Sexual Reproduction in Flowering Plants — Class 12 Biology NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 12 Biology chapter "Sexual Reproduction in Flowering Plants" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 12 Biology chapter "Sexual Reproduction in Flowering Plants" — 8 important questions with detailed answers…
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NCERT Solutions for Class 12 Biology — Sexual Reproduction in Flowering Plants. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Sexual Reproduction in Flowering Plants — All 8 Questions Solved
Q1. Define carpel and stamen.
Stamen is the male reproductive organ of a flower consisting of anther and filament. The anther produces pollen grains containing male gametes. Carpel is the female reproductive organ consisting of stigma, style, and ovary. The ovary contains ovules where female gametes develop.
Q2. What is pollination? Distinguish between self-pollination and cross-pollination.
Pollination is the transfer of pollen from anther to stigma.
Self-pollination: Pollen from anther of one flower is transferred to stigma of the same flower or another flower of the same plant. Example: wheat, pea, tomato.
Cross-pollination: Pollen from anther of one flower is transferred to stigma of a flower on a different plant of the same species. Example: maize, coconut, cucumber. Cross-pollination brings genetic variation and hybrid vigor.
Q3. Describe the structure of a pollen grain with the help of a labeled diagram description.
A pollen grain is a microscopic structure with thick protective wall:
- Outer wall: exine (thick, sculptured, protects pollen)
- Inner wall: intine (thin, flexible)
- Cytoplasm containing: generative nucleus (smaller, will form sperm) and vegetative nucleus (larger, controls pollen tube growth)
- Apertures: pores or furrows where intine is exposed, aid in pollen tube emergence
The two-celled pollen has generative and vegetative nuclei; three-celled pollen has two sperm cells formed already.
Q4. What is double fertilization? Explain its significance in flowering plants.
Double fertilization is the fusion of two male gametes (sperm) with female gametophyte in angiosperms:
- First fusion: one sperm fuses with egg cell forming diploid zygote (2n) that develops into embryo
- Second fusion: second sperm fuses with two polar nuclei forming triploid central cell (3n) that develops into endosperm (nutritive tissue)
Significance:
- Ensures nutritive tissue develops only when embryo develops
- Endosperm provides nutrition to developing embryo
- Unique to flowering plants, increases reproductive efficiency
- Prevents wastage of energy on seed without viable embryo
Q5. Describe the process of microsporogenesis and development of male gametophyte in flowering plants.
Microsporogenesis occurs in pollen sacs (anther lobes):
1. Microspore mother cells (diploid) undergo meiosis
2. Each microspore mother cell produces four haploid microspores
3. Microspores separate and develop thick wall
Male gametophyte (pollen) development:
1. Nucleus of microspore undergoes first mitotic division forming generative and vegetative nuclei (two-celled pollen)
2. Pollen wall develops (exine and intine)
3. Before or after pollination, generative nucleus divides by mitosis forming two sperms (three-celled pollen)
4. Mature male gametophyte is three-celled pollen with two sperms and one vegetative nucleus
Q6. Explain megasporogenesis and development of female gametophyte in angiosperms.
Megasporogenesis occurs in nucellus of ovule:
1. One megaspore mother cell (diploid) undergoes meiosis
2. Produces four haploid megaspores
3. Three degenerate; one functional megaspore survives
Female gametophyte (embryo sac) development (most common type - Polygonum):
1. Functional megaspore nucleus undergoes three mitotic divisions
2. Forms eight nuclei arranged in seven-celled stage:
- Egg apparatus at micropylar end: one egg cell (female gamete) and two synergids (help guide pollen tube)
- Three antipodal cells at chalazal end (nutritive function)
- Two polar nuclei in central cell (fuse later)
3. Seven-celled, eight-nucleate stage is mature female gametophyte
Q7. What is apomixis? How is it different from sexual reproduction?
Apomixis is asexual reproduction in plants producing seeds without meiosis and fertilization.
Types:
- Vegetative apomixis: buds develop into seeds
- Adventitious embryony: embryo develops from nucellus or integument
- Apospory: embryo sac develops from somatic cell instead of megaspore
Differences from sexual reproduction:
- No meiosis or reduction division
- No fusion of gametes
- Genetically identical to parent (clones)
- Produces seeds without pollination
- No genetic variation
- Examples: citrus, mango, some grasses
Advantage: maintains desirable traits; disadvantage: no genetic variation limits adaptation
Q8. Describe the structure and function of ovule with a labeled diagram description.
Ovule is the structure that develops into seed after fertilization.
