Reproduction in Plants - Class 7 Science (CBSE)
Based on the 2025-26 NCERT syllabus for Class 7 Science. This chapter covers the different ways plants reproduce, both asexually and sexually, and the importance of seed dispersal.
1. Why this chapter matters
Reproduction ensures the survival of plant species. Understanding how plants reproduce helps us in agriculture, horticulture, and conservation. In CBSE exams, this chapter contributes 6-8 marks.
2. Asexual reproduction in plants
Asexual reproduction involves only one parent. The offspring are genetically identical to the parent (clones).
3. Budding
In budding, a small outgrowth (bud) develops on the parent body. The bud grows, detaches, and becomes a new individual.
- Example: Yeast (a fungus).
- In yeast, the bud may remain attached for some time, forming a chain of buds.
Budding in hydra
Hydra (a small aquatic animal) also reproduces by budding, but this is usually covered in animal reproduction. In plants, budding is seen in yeast.
4. Fragmentation
In fragmentation, the parent body breaks into two or more fragments, each of which grows into a new individual.
- Example: Spirogyra (an algae).
- Spirogyra filaments break into pieces, and each piece grows into a new filament.
5. Spore formation
Spores are tiny reproductive bodies protected by a thick wall. They can survive harsh conditions and grow into new plants when conditions are favourable.
- Examples: Bread mould (Rhizopus), ferns, mosses.
- Bread mould produces spores in structures called sporangia (black dots on mouldy bread).
Advantages of spore formation
- Spores can survive unfavourable conditions (heat, cold, drought).
- Spores are light and can be carried by wind over long distances.
- One plant can produce millions of spores.
6. Comparison of asexual methods
| Method | Description | Example | Key feature |
|---|---|---|---|
| Budding | Small bud grows and detaches | Yeast | Bud visible on parent |
| Fragmentation | Body breaks into pieces | Spirogyra | Each piece grows |
| Spore formation | Spores grow into new plants | Bread mould | Resistant to conditions |
| Vegetative propagation | New plant from vegetative parts | Potato, ginger | Uses stem/root/leaf |
7. Sexual reproduction in plants
Sexual reproduction involves two parents (male and female) and produces offspring that are genetically different from the parents.
8. Parts of a flower
A flower is the reproductive organ of a plant.
Whorls of a flower (from outside to inside)
| Whorl | Parts | Function |
|---|---|---|
| Calyx | Sepals | Protect the flower in bud stage |
| Corolla | Petals | Attract pollinators (colour, scent) |
| Androecium | Stamens (male part) | Produce pollen grains |
| Gynoecium | Pistil/Carpel (female part) | Produces ovules |
Male part: Stamen
Each stamen has:
- Anther: Produces pollen grains (male gametes).
- Filament: Stalk that supports the anther.
Female part: Pistil
Each pistil has:
- Stigma: Sticky top that receives pollen.
- Style: Tube connecting stigma to ovary.
- Ovary: Contains ovules (female gametes).
9. Pollination
Pollination is the transfer of pollen grains from the anther to the stigma.
Self-pollination
Pollen from the same flower (or another flower on the same plant) lands on the stigma.
Cross-pollination
Pollen from one flower lands on the stigma of a different flower (on a different plant of the same species).
Agents of pollination
| Agent | How it works | Example flowers |
|---|---|---|
| Wind | Light, small pollen carried by wind | Grasses, corn, wheat |
| Insects | Bright colours and scent attract insects; pollen sticks to them | Sunflower, rose |
| Birds | Large, colourful flowers attract birds | Bottlebrush |
| Water | Pollen floats on water surface | Water plants (Hydrilla) |
10. Fertilisation
After pollination, the pollen grain germinates on the stigma. A pollen tube grows through the style down to the ovary. The male gamete travels through this tube and fuses with the female gamete (ovule).
Fusion of male and female gametes = fertilisation.
After fertilisation:
- The ovule becomes the seed.
- The ovary becomes the fruit.
- The other flower parts wither away.
