CBSE Important Questions Class 12 Biology Chapter 1 – Sexual Reproduction in Flowering Plants

Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants is the first chapter of the NCERT Class 12 Biology textbook. It explains how flowering plants (angiosperms) reproduce: the parts of a flower, the male part (stamen) and the female part (carpel or pistil), how pollen grains are formed and carried to the stigma (pollination), how the male gamete fuses with the egg (fertilisation), and how the ovule becomes a seed.

These CBSE important questions for Class 12 Biology Chapter 1 cover the parts of the carpel, the stamen and pistil with a labelled diagram, the pollen tube and fertilisation, strategies that stop self-pollination, self-incompatibility, agents of pollination and the fire lily example of cross-pollination. The set has multiple-choice, short-answer and long-answer questions with answers, and it is useful for students revising for the board exam and for teachers preparing class tests.

Q1. Identify the given images below:

Image (a): carpel of a flower

Image (b): flower with arrow pointing to petals

Answer: (a) Carpel (b) Petals
Image (a) shows a slender green structure with a swollen base and a three-lobed tip. The swollen base is the ovary, the stalk is the style and the tip is the stigma. Together they form the carpel. Image (b) points to the brightly coloured, leaf-like parts around the flower. These are the petals, which attract pollinators.

Q2. Discuss the different parts of a carpel.

Answer: The carpel is the innermost, female part of a flower. It has three parts:
(a) Stigma: It is the upper, sticky part of the carpel. Pollen grains land and stick here during pollination.
(b) Style: It is the middle part of the carpel. It is a long tube that connects the stigma to the ovary. The pollen tube grows through it towards the ovules.
(c) Ovary: It is the lower, swollen part of the carpel. It contains ovules that have the egg. After fertilisation, each ovule develops into a seed.

Q3. Describe the reproductive parts of a plant with the help of a labelled diagram.

Answer: Flowers are the reproductive parts of a plant. The stamens are the male reproductive part and the pistil is the female reproductive part.
Stamen: A stamen is formed of an anther and a filament. The anther contains pollen grains, which produce the male gametes. The filament is the stalk that holds the anther.
Pistil (carpel): A pistil consists of a stigma, style and ovary. The stigma receives pollen grains during pollination, the style connects the stigma to the ovary, and the ovary contains one or more ovules. The female gamete or egg is formed in an ovule. After fertilisation the ovules develop into seeds.

Labelled diagram of stamen (anther, filament) and pistil (stigma, style, ovary, ovule)

Q4. Mention the four parts of the human female reproductive system.

Answer: a) Fallopian tubes
b) Uterus
c) Ovaries
d) Vagina
The fallopian tubes carry the ovum from the ovary to the uterus and are the site of fertilisation. The uterus is a muscular organ where the embryo implants and develops during pregnancy. The ovaries produce ova and secrete the female sex hormones estrogen and progesterone. The vagina is a muscular canal that serves as the passage for menstrual flow and acts as the birth canal.

Q5. Name the cell division responsible for gametogenesis. Give one morphological difference between the two types of gametes in a heterogametic organism.

Answer: Meiosis is the cell division responsible for gametogenesis. It is a reductional division that halves the chromosome number, so the gametes are haploid (n). When the male and female gametes fuse during fertilisation, the diploid (2n) number is restored in the zygote.
Morphological difference: The male gamete is usually small and has a flagellum (motile), while the female gamete is usually big and non-flagellated (non-motile).

Q6. Define fertilisation.

Answer: The process of fusion of the male and female gametes to form a zygote is called fertilisation. The sperm (male gamete) and the ovum (female gamete) are haploid. Their fusion forms a diploid zygote, which develops into a new organism.

Q7. In flowering plants, fertilisation involves the fusion of male and female gametes. Which of the following statements is most correct about this process?
(a) The male gamete from the pollen grain directly fuses with the ovary to form a zygote.
(b) Each ovule contains multiple egg cells, and fertilisation occurs only if all are fertilised.
(c) The pollen tube carries the male germ-cell to the ovule, where it fuses with the egg cell to form a zygote.
(d) Fertilisation in plants occurs in the stigma, where the pollen grain meets the female gamete.

Answer: (c) The pollen tube carries the male germ-cell to the ovule, where it fuses with the egg cell to form a zygote.
A pollen grain lands on the stigma and germinates to form a pollen tube. The pollen tube grows through the style and enters the ovule through the micropyle. It carries the male gamete into the embryo sac, where it fuses with the egg cell to form the zygote. The male gamete does not fuse with the ovary directly, each ovule has a single egg cell, and fertilisation takes place inside the ovule, not on the stigma.

Q8. Mention two strategies evolved to prevent self-pollination in flowers.

Answer: The two strategies evolved by flowers to prevent self-pollination are:
1. In some species, pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive, or the stigma becomes receptive much before the release of pollen (dichogamy).
2. In some other species, the anther and the stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower (herkogamy).

Q9. Observe the fire lily flower, which has a bright coloured single accessory whorl and its stamens exserted beyond the corolla. How does this arrangement ensure better variation and adaptation to environmental changes in this plant?

Fire lily flower with bright coloured whorl and stamens exserted beyond the corolla

Answer: Exserted stamens prevent self-pollination. Thus, in fire lily plants, cross-pollination is observed, wherein pollen grains of one flower are transferred to the stigma of another flower by a pollinating agent such as an insect or a bird. Cross-pollination between genetically different plants produces new combinations of genes and increases genetic variation. This ensures better adaptation to environmental changes and increased chances of perpetuation of the species.

Q10. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Answer: Self-incompatibility is a genetic mechanism of preventing self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules. This is achieved by inhibiting pollen germination or pollen tube growth in the pistil. Self-incompatibility is a widespread mechanism in flowering plants that prevents inbreeding and promotes outcrossing. This genetic response is controlled by one or more multi-allelic loci and relies on a series of complex cellular interactions between the self-incompatible pollen and the pistil. Example: The flowers of the Brassicaceae family are self-incompatible due to the presence of a receptor kinase signalling pathway that is activated in the pistil, leading to pollen rejection.
In self-incompatible species, seeds are not formed on self-pollination because the flowers are genetically programmed to inhibit pollen germination or pollen tube growth in the pistil. There is no fertilisation and thus no further development leading to seed formation in such flowers.

Q11. It is observed that in the flower of Catharanthus, the growth of the style brings the stigma in contact with the ripe anthers present at the mouth of the corolla tube. Which of the following conditions is promoted by such a physiological change in the flower?
(a) Genetic variability in the offspring
(b) Gametophytic self-incompatibility
(c) Assured seed-set
(d) Sporophytic self-incompatibility

Answer: (c) Assured seed-set
In Catharanthus, after the anthers open, the style continues to grow and brings the stigma into contact with the ripe anthers at the mouth of the corolla tube. This lets pollen move from the anther to the stigma of the same flower (autonomous self-pollination). Fertilisation then takes place even when no pollinator or wind is available, so fruit and seed formation is guaranteed.

Q12. What are the agents of pollination?

Answer: Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same or another flower. The agents of pollination are:
Biotic agents (biotic pollination): insects, birds, animals, etc.
Abiotic agents (abiotic pollination): wind, water, etc.

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