CBSE Class 12 Biology (2026–27)
Chapter 1: Sexual Reproduction in Flowering Plants
20 Important Questions & Answers
The chapter covers flower structure, microsporogenesis, megasporogenesis, pollination, pollen-pistil interaction, double fertilization, seed and fruit development, apomixis, polyembryony, and related concepts as prescribed in the CBSE 2026–27 syllabus.
Q1. What is microsporogenesis? Explain its significance.
Answer:
Microsporogenesis is the process of formation of microspores or pollen grains from microspore mother cells (MMCs) present in the anther. Each MMC undergoes meiosis and produces four haploid microspores arranged in a tetrad. These microspores later develop into pollen grains, which represent the male gametophyte of flowering plants. Microsporogenesis occurs inside the microsporangia of the anther. The process is important because it ensures the production of genetically varied male gametes through meiosis. Healthy pollen grains are essential for successful pollination and fertilization. Thus, microsporogenesis plays a vital role in sexual reproduction and continuation of plant species.
Q2. Describe the structure of a mature pollen grain.
Answer:
A mature pollen grain is generally spherical and consists of two layers. The outer layer is called exine, which is made of sporopollenin, one of the most resistant organic substances known. The exine has germ pores through which the pollen tube emerges during germination. The inner layer is called intine, composed of cellulose and pectin. The cytoplasm contains a vegetative cell and a generative cell. The vegetative cell is larger and contains abundant food reserves, while the generative cell divides to form two male gametes. The structure of the pollen grain protects male gametes and facilitates their transfer to the stigma for fertilization.
Q3. What is megasporogenesis?
Answer:
Megasporogenesis is the process by which megaspores are formed from the megaspore mother cell (MMC) present inside the ovule. The diploid MMC undergoes meiosis and produces four haploid megaspores. Generally, only one megaspore remains functional, while the other three degenerate. The functional megaspore develops into the female gametophyte or embryo sac through mitotic divisions. Megasporogenesis occurs within the nucellus of the ovule. This process is significant because it produces the female reproductive structure necessary for fertilization. It also contributes to genetic variation by meiosis and ensures the formation of healthy seeds after fertilization.
Q4. Explain the structure of a mature embryo sac.
Answer:
A typical mature embryo sac is a seven-celled and eight-nucleate structure. At the micropylar end, there is an egg apparatus consisting of one egg cell and two synergids. At the chalazal end, there are three antipodal cells. The central cell contains two polar nuclei. Thus, the embryo sac contains seven cells but eight nuclei. The egg cell participates in fertilization, while synergids help in guiding the pollen tube. Polar nuclei fuse with one male gamete during triple fusion to form the primary endosperm nucleus. This organized structure ensures successful fertilization and seed development in flowering plants.
Q5. Differentiate between autogamy and geitonogamy.
Answer:
Autogamy is the transfer of pollen grains from the anther to the stigma of the same flower. It does not require any external pollinating agent and promotes self-pollination. Geitonogamy is the transfer of pollen grains from one flower to another flower of the same plant. Although genetically similar to self-pollination, it requires a pollinating agent. In autogamy, both male and female reproductive organs are present in the same flower. In geitonogamy, different flowers of the same plant are involved. Both methods maintain parental characteristics, but geitonogamy allows greater chances of pollination through external agents.
Q6. What are outbreeding devices?
Answer:
Outbreeding devices are adaptations that prevent self-pollination and promote cross-pollination in flowering plants. These include dichogamy, where pollen release and stigma receptivity occur at different times; herkogamy, where physical barriers prevent self-pollination; self-incompatibility, where pollen from the same plant fails to fertilize; and unisexuality, where male and female flowers are separate. These mechanisms increase genetic diversity and reduce inbreeding depression. By encouraging the exchange of genetic material between different plants, outbreeding devices improve adaptability, vigor, and survival of offspring. Therefore, they play an important role in the evolution and success of flowering plants.
