Read the statements below on cell division and ploidy during gametogenesis:
(p) Unicellular monerans, fungi, algae, and bryophytes possess a haploid parental body. (q) Pteridophytes, gymnosperms, angiosperms, and humans possess a diploid parental body. (r) A haploid parent produces gametes via meiosis, while a diploid parent produces gametes via mitosis. (s) Meiocytes (gamete mother cells) are specialized diploid cells that undergo reduction division.
Choose the correct option.
Haploid parents produce gametes by mitosis because their cells are already haploid, whereas diploid parents produce gametes by meiosis. Meiocytes are specialized diploid cells undergoing reduction division. Therefore statement (r) is incorrect.
Question 42 of 100
📘 CLASS XII
Evaluate the chromosome numbers in meiocytes (2n) and gametes (n) based on NCERT Table 1.1:
(1) In a housefly, the meiocyte contains 12 chromosomes, and the gamete contains 6. (2) In a butterfly, the gamete contains 380 chromosomes. (3) In Ophioglossum (a fern), the gamete has 630 chromosomes, which is the highest listed number. (4) In an onion, the meiocyte contains 16 chromosomes, and the gamete contains 8.
Choose the correct option.
In butterflies, the meiocyte (2n) contains 380 chromosomes, so the gamete (n) contains 190 chromosomes. Therefore statement (2) is incorrect.
Question 43 of 100
📘 CLASS XII
Select the correct morphological classification of gametes:
(a) In algae like Cladophora, gametes are homogametes because they are morphologically identical. (b) In humans and the alga Fucus, gametes are heterogametes because they are morphologically distinct. (c) In all sexually reproducing organisms on Earth, the male gamete is always motile and the female gamete is always non-motile.
Choose the correct option.
In most organisms, the male gamete is motile and the female gamete is non-motile. However, some algae and fungi possess motile male and female gametes. Hence statement (c) is incorrect.
Question 44 of 100
📘 CLASS XII
Study the gamete transfer mechanisms in lower and higher plants:
(i) Algae, bryophytes, and pteridophytes utilize wind as the primary medium for gamete transfer. (ii) In seed plants, non-motile male gametes are carried to the female gamete inside the ovule by pollen tubes. (iii) To compensate for the heavy loss of male gametes during transport, the number of male gametes produced is several thousand times more than female gametes.
Choose the correct option.
Algae, bryophytes and pteridophytes require water as the medium for gamete transfer, not wind. Statements (ii) and (iii) are correct.
Question 45 of 100
📘 CLASS XII
Read these statements regarding pollen transfer in bisexual versus dioecious plants:
(I) In self-fertilizing bisexual plants like peas, pollination is relatively easy because the anther and stigma are located in close proximity. (II) In cross-pollinating and dioecious plants, a specialized event called pollination is required to transfer pollen grains. (III) Pollen grains germinate directly inside the ovule to release male gametes without touching the stigma.
Choose the correct option.
Pollen grains first land on the stigma, germinate there, and the pollen tube grows through the style to reach the ovule. Therefore statement (III) is incorrect.
Question 46 of 100
📘 CLASS XII
Analyze the nature and examples of Parthenogenesis:
(a) It is a process where the female gamete undergoes development to form a new organism without fertilization. (b) It is observed in rotifers, honeybees, some lizards, and birds like turkey. (c) It results in the production of offspring that are genetically identical to the male parent.
Choose the correct option.
Parthenogenesis involves the development of an organism directly from an unfertilized egg. Hence offspring are not genetically identical to a male parent. Statement (c) is incorrect.
Question 47 of 100
📘 CLASS XII
Evaluate the differences in syngamy between aquatic and terrestrial organisms:
(p) In external fertilization (e.g., frogs, bony fishes), syngamy occurs in the external medium, which is water. (q) Internal fertilization involves fusion of gametes inside the body of the female parent (e.g., reptiles, birds, mammals). (r) Organisms displaying external fertilization release a very small number of gametes to prevent sperm competition. (s) Offspring of external fertilizers are highly safe from predators, ensuring high survival rates.
Choose the correct option.
External fertilizers release a large number of gametes to increase the chances of fertilization, and their offspring remain highly vulnerable to predators. Hence statements (r) and (s) are incorrect.
Question 48 of 100
📘 CLASS XII
Study the behavior of the zygote across different life cycles:
(1) Zygote is a universal, diploid structure formed in all sexually reproducing organisms. (2) In fungi and algae, the zygote develops a thick wall resistant to desiccation and damage, and undergoes a period of rest. (3) In haplontic life cycles, the diploid zygote undergoes mitosis to form a diploid plant body.
Choose the correct option.
In haplontic life cycles, the zygote undergoes meiosis to produce haploid spores rather than mitosis to form a diploid plant body. Therefore statement (3) is incorrect.
Question 49 of 100
📘 CLASS XII
Understand the processes of cell division and differentiation during embryogenesis:
(i) Embryogenesis is the process of development of the embryo from the diploid zygote. (ii) Cell division (mitosis) increases the number of cells, while cell differentiation helps cells form specialized tissues. (iii) Meiosis occurs during embryogenesis to ensure the embryo's tissues remain diploid.
Choose the correct option.
Embryogenesis proceeds through repeated mitotic divisions followed by cell differentiation. Meiosis occurs during gamete formation, not embryogenesis. Hence statement (iii) is incorrect.
Question 50 of 100
📘 CLASS XII
Analyze the post-fertilization changes occurring in flowering plants:
(a) The zygote develops into the embryo, and ovules develop into seeds. (b) The ovary develops into the fruit, which develops a thick, protective wall called the pericarp. (c) The sepals, petals, and stamens of the flower always remain firmly attached to the developing fruit.
Choose the correct option.
After fertilization, the zygote develops into the embryo, ovules become seeds, and the ovary becomes the fruit. In most flowering plants, sepals, petals and stamens wither and fall off after fertilization. Hence statement (c) is incorrect.