11. Seed dispersal
Seed dispersal is the scattering of seeds away from the parent plant. This prevents competition for resources and helps plants colonise new areas.
Methods of seed dispersal
| Method | Adaptation | Examples |
|---|---|---|
| Wind | Light seeds with wings or hairs | Maple, dandelion, cotton |
| Water | Seeds with air pockets or waterproof coats | Coconut, lotus |
| Animals | Hooked or sticky seeds attach to fur; fleshy fruits eaten | Xanthium, burrs, mango |
| Explosion | Pod bursts open, scattering seeds | Balsam, pea, castor |
12. Vegetative propagation
Vegetative propagation is reproduction from vegetative parts of a plant (root, stem, leaf) rather than seeds.
| Plant part | Example | How it propagates |
|---|---|---|
| Stem (tuber) | Potato | Eyes (buds) on tuber grow into new plants |
| Stem (bulb) | Onion, garlic | Fleshy leaves store food, new plant grows |
| Stem (runner) | Strawberry, grass | Horizontal stems that root at nodes |
| Root | Sweet potato, dahlia | Adventitious buds on roots |
| Leaf | Bryophyllum | Leaf margin has buds that grow into new plants |
13. Worked examples
Example 1: Why do flowers have bright colours and scent?
Bright colours and scent attract insects and birds for pollination. This is an adaptation for cross-pollination.
Example 2: Differentiate between self-pollination and cross-pollination.
Self-pollination: pollen from same flower. Cross-pollination: pollen from a different plant. Cross-pollination produces more genetic diversity.
Example 3: Why is seed dispersal important?
It prevents overcrowding, reduces competition for water/nutrients/sunlight, and helps plants spread to new areas.
14. Common mistakes and how to fix them
| Mistake | Fix |
|---|---|
| Thinking all plants reproduce only by seeds | Many plants reproduce asexually (budding, spores, vegetative) |
| Confusing pollination with fertilisation | Pollination is pollen transfer; fertilisation is gamete fusion |
| Believing fruits develop from all flower parts | Fruits develop from the ovary only |
| Saying seeds are only dispersed by wind | Many seeds are dispersed by animals, water, or explosion |
| Calling vegetative propagation a type of sexual reproduction | Vegetative propagation is ASEXUAL (no seeds, no gametes) |
15. CBSE exam focus
| Question type | Marks | Frequency |
|---|---|---|
| Asexual reproduction methods | 2-3 marks | 1 question |
| Parts of a flower (diagram) | 3 marks | 1 question |
| Pollination and its types | 2-3 marks | 1 question |
| Fertilisation process | 2 marks | 1 question |
| Seed dispersal methods | 2 marks | 1 question |
16. Self-test
- Name three methods of asexual reproduction in plants with examples.
- Draw and label the parts of a flower.
- Differentiate between self-pollination and cross-pollination.
- What is fertilisation? What happens after fertilisation in a flower?
- List four methods of seed dispersal with one example each.
- How does a potato plant reproduce?
17. Answer key
- Budding (yeast), fragmentation (Spirogyra), spore formation (bread mould).
- Diagram: sepals, petals, stamens (anther + filament), pistil (stigma + style + ovary).
- Self: pollen from same flower. Cross: pollen from different plant (more diversity).
- Fertilisation is fusion of male and female gametes. After fertilisation: ovule becomes seed, ovary becomes fruit.
- Wind (maple), water (coconut), animals (xanthium), explosion (balsam).
- Potatoes reproduce through vegetative propagation. The potato tuber has buds (eyes) that grow into new plants.
18. Quick revision
- Asexual: one parent, clones (budding, fragmentation, spores, vegetative).
- Sexual: two parents, genetic variation (flowers, pollination, fertilisation).
- Flower parts: sepals (protection), petals (attraction), stamens (male), pistil (female).
- Pollination: transfer of pollen to stigma.
- Fertilisation: male + female gametes fuse in ovary.
- Seed and fruit develop after fertilisation.
- Seed dispersal: wind, water, animals, explosion.
- Vegetative propagation: from stem, root, or leaf.
