Class 7 Science Notes Chapter 12 (Chapter 12) – Examplar Problems Book

Detailed Notes with MCQs of Chapter 12, 'Reproduction in Plants', from your Science Exemplar book. This is a fundamental chapter, and understanding these concepts well is crucial, not just for your class exams, but also for various competitive government exams where basic science is tested.

Chapter 12: Reproduction in Plants - Detailed Notes

1. What is Reproduction?

• Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parents".
• It is essential for the continuation of species, generation after generation.

2. Modes of Reproduction in Plants:
Plants reproduce mainly through two modes:

• Asexual Reproduction: New plants are produced from a single parent without the involvement of gametes (sex cells) or seeds. The offspring are genetically identical to the parent.
• Sexual Reproduction: New plants are produced from seeds, which are formed by the fusion of male and female gametes. Offspring show characteristics of both parents.

3. Asexual Reproduction Methods:

• (a) Vegetative Propagation:

  • This is a type of asexual reproduction where new plants grow from vegetative parts like roots, stems, leaves, or buds.
  • From Stems:
    • Runners: Stems that grow horizontally above the ground (e.g., Grass, Strawberry).
    • Tubers: Underground stems that store food. The 'eyes' of a potato are buds from which new plants can grow (e.g., Potato).
    • Rhizomes: Horizontal underground stems (e.g., Ginger, Turmeric).
    • Bulbs: Underground stems with fleshy leaves (e.g., Onion, Garlic).
    • Stem Cuttings: A piece of stem is cut and planted, which develops roots (e.g., Rose, Sugarcane, Bougainvillea).
  • From Roots: Some plants can develop new shoots from their roots (e.g., Sweet Potato, Dahlia).
  • From Leaves: Some plants have buds on the margins of their leaves. When a leaf falls on moist soil, these buds can develop into new plantlets (e.g., Bryophyllum - Sprout leaf plant).
  • Advantages: Plants produced take less time to grow and bear flowers/fruits earlier than those grown from seeds. They are exact copies of the parent plant, preserving desired characteristics.

• (b) Budding:

  • Common in unicellular organisms like Yeast.
  • A small bulb-like projection (bud) grows out from the parent cell.
  • The bud gradually grows and gets detached from the parent cell to form a new yeast cell. Sometimes, a chain of buds may form.

• (c) Fragmentation:

  • The body of the parent organism breaks into distinct pieces (fragments).
  • Each fragment grows into a new individual.
  • Example: Spirogyra (an alga found in ponds and lakes).

• (d) Spore Formation:

  • Spores are tiny, asexual reproductive bodies covered by a hard protective coat to withstand unfavourable conditions (like high temperature, low humidity).
  • When conditions become favourable (moisture, suitable temperature), the spore germinates and develops into a new individual.
  • Examples: Fungi (like bread mould - Rhizopus), Mosses, and Ferns. Spores are often found in structures called sporangia.

4. Sexual Reproduction:

• Involves the fusion of male and female gametes to form a zygote, which develops into an embryo within a seed.

• Flowers are the reproductive parts of a plant.

• (a) Parts of a Flower:

  • Sepals: Green, leaf-like structures that protect the flower in the bud stage. Collectively called the calyx.
  • Petals: Usually brightly coloured to attract insects for pollination. Collectively called the corolla.
  • Stamen: The male reproductive part. Consists of:
    • Anther: Contains pollen grains, which produce male gametes.
    • Filament: The stalk that supports the anther.
  • Pistil (or Carpel): The female reproductive part. Consists of:
    • Stigma: The sticky tip that receives pollen grains.
    • Style: The tube connecting the stigma to the ovary.
    • Ovary: The swollen base containing ovules. Each ovule contains the female gamete (egg cell).

• (b) Types of Flowers:

  • Unisexual Flowers: Flowers containing either only the pistil (female flower) or only the stamens (male flower). Examples: Corn (Maize), Papaya, Cucumber.
  • Bisexual Flowers: Flowers containing both stamens and pistil. Examples: Mustard, Rose, Petunia, Hibiscus.

