501. Which statement best explains why polyembryony does not automatically mean apomixis?
ⓐ. Because one or more embryos in a polyembryonic seed may arise through normal fertilisation.
ⓑ. Because polyembryony always refers only to fruit formation.
ⓒ. Because apomixis requires two pollen grains to enter one ovule.
ⓓ. Because polyembryony can occur only in unisexual flowers.
Correct Answer: Because one or more embryos in a polyembryonic seed may arise through normal fertilisation.
Explanation: Polyembryony is defined by the presence of more than one embryo in a single seed. It does not specify that fertilisation must be absent. In many cases, one embryo may be zygotic while others may arise from nucellar tissue. That is why polyembryony and apomixis are not identical concepts.
502. In Citrus, additional embryos associated with polyembryony commonly arise from
ⓐ. synergids
ⓑ. polar nuclei
ⓒ. nucellar cells
ⓓ. endosperm cells
Correct Answer: nucellar cells
Explanation: Citrus is a classic example in which extra embryos may arise from nucellar tissue of the ovule. Nucellar cells are diploid sporophytic cells surrounding the embryo sac. When they produce embryos, those embryos are not formed through the usual zygotic route. This makes Citrus an important example in discussions of polyembryony.
503. Which statement best describes polyembryony in relation to fertilisation?
ⓐ. It always indicates that fertilisation was absent.
ⓑ. It refers only to seedless fruit formation.
ⓒ. It may occur even when one embryo has formed through normal fertilisation.
ⓓ. It always begins with failure of pollen-pistil interaction.
Correct Answer: It may occur even when one embryo has formed through normal fertilisation.
Explanation: Polyembryony is about the presence of more than one embryo in a seed. One of those embryos may be zygotic, so normal fertilisation may still have occurred. Additional embryos may arise from nucellar tissue in some species.
504. A seed contains three embryos: one formed from the zygote and two formed from surrounding ovular tissue. The overall condition is called
ⓐ. parthenocarpy
ⓑ. polyembryony
ⓒ. double fertilisation
ⓓ. geitonogamy
Correct Answer: polyembryony
Explanation: The defining feature here is the presence of more than one embryo within a single seed. Their exact origin may differ, but the condition remains polyembryony. One embryo may be zygotic and others may be nucellar, yet all are counted together under the same term. The concept is based on embryo number, not on a single uniform origin.
505. Which pair is correctly matched?
ⓐ. Parthenocarpy — seed formation without fertilisation
ⓑ. Polyembryony — more than one embryo in a seed
ⓒ. Apomixis — fruit formation without fertilisation
ⓓ. Xenogamy — pollination within the same flower
Correct Answer: Polyembryony — more than one embryo in a seed
Explanation: Polyembryony means more than one embryo in a seed. Apomixis is seed formation without fertilisation, parthenocarpy is fruit development without fertilisation, and xenogamy is pollination between different plants of the same species.
506. Assertion: A polyembryonic seed may contain both a zygotic embryo and additional nucellar embryos.
Reason: More than one embryo can arise within the same seed from different origins.
ⓐ. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
ⓑ. Both Assertion and Reason are true, but the Reason does not correctly explain the Assertion.
ⓒ. Assertion is true, but Reason is false.
ⓓ. Assertion is false, but Reason is true.
Correct Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Explanation: Polyembryony refers to the occurrence of more than one embryo in a seed, and those embryos need not all have the same origin. A zygotic embryo may coexist with additional embryos arising from nucellar tissue. The reason therefore explains the assertion directly.
507. Which sequence correctly traces the overall reproductive flow in a flowering plant?
ⓐ. flower formation → sporogenesis → gametophyte development → pollination → pollen-pistil interaction → double fertilisation → seed and fruit formation
ⓑ. gametophyte development → fruit formation → pollination → embryo sac formation → double fertilisation
ⓒ. pollination → flower formation → sporogenesis → fertilisation → seed coat formation
ⓓ. seed formation → pollen tube growth → embryo development → sporogenesis
Correct Answer: flower formation → sporogenesis → gametophyte development → pollination → pollen-pistil interaction → double fertilisation → seed and fruit formation
Explanation: This sequence follows the biological order of events: floral structures are formed first, then spores and gametophytes develop, followed by pollination, pollen-pistil interaction, and double fertilisation. After that, the ovule and ovary undergo post-fertilisation changes to form seed and fruit.
