Reproduction in Plants
Concept: Seeds—Types, Parts and Dispersal
- After fertilisation, the ovary of the flower gets converted into fruit, and the ovules get converted into seeds.
- These seeds are responsible for carrying the process of reproduction ahead.
- Seeds contain tiny baby plants that come out in suitable environmental conditions.
- Seeds can remain dormant for years and protect the baby plant inside.
Parts of a seed:
The different parts of a seed are discussed below—
- Seed coat: It is the outermost protective covering of the seed. The seed coat protects the tiny baby plant inside.
- Hilum: The hilum can be identified by the scar present on the seed. It is the point where the seed is attached to the flower's ovary.
- Micropyle: The tiny opening on the seed from where air and water enter the seed.
- Radicle: The part of the seed that develops into the new plant's root system.
- Plumule: The part of the seed that develops into the new plant's shoot system.
- Cotyledon: The storehouse of seed nourishes the developing baby plant until the root system is established.
Functions of a seed:
- They ensure the continuity of plant species.
- They protect the embryo (baby plant) inside from external harsh environmental conditions.
- They undergo dormancy under unfavourable conditions.
- They ensure the supply of food till the baby plant is mature enough to grow and synthesise food.
Germination of a seed:
- Seeds germinate in the presence of suitable conditions.
- On absorbing adequate water, the seed swells up, leading to the seed coat's bursting.
- It gives rise to a baby plant called seedling.
- The embryo receives nourishment from the cotyledon till the root system is developed.
- The radicle grows into the root system.
- The plumule is phototrophic and grows into the shoot system.
Conditions necessary for the germination of seeds:
- Water: Seeds need a considerable amount of water to swell and open up as most seeds are dry. Water performs the following vital functions—
- Softens the seed coat and increases its permeability.
- Provides dissolved oxygen to the embryo inside.
- Converts insoluble food materials into soluble food materials that the embryo can utilise.
All cereals are monocots.
Examples: Rice, Wheat, Maize.
All pulses and dicots.
Examples: Moong, Gram, Rajma.
Dispersal of seeds:
- Dispersal stands for the scattering of seeds to far-off places.
- It is necessary so that the plant species grow in various places.
- The absence of dispersal may lead to the following situations—
- The plant species would be limited to certain areas only.
- The new plants will grow only near the mother plant, which would lead to overcrowding and competition for food, light, and space.
Seeds dispersed by wind:
- The seeds which are light weighted generally get dispersed by wind.
- The seeds which are dispersed by wind may often get destroyed if the wind is too hard. Hence, to compensate for this loss, the plants that depend on wind for dispersal produce many seeds.
- These seeds may have an additional feather or wing-like structure which helps them float away to distant places.
Examples: Dandelion, Cottonweed, Cattail, Orchid
Seeds dispersed by water:
- Plants that live near or in water are adapted to disperse their seeds through the water.
- Such seeds have a hard covering outside, enabling them to float on water.
Examples: Mangroves, Coconut, Lotus.
Seeds dispersed by animals:
- Birds and animals eat fleshy fruits and disperse the seeds to faraway places through their droppings.
Examples:Watermelon, Lichi, Guava, and Mango.
- Some seeds have hooks on their outer surface, which allow them to stick to the animal fur, and in this way, they are carried to different places.
Examples: Cocklebur, Beggar tick.
Seeds dispersed by explosion:
- The pod-bearing plants are adapted to this method of dispersal.
- The pod of fruits bursts open with force on ripening.
- The explosion mechanism leads to the scattering of seeds in the nearby areas.
Examples: Ladyfinger, Pea.
Dormant stage: A stage when the seed is inactive.
Droppings: Animal or bird waste.
Permeability: The ability to absorb something.
Phototrophic:The capability of a plant to bend towards the direction of light.
Did You Know?
- The seeds of orchids are as fine as dust.
- Dandelion seeds land on the ground like a parachute.
- Ants take the fruit to their colonies and discard the seeds in fertile areas after eating the fleshy part.
- Some fruit-eating fish like Pacus consume fallen fruits and disperse the seeds to flooded areas.
- Alsomitra macrocarpa is the world’s largest gliding seed, with a wingspan of 5.5 inches.