Biology Questions and Answers

Answer: D

The best explanation is that auxin accumulates towards the darker side to induce greater cell elongation.

This bending is phototropism. Light falling on one side of the shoot tip causes the growth hormone auxin to move towards the shaded side. The cells on the shaded side, with more auxin, elongate faster than those on the lit side, so the shoot curves towards the light. Darwin's and Went's experiments on oat coleoptiles established this.

The illuminated side does not grow more, it grows less, so the first option has it backwards. Shoot tips are not 'attracted' to light, and the need for light in photosynthesis is the benefit of bending, not its mechanism.

Answer: A

Statements a, b and c are correct, so the answer is a,b and c.

(a) Vitamins are organic compounds needed in small amounts for normal health. (b) Many act as coenzymes; the B vitamins in particular are needed to metabolise carbohydrates, fats and proteins. (c) They are needed for growth and for forming blood cells, bones and tissues; vitamin D, for example, is essential for bone formation in children.

(d) is false. Most vitamins must come from food. The body makes only a few, such as vitamin D in skin exposed to sunlight, and vitamin K and some B vitamins are made by gut bacteria. So any option including d is wrong, and 'a only' leaves out two true statements.

Answer: D

The vitamins that are not fat soluble are the B vitamins.

Vitamins fall into two groups. The fat-soluble vitamins, A, D, E and K, dissolve in fats, are absorbed with dietary fat and can be stored in the liver and fatty tissue. The water-soluble vitamins, the B complex and vitamin C, dissolve in water, are not stored to any great extent and are lost in urine, so they are needed regularly.

A, D and K are all in the fat-soluble group, so they are the wrong choices.

Answer: B

The answer is DNA and protein.

A chromosome is made of chromatin, which is DNA wound around and packed by proteins. The proteins are of two kinds: histones, around which the DNA is coiled to form nucleosomes, and non-histone proteins, which include structural and regulatory proteins. So chromosomes are, in the standard textbook phrase, made of DNA and protein.

'Protein only' leaves out DNA, the genetic material itself. 'DNA, RNA and histone' leaves out the non-histone proteins. The last option lists components found in chromatin, but RNA is only a small, transient part (transcripts being made on it) rather than a structural constituent, so the model answer takes the two main components, DNA and protein.

Answer: C

A heterocoelous centrum is characteristic of birds.

The centrum is the body of a vertebra, and it is classified by the shape of its two ends. In a heterocoelous centrum both ends are saddle-shaped, which lets neighbouring vertebrae turn freely in two planes. This is typical of the neck vertebrae of birds, and gives the bird neck its great flexibility.

Amphibians and reptiles typically have procoelous or opisthocoelous centra (one end concave, the other convex), and mammals have acoelous (amphiplatyan) centra with flat ends.

Answer: B

The life span of red blood cells is 100-120 days.

Human red blood cells (erythrocytes) have no nucleus, so they cannot repair themselves. After about 120 days in circulation they become fragile and are removed, chiefly in the spleen (the 'graveyard of RBCs') and the liver, where their haemoglobin is broken down and the iron recycled.

90-100 and 70-90 days are too short. 120-180 days is too long; the usual textbook figure is 120 days, which the keyed range includes at its upper end.

Answer: A

Malaria is caused by protozoa.

Malaria is caused by single-celled protozoan parasites of the genus Plasmodium (chiefly P. falciparum and P. vivax). The parasites are transmitted by the bite of an infected female Anopheles mosquito, multiply in the liver and then infect red blood cells, causing the cycles of fever and chills.

Bacteria cause diseases such as tuberculosis and cholera, viruses cause dengue and influenza, and fungi cause ringworm. None of them causes malaria.

Answer: C

The tuberculosis vaccine is BCG.

Bacillus Calmette-Guerin (BCG) vaccine, developed by Albert Calmette and Camille Guerin and first used in 1921, is a live attenuated strain of Mycobacterium bovis. In India it is given at birth under the Universal Immunisation Programme, and it protects young children particularly against severe forms of tuberculosis.

PAS (para-aminosalicylic acid) is an anti-tuberculosis drug, not a vaccine. OPV is the oral polio vaccine, and DPT protects against diphtheria, pertussis and tetanus.

Answer: C

On the key, the normal temperature of blood is slightly higher than the body temperature.

The 'body temperature' usually quoted, about 37°C (98.6°F), is measured in the mouth or under the arm. Blood circulating through the body core, warmed by the liver, muscles and other active organs, is typically a little warmer, around 38°C, which is the reading the key relies on.

Blood temperature is closely linked to body temperature, since blood distributes heat round the body, so 'no relation' is wrong; and it is not normally below the measured body temperature.

Answer: C

On the key, the kinetochore is generally called the centromere.

The centromere is the constricted region of a chromosome where the two sister chromatids are held together. The kinetochore is the protein disc assembled on the centromere, to which spindle fibres attach during cell division. Because the two are found at the same place and work together, older textbooks often use 'kinetochore' and 'centromere' interchangeably, which is the sense of the question.

The centrosome is the organelle with the centrioles that organises the spindle, the chromosome is the whole structure, and the mesosome is an infolding of the membrane in bacteria.