Notes For All Chapters Science Class 7
1. Reproduction
- Reproduction is the process by which living organisms produce new individuals of their own kind.
- In plants, reproduction helps in the continuation of the species.
- Flowers are the reproductive parts of plants.
2. Modes of Reproduction in Plants
- Plants reproduce by two main modes:
- Asexual Reproduction
- Sexual Reproduction
3. Asexual Reproduction
- In asexual reproduction, new plants are produced without seeds.
- Only one parent is involved.
- The new plants are exact copies of the parent plant.
3.1 Vegetative Propagation
A type of asexual reproduction.
New plants grow from vegetative parts like:
- Roots
- Stems
- Leaves
- Buds
Examples of Vegetative Propagation
- Stem: Rose (cutting), sugarcane
- Eyes of potato: Buds present in scars called “eyes”
- Rhizome: Ginger, turmeric
- Leaves: Bryophyllum (buds on leaf margins)
- Roots: Sweet potato, dahlia
- Detached plant parts: Cactus
Vegetative Buds
- Found in the axil of leaves.
- Can grow into new shoots and plants.
Advantages of Vegetative Propagation
- Plants grow faster.
- Plants bear flowers and fruits earlier.
- New plants are identical to the parent plant.
3.2 Budding
- Seen in yeast.
- A small outgrowth called a bud forms on the parent cell.
- The bud grows and separates to form a new organism.
- Sometimes buds form a chain.
3.3 Fragmentation
- Seen in algae (Spirogyra).
- The plant body breaks into fragments.
- Each fragment grows into a new plant.
- Happens rapidly when water and nutrients are available.
3.4 Spore Formation
Seen in fungi, mosses, and ferns.
Spores are:
- Very light
- Covered with a hard protective coat
- Spores can survive unfavourable conditions.
- Under favourable conditions, spores germinate into new plants.
4. Sexual Reproduction
- Involves two parents.
- New plants are produced from seeds.
- Involves fusion of male and female gametes.
5. Reproductive Parts of a Flower
5.1 Male Reproductive Part – Stamen
Consists of:
- Anther – produces pollen grains
- Filament – supports the anther
Pollen grains contain male gametes.
5.2 Female Reproductive Part – Pistil
Consists of:
- Stigma – receives pollen
- Style – connects stigma to ovary
- Ovary – contains ovules
Ovules contain female gametes (egg).
6. Types of Flowers
- Unisexual flowers: Have either stamens or pistil
- Examples: Corn, papaya, cucumber
- Bisexual flowers: Have both stamens and pistil
- Examples: Mustard, rose, petunia
7. Pollination
Pollination is the transfer of pollen grains from anther to stigma.
Types of Pollination
1. Self-pollination
Pollen is transferred to the stigma of the same flower or same plant.
2. Cross-pollination
Pollen is transferred to a flower of another plant of the same kind.
Agents of Pollination
- Wind
- Water
- Insects
8. Fertilisation
Fertilisation is the fusion of male and female gametes.
After fertilisation:
- A zygote is formed.
- Zygote develops into an embryo.
9. Fruit and Seed Formation
After fertilisation:
- Ovary develops into a fruit
- Ovules develop into seeds
A seed contains:
- An embryo
- A protective seed coat
Fruits may be:
- Fleshy (mango, orange)
- Hard (almond, walnut)
10. Seed Dispersal
- Seed dispersal is the process by which seeds are scattered away from the parent plant.
- It prevents overcrowding and competition.
Methods of Seed Dispersal
By Wind
- Winged seeds: Drumstick, maple
- Hairy seeds: Madar, sunflower
By Water
Floating fruits/seeds: Coconut
By Animals
Seeds with hooks: Xanthium, Urena
By Explosion
Fruits burst and scatter seeds: Castor, balsam
11. Importance of Seed Dispersal
- Prevents overcrowding
- Reduces competition for resources
- Helps plants spread to new areas
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