Chapter: Reproduction in Organisms: Class 12
Multiple Choice Questions (MCQ)
1. Which of the following is NOT a mode of asexual reproduction? a) Binary fission b) Sporulation c) Fertilization d) Budding Answer: c) Fertilization
2. What is the primary function of a flower in a plant? a) Photosynthesis b) Support the plant c) Reproduction d) Water absorption Answer: c) Reproduction
3. The fusion of male and female gametes is known as: a) Pollination b) Germination c) Fertilization d) Sporulation Answer: c) Fertilization
4. Which of the following is an example of vegetative propagation? a) Seed formation in mango b) Spore formation in ferns c) Tuber formation in potato d) Zygote formation in humans Answer: c) Tuber formation in potato
5. What is double fertilization unique to? a) Fungi b) Algae c) Angiosperms d) Gymnosperms Answer: c) Angiosperms
6. Apomixis is the production of seeds without: a) Pollination b) Fertilization c) Seed dispersal d) Fruit formation Answer: b) Fertilization
7. Pollen grains are developed in the: a) Pistil b) Ovary c) Anther d) Stigma Answer: c) Anther
8. What is the product of double fertilization that provides nourishment to the developing embryo? a) Embryo sac b) Zygote c) Endosperm d) Seed coat Answer: c) Endosperm
9. The transfer of pollen grains from the anther to the stigma is called: a) Fertilization b) Germination c) Pollination d) Dispersal Answer: c) Pollination
10. Polyembryony is the occurrence of more than one embryo in a: a) Flower b) Fruit c) Seed d) Root Answer: c) Seed
11. Which of the following is a multicellular organism that reproduces by budding? a) Amoeba b) Yeast c) Hydra d) Bacteria Answer: c) Hydra
12. The process of formation of fruit without fertilization is called: a) Apomixis b) Parthenocarpy c) Polyembryony d) Vegetative propagation Answer: b) Parthenocarpy
13. In which of the following is binary fission a common mode of reproduction? a) Fungi b) Algae c) Bacteria d) Flowering plants Answer: c) Bacteria
14. The outermost whorl of a flower is: a) Corolla b) Androecium c) Gynoecium d) Calyx Answer: d) Calyx
15. Which of the following statements about outbreeding devices is incorrect? a) They promote self-pollination. b) They prevent self-pollination. c) They encourage cross-pollination. d) They increase genetic variability. Answer: a) They promote self-pollination.
Short Answer Questions (2-3 marks)
1. Define reproduction. Why is it considered a characteristic feature of all organisms? Answer: Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parents". It is considered a characteristic feature of all organisms because it ensures the continuity of species from one generation to the next, preventing their extinction.
2. Differentiate between asexual and sexual reproduction. Answer: * Asexual Reproduction: Involves a single parent and produces offspring that are genetically identical to the parent. No fusion of gametes occurs. * Sexual Reproduction: Involves two parents (usually) and produces offspring that are genetically different from the parents. It involves the formation and fusion of gametes.
3. Name and explain any two modes of asexual reproduction. Answer: * Binary Fission: A single-celled organism divides into two new, genetically identical organisms. (e.g., Amoeba, Bacteria) * Budding: A small outgrowth or 'bud' forms on the parent organism, which then detaches and develops into a new individual. (e.g., Yeast, Hydra)
4. What is fragmentation? Give an example. Answer: Fragmentation is a mode of asexual reproduction where the body of an organism breaks into two or more pieces, each of which then develops into a new, complete organism. Example: Spirogyra, Planaria.
5. Define vegetative propagation. Why is it beneficial in some plants? Answer: Vegetative propagation is a type of asexual reproduction in plants where new plants are produced from vegetative parts of the parent plant such as roots, stems, leaves, or buds. It is beneficial as it allows for rapid propagation of desired traits, maintains genetic purity, and can produce plants faster than from seeds (e.g., in plants that do not produce viable seeds).
6. Draw a well-labelled diagram of a typical flower, indicating its four whorls. Answer: (Diagram not possible in text, but key labels should include: Sepal, Petal, Stamen (Anther, Filament), Pistil/Carpel (Stigma, Style, Ovary, Ovule)).
7. Briefly describe the development of the male gametophyte in flowering plants. Answer: The male gametophyte (pollen grain) develops inside the microsporangium (pollen sac) within the anther. Microspore mother cells undergo meiosis to form microspores. Each microspore then develops into a pollen grain, containing two cells: a vegetative cell and a generative cell. The generative cell later divides to form two male gametes.