508. Which event most directly connects pollination with actual fertilisation in angiosperms?
ⓐ. Anther dehiscence
ⓑ. Formation of the embryo sac
ⓒ. Growth of the pollen tube through the pistil toward the ovule
ⓓ. Differentiation of tapetum
Correct Answer: Growth of the pollen tube through the pistil toward the ovule
Explanation: Pollination alone only places the pollen on the stigma. Fertilisation becomes possible only when the pollen tube grows through the style, reaches the ovule, and delivers the male gametes into the embryo sac. This makes pollen tube growth the direct functional bridge between pollen transfer and gamete fusion. Without it, syngamy and triple fusion cannot occur.
509. Which integrated developmental chain on the male side is correct?
ⓐ. tapetum → embryo sac → pollen mother cell → pollen tube
ⓑ. vegetative cell → megaspore → pollen grain → zygote
ⓒ. pollen mother cell $(2n)$ → microspores $(n)$ → pollen grain → pollen tube
ⓓ. endothecium → microsporangium → ovule → male gamete
Correct Answer: pollen mother cell $(2n)$ → microspores $(n)$ → pollen grain → pollen tube
Explanation: The pollen mother cell undergoes meiosis to form haploid microspores. These microspores develop into pollen grains, which later germinate to produce pollen tubes after compatible pollination. This chain therefore connects microsporogenesis with the functional male gametophyte stage. It is an integrated male-side sequence from anther to fertilisation pathway.
510. Which combined source-to-product mapping is correct?
ⓐ. one male gamete + egg → zygote; other male gamete + polar nuclei → primary endosperm nucleus; ovule → seed; ovary → fruit
ⓑ. one male gamete + synergid → zygote; other male gamete + egg → endosperm; ovary → seed
ⓒ. microsporangium → seed; ovule → fruit; zygote → seed coat
ⓓ. integuments → fruit wall; ovary → embryo; central cell → micropyle
Correct Answer: one male gamete + egg → zygote; other male gamete + polar nuclei → primary endosperm nucleus; ovule → seed; ovary → fruit
Explanation: This option brings together the key products of fertilisation and post-fertilisation development. Syngamy produces the zygote, triple fusion produces the primary endosperm nucleus, the ovule becomes the seed, and the ovary becomes the fruit.
511. Which event occurs after megasporogenesis but before double fertilisation in the usual angiosperm sequence?
ⓐ. Transformation of ovary into fruit
ⓑ. Formation of seed coat from integuments
ⓒ. Development of the seven-celled, eight-nucleate embryo sac
ⓓ. Formation of the primary endosperm nucleus
Correct Answer: Development of the seven-celled, eight-nucleate embryo sac
Explanation: Megasporogenesis produces the functional megaspore, but the mature female gametophyte appears only after embryo sac development. Double fertilisation occurs later, once pollen tube growth delivers the male gametes. Therefore, the fully organized embryo sac belongs to the intermediate stage between sporogenesis and fertilisation. This helps place female gametophyte development correctly in the overall sequence.
512. After a compatible pollen grain lands on the stigma and germinates, which sequence must occur before syngamy can take place?
ⓐ. fruit formation → seed coat development → endosperm persistence
ⓑ. pollen tube growth through style → entry into ovule through micropyle → discharge into a synergid
ⓒ. triple fusion → zygote formation → embryo development
ⓓ. degeneration of three megaspores → embryo sac formation → ovary wall thickening
Correct Answer: pollen tube growth through style → entry into ovule through micropyle → discharge into a synergid
Explanation: Syngamy cannot occur immediately after pollen germination. The pollen tube must first grow through the style, reach the ovule, enter through the micropyle, and discharge the male gametes into one synergid of the embryo sac. Only after this delivery can one male gamete fuse with the egg. This sequence is the final prelude to double fertilisation.
513. Which sequence correctly traces the female side from megaspore mother cell to seed formation in a flowering plant?
ⓐ. megaspore mother cell → functional megaspore → embryo sac → fertilisation → seed
ⓑ. megaspore mother cell → embryo sac → pollen grain → fruit → seed
ⓒ. embryo sac → megaspore mother cell → fertilisation → ovary → seed
ⓓ. functional megaspore → megaspore mother cell → embryo sac → seed coat
Correct Answer: megaspore mother cell → functional megaspore → embryo sac → fertilisation → seed
Explanation: The megaspore mother cell undergoes meiosis to form megaspores, of which usually one remains functional. That functional megaspore develops into the embryo sac, which is the female gametophyte. After fertilisation, the ovule containing the embryo sac develops into the seed. This sequence follows the normal female reproductive line from sporogenesis to seed formation.
514. Which event comes immediately after pollen-pistil recognition of compatible pollen but before discharge of male gametes?
