Biology Questions and Answers

Answer: A

The earthworm is a detritivore: it feeds on dead and decaying organic matter (detritus) and breaks it down, which returns nutrients to the soil.

The crow is an omnivore and scavenger, the vulture is a carrion eater (a scavenger and not a detritus feeder), and fungi are decomposers that digest matter outside their bodies by enzymes, not detritivores that ingest it.

Detritivores differ from decomposers: a detritivore swallows dead matter and digests it inside its body, as earthworms, millipedes and woodlice do, while decomposers such as fungi and bacteria digest it outside the body by releasing enzymes. This distinction rules out fungi, and crow and vulture are scavengers or predators that eat dead animals, not detritus.

Answer: D

Hyponasty is the growth movement in which the lower surface of an organ grows faster, so the organ bends upward. Epinasty is the opposite, with greater growth of the upper surface, causing downward bending of leaves.

Phototropism and geotropism are tropisms directed by light and gravity, not nastic responses to growth on one surface.

Nastic movements are responses of plant organs to stimuli that do not depend on the direction of the stimulus, unlike tropisms. Epinasty and hyponasty are due to unequal growth on the two sides of an organ, with epinasty being faster growth on the upper side and hyponasty on the lower.

Answer: A

Pfeffer's auxanometer is used to measure plant growth: it magnifies the small increase in the length of a growing shoot and records it.

The temperature of cooking jelly, the pectin content of a fruit extract and the tenderness of peas are measured by other instruments (a thermometer, a pectinometer and a tenderometer).

An auxanometer records growth in length by means of a thread that passes over a pulley to a pointer. Pfeffer's version magnifies the growth of the plant on a scale, which gives the rate of growth.

Answer: C

Brassinosteroids were first extracted from the pollen of rape (Brassica napus). They are plant growth hormones that promote cell elongation.

Potato, radish and onion are not the source.

Brassinolide, the first brassinosteroid, was isolated from rape pollen in the 1970s. These steroids promote cell elongation and division and increase stress tolerance in plants.

Answer: B

Myricetin is the one that is not a pigment, according to the key: it is a flavonol, a colourless to pale yellow compound. Anthocyanins and betacyanins are plant pigments (red to blue and red-violet) and lutein is a yellow carotenoid pigment.

I could not confirm from a source that myricetin counts as a non-pigment, so the choice rests on the key.

Anthocyanins give red, blue and purple colour, betacyanins give red-violet, and lutein gives yellow. Myricetin is a flavonol that has little visible colour, which is why the key treats it as not a pigment.

Answer: C

Starch is not a secondary metabolite: it is a primary metabolite, a storage carbohydrate made in basic metabolism. Alkaloids, glycosides and steroids are secondary metabolites, which are not needed for basic growth.

Primary metabolites such as sugars, starch, amino acids and fats are needed for growth, and secondary metabolites such as alkaloids, glycosides, steroids and terpenes serve defence and other roles. Starch is a storage carbohydrate and so a primary product.

Answer: B

Ribosomes make proteins, so Ribosome - Protein synthesis is the correct pair. Mitochondria produce ATP through respiration and do not synthesise proteins as their main role. The nucleus holds the genetic material and controls cell activity; it does not carry minerals. Chloroplasts carry out photosynthesis, while transpiration is loss of water vapour through stomata of leaves.

Ribosomes are found free in the cytoplasm and on the rough endoplasmic reticulum, where they read messenger RNA to join amino acids into proteins.

Answer: C

Nematodes is the odd one out. Cold and frost, heat and salinity are all abiotic stresses, that is, non-living physical or chemical factors that harm plants. Nematodes are tiny worms that parasitise plants, so they are a biotic stress caused by living organisms. Abiotic factors are the non-living physical and chemical conditions, such as temperature, salt content and water, while biotic factors are the living organisms. Because three options are of the first kind and one is of the second kind, the odd one is the biotic factor.

Answer: D

The incorrect statement is that threads of chromatin in the nucleus contain ribonucleic acid (RNA). Chromatin is made of DNA (deoxyribonucleic acid) wound on histone proteins, and it forms the chromosomes when the cell divides.

The other statements are correct: the nucleus is the control centre of the cell, it determines how the cell functions and its basic structure, and it is separated from the cytoplasm by the nuclear membrane. The fourth option is therefore the incorrect one.

Answer: A

The correct statement is that algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic organisms, found in both fresh water and the sea. Their body is a thallus, without roots, stems or leaves, and they make their food by photosynthesis.

The other statements describe other plants or are wrong: mosses and liverworts are bryophytes, not algae; gemmae are the means of asexual reproduction of liverworts; and the dominant stage of the life cycle of a bryophyte is the gametophyte, which does not fit algae in general. The first option is the answer.