8. What is pollination? Name the two main types of pollination. Answer: Pollination is the process of transfer of pollen grains from the anther to the stigma of a flower. The two main types are: * Self-pollination: Transfer of pollen within the same flower or between flowers on the same plant. * Cross-pollination: Transfer of pollen between flowers of different plants of the same species.
9. Give two examples of agencies of pollination. Answer: * Biotic Agents: Insects (bees, butterflies), birds, bats. * Abiotic Agents: Wind, Water.
10. What are outbreeding devices? Give one example. Answer: Outbreeding devices are mechanisms developed by flowering plants to discourage self-pollination and encourage cross-pollination, thereby promoting genetic recombination. Example: Dioecy (unisexual flowers on different plants), Dichogamy (pollen release and stigma receptivity are not synchronized), Herkogamy (physical barrier between anther and stigma).
11. Explain pollen-pistil interaction. Answer: Pollen-pistil interaction is a dynamic process that involves pollen recognition by the stigma, followed by pollen germination and the growth of the pollen tube through the style to reach the ovule. This interaction is crucial for ensuring that only compatible pollen fertilizes the ovule.
12. What are the two fusions that occur during double fertilization? Answer: The two fusions are: * Syngamy (Generative fertilization): Fusion of one male gamete with the egg cell to form a diploid zygote. * Triple fusion (Vegetative fertilization): Fusion of the second male gamete with the diploid central cell (containing two polar nuclei) to form a triploid primary endosperm nucleus (PEN).
13. Differentiate between endosperm and embryo development. Answer: * Endosperm Development: Begins immediately after triple fusion. The primary endosperm nucleus divides repeatedly to form endosperm tissue, which provides nourishment to the developing embryo. * Embryo Development: Begins after syngamy. The zygote undergoes mitotic divisions to form a proembryo, then globular, heart-shaped, and mature embryo stages.
14. What is parthenocarpy? Give an example of a parthenocarpic fruit. Answer: Parthenocarpy is the development of fruit without fertilization of the ovules. These fruits are typically seedless. Example: Banana, Grapes (seedless varieties).
15. Briefly explain the significance of seed and fruit formation. Answer: * Seed: Contains the embryo, providing protection and nourishment for the young plant, and facilitating dispersal. Seeds are a basis for agriculture. * Fruit: Protects the developing seeds and aids in their dispersal, ensuring the spread of the species to new areas.
Long Answer Questions (5-6 marks)
1. Describe the process of sexual reproduction in flowering plants, starting from pollination and ending with seed and fruit formation. Highlight the significance of double fertilization.
Answer: Sexual reproduction in flowering plants begins with pollination, the transfer of pollen grains from the anther to the stigma. Pollen can be transferred by various agencies like wind, water, or animals. Upon landing on a compatible stigma, the pollen grain absorbs moisture and nutrients, swells, and germinates, producing a pollen tube. This pollen tube grows through the style, secreting enzymes to digest its way, and reaches the ovule in the ovary. The pollen tube carries two non-motile male gametes.
Once the pollen tube enters the embryo sac, it releases the two male gametes. This leads to double fertilization, a unique event in angiosperms:
Syngamy: One male gamete fuses with the egg cell (oosphere) to form a diploid zygote. The zygote will develop into the embryo.
Triple Fusion: The second male gamete fuses with the diploid central cell (containing two polar nuclei) to form a triploid Primary Endosperm Nucleus (PEN). The PEN then develops into the endosperm, a nutritive tissue that provides food for the developing embryo.
Following double fertilization, post-fertilization events occur:
The zygote develops into the embryo. It undergoes a series of mitotic divisions, passing through globular, heart-shaped, and mature stages, eventually forming a complete embryo with radicle, plumule, and cotyledons.
The Primary Endosperm Nucleus develops into the endosperm, which can be cellular, nuclear, or helobial. It serves as the primary food source for the developing embryo, either persisting in the mature seed (endospermic seeds like castor) or being consumed by the embryo during development (non-endospermic seeds like pea).
The ovules mature and transform into seeds. The integuments of the ovule develop into the protective seed coats.
The ovary matures and ripens into a fruit. The ovary wall develops into the fruit wall (pericarp), which can be fleshy or dry, protecting the seeds and aiding in their dispersal.
