Class 9 Biology Notes Chapter 10

Chapter 10: Reproduction in Plants

Exercise Solution

A. Select the Correct Answers for the Following Questions

1. Which of the following organisms commonly reproduce by binary fission?

a) Yeast
b) Bacteria
c) Rhizopus
d) Plants

Correct Answer: (b) Bacteria

2. What is the primary method of reproduction in yeast?

a) Binary fission
b) Spore formation
c) Budding
d) Fragmentation

Correct Answer: (c) Budding

3. Which of the following statements is true about spore formation in fungi?

a) They produce spores during sexual reproduction
b) They produce two kinds of spores
c) Spores can only grow into new fungi in dry environments
d) Spores are produced to withstand harsh conditions

Correct Answer: (d) Spores are produced to withstand harsh conditions

4. What happens in some bacteria during harsh conditions?

a) Creation of a bud that detaches from the cell
b) Formation of thick-walled endospores
c) Splitting the cell into two identical daughter cells
d) Fusion of two bacterial cells

Correct Answer: (b) Formation of thick-walled endospores

5. Which of the following is an example of vegetative propagation through runners?

a) Potato
b) Strawberry
c) Onion
d) Ginger

Correct Answer: (b) Strawberry

6. Which plant propagates through tubers?

a) Onion
b) Potato
c) Ginger
d) Garlic

Correct Answer: (b) Potato

7. The horizontal aboveground stem, which produces leaves and roots at its nodes, is called:

a) Stolon
b) Bulb
c) Rhizome
d) Corm

Correct Answer: (a) Stolon

8. Which of these does NOT help a plant in vegetative propagation?

a) Rhizome
b) Corm
c) Runner
d) Flower

Correct Answer: (d) Flower

9. Which part of the flower is responsible for producing pollen?

a) Stigma
b) Anther
c) Ovary
d) Petal

Correct Answer: (b) Anther

10. Which of the following is NOT a part of the carpel?

a) Filament
b) Style
c) Stigma
d) Ovary

Correct Answer: (a) Filament

11. Which structure forms the female gametophyte in flowering plants?

a) Pollen grain
b) Ovule
c) Anther
d) Sepal

Correct Answer: (b) Ovule

12. The male gametophyte in flowering plants is known as:

a) Pollen grain
b) Embryo sac
c) Ovary
d) Carpel

Correct Answer: (a) Pollen grain

13. In the life cycle of flowering plants, which structure is triploid (3n)?

a) Egg
b) Fusion nucleus
c) Endosperm nucleus
d) Sperm

Correct Answer: (c) Endosperm nucleus

14. The embryo sac is formed inside the:

a) Filament
b) Anther
c) Style
d) Ovule

Correct Answer: (d) Ovule

15. Double fertilization involves:

a) Fertilization of the egg by two male gametes
b) Fertilization of two eggs in the same embryo sac by two sperms
c) Fertilization of the egg and the fusion nucleus by two sperms
d) Fertilization of the egg and the tube cell by two sperms

Correct Answer: (c) Fertilization of the egg and the fusion nucleus by two sperms

B. Write Short Answers

1. Write a short note on budding in yeast.

Answer: Budding is a form of asexual reproduction in yeast in which a small outgrowth called a bud develops on the parent cell. The nucleus divides mitotically, and one daughter nucleus migrates into the bud. The bud grows and eventually pinches off, living independently or remaining attached as a colony.

2. Write a short note on spore formation in fungi.

Answer: Fungi produce microscopic, single-celled reproductive structures called spores inside specialized spore cases known as sporangia. These spores are lightweight, produced in large numbers, and dispersed by wind or water. When they land in favourable, moist environments, they germinate directly into new fungal mycelia.

3. What are the advantages of spore formation in fungi and bacteria?

Answer: Spores possess protective walls that allow them to withstand unfavourable environmental conditions such as desiccation, high temperatures, and freezing. Their small size and light weight facilitate wide dispersal over long distances.

4. Describe how vegetative propagation occurs through runners.

Answer: Runners (stolons) are specialized horizontal stems that grow just above the ground surface. As they extend outward, nodes along the runner touch the soil, producing adventitious roots downward and shoots upward. These eventually develop into independent daughter plants, as seen in strawberries.

5. State how potatoes reproduce through tubers.

Answer: Potatoes reproduce through stem tubers, which are swollen underground stems packed with stored starch. The surface of a tuber features buds known as “eyes.” When planted, these eyes sprout stems and roots, using the stored food reserves of the tuber to grow into new potato plants.

