Biology Questions and Answers

Answer: C

The key's answer is Three molecules of ATP.

NADH from the mitochondrial matrix passes its electrons to complex I of the electron transport chain. The classical textbook value, based on a P/O ratio of 3, is that this yields three ATP, against two for FADH₂, which enters at complex II.

Modern measurements give a lower figure of about 2.5 ATP per NADH, but that is not among the options, so the textbook value of three is the one the question expects. Two is the figure for FADH₂, and five and one fit neither.

Answer: A

Oxidative phosphorylation occurs at the Inner mitochondrial membrane.

The electron transport chain (complexes I to IV) and ATP synthase are embedded in the inner mitochondrial membrane, folded into cristae. Electron transport pumps protons out across this membrane, and the protons flowing back through ATP synthase drive the formation of ATP.

The mitochondrial matrix is where the Krebs cycle runs. The chloroplast carries out photophosphorylation, on its thylakoid membranes, and its stroma (matrix) is the site of the Calvin cycle, so neither chloroplast option is correct.

Answer: C

Deoxyribose and the bases are joined by a Glycosidic bond.

In each nucleotide of DNA, the nitrogenous base is attached to carbon 1 of the deoxyribose sugar by an N-glycosidic bond, forming a nucleoside. A phosphate group then links to carbon 5 of the sugar.

Phosphodiester bonds join the sugar of one nucleotide to the phosphate of the next, forming the sugar-phosphate backbone, not sugar to base. The two strands are held together by hydrogen bonds between bases, and peptide bonds join amino acids in proteins.

Answer: C

The enzyme is DNA helicase.

Helicase moves along the DNA at the replication fork and breaks the hydrogen bonds between the base pairs, using ATP, so the two strands separate and can serve as templates.

The others act at other steps. Topoisomerase (DNA gyrase in bacteria) relieves the twisting strain that builds up ahead of the fork as the helix is unwound, but it does not separate the strands. DNA polymerase I removes RNA primers and fills the gaps. DNA ligase seals the nicks between Okazaki fragments.

Answer: A

DNA does not contain Uracil.

The four bases of DNA are adenine, guanine, cytosine and thymine. Uracil is found in RNA, where it takes the place of thymine and pairs with adenine.

Thymine, adenine and guanine are all DNA bases: adenine pairs with thymine and guanine with cytosine in the double helix. So each of the other three options is present in DNA.

Answer: C

The dance is the Waggle dance.

Karl von Frisch showed that a forager bee returning from a distant food source performs a figure-of-eight dance on the comb, waggling her abdomen on the straight run. The angle of that run from the vertical shows the direction of the food relative to the sun, and the length of the waggle run shows the distance. For food close to the hive bees perform the simpler round dance.

'Squiggle dance' and 'wiggle dance' are not the names of these communication dances, so 'All of these' is also wrong.

Answer: A

The main host plant is Terminalia arjuna.

Tropical tasar silk is produced by Antheraea mylitta, which feeds on the leaves of arjun (Terminalia arjuna) and asan (Terminalia tomentosa) as its primary food plants, mainly in the forests of Jharkhand, Chhattisgarh and Odisha. Sal is a secondary host.

Phalaris minor is not a silkworm host at all; it is the major grassy weed of wheat. Castor (Ricinus communis, printed here as 'Ricinus recini') is the food plant of the eri silkworm, Samia ricini, not of the tasar silkworm, so 'All of these' is also wrong.

Answer: B

The process is apoptosis.

In apoptosis (programmed cell death), caspases activate endonucleases that cut DNA between nucleosomes into fragments of about 180-200 base pairs and multiples of that. On a gel these give the typical 'ladder'. The nucleus condenses (pyknosis) and breaks into fragments (karyorrhexis), and the cell splits into apoptotic bodies without inflammation.

Necrosis breaks DNA randomly and gives a smear, not a ladder, and it causes inflammation. Reversible injury does not fragment the nucleus. Inflammation is a tissue response, not a pattern of nuclear breakdown.

Answer: C

The largest gland in the human body is the liver.

The liver weighs about 1.5 kg in an adult. It counts as a gland because it secretes bile, which passes to the small intestine to help digest fats, and it also stores glycogen, makes blood proteins and breaks down toxins.

The thyroid is the largest purely endocrine gland, but it is far smaller than the liver. The pancreas is the second largest gland. The kidney is an excretory organ that filters blood, not a gland.

Answer: C

The vitamin necessary for blood clotting is vitamin K.

The liver needs vitamin K to make several clotting factors, including prothrombin (factor II) and factors VII, IX and X. Without enough of it, blood takes much longer to clot and bleeding becomes hard to stop. The K comes from Koagulation, the German word for clotting.

Vitamin A is needed for vision, vitamin D for calcium absorption and bone health, and vitamin C for collagen formation and wound healing; none of them is a clotting factor.