Chapter 9: Plant Reproduction

Select the correct answer:

(i) Which of the following is incorrect about asexual reproduction?

A) a single parent contributes genetic material

B) no gamete formation is involved

C) offspring are genetically identical

D) contributes in evolution of new species

Answer: D) contributes in evolution of new species

Explanation: Asexual reproduction produces genetically identical offspring (clones), which reduces genetic variation. Genetic variation is essential for evolution. Therefore, asexual reproduction does not directly contribute to the evolution of new species.

(ii) Which of the following is the benefit of sexual reproduction?

A) this is a rapid way of reproduction

B) this is a complex mechanism of reproduction

C) it can occur any time in lifecycle

D) it contributes genetic variability in successive generations

Answer: D) it contributes genetic variability in successive generations

Explanation: Sexual reproduction involves the fusion of gametes from two parents, creating new genetic combinations. This genetic variability is the raw material for natural selection and evolution.

(iii) Which of the following modes of asexual reproduction generally occurs during unfavorable conditions?

A) Binary fission

B) Budding

C) Spore formation

D) parthenogenesis

Answer: C) Spore formation

Explanation: Spores are typically produced by fungi and some bacteria during unfavorable conditions. They are resistant to heat, desiccation, and radiation, allowing the organism to survive until conditions improve.

(iv) Which of the following processes is also known as apomixis?

A) Binary fission

B) Budding

C) Spore formation

D) parthenogenesis

Answer: D) parthenogenesis

Explanation: Apomixis is a type of asexual reproduction in plants where seeds are produced without fertilization. Parthenogenesis (development of an embryo from an unfertilized egg) is a form of apomixis.

(v) Which of the following is compact, thickened, vertically growing, underground stem enveloped by thick, succulent (fleshy) leaves, serving as reservoir of stored nutrients:

A) Bulb

B) Corm

C) Rhizome

D) Stem tuber

Answer: A) Bulb

Explanation: A bulb (e.g., onion, tulip) consists of a short, thickened underground stem surrounded by fleshy, scale-like leaves that store food.

(vi) In Bryophyllum, small plantlets that are much like tiny versions of the parent plant, are created along the:

A) root tip

B) edges of its leaves

C) stem surface

D) all of these

Answer: B) edges of its leaves

Explanation: Bryophyllum (mother of thousands) produces plantlets along the margins (edges) of its leaves. These plantlets drop off and grow into new plants.

(vii) If sometimes, the stem cutting does not start growth, then the cut ends must be treated with which of the following special plant hormone to stimulate the growth?

A) somatotropin

B) Abscisic acid

C) auxin

D) Ethene

Answer: C) auxin

Explanation: Auxins (e.g., IAA, NAA) are plant hormones that promote root initiation and growth. Treating stem cuttings with auxin stimulates root formation.

(viii) The first cell or tiny piece of the parent plant used in tissue culture is called:

A) baby plant

B) plantlet

C) seedling

D) explant

Answer: D) explant

Explanation: An explant is a small piece of plant tissue (e.g., leaf, stem, root) used to initiate a tissue culture.

(ix) Which of the following part of the plant that's been changed and adapted for the job of reproduction:

A) flower

B) leave

C) root

D) meristematic tissue

Answer: A) flower

Explanation: The flower is the reproductive organ of angiosperms. Its parts (stamens, carpels) are specialized for producing gametes and facilitating fertilization.

(x) Which of the following parts of the flower are called accessory whorls?

A) Androecium and gynoecium

B) calyx and corolla

C) Androecium and corolla

D) calyx and gynoecium

Answer: B) calyx and corolla

Explanation: The calyx (sepals) and corolla (petals) are accessory whorls because they do not directly participate in reproduction. They protect the reproductive whorls (androecium and gynoecium) and attract pollinators.

1. Define cloning. Which process of plant is supposed to be a cloning?

Answer: Cloning is the process of producing genetically identical individuals from a single parent. In plants, vegetative propagation (asexual reproduction) is considered a form of cloning because it produces offspring that are genetically identical to the parent plant. Examples include runners, tubers, bulbs, and cuttings. Tissue culture is also a form of cloning. Cloning is important for preserving desirable traits in agriculture and horticulture.

2. Enlist any two suitable conditions for germination of seed.

Answer: Two essential conditions for seed germination are:

1. Water: Water is required to rehydrate the seed, activate enzymes, and facilitate metabolic processes. It also softens the seed coat.