Significance of Double Fertilization:
It ensures that the nutritive tissue (endosperm) is formed only if the egg is successfully fertilized, thus preventing wastage of energy.
It provides nourishment to the developing embryo, leading to the formation of a viable seed.
It is a unique feature of angiosperms and contributes to their evolutionary success.
2. Explain different modes of asexual reproduction in organisms. Discuss vegetative propagation in plants in detail, providing suitable examples.
Answer: Asexual reproduction is a mode of reproduction that involves a single parent and results in offspring that are genetically identical to the parent. It does not involve the fusion of gametes.
Different Modes of Asexual Reproduction:
Binary Fission: Common in single-celled organisms like bacteria and Amoeba. The parent cell divides into two equal halves, each developing into a new individual.
Sporulation (Spore Formation): Organisms like fungi (e.g., Rhizopus) and algae produce spores, which are microscopic, asexual reproductive bodies. These spores are dispersed and germinate under favorable conditions to form new individuals.
Budding: Seen in organisms like yeast and Hydra. An outgrowth or 'bud' develops on the parent body due to cell division. This bud grows, eventually detaches from the parent, and develops into a new, independent organism.
Gemmule Formation: Observed in sponges (e.g., Spongilla). Gemmules are internal buds containing a mass of undifferentiated cells enclosed by a protective coat. They help in surviving unfavorable conditions and develop into new sponges when conditions are favorable.
Fragmentation: The body of the parent organism breaks into two or more fragments, and each fragment develops into a new, complete individual. Examples include Spirogyra (algae) and Planaria (flatworm).
Vegetative Propagation in Plants: Vegetative propagation is a specific type of asexual reproduction found in plants, where new plants are produced from the vegetative parts (non-reproductive parts) of the parent plant. This method is widely used in horticulture and agriculture.
Types of Vegetative Propagation:
A. Natural Vegetative Propagation: Occurs naturally in plants through specialized structures:
By Stems:
Underground Stems:
Rhizome: Fleshy, horizontal underground stem with nodes and internodes. New plants arise from buds at the nodes. (e.g., Ginger, Turmeric)
Tuber: Swollen, underground stem tips storing food. "Eyes" on the potato tuber are axillary buds that can grow into new plants. (e.g., Potato)
Corm: Short, vertical, swollen underground stem. (e.g., Colocasia, Gladiolus)
Bulb: Shortened, flattened stem with fleshy leaves storing food. (e.g., Onion, Garlic)
Subaerial Stems:
Runner: Slender, prostrate stem growing horizontally above the ground, producing roots and leaves at nodes. (e.g., Grasses, Oxalis)
Stolon: Similar to a runner, but grows for a short distance before arching downwards to form a new plant. (e.g., Jasmine, Strawberry)
Offset: Short, thick runner-like stem found in aquatic plants. (e.g., Water Hyacinth (Eichhornia), Pistia)
By Roots: Adventitious buds on modified roots can give rise to new plants. (e.g., Dahlia, Sweet Potato, Asparagus)
By Leaves: Some plants develop adventitious buds on their leaves, which detach and grow into new plants. (e.g., Bryophyllum)
By Bulbils: Fleshy buds that develop in the axil of leaves and detach to grow into new plants. (e.g., Agave)
B. Artificial Vegetative Propagation: Methods developed by humans for commercial propagation:
Cutting: Parts of stem, root, or leaf are cut and planted in soil to grow into new plants. (e.g., Rose, Sugarcane - stem cutting; Lemon - root cutting; Sansevieria - leaf cutting)
Layering: A branch of the parent plant is bent and covered with soil while still attached to the parent. Roots develop from the buried part, which is then cut and grown independently. (e.g., Jasmine, Lemon)
Grafting: Parts of two different plants (scion - upper part; stock - lower part) are joined so that they grow as a single plant. (e.g., Mango, Apple, Rose)
Tissue Culture (Micropropagation): Growing plant cells, tissues, or organs in a sterile nutrient medium under controlled conditions to produce a large number of plantlets. This is a very efficient method for rapid multiplication of desired varieties. (e.g., Orchids, Banana)
Vegetative propagation is advantageous as it allows rapid multiplication of plants, maintains genetic purity, helps in propagating plants that do not produce viable seeds (e.g., banana), and enables the production of fruit earlier than plants grown from seeds.