6. Describe the advantages and disadvantages of vegetative propagation.

Answer:

Advantages:

1. Rapid reproduction.

2. Exact genetic replication of desirable parental traits (true-to-type).

3. Bypasses vulnerable early seedling stages.

Disadvantages:

1. Lack of genetic diversity makes populations highly susceptible to diseases and environmental changes.

2. It may cause overcrowding due to the production of many plants in a limited area.

7. Name the four whorls present in a flower and state the components of each whorl.

Answer:

1. Calyx: The outer whorl, composed of individual sepals.

2. Corolla: Composed of individual, often brightly coloured petals.

3. Androecium: The male reproductive whorl, composed of stamens, each containing an anther and a filament.

4. Gynoecium: The female reproductive whorl, composed of carpels or pistils, each containing a stigma, style, and ovary.

8. Briefly describe the formation of the egg cell and polar nuclei within the embryo sac of a flower.

Answer: Inside the ovule, a megaspore mother cell undergoes meiosis to produce four haploid megaspores. Three degenerate, while one survives. The surviving megaspore nucleus divides mitotically three times to form an eight-nucleate, seven-celled embryo sac. One cell differentiates into the female gamete (egg cell), while two polar nuclei are present in the central cell and may fuse to form a secondary nucleus.

9. Differentiate between the following:

i. Asexual and Sexual Reproduction

Asexual Reproduction: Involves a single parent producing offspring without the fusion of gametes. The offspring are generally genetically identical to the parent.

Sexual Reproduction: Involves the fusion of male and female gametes to produce genetically varied offspring.

ii. Binary Fission in Bacteria and Amoeba

Binary Fission in Bacteria: Bacterial DNA replicates, and the cell divides into two daughter cells without a true mitotic spindle.

Binary Fission in Amoeba: The nucleus divides by mitosis, followed by division of the cytoplasm to form two daughter cells.

iii. Stolon and Rhizome

Stolon: A horizontal aboveground stem that produces roots and shoots at its nodes.

Rhizome: A horizontal underground stem modified for food storage and perennation.

iv. Bulb and Corm

Bulb: Consists of a short underground stem surrounded by fleshy, scale-like leaf bases, as in onion.

Corm: A solid, swollen, vertical underground stem storage organ covered by dry, papery scale leaves, as in gladiolus.

v. Cutting and Grafting

Cutting: Involves planting a severed stem or root piece to induce adventitious root growth and develop a new plant.

Grafting: Involves joining the tissues of two plants, called the scion and stock, so that they grow together as a single plant.

vi. Vegetative Propagation and Artificial Propagation

Vegetative Propagation: Natural vegetative propagation occurs through plant organs, such as runners and tubers, without human intervention.

Artificial Propagation: Involves human-directed techniques such as cutting, layering, grafting, and tissue culture.

vii. Male and Female Gametophytes

Male Gametophyte: Represented by the pollen grain, which develops and produces the male gametes.

Female Gametophyte: Represented by the embryo sac within the ovule, which contains the egg cell and other cells.

viii. Calyx and Corolla

Calyx: Consists of sepals, which are usually green and protect the flower bud.

Corolla: Consists of petals, which are often brightly coloured and help attract pollinators.

ix. Stamen and Carpel

Stamen: The male reproductive organ of a flower, comprising an anther and a filament.

Carpel: The female reproductive organ of a flower, comprising a stigma, style, and ovary.

10. Label the given diagram of a flower.

Answer: Based on a standard floral diagram, the labels are:

1. Stigma

2. Style

3. Anther

4. Filament

5. Ovary

6. Ovule

7. Petal

8. Sepal

9. Receptacle

C. Write Answers in Detail

1. Explain the process of binary fission in bacteria and describe how it leads to the formation of two daughter bacteria.

Answer: Binary fission is a form of asexual reproduction in prokaryotes. It occurs through the following steps:

1. The single circular bacterial chromosome replicates, producing two identical copies.

2. The bacterial cell elongates, and the two chromosome copies move apart.

3. The cell membrane grows inward between the two chromosome copies.

4. A transverse cell wall called the septum forms across the centre, dividing the cytoplasm.

5. The cell separates completely, producing two genetically similar daughter bacteria.

2. What do you mean by vegetative propagation? Differentiate among different plant structures modified for vegetative propagation.

Answer: Vegetative propagation is a form of asexual reproduction in which new plants grow from vegetative parts of the parent plant, such as roots, stems, or leaves, rather than from seeds.