Q7. What is pollination? Mention its types.
Answer:
Pollination is the transfer of pollen grains from the anther to the stigma of a flower. It is a necessary step before fertilization. There are three main types of pollination. Autogamy occurs within the same flower. Geitonogamy occurs between different flowers of the same plant. Xenogamy occurs between flowers of different plants of the same species. Xenogamy promotes maximum genetic variation, whereas autogamy maintains parental traits. Pollination may occur through agents such as wind, water, insects, birds, and bats. Successful pollination leads to pollen germination, fertilization, and ultimately seed and fruit formation.
Q8. Explain wind pollination with suitable adaptations.
Answer:
Wind pollination, also called anemophily, is the transfer of pollen grains through wind currents. Wind-pollinated flowers are generally small, inconspicuous, and lack fragrance or nectar. They produce a large quantity of light, dry, and non-sticky pollen grains to increase the chances of successful pollination. Their stigmas are usually large and feathery to trap airborne pollen effectively. Examples include maize and grasses. Since pollination by wind is uncertain, plants compensate by producing abundant pollen. Wind pollination is an efficient mechanism in open habitats where pollinating animals are scarce. It helps maintain reproduction without dependence on living pollinators.
Q9. What is pollen-pistil interaction?
Answer:
Pollen-pistil interaction refers to the sequence of events that occur between pollen grains and the pistil after pollination. The stigma recognizes whether the pollen is compatible or incompatible. Compatible pollen grains germinate and form pollen tubes that grow through the style toward the ovule. Incompatible pollen is rejected and fails to germinate. This interaction involves chemical signaling and recognition mechanisms. It ensures that fertilization occurs only with suitable pollen grains. Pollen-pistil interaction is important for maintaining species specificity, preventing undesirable fertilization, and ensuring successful sexual reproduction in flowering plants.
Q10. What is double fertilization?
Answer:
Double fertilization is a unique feature of flowering plants. It involves two fusion events within the embryo sac. One male gamete fuses with the egg cell to form a diploid zygote. This process is called syngamy. The second male gamete fuses with the two polar nuclei of the central cell to form a triploid primary endosperm nucleus. This process is known as triple fusion. Together, syngamy and triple fusion constitute double fertilization. The zygote develops into an embryo, while the endosperm provides nourishment to the developing embryo. Double fertilization ensures efficient utilization of resources and successful seed formation.
Q11. Differentiate between syngamy and triple fusion.
Answer:
Syngamy is the fusion of one male gamete with the egg cell, resulting in the formation of a diploid zygote. It leads to embryo development. Triple fusion is the fusion of the second male gamete with two polar nuclei present in the central cell, resulting in a triploid primary endosperm nucleus. It leads to endosperm formation. Syngamy produces the future plant body, whereas triple fusion produces nutritive tissue for the embryo. Both processes occur during double fertilization and are essential for successful reproduction in flowering plants. Together they ensure coordinated embryo and endosperm development.
Q12. What is endosperm? State its functions.
Answer:
Endosperm is a nutritive tissue formed after triple fusion during double fertilization. It develops from the triploid primary endosperm nucleus and serves as a food reservoir for the growing embryo. The endosperm stores nutrients such as starch, proteins, and oils. It nourishes the embryo during seed development and germination. In many seeds, such as maize and coconut, the endosperm persists in mature seeds. In others, such as pea and bean, it is consumed during embryo development. Endosperm is therefore essential for proper growth, survival, and establishment of young seedlings after germination.
Q13. Explain embryo development in flowering plants.
Answer:
Embryo development begins after fertilization when the zygote undergoes repeated mitotic divisions. The zygote first forms a proembryo, which later differentiates into various embryonic structures. In dicot plants, the mature embryo consists of two cotyledons, an embryonal axis, plumule, and radicle. The plumule develops into the shoot system, while the radicle forms the root system. During development, the embryo receives nourishment from the endosperm. Embryogenesis establishes the basic body plan of the future plant. Proper embryo development is essential for seed viability and successful germination under favorable environmental conditions.