2. Oxygen: Oxygen is needed for aerobic respiration to provide energy for growth. Other conditions include suitable temperature, light (for some seeds), and sometimes a period of dormancy.

3. Explain the structure of embryonic stem.

Answer: The embryonic stem (embryonic axis) is the part of the embryo that develops into the shoot and root. It consists of:

Plumule (Epicotyl): The upper part that develops into the shoot. It bears young leaves. Radicle (Hypocotyl): The lower part that develops into the root. Cotyledons: Seed leaves that store or absorb food. In dicots, the embryonic axis is between the two cotyledons. In monocots, it is protected by a coleoptile (shoot) and coleorhiza (root).

4. Explain the role of livestock.

Answer: Livestock (domesticated animals like cattle, sheep, goats, poultry) play a vital role in agriculture and human welfare:

Food: Provide meat, milk, eggs, and other dairy products. Fiber: Provide wool, leather, and hair. Labor: Used for plowing, transport, and other farm work. Manure: Provide organic fertilizer for crops. Income: Source of livelihood for millions of farmers. By-products: Used in pharmaceuticals, cosmetics, and other industries.

5. Explain the event of double fertilization in angiosperms.

Answer: Double fertilization is a unique event in angiosperms where two fertilization events occur simultaneously:

1. Syngamy: One sperm fuses with the egg cell to form the diploid (2n) zygote, which develops into the embryo.

2. Triple Fusion: The other sperm fuses with two polar nuclei in the central cell to form the triploid (3n) primary endosperm

nucleus, which develops into the endosperm (nutritive tissue). This process ensures that the embryo has a food supply. It was discovered by Nawaschin in 1898.

6. Explain the structure of embryo sac.

Answer: The embryo sac (female gametophyte) is a 7-celled, 8-nucleate structure found in the ovule of angiosperms. It consists of:

Egg Apparatus: Located at the micropylar end. Consists of one egg cell (female gamete) and two synergids (which help guide the pollen tube). Central Cell: Contains two polar nuclei (which fuse to form a diploid secondary nucleus). Antipodal Cells: Three cells at the chalazal end, which are involved in nutrient transfer. The embryo sac is formed from a single megaspore through three mitotic divisions (monosporic development).

7. Justify that sexual reproduction in plants is more beneficial than asexual reproduction.

Answer: Sexual reproduction is more beneficial than asexual reproduction because:

Genetic Variation: It creates new genetic combinations through meiosis and fertilization, increasing genetic diversity. Adaptation: Genetic diversity allows populations to adapt to changing environments. Evolution: It provides the raw material for natural selection and evolution. Disease Resistance: Genetic diversity reduces the risk of a single disease wiping out an entire population. Elimination of Harmful Mutations: Harmful mutations can be eliminated through recombination. In contrast, asexual reproduction produces genetically identical clones, making populations vulnerable to environmental changes.

8. Define/Describe/Explain briefly: Apomixis:

Answer: Apomixis is a type of asexual reproduction in plants where seeds are produced without fertilization. The embryo develops from an unfertilized egg or other diploid cells of the ovule. It results in offspring that are genetically identical to the parent. Pollination:

Answer: Pollination is the transfer of pollen grains from the anther to the stigma of a flower. It can be self-pollination or cross- pollination. Male gametophyte:

Answer: The male gametophyte in angiosperms is the pollen grain. It contains two sperm cells and a tube nucleus. It is formed from a microspore. Epigeal germination:

Answer: Epigeal germination is a type of seed germination where the cotyledons are pushed above the soil surface (e.g., bean, castor). The hypocotyl elongates. Fertilization:

Answer: Fertilization is the fusion of male and female gametes (sperm and egg) to form a diploid zygote. In angiosperms, it involves double fertilization. Binary fission:

Answer: Binary fission is a type of asexual reproduction where a parent cell divides into two identical daughter cells (e.g., bacteria, amoeba). Budding:

Answer: Budding is a type of asexual reproduction where a new individual develops from a small outgrowth (bud) on the parent body (e.g., yeast, Hydra). Sporangia:

Answer: Sporangia are structures that produce and contain spores. They are found in fungi, algae, and some plants. Rootstock:

Answer: Rootstock is an underground stem or root that is used for vegetative propagation. It includes rhizomes, tubers, corms, and bulbs. Bulb:

Answer: A bulb is an underground storage organ consisting of a short stem surrounded by fleshy leaves (e.g., onion, tulip). Rhizome:

Answer: A rhizome is a horizontal underground stem that stores food and produces new shoots (e.g., ginger, turmeric).

