Rapid Revision – Class 7 Science- Chapter 12 – Reproduction in Plants

Modes of Plant Reproduction

• Sexual Reproduction: Involves flowers and the production of seeds through pollination and fertilisation. This method leads to genetic diversity as offspring inherit genetic material from two parents. Seeds are then dispersed through various means to new areas.
• Asexual Reproduction: Involves the production of new plants without seeds or flowers, directly from plant parts like stems, roots, or leaves. It results in rapid propagation of new plants that are clones of the parent.

Vegetative Propagation (Asexual Reproduction)

• Definition: Growth of new plants from vegetative parts (non-flower parts).
• Mechanisms: Utilises roots, stems, leaves, and buds.
• Flower Buds vs. Vegetative Buds: Flower buds lead to sexual reproduction, while vegetative buds can grow into new stems and leaves or even new plants.

Also Check – Class 7 Science- Chapter 12 – Reproduction in Plants- (Complete Notes)

Advantages of Vegetative Propagation

• Rapid multiplication of plants.
• Uniformity of traits among new plants.
• Earlier maturity than seed-grown plants.
• Bypasses the need for pollination.
• Maintains hybrid characteristics.

Roles of Different Plant Parts in Propagation

• Stems: Can develop roots and new plants (e.g., potato eyes, rhizomes).
• Leaves: Some have buds that can grow into new plants (e.g., Bryophyllum).
• Roots: In certain plants, new individuals can sprout.
• Buds: Can develop into new shoots or plants, depending on their type (vegetative or flower buds).

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Yeast and Budding:

• Yeast is a microscopic single-celled fungus with significant roles in baking and brewing.
• Budding in yeast’s asexual reproduction method where a new cell (bud) forms on a parent yeast cell and eventually detaches to live independently.
• Yeast can rapidly reproduce in favourable conditions, ensuring quick population growth and survival in various environments.

Yeast Budding 

• Budding involves initiation (small bump forms on the cell), growth (bud enlarges and nucleus divides), and separation (bud detaches to form a new cell).

Fragmentation in Algae:

• Fragmentation is asexual reproduction by breaking into parts, each capable of growing into a new individual.
• Algae utilise fragmentation to rapidly multiply and adapt to environments, forming green patches in aquatic environments.

Spore Formation in Plants:

• Spores are lightweight reproductive bodies produced by plants like fungi, moss, and ferns, capable of surviving harsh conditions.
• Spores develop in specialised structures (sporangia), disperse through air, and germinate under favourable conditions to form new organisms.

Sexual Reproduction in Plants:

• Plants reproduce sexually through flowers, which contain male (stamen) and female (pistil) parts.
• The stamen includes the anther (produces pollen) and filament (supports the anther).
• The pistil is made of the stigma (captures pollen), style (guides pollen tubes), and ovary (contains ovules where fertilisation occurs leading to seeds and fruits).

Types of Flowers:

• Unisexual Flowers: Contain either stamen or pistil. Promote cross-pollination, increasing genetic diversity. Examples: corn, papaya, cucumber.
• Bisexual Flowers: Have both stamens and pistils, allowing for self-pollination and cross-pollination. Examples: mustard, rose, petunia.

Gamete Formation:

• Male Gamete Formation: Occurs in the anther, producing pollen grains that carry the male gametes for fertilisation.
• Female Gamete Formation: Takes place in the ovules within the ovary, where the female gametes or eggs are present.

Fertilisation Process:

• Fusion of Gametes: Male and female gametes unite, typically through pollination.
• Formation of Zygote: The united gametes form a zygote, which will develop into a new plant.
• Development into a New Plant: The zygote undergoes cell division and differentiation to grow into a new plant.

Pollination:

• Pollen Grains: Are male genetic carriers with protective layers for durability and transfer.
• Agents of Pollination: Include wind (light, dry pollen), water (plants releasing pollen into water), and insects (nectar-producing flowers attracting pollinators).
• Types of Pollination:
  • Self-Pollination: Pollen from the same flower or plant facilitates reproduction with or without external agents.
  • Cross-Pollination: Pollen from different plants of the same species promotes genetic diversity.

Significance of Pollination:

• Genetic Diversity: Cross-pollination increases genetic variation, essential for adaptability and survival.
• Plant Survival and Evolution: Pollination continues species propagation and contributes to evolutionary changes.
• Fruit and Seed Formation: It leads to fruit and seed production, key to species continuity.
• Ecosystem Diversity: Pollinators support biodiversity and ecosystem balance.

Fertilisation in Plants:

• Definition: Union of male and female gametes to form a zygote, an essential part of sexual reproduction.
• Components: Male gamete inside pollen from the anther, female gamete (egg cell) within the ovule in the ovary.
• Process:
  • Pollen transfers to stigma.
  • Pollen germination and pollen tube formation.
  • Fusion of gametes within the ovule to create a zygote.
• Location: Occurs inside the ovule of the flower.
• Post-Fertilization Development:
  • Zygote develops into an embryo within the seed.
  • Genetic diversity arises from the mix of genetic materials.
  • Continuation of species through new plant generation.

Fruit and Seed Formation:

• Fruit Formation:
  • The ovary transforms into fruit post-fertilization.
  • Fruits, either fleshy or hard, act as protective enclosures for seeds.
  • Ripening involves biochemical changes impacting the fruit’s properties.
• Seed Formation:
  • Initiated by fertilisation; the embryo develops within the ovule.
  • Seeds consist of an embryo and a protective seed coat.
  • Diversity in seed types affects dispersal and germination environments.
  • Seeds are central to plant reproduction and species continuity.

Seed Dispersal:

• Necessity: Essential for species survival and propagation.
• Avoidance of Competition: Spreads out plants to reduce resource competition.
• Methods:
  • Wind (e.g., winged seeds like maple).
  • Water (e.g., floating seeds like coconut).
  • Animals (e.g., seeds with hooks like Xanthium).
  • Explosive action (e.g., balsam pods that burst).
• Significance: Seed dispersal helps in colonisation of new areas, ensures genetic diversity, and allows plants to thrive in various ecological niches.

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