• (c) Pollination:

  • The transfer of pollen grains from the anther to the stigma.
  • Self-Pollination: Pollen lands on the stigma of the same flower or another flower on the same plant. Occurs mainly in bisexual flowers.
  • Cross-Pollination: Pollen lands on the stigma of a flower on a different plant of the same kind. Requires agents.
  • Agents of Pollination: Wind, Water, Insects (most common), Birds, Bats.
    • Wind-pollinated flowers: Often small, not brightly coloured, produce large amounts of light pollen (e.g., Grasses, Maize, Pine).
    • Insect-pollinated flowers: Usually large, brightly coloured, produce nectar and fragrance to attract insects (e.g., Rose, Sunflower).
    • Water-pollinated flowers: Occurs in some aquatic plants (e.g., Vallisneria, Hydrilla).

• (d) Fertilization:

  • The fusion of the male gamete (from the pollen grain) with the female gamete (egg cell inside the ovule).
  • Process:
    1. Pollen grain lands on the stigma.
    2. If compatible, it germinates, forming a pollen tube that grows down through the style to reach the ovule in the ovary.
    3. The male gamete travels down the pollen tube and fuses with the female gamete inside the ovule.
  • The fused cell is called the Zygote.

• (e) Post-Fertilization Changes: Fruit and Seed Formation:

  • After fertilization, the zygote develops into the embryo.
  • The ovule develops into the seed. The seed contains the embryo and stored food, protected by a seed coat.
  • The ovary grows and ripens to become the fruit.
  • Other parts of the flower (sepals, petals, stamens, style, stigma) usually wither and fall off.
  • The fruit protects the seed(s). Fruits can be fleshy (e.g., Mango, Apple, Orange) or dry (e.g., Pea, Mustard, Groundnut).

• (f) Seed Dispersal:

  • The scattering of seeds away from the parent plant. This is important to avoid overcrowding, reduce competition for sunlight, water, and minerals, and colonize new habitats.
  • Agents of Dispersal:
    • Wind: Seeds are light, small, may have wings (e.g., Drumstick, Maple) or hair-like structures (e.g., Sunflower, Madar/Aak).
    • Water: Seeds/fruits can float (e.g., Coconut - fibrous outer coat; Lotus).
    • Animals: Seeds have hooks/spines to attach to fur (e.g., Xanthium, Urena), or are present in fleshy fruits which animals eat (seeds pass out undigested).
    • Explosion/Bursting: Some fruits burst open suddenly when dry, scattering the seeds (e.g., Castor, Balsam, Pea).

Multiple Choice Questions (MCQs):

1. Which of the following plants reproduces vegetatively through its leaves?
   (a) Potato
   (b) Bryophyllum
   (c) Ginger
   (d) Yeast

2. The process of fusion of male and female gametes is called:
   (a) Pollination
   (b) Germination
   (c) Fertilization
   (d) Fragmentation

3. Flowers which contain both stamens and pistil are called:
   (a) Unisexual flowers
   (b) Bisexual flowers
   (c) Asexual flowers
   (d) Neuter flowers

4. Which part of the flower develops into a fruit after fertilization?
   (a) Ovule
   (b) Sepal
   (c) Petal
   (d) Ovary

5. Spore formation is a common method of asexual reproduction in:
   (a) Yeast
   (b) Spirogyra
   (c) Ferns
   (d) Rose

6. Maple seeds are dispersed by wind because they possess:
   (a) Hairy structures
   (b) Wing-like structures
   (c) Hooks or spines
   (d) Light, spongy structure

7. Yeast reproduces asexually by which of the following methods?
   (a) Fragmentation
   (b) Spore formation
   (c) Budding
   (d) Vegetative propagation

8. The male reproductive part of a flower is the:
   (a) Pistil
   (b) Stamen
   (c) Sepal
   (d) Petal

9. Transfer of pollen from the anther to the stigma of the same flower is called:
   (a) Cross-pollination
   (b) Fertilization
   (c) Self-pollination
   (d) Germination

10. In vegetative propagation by stem tubers, the structures that grow into new plants are called:
    (a) Buds or 'eyes'
    (b) Rhizomes
    (c) Spores
    (d) Fragments

Answer Key for MCQs:

1. (b) Bryophyllum
2. (c) Fertilization
3. (b) Bisexual flowers
4. (d) Ovary
5. (c) Ferns (also Fungi, Mosses)
6. (b) Wing-like structures
7. (c) Budding
8. (b) Stamen
9. (c) Self-pollination
10. (a) Buds or 'eyes'

Study these notes carefully. Pay special attention to the examples provided for each type of reproduction and dispersal method, as questions are often framed around them. Good luck with your preparation!