Science: Class 7 — Chapter 8: Reproduction in Plants

8.1 Modes of Reproduction

The production of new individuals from their parents is known as reproduction. Plants have two main modes of reproduction:

A type of asexual reproduction where new plants are produced from vegetative parts: roots, stems, leaves, and buds.
Node: The part of a stem or branch where a leaf arises. Stem cuttings (e.g., rose, champa) can grow into new plants when buried in soil.
Vegetative buds: Buds in the axil (point of attachment of leaf at the node) that develop into shoots.
Eyes: Scars on a potato containing buds that can sprout into new plants.
Other examples: Ginger and turmeric grow from underground stems; Bryophyllum reproduces via buds on leaf margins; sweet potato and dahlia reproduce via roots; cacti reproduce when detached parts fall on soil.
Advantages: Takes less time to grow, bears flowers and fruits earlier, and produces exact genetic copies (clones) of the parent plant.

Budding: Observed in yeast (single-celled organism). A small bulb-like projection called a bud grows from the parent cell, matures, detaches, and forms a new cell. Can form chains of buds rapidly.
Fragmentation: Observed in algae like Spirogyra. The organism breaks into two or more fragments, each growing into a new individual.
Spore formation: Observed in fungi (bread mould), mosses, and ferns. Spores are asexual bodies covered by a hard protective coat to withstand unfavorable conditions (high temperature, low humidity). They germinate under favorable conditions.

8.2 Sexual Reproduction

Sexual reproduction involves the fusion of male and female gametes. Flowers are the reproductive parts of a plant.

Stamens: The male reproductive parts. Consist of an anther (which produces pollen grains containing male gametes) and a filament.
Pistil: The female reproductive part. Consists of a stigma, style, and ovary. The ovary contains ovules, where the female gamete (egg) is formed.
Unisexual flowers: Contain either only pistil or only stamens (e.g., corn, papaya, cucumber).
Bisexual flowers: Contain both stamens and pistil (e.g., mustard, rose, petunia).

The transfer of pollen grains from the anther to the stigma of a flower.
Self-pollination: Pollen lands on the stigma of the same flower or another flower of the same plant.
Cross-pollination: Pollen lands on the stigma of a flower of a different plant of the same kind.
Pollen is carried by agents like wind, water, and insects.

The fusion of male and female gametes to form a cell called a zygote is called fertilisation.
The zygote develops into an embryo.

8.3 Fruits and Seed Formation

After fertilisation, the ovary grows into a fruit (ripened ovary), and other parts of the flower fall off.
The ovules develop into seeds, which contain the embryo enclosed in a protective seed coat.
Fruits can be fleshy and juicy (e.g., mango, orange) or hard (e.g., almonds, walnuts).

8.4 Seed Dispersal

Seed dispersal prevents competition among seedlings for sunlight, water, minerals, and space, and helps plants invade new habitats.

Dispersal by Wind: Winged seeds (drumstick, maple), light seeds (grasses), or hairy seeds/fruits (aak, sunflower).
Dispersal by Water: Spongy or fibrous outer coats that float (e.g., coconut).
Dispersal by Animals: Spiny seeds with hooks that cling to animal bodies (e.g., Xanthium, Urena).
Dispersal by Sudden Jerks: Fruits burst open, scattering seeds far from the parent plant (e.g., castor, balsam).