Reproduction in Plants – Ncert Notes

Reproduction in Plants

Reproduction in Plants- Reproduction is a vital process through which living organisms produce new individuals of their own kind, ensuring the continuation of their species. In plants, reproduction can occur in two main ways: asexual reproduction and sexual reproduction. This chapter explores how plants reproduce, the structures involved, and the processes that help plants multiply.

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1. Modes of Reproduction in Plants

Plants reproduce using two primary methods:

A. Asexual Reproduction

• In asexual reproduction, a single parent plant produces offspring without the involvement of seeds or gametes (reproductive cells).
• The new plants are genetically identical to the parent plant.
• This method is common in plants that do not produce flowers or seeds.

Examples of Asexual Reproduction:

1. Vegetative Propagation: New plants grow from vegetative parts like roots, stems, or leaves.
   • Roots: Sweet potato and dahlia grow new plants from their roots.
   • Stems: Potato (tubers), ginger (rhizomes), and onion (bulbs) reproduce through modified stems.
   • Leaves: Bryophyllum grows tiny plantlets along the edges of its leaves.
2. Budding: Seen in yeast (a simple plant-like organism), where a small bud grows on the parent and detaches to form a new individual.
3. Fragmentation: In algae like Spirogyra, the body breaks into fragments, and each fragment grows into a new plant.
4. Spore Formation: Ferns and mosses produce spores in sporangia, which germinate into new plants under favorable conditions.

Advantages of Asexual Reproduction:

• Faster and simpler process.
• Does not require pollination or seed formation.
• Produces identical offspring, preserving desirable traits.

B. Sexual Reproduction

• Sexual reproduction involves the fusion of male and female reproductive cells (gametes) to form a seed, which grows into a new plant.
• It occurs in flowering plants and requires the formation of flowers, pollination, and fertilization.
• The offspring are not identical to the parent due to genetic variation.

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2. Vegetative Propagation: A Closer Look

Vegetative propagation is a widely studied form of asexual reproduction in plants. It can occur naturally or be induced artificially by humans.

Natural Vegetative Propagation

• Runners/Stolons: Grass and strawberry plants spread through horizontal stems called runners that develop roots and shoots.
• Tubers: Potatoes have “eyes” (buds) that grow into new plants.
• Rhizomes: Ginger and turmeric grow underground stems that sprout new plants.
• Bulbs: Onions and tulips have underground bulbs that produce new shoots.

Artificial Vegetative Propagation

• Humans use techniques to propagate plants with desired traits:
  1. Cutting: A stem or leaf is cut and planted (e.g., rose, sugarcane).
  2. Layering: A branch is bent and buried in soil to develop roots (e.g., jasmine).
  3. Grafting: A stem (scion) from one plant is attached to the root system (stock) of another (e.g., mango, apple).

Advantages of Artificial Propagation:

• Produces plants faster than seeds.
• Ensures the new plant inherits specific qualities (e.g., fruit taste or flower color).

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3. Sexual Reproduction in Flowering Plants

Sexual reproduction in plants involves flowers, which are the reproductive organs. Let’s break down the process step-by-step.

A. Structure of a Flower

A typical flower has four main parts:

1. Sepals: Green, leaf-like structures that protect the flower bud.
2. Petals: Brightly colored parts that attract pollinators like insects and birds.
3. Stamens: Male reproductive part, consisting of:
   • Anther: Produces pollen grains (male gametes).
   • Filament: Supports the anther.
4. Pistil/Carpel: Female reproductive part, consisting of:
   • Stigma: Sticky top that receives pollen.
   • Style: Tube connecting stigma to ovary.
   • Ovary: Contains ovules (female gametes or egg cells).

Flowers can be:

• Unisexual: Have either stamens or pistil (e.g., papaya, watermelon).
• Bisexual: Have both stamens and pistil (e.g., mustard, hibiscus).

B. Pollination

• Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a pistil.
• Two types of pollination:
  1. Self-Pollination: Pollen transfers to the stigma of the same flower or another flower on the same plant.
  2. Cross-Pollination: Pollen transfers to the stigma of a flower on a different plant of the same species.
• Agents of Pollination: Insects, wind, water, birds, or animals carry pollen.

Features aiding Pollination:

• Wind-pollinated flowers (e.g., corn) produce light, dry pollen and have feathery stigmas.
• Insect-pollinated flowers (e.g., sunflower) have bright petals, nectar, and sticky pollen.

C. Fertilization

• After pollination, the pollen grain on the stigma grows a pollen tube down the style to reach the ovary.
• The male gamete from the pollen fuses with the female gamete (egg) in the ovule.
• This fusion is called fertilization and forms a zygote.

D. Post-Fertilization Changes

• The zygote develops into an embryo.
• The ovule becomes a seed.
• The ovary ripens into a fruit, which protects the seed.
• Other flower parts (petals, sepals, stamens) dry up and fall off.

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4. Seed and Fruit Formation

A. Structure of a Seed

• A seed has:
  1. Seed Coat: Protective outer layer.
  2. Cotyledons: Stored food for the embryo (one in monocots like wheat, two in dicots like pea).
  3. Embryo: Tiny plant with a radicle (future root), plumule (future shoot), and cotyledons.

B. Types of Fruits

• Fleshy Fruits: Mango, apple (edible and juicy).
• Dry Fruits: Peanut, walnut (hard and dry).

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5. Seed Dispersal

Seeds need to be dispersed away from the parent plant to avoid competition for sunlight, water, and nutrients. Methods of seed dispersal include:

1. Wind: Light seeds with wings or hair (e.g., dandelion, cotton).
2. Water: Seeds that float (e.g., coconut).
3. Animals: Seeds with hooks or sticky surfaces (e.g., xanthium) or edible fruits (e.g., mango, eaten and dispersed by animals).
4. Explosion: Some plants (e.g., pea) burst open to scatter seeds.

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6. Germination

• Germination is the process by which a seed grows into a new plant.
• Conditions Required:
  • Water: Softens the seed coat and activates enzymes.
  • Oxygen: Needed for respiration.
  • Warmth: Optimal temperature for growth.
• Process:
  1. The seed absorbs water and swells.
  2. The radicle emerges and grows downward to form the root.
  3. The plumule grows upward to form the shoot.
  4. Cotyledons provide food until the plant can photosynthesize.

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7. Importance of Reproduction in Plants

• Ensures the survival of plant species.
• Helps plants spread to new areas through seed dispersal.
• Sexual reproduction introduces variation, making plants adaptable to changing environments.
• Vegetative propagation allows humans to cultivate crops efficiently.

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Key Terms to Remember

• Asexual Reproduction: Reproduction without gametes.
• Sexual Reproduction: Reproduction involving gamete fusion.
• Pollination: Transfer of pollen from anther to stigma.
• Fertilization: Fusion of male and female gametes.
• Vegetative Propagation: Growth of new plants from vegetative parts.
• Seed Dispersal: Spreading of seeds away from the parent plant.

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Conclusion

Chapter 8 introduces students to the fascinating ways plants reproduce, from simple asexual methods like budding to complex sexual processes involving flowers, pollination, and seed formation. Understanding these processes highlights the diversity of plant life and their adaptations for survival. Whether through natural means or human intervention, reproduction ensures that plants continue to thrive and support life on Earth.

Ch 08 Reproduction In Plants