ⓐ. triple fusion
ⓑ. ovary becomes fruit
ⓒ. pollen tube growth through the style
ⓓ. development of seed coat
Correct Answer: pollen tube growth through the style
Explanation: Compatibility recognition on the stigma is followed by hydration and germination of the pollen grain. The next essential step is growth of the pollen tube through the style toward the ovary and ovule. Male gamete discharge occurs only after the pollen tube reaches the embryo sac. So pollen tube growth is the correct intervening event.
515. Which integrated chain on the male side is correct from diploid stage to fertilisation product?
ⓐ. vegetative cell → pollen mother cell → male gamete → zygote
ⓑ. anther wall → microspore tetrad → endosperm → embryo
ⓒ. pollen grain → microspore mother cell → male gamete → fruit
ⓓ. pollen mother cell $(2n)$ → microspores $(n)$ → pollen grain → male gamete → zygote $(2n)$
Correct Answer: pollen mother cell $(2n)$ → microspores $(n)$ → pollen grain → male gamete → zygote $(2n)$
Explanation: The pollen mother cell is diploid and undergoes meiosis to produce haploid microspores. These microspores develop into pollen grains, which eventually produce the male gametes. One male gamete then fuses with the egg to form the diploid zygote. This chain integrates ploidy change with later reproductive function.
516. Which event correctly marks the transition from pre-fertilisation phase to fertilisation phase in angiosperms?
ⓐ. formation of microspore tetrad
ⓑ. fusion of male and female gametic nuclei
ⓒ. development of endosperm
ⓓ. formation of seed coat
Correct Answer: fusion of male and female gametic nuclei
Explanation: Pre-fertilisation events include gametophyte formation, pollination, pollen germination, and pollen tube growth. The actual fertilisation phase begins only when fusion events occur inside the embryo sac. That includes syngamy and triple fusion. So gamete fusion marks the real shift from preparation to fertilisation.
517. Which event must occur before both embryo development and endosperm development can begin in the normal angiosperm life cycle?
ⓐ. fruit ripening
ⓑ. perisperm formation
ⓒ. double fertilisation
ⓓ. seed dormancy
Correct Answer: double fertilisation
Explanation: Embryo development begins from the zygote formed by syngamy, and endosperm development begins from the primary endosperm nucleus formed by triple fusion. These two events together make up double fertilisation. Therefore, both embryo and endosperm depend on double fertilisation in the usual reproductive sequence. This makes it the central turning point of post-fertilisation development.
518. Which source-to-product chain is fully correct?
ⓐ. integuments → seed coat; zygote → embryo; primary endosperm nucleus → endosperm
ⓑ. ovary wall → seed coat; polar nuclei → embryo; micropyle → fruit
ⓒ. embryo sac → pericarp; nucellus → zygote; ovule → pollen grain
ⓓ. tapetum → endosperm; synergid → seed coat; ovary → embryo
Correct Answer: integuments → seed coat; zygote → embryo; primary endosperm nucleus → endosperm
Explanation: These are three standard post-fertilisation mappings in flowering plants. Integuments form the seed coat, the zygote develops into the embryo, and the primary endosperm nucleus gives rise to endosperm.
519. A flower is pollinated successfully, pollen tube enters the ovule through the micropyle, and two male gametes are released into the embryo sac. Which event occurs next in the normal sequence?
ⓐ. ovary becomes fruit immediately
ⓑ. seed coat develops from integuments immediately
ⓒ. pollen mother cell undergoes meiosis
ⓓ. syngamy and triple fusion
Correct Answer: syngamy and triple fusion
Explanation: Once the male gametes are released into the embryo sac, the next defining events are the two fusion processes. One male gamete fuses with the egg, and the other fuses with the polar nuclei. These are syngamy and triple fusion respectively. Seed and fruit development happen later, after these fertilisation events.
520. Which statement best connects pollination type with genetic consequence?
ⓐ. Autogamy and xenogamy are genetically identical because both involve one flower.
ⓑ. Geitonogamy is genetically similar to self-pollination, whereas xenogamy brings gametes from different plants.
ⓒ. Autogamy always produces more variation than xenogamy.
ⓓ. Geitonogamy never requires a pollinating agent.
Correct Answer: Geitonogamy is genetically similar to self-pollination, whereas xenogamy brings gametes from different plants.
Explanation: In geitonogamy, pollen moves between flowers of the same plant, so its genetic effect resembles self-pollination. In xenogamy, pollen comes from a different plant of the same species, increasing the chance of new genetic combinations. This makes xenogamy the true cross-pollination condition in genetic terms. The distinction is important because physical transfer and genetic consequence do not always match.