9. Write the differences between:

(a) Asexual reproduction and sexual reproduction:

Answer: Asexual: one parent, no gametes, genetically identical offspring, rapid. Sexual: two parents, gametes involved, genetic variation, slower.

(b) Artificial vegetative propagation and natural vegetative propagation:

Answer: Artificial: human-assisted (e.g., cuttings, grafting). Natural: occurs without human intervention (e.g., runners, bulbs).

(c) Scion and rootstock:

Answer: Scion is the desired plant part grafted onto the rootstock. Rootstock is the rooted plant part that provides support and nutrients.

(d) Grafting and stem cutting:

Answer: Grafting: joining a scion to a rootstock. Stem cutting: rooting a piece of stem to form a new plant. (e) Bud and rhizome:

Answer: Bud: a small outgrowth that develops into a new plant. Rhizome: an underground stem that produces new shoots. (f) Binary fission and budding:

Answer: Binary fission: parent divides into two identical cells. Budding: new individual develops from an outgrowth. (g) Hypogeal and epigeal germination:

Answer: Hypogeal: cotyledons remain underground (e.g., pea). Epigeal: cotyledons are pushed above ground (e.g., bean). (h) Self and cross pollination:

Answer: Self: pollen from same flower or plant. Cross: pollen from a different plant of the same species.

1. Explain the procedure of plant tissue culture and illustrate your answer with suitable diagram.

Answer: Plant Tissue Culture: Plant tissue culture is a technique used to grow plant cells, tissues, or organs in vitro (in a controlled environment) on a nutrient medium. It is used for rapid propagation, disease elimination, and genetic engineering.

Procedure:

1. Selection of Explant: A small piece of plant tissue (explant) is selected from a disease-free parent plant. It could be a leaf, stem, root, or meristem.

2. Sterilization: The explant is surface-sterilized to remove microorganisms. This is done using chemicals like ethanol, sodium hypochlorite, or mercuric chloride.

3. Preparation of Nutrient Medium: A suitable nutrient medium is prepared containing:

Macronutrients: N, P, K, Ca, Mg, S. Micronutrients: Fe, Mn, Zn, Cu, B, Mo. Vitamins: B-complex vitamins. Carbon Source: Sucrose. Plant Hormones: Auxins and cytokinins (for cell division and differentiation). Solidifying Agent: Agar.

4. Inoculation: The sterilized explant is placed on the nutrient medium under aseptic conditions (laminar flow hood).

5. Callus Formation: The explant undergoes dedifferentiation to form a mass of undifferentiated cells called a callus.

6. Organogenesis: The callus is transferred to a medium with different hormone concentrations to induce organogenesis (formation of shoots and roots).

7. Hardening: The plantlets are gradually acclimatized to the external environment.

8. Transfer to Soil: The hardened plantlets are transferred to soil for further growth.

Diagram Description: (A diagram would show the steps: explant, callus, shoot formation, root formation, plantlet, and transfer to

soil.)

In summary, plant tissue culture is a powerful technique for rapid and mass propagation of plants.

2. Describe the structure and development of male and female gametophytes.

Answer: Male Gametophyte (Pollen Grain):

Structure: A mature pollen grain consists of two cells: a large vegetative cell (tube cell) and a small generative cell. The generative cell divides to form two sperm cells. The pollen grain is surrounded by two layers: the outer exine (sporopollenin) and the inner intine (cellulose). Development: The pollen grain develops from a microspore mother cell (2n) in the anther. The microspore mother cell undergoes meiosis to form four haploid microspores. Each microspore develops into a pollen grain.

Female Gametophyte (Embryo Sac):

Structure: A mature embryo sac is 7-celled and 8-nucleate. It consists of:

Egg Apparatus: One egg cell and two synergids. Central Cell: Contains two polar nuclei. Antipodal Cells: Three cells at the chalazal end.

Development: The embryo sac develops from a megaspore mother cell (2n) in the ovule. The megaspore mother cell undergoes meiosis to form four haploid megaspores. Three degenerate, and one survives (monosporic development). The surviving megaspore undergoes three mitotic divisions to form the 8-nucleate embryo sac.

