CBSE 12th Biology Question Paper 2024 (Set 4)

The correct answer is (b) cytoplasm and generative cell. In a germinating pollen grain, the pollen tube develops from the vegetative cell and carries the generative cell through the tube. The generative cell later divides to form two male gametes. Option (a) is incorrect because the vegetative and generative cells are not both carried as separate complete cells in the mature pollen tube contents in the usual NCERT description. Option (c) is incorrect because the generative cell is also carried along. Option (d) is incorrect because one male gamete is formed later from the generative cell, not carried initially.

The correct answer is (b) Cotyledon. In maize grain, the scutellum is the single cotyledon of the monocot embryo. It helps absorb nutrients from the endosperm and transfer them to the embryo. It is not the endosperm, embryo as a whole, or the coleoptile.

The correct answer is (a) very low recombination. Tightly linked genes lie very close together on the same chromosome, so crossing over between them is rare. Therefore recombination frequency is very low. They do not show no recombination at all, but the chance is greatly reduced. Non-parental combinations arise only when recombination occurs.

The correct answer is (c) Haplodiploidy. In honeybees, sex determination follows haplodiploidy: males develop from unfertilised haploid eggs, while females develop from fertilised diploid eggs. Hence the system is called haplodiploidy. 'Haplodiploid' and 'diplohaplodiploid' are not the standard NCERT term for this mechanism.

The correct answer is (d) Conifers. During the Mesozoic era, gymnosperms, especially conifers, were the dominant plant group and flourished along with dinosaurs. Progymnosperms are older than the Mesozoic, bryophytes are primitive non-vascular plants, and tracheophytes is a broad group of vascular plants, not the specific dominant Mesozoic form asked here.