Structure:
- Funicle: stalk attaching ovule to placenta
- Hilum: point of attachment on ovule body
- Integument: outer protective layer(s), surrounding nucellus
- Nucellus: inner tissue surrounding embryo sac, provides nutrition
- Embryo sac: female gametophyte containing egg cell and polar nuclei
- Micropyle: opening in integument where pollen tube enters
- Chalaza: end opposite to micropyle
Types based on position: orthotropous (straight), campylotropous (curved), anatropous (inverted - most common in angiosperms)
Function: protects and nourishes female gametophyte; develops into seed after fertilization
Sexual Reproduction in Flowering Plants — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Which part of the flower serves as the site for pollen grain production?
- A. Stigma
- B. Filament
- C. Anther
- D. Ovary
Answer: C. Anther — The anther is the terminal bilobed structure of the stamen that contains microsporangia, where pollen grains are produced through microsporogenesis. The filament supports the anther.
MCQ 2. The primary parietal cell, after repeated divisions, forms the wall layers of the microsporangium. Which of the following layers nourishes the developing pollen grains?
- A. Epidermis
- B. Endothecium
- C. Middle layers
- D. Tapetum
Answer: D. Tapetum — The tapetum is the innermost layer of the microsporangium wall and provides nourishment to the developing pollen grains. It is characterized by dense cytoplasm and usually has more than one nucleus.
MCQ 3. What is the ploidy level of the cells of the primary endosperm nucleus (PEN) in angiosperms?
- A. Haploid (n)
- B. Diploid (2n)
- C. Triploid (3n)
- D. Tetraploid (4n)
Answer: C. Triploid (3n) — The primary endosperm nucleus (PEN) is formed by the fusion of one male gamete (n) with two polar nuclei (n+n). Therefore, its ploidy level is triploid (3n).
MCQ 4. Which of the following conditions is most likely to promote self-pollination in a bisexual flower?
- A. Dichogamy
- B. Heterostyly
- C. Herkogamy
- D. Cleistogamy
Answer: D. Cleistogamy — Cleistogamy refers to flowers that remain closed and are never exposed, ensuring self-pollination. This mechanism guarantees seed set even in the absence of pollinators.
MCQ 5. In a typical angiosperm ovule, the embryo sac is formed after megasporogenesis. What is the usual number of nuclei in a mature embryo sac just before fertilization?
- A. 5
- B. 6
- C. 7
- D. 8
Answer: D. 8 — A mature angiosperm embryo sac is typically 7-celled and 8-nucleate. It consists of an egg cell, two synergids, three antipodal cells, and one central cell with two polar nuclei.
MCQ 6. Which of the following statements correctly describes the 'filiform apparatus'?
- A. It is part of the pollen grain wall.
- B. It guides the pollen tube into the egg cell.
- C. It provides nourishment to the developing embryo.
- D. It is involved in the formation of the endosperm.
Answer: B. It guides the pollen tube into the egg cell. — The filiform apparatus is a finger-like projection found on the synergids at the micropylar end of the embryo sac. Its primary role is to guide the pollen tube towards the egg cell.
MCQ 7. Which post-fertilisation event involves the conversion of the ovule into a seed and the ovary into a fruit?
- A. Embryogenesis and endosperm development
- B. Seed and fruit development
- C. Double fertilisation
- D. Pollen-pistil interaction
Answer: B. Seed and fruit development — After double fertilisation, the ovule develops into a seed and the ovary matures into a fruit. These processes involve significant changes in the post-fertilisation structures.
MCQ 8. The persistent nucellus in some seeds like black pepper and beet is known as:
- A. Pericarp
- B. Perisperm
- C. Endosperm
- D. Hilum
Answer: B. Perisperm — Perisperm refers to the remnant of persistent nucellus found in some seeds, such as black pepper and beet. It serves as a nutritive tissue.
MCQ 9. Which type of pollination is exclusively dependent on wind and produces light, non-sticky pollen grains?
- A. Hydrophily
- B. Entomophily
- C. Anemophily
- D. Ornithophily
Answer: C. Anemophily — Anemophily is pollination by wind, characterized by lightweight, non-sticky pollen, often with feathery stigmas to trap airborne pollen. Hydrophily is by water, entomophily by insects, and ornithophily by birds.
MCQ 10. Dioecy in plants is an outbreeding device that prevents which of the following?
- A. Autogamy only
- B. Geitonogamy only
- C. Both autogamy and geitonogamy
- D. Xenogamy
Answer: C. Both autogamy and geitonogamy — Dioecy means male and female flowers are on different plants. This prevents both autogamy (self-pollination within the same flower) and geitonogamy (pollination between flowers on the same plant).
