Page 122 - Science Class 07

v The zygote forms the embryo which is v Seeds of co on, calotropis and dandelion
enclosed in a seed coat. have hair around them to float in air easily.

v The ovary matures into the fruit.

v The size, shape and colour of fruits and
seeds vary enormously and there are
various strategies adopted by plants to
disseminate them.
Seeds
Types of Fer liza on Water
External Fer liza on : When fer liza on takes
Some seeds and fruits are carried to long
place outside the animal’s body, it is external
distances by water before they develop into
fer liza on. Most of the aqua c animals show
new plants.
external fer liza on, e.g., fish and frog. A large
number of eggs need to be fer lized in this For example : The coconut seeds are carried
method because most of the fer lized eggs get away by sea water and are thrown away at
washed away by water or are eaten by other places where they grow into new plants.

predators. A large number of eggs ensures the The lotus fruit has a spongy part that floats
survival of some of the offspring. easily on water.
Internal Fer liza on : When fer liza on takes Animals
place inside the animal’s body, it is internal
Animals are also an important medium for the
fer liza on. Internal fer liza on happens in
dispersal of seeds. For example:
most of the terrestrial animals. Unlike external
v Some seeds possess spines or hooks which
fer liza on, there is no need to produce a large
enable them to s ck to the body of animals
number of eggs in internal fer liza on.
and are carried from one place to another.
DISPERSAL OF SEEDS
Plants make seeds that can grow into new
plants, but if the seeds just fall to the ground
under the parent plant, they might not get
enough sun, water or nutrients from the soil.
Because plants cannot walk around and take
Seeds Having Hooks
their seeds to other places, they have
developed other methods to disperse (move) v Fruits are eaten by animals such as birds
their seeds. The most common methods are and the enclosed seeds may be taken to
wind, water, animals, explosion and fire. distant places before they are passed out in
Wind their excreta without any damage to the
There are certain seeds of plants that have embryo.

wings or tu s of hairs which make their
Explosion of Fruits
movement in air easy.
Fruits of some plants burst when they get
For example:
ripen. This results in sca ering of seeds in
v Seeds of drums ck and maple have wings
adjoining areas. Example of such plants are
that helps them move with air.
balsam, pea, geranium, castor, etc.

122 Science-7