Biology Questions and Answers

Answer: B

The key is Both A and R are correct but R is not the correct explanation of A.

Vomiting is preceded by nausea and a burst of autonomic activity. Excess salivation, sweating, pallor and a fast heart rate are the usual signs (Assertion). Clinical nursing references also list a slow heart rate among the findings before vomiting, because the vagus nerve is active as well, so the Reason is true.

R does not explain A: slowing of the heart is a different effect and cannot be the reason for hyper salivation, sweating or a fast pulse, so option A is wrong. Options C and D each call a true statement false.

Answer: D

The enzyme is pyruvate dehydrogenase.

After glycolysis, pyruvic acid enters the mitochondrion, where the pyruvate dehydrogenase complex carries out oxidative decarboxylation: one carbon is removed as CO₂, NAD⁺ is reduced to NADH, and the remaining two-carbon acetyl group is joined to coenzyme A as acetyl CoA, which then enters the Krebs cycle.

Aconitase works inside the Krebs cycle, converting citrate to isocitrate. 'Pyruvic acid oxidase' and 'pyruvate synthetase' are not the enzymes that link glycolysis to the Krebs cycle in respiration.

Answer: A

The correct code is a-2, b-4, c-1, d-3.

• Chlorophyll: green, the main photosynthetic pigment.
• Xanthophyll: yellow, an oxygen-containing carotenoid.
• Carotenoid (carotene): orange.
• Phycocyanin: blue green, the pigment that gives blue-green algae (cyanobacteria) their colour.

The other codes go wrong at once: a-2, b-4, c-3, d-1 makes carotenoid blue green and phycocyanin orange, a-1, b-2, c-3, d-4 makes chlorophyll orange, and a-4, b-1, c-3, d-2 makes chlorophyll yellow.

Answer: D

Only statement IV is correct, so the answer is IV only.

Systole is the phase of the cardiac cycle in which the heart muscle contracts and pumps blood out of the chambers. The opposite phase, when the heart relaxes and fills with blood, is diastole.

Statements I and II wrongly link the term with the lungs, which are emptied and filled by breathing movements, not by systole. Statement III describes diastole, not systole. So every option containing I, II or III is wrong.

Answer: A

Aestivation is seen in amphibians.

Aestivation is 'summer sleep': a state of dormancy that some animals enter to survive heat and drought. Frogs and toads, whose moist skin dries out easily, burrow into mud and remain inactive until the rains return; lungfish, snails and some insects do the same.

The chimpanzee does not become dormant at all. Squirrels are known for winter dormancy (hibernation) in cold regions, the opposite season. Salmon respond to the seasons by migrating between sea and river to breed, not by aestivating.

Answer: B

The correct code is a-2, b-3, c-4, d-1.

• Leprosy: Lepromin test, a skin test of the response to Mycobacterium leprae antigen.
• Typhoid fever: Widal test, which detects antibodies against Salmonella typhi.
• Tuberculosis: Mantoux (tuberculin) test.
• Diabetes: glycosylated haemoglobin (HbA1c) test, which shows the average blood sugar over the previous two to three months.

The other codes swap the Widal and Mantoux tests or give leprosy the diabetes test.

Answer: D

The micronutrient is zinc.

Micronutrients are essential elements needed by plants in very small amounts, typically less than 10 mg per kg of dry matter: iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel. Zinc is needed for enzymes and for making the growth hormone auxin; its deficiency causes 'khaira' disease of rice.

Oxygen, hydrogen and nitrogen are macronutrients, required in large amounts; carbon, hydrogen and oxygen form the bulk of plant tissue.

Answer: B

The microbe is Frankia.

Frankia is a filamentous actinomycete that forms nitrogen-fixing root nodules on non-leguminous plants such as Casuarina and Alnus (alder); such plants are called actinorhizal plants.

Rhizobium forms nodules on legumes such as peas and beans. Anabaena is a cyanobacterium that fixes nitrogen in water and in association with the fern Azolla, and Azotobacter is a free-living soil bacterium that fixes nitrogen without forming nodules.

Answer: C

The acrosome is formed by the Golgi complex.

During spermiogenesis, vesicles from the Golgi apparatus fuse to form the acrosome, a cap over the head of the sperm. It contains enzymes such as hyaluronidase and acrosin that help the sperm penetrate the layers around the egg.

Lysosomes are digestive vesicles that themselves come from the Golgi, but the acrosome is attributed to the Golgi complex. Chloroplasts are found only in plant cells, and chromosomes carry genes in the nucleus rather than forming cell structures.

Answer: A

Deficiency of folic acid leads to anaemia.

Folic acid (vitamin B₉) is needed for DNA synthesis in rapidly dividing cells, including red blood cell precursors in the bone marrow. Without it, red cells mature abnormally and become large and few, causing megaloblastic anaemia. Folic acid deficiency in pregnancy also causes neural tube defects in the foetus.

Scurvy results from a lack of vitamin C, and night blindness from a lack of vitamin A. 'Mental disorder' is not the characteristic deficiency disease of folic acid.