MCQ 11. What is the primary function of the germ pore in a pollen grain?
- A. Absorption of water for hydration.
- B. Storage of genetic material.
- C. Emergence of the pollen tube.
- D. Protection from desiccation.
Answer: C. Emergence of the pollen tube. — The germ pore is a prominent aperture in the exine of the pollen grain where the sporopollenin is absent. It is through this pore that the pollen tube emerges during germination.
MCQ 12. Which part of the ovule develops into the seed coat after fertilization?
- A. Nucellus
- B. Integuments
- C. Chalaza
- D. Hilum
Answer: B. Integuments — The integuments, which are protective layers surrounding the ovule, harden and transform into the seed coats after fertilization. The nucellus usually degenerates.
MCQ 13. A fruit developed from the ovary of a single flower is called a true fruit. Which of the following is an example of a false fruit, where other floral parts also contribute to fruit formation?
- A. Mango
- B. Tomato
- C. Apple
- D. Pea
Answer: C. Apple — An apple is a false fruit because, in its formation, the thalamus also contributes significantly along with the ovary. Mango, tomato, and pea are examples of true fruits.
MCQ 14. What is the typical ploidy of the nucellus cells in an angiosperm ovule?
- A. Haploid (n)
- B. Diploid (2n)
- C. Triploid (3n)
- D. Polyploid (multiple sets)
Answer: B. Diploid (2n) — The nucellus is a part of the ovule that is diploid (2n), as it is somatic tissue of the parent plant. The megaspore mother cell develops within it.
MCQ 15. In the process of double fertilisation, one male gamete fuses with the egg cell, forming the zygote. What is the fate of the other male gamete?
- A. It degenerates.
- B. It fuses with the antipodal cells.
- C. It fuses with the polar nuclei.
- D. It forms the embryo sac wall.
Answer: C. It fuses with the polar nuclei. — During double fertilisation, the second male gamete fuses with the two polar nuclei located in the central cell to form the primary endosperm nucleus (PEN), which develops into the endosperm.
MCQ 16. Which of the following is an advantage of apomixis in hybrid seed production?
- A. It leads to genetic recombination.
- B. It produces progeny with varied genetic makeup.
- C. It helps in retaining desirable hybrid characters indefinitely.
- D. It requires repeated hybridisation every year.
Answer: C. It helps in retaining desirable hybrid characters indefinitely. — Apomixis is a form of asexual reproduction that mimics sexual reproduction, producing seeds without fertilisation. It is advantageous for hybrid seed production as it helps to retain desirable hybrid characters indefinitely without segregation.
MCQ 17. A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. The part of the embryonal axis above the level of cotyledons is the:
- A. Hypocotyl
- B. Radicle
- C. Coleoptile
- D. Epicotyl
Answer: D. Epicotyl — The epicotyl is the part of the embryonal axis above the level of cotyledons, terminating with the plumule (which gives rise to the shoot). The hypocotyl is below the cotyledons.
MCQ 18. What happens to the zygote and the primary endosperm nucleus (PEN) after double fertilisation?
- A. Both develop into the embryo.
- B. Zygote develops into embryo; PEN into endosperm.
- C. Zygote develops into endosperm; PEN into embryo.
- D. Both degenerate after some time.
Answer: B. Zygote develops into embryo; PEN into endosperm. — After double fertilisation, the diploid zygote (2n) develops into the embryo, and the triploid primary endosperm nucleus (3n) develops into the endosperm, which provides nourishment to the developing embryo.
MCQ 19. Even in the absence of external pollinating agents, seed set is guaranteed in:
- A. Geitonogamous flowers
- B. Chasmogamous flowers
- C. Cleistogamous flowers
- D. Dioecious plants
Answer: C. Cleistogamous flowers — Cleistogamous flowers never open, ensuring self-pollination and guaranteed seed set even in the absence of pollinators. Chasmogamous flowers open and expose their anthers and stigmas.
MCQ 20. Which of the following cellular events leads to the formation of a 4-nucleate stage during megagametogenesis?
- A. One mitotic division of the functional megaspore.
- B. Two successive mitotic divisions of the functional megaspore.
- C. Three successive mitotic divisions of the functional megaspore.
- D. Meiosis of the megaspore mother cell.
Answer: B. Two successive mitotic divisions of the functional megaspore. — The functional megaspore undergoes two successive mitotic divisions to form a 4-nucleate embryo sac. The first mitosis yields a 2-nucleate stage, and the second yields a 4-nucleate stage.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.