In summary, male and female gametophytes are highly reduced in angiosperms and are essential for sexual reproduction.

3. Define seed germination. Explain its two types and write down the conditions for germination.

Answer: Seed Germination: Seed germination is the process by which a seed develops into a new plant. It begins with the imbibition of water and ends with the emergence of the radicle and plumule.

Types of Germination:

1. Epigeal Germination: The cotyledons are pushed above the soil surface during germination. The hypocotyl elongates and forms a hook, pulling the cotyledons out of the soil. Example: Bean, castor, cotton.

2. Hypogeal Germination: The cotyledons remain underground during germination. The epicotyl elongates, pushing the plumule above the soil. Example: Pea, gram, maize.

Conditions for Germination:

1. Water: Required for imbibition, enzyme activation, and transport.

2. Oxygen: Required for aerobic respiration to provide energy.

3. Temperature: Optimal temperature is required for enzyme activity.

4. Light: Some seeds require light for germination (photoblastic).

5. Dormancy Break: Some seeds require a period of dormancy or scarification.

In summary, seed germination is a complex process that requires specific environmental conditions.

4. Explain the mechanism of binary fission and budding in bacteria and yeast respectively.

Answer: Binary Fission in Bacteria:

1. DNA Replication: The circular DNA molecule replicates.

2. Cell Elongation: The cell grows and elongates.

3. Septum Formation: A septum (cross wall) forms in the middle of the cell.

4. Cell Division: The cell divides into two identical daughter cells. This is a rapid process, with some bacteria dividing every 20 minutes.

Budding in Yeast:

1. Bud Formation: A small outgrowth (bud) forms on the parent cell.

2. Nuclear Division: The nucleus divides, and one daughter nucleus moves into the bud.

3. Septum Formation: A septum forms between the parent and the bud.

4. Separation: The bud detaches from the parent cell and grows into a new yeast cell. Sometimes, buds remain attached, forming a chain of cells.

In summary, binary fission and budding are rapid modes of asexual reproduction in bacteria and yeast, respectively.

5. Describe any two methods of artificial vegetative propagation in plants.

Answer:

1. Stem Cutting:

A piece of stem (10-15 cm) with at least one bud is cut from the parent plant. The lower end is dipped in auxin (rooting hormone). The cutting is planted in moist soil or sand. Roots develop from the cut end, and a new plant grows. Examples: Rose, sugarcane, hibiscus.

2. Grafting:

A scion (desired shoot) is joined to a rootstock (rooted plant).

The cut surfaces are aligned so that the cambium layers meet. The joint is tied and covered with wax or tape. The scion grows, and the rootstock provides support and nutrients. Examples: Mango, apple, citrus.

In summary, stem cutting and grafting are important artificial methods for propagating desired plant varieties.

6. Describe the structure if a typical flower and draw its suitable diagram.

Answer: Structure of a Typical Flower: A typical flower consists of four whorls arranged on a receptacle:

1. Calyx (Sepals): Outermost whorl, usually green. Protects the flower bud.

2. Corolla (Petals): Second whorl, often brightly colored. Attracts pollinators.

3. Androecium (Stamens): Male reproductive whorl. Each stamen consists of an anther (produces pollen) and a filament.

4. Gynoecium (Carpels/Pistils): Female reproductive whorl. Each carpel consists of an ovary (contains ovules), a style, and a stigma.

Diagram Description: (A diagram would show a flower with sepals, petals, stamens, and carpel, labeled.)

In summary, the flower is a modified shoot specialized for sexual reproduction.

7. Describe the methods of natural vegetative propagation in plants.

Answer: Natural vegetative propagation occurs without human intervention. Methods include:

1. Runners (Stolons): Horizontal stems that grow above ground and produce new plants at nodes. Example: Strawberry, grass.

2. Rhizomes: Horizontal underground stems that produce new shoots. Example: Ginger, turmeric.

3. Tubers: Swollen underground stems with buds (eyes). Example: Potato.

4. Bulbs: Underground storage organs with fleshy leaves. Example: Onion, tulip.

5. Corms: Solid, swollen underground stems. Example: Crocus, gladiolus.

6. Suckers: New shoots that grow from roots. Example: Banana, mint.

7. Leaf Plantlets: Plantlets that grow on leaf margins. Example: Bryophyllum.

In summary, natural vegetative propagation allows plants to spread and reproduce without seeds.