Q14. What changes occur in the ovule and ovary after fertilization?
Answer:
After fertilization, significant transformations occur in the flower. The ovule develops into a seed, while the ovary develops into a fruit. The integuments of the ovule become the seed coat. The zygote develops into the embryo, and the primary endosperm nucleus forms the endosperm. The ovary wall differentiates into the fruit wall or pericarp. Other floral parts such as petals, sepals, stamens, and stigma usually wither and fall off. These post-fertilization changes ensure protection and nourishment of the developing embryo and aid in seed dispersal and propagation of the species.
Q15. Define seed and mention its importance.
Answer:
A seed is a mature fertilized ovule containing an embryo, stored food, and a protective seed coat. It is the reproductive unit of flowering plants. Seeds help in the dispersal of plant species to new habitats. They protect the embryo from unfavorable environmental conditions and remain dormant until suitable conditions arise. Seeds store food materials necessary for germination and early seedling growth. They also serve as an important source of food for humans and animals. Due to their ability to survive adverse conditions, seeds ensure continuity and successful propagation of flowering plants.
Q16. What is parthenocarpy? Mention its significance.
Answer:
Parthenocarpy is the development of fruits without fertilization. Such fruits are seedless because no embryo or seed formation occurs. Parthenocarpy may occur naturally or can be induced artificially using plant hormones such as auxins and gibberellins. Common examples include banana and seedless grapes. The significance of parthenocarpy lies in the production of commercially valuable seedless fruits preferred by consumers. These fruits often have better quality and market demand. Parthenocarpy also ensures fruit production even when pollination and fertilization are unsuccessful due to environmental factors.
Q17. What is apomixis? Why is it important?
Answer:
Apomixis is a special mode of reproduction in which seeds are formed without fertilization. The embryo develops from diploid cells of the ovule without the fusion of gametes. As a result, offspring produced through apomixis are genetically identical to the parent plant. Apomixis is important because it preserves desirable genetic traits generation after generation. It can help plant breeders maintain hybrid vigor without repeated hybridization. This phenomenon has great agricultural significance, as it can lead to stable crop varieties with high yield and uniform characteristics.
Q18. Define polyembryony and give an example.
Answer:
Polyembryony is the occurrence of more than one embryo within a single seed. It may arise due to the development of multiple embryo sacs or the formation of embryos from nucellar cells in addition to the zygote. As a result, several seedlings may emerge from one seed. Polyembryony is commonly observed in Citrus and mango. This phenomenon is important because it can produce genetically uniform plants and improve the survival chances of seedlings. In horticulture, polyembryony is utilized for producing healthy and vigorous plants with desirable characteristics.
Q19. Why is cross-pollination considered advantageous?
Answer:
Cross-pollination involves the transfer of pollen grains between flowers of different plants of the same species. It introduces new genetic combinations and increases genetic diversity among offspring. Such variation enhances adaptability to changing environmental conditions and improves disease resistance. Cross-pollination reduces the chances of inbreeding depression and the expression of harmful recessive traits. The resulting progeny are generally more vigorous and productive. Although it depends on pollinating agents, cross-pollination plays a crucial role in evolution and species survival by promoting genetic recombination and healthy populations.
Q20. Explain the significance of double fertilization in flowering plants.
Answer:
Double fertilization is highly significant because it simultaneously produces both the embryo and the endosperm. The zygote formed by syngamy develops into the future plant, while the endosperm formed through triple fusion provides nourishment to the embryo. This mechanism ensures efficient utilization of nutrients because endosperm develops only after successful fertilization. It prevents wastage of resources and supports proper seed development. Double fertilization is a unique characteristic of angiosperms and contributes greatly to their evolutionary success. The coordinated formation of embryo and nutritive tissue increases the chances of successful seed germination and plant establishment.