Modified structures include:

1. Runners/Stolons: Horizontal surface stems that produce roots and shoots at their nodes. Example: Strawberry.

2. Rhizomes: Underground horizontal stems with nodes and buds. Example: Ginger.

3. Tubers: Swollen underground stem storage organs containing buds or eyes. Example: Potato.

4. Bulbs: Short underground stems surrounded by fleshy leaves. Example: Onion.

5. Corms: Solid, swollen, vertical underground stems. Examples: Gladiolus and crocus.

3. Describe the ways by which humans can grow new plants by using the vegetative parts of parent plants.

Answer: Humans use several artificial propagation techniques to grow new plants from vegetative parts.

1. Stem Cuttings: A section of stem containing nodes is cut and placed in moist soil or another suitable medium to induce root growth. Examples include rose and sugarcane.

2. Grafting: The shoot system of a desired plant variety, called the scion, is joined to the root system of another plant, called the stock. They grow together as a single plant.

3. Layering: A low-growing stem is bent towards the ground, and a section is covered with soil to induce root formation. The rooted section is then separated from the parent plant.

4. Tissue Culture (Micropropagation): Plant cells or tissues are grown on a nutrient medium under sterile conditions to produce large numbers of genetically similar plants rapidly.

4. Define sporophyte and gametophyte. State their roles in the life cycle of plants.

Answer:

Sporophyte: The diploid (2n), spore-producing phase of a plant. It produces haploid spores through meiosis.

Gametophyte: The haploid (n), gamete-producing phase of a plant. It produces male and female gametes through mitosis.

Role in the Life Cycle: Both generations participate in the alternation of generations, in which the multicellular diploid sporophyte alternates with the multicellular haploid gametophyte to complete the plant’s reproductive cycle.

5. Explain the life cycle of flowering plants, focusing on the alternation between the gametophyte and sporophyte generations.

Answer: Flowering plants exhibit alternation of generations through the following stages:

1. The dominant plant body is the diploid sporophyte (2n).

2. Inside its flowers, specialized cells undergo meiosis to produce haploid (n) spores.

3. These spores develop into microscopic gametophytes, represented by pollen grains and embryo sacs.

4. The gametophytes produce haploid gametes, including sperm cells and egg cells.

5. During fertilization, a male gamete fuses with the egg cell to form a diploid zygote (2n).

6. The zygote develops into an embryo within a seed, producing a new sporophyte and restarting the life cycle.

6. Describe how the female gametophyte (embryo sac) develops within the ovule of a flower.

Answer: The female gametophyte develops within the ovule through the following stages:

1. An ovule inside the plant ovary contains a diploid megaspore mother cell.

2. This cell undergoes meiosis to produce four haploid megaspores.

3. Three megaspores disintegrate, while one survives and enlarges.

4. The nucleus of the surviving functional megaspore undergoes three successive mitotic divisions, producing eight haploid nuclei.

5. These nuclei organize into a seven-celled embryo sac, which forms the female gametophyte.

6. The mature embryo sac consists of an egg cell near the micropyle, two synergids, three antipodal cells, and a central cell containing two polar nuclei.

D. Inquisitive Questions

1. Why are spores considered an adaptation for survival in harsh environmental conditions?

Answer: Spores are adapted for survival because they possess protective walls that help protect their internal genetic material against unfavourable conditions such as extreme heat, drought, ultraviolet radiation, and certain toxic chemicals. Their low metabolic activity allows them to remain dormant for extended periods until environmental conditions become favourable for germination.

2. How do asexual and sexual reproduction contribute differently to the genetic diversity of plant populations?

Answer:

Asexual Reproduction: Asexual reproduction produces offspring that are generally genetic clones of the parent plant. Although it is efficient in stable environments, it produces little genetic variation, leaving populations potentially vulnerable to sudden environmental changes and diseases.

Sexual Reproduction: Sexual reproduction introduces genetic diversity through meiosis, including crossing over and independent assortment, and the random fusion of gametes. This diversity provides the raw material for natural selection, adaptation, and evolutionary resilience.

3. How does the pollen tube facilitate the process of fertilization in flowering plants?

Answer: When a pollen grain lands on a compatible stigma, it germinates and grows a pollen tube down through the style towards the ovary. The pollen tube acts as a protected passage, transporting the two male gametes to the ovule through the micropyle and into the embryo sac. One male gamete fuses with the egg cell to form the zygote, while the other fuses with the polar nuclei to help form the endosperm. This process is called double fertilization.

Notes by Sir Dilawar

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