch.

DDT accumulates up the food chain, and in birds of prey it interferes with calcium deposition so the shells are too thin to bear the weight of the incubating parent. The effect nearly extinguished the peregrine and the bald eagle.

Answer: A

Leghaemoglobin absorbs oxygen in the root nodule.

Nitrogenase, the enzyme that fixes nitrogen, is destroyed by oxygen, yet the bacteria need oxygen for their own respiration. Leghaemoglobin binds the oxygen and delivers it at a very low free concentration, protecting the enzyme while feeding the bacteria. It is what makes an active nodule pink inside.

Answer: B

Photosynthesis is fastest in white light, because it contains every wavelength chlorophyll can use.

Chlorophyll absorbs most strongly in the blue-violet and red, and the accessory pigments capture parts of the spectrum chlorophyll misses, so the full white spectrum drives the process harder than any single colour.

Answer: D

Bacterial replication begins with DNA replication.

The circular chromosome is copied from a single origin; the two copies then attach to the plasma membrane and are drawn apart as the cell grows, and only then does the membrane pinch inward and the daughter cells separate.

Answer: C

A successful experiment results only in the rejection of one or more hypotheses.

Evidence can disprove a hypothesis conclusively but can never prove one, since the next observation may contradict it. A hypothesis that survives repeated attempts to refute it is provisionally accepted, not proved.

Answer: C

Deductive reasoning applies general principles to predict or explain specific cases.

Its conclusion follows necessarily from its premises: if the general rule is true, the particular consequence must be. Inductive reasoning runs the other way, from particular observations to a general rule.