Page 120 - Science Class 07

plant takes form. This plant is again shi ed to a Sexual Reproduc on In Plants
new jelly and new shoots begin growing on it.
Chrysanthemums and orchids are examples.
1. Why reproduc on is important?
2. Differen ate between binary fission and
mul ple fission.
3. How do yeasts reproduce?
4. What do you mean by vegeta ve
reproduc on by stems?
5. What is gra ing?
6. How do we carry on ssues culture?
SEXUAL REPRODUCTION
Sexual reproduc on is a natural way of
reproduc on in humans, animals and the
majority of plants also choose to reproduce
sexually. This type of reproduc on is more
complex and lengthy as compared to asexual
reproduc on. Moreover, reproducing sexually
gives the benefit of varia on and offsprings are
unique. Sexual reproduc on consists of a set of
events.
In this method, one male cell and one female
cell fuse together to form a third cell. The
male-cell is called sperm while the female-cell
is called ovum or egg and the resultant cell is
called zygote. The process of the fusion of the
male and the female cells is called fer liza on.
A er that, the zygote begins to develop as a
new organism in the female’s womb. In due
course, the female gives birth to the baby from
her body.
But in case of egg-laying animals, the female
lays an egg with a developing zygote in it. In
due course, a baby hatches out of it.
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Common plants reproducing sexually are
flowering plants as they have reproduc ve
organs. Some flowers have both male and
female reproduc ve organs in them.
The male organ in a long slender structure is
called stamen. It has a sack-like upper p called
anther. The tube below it is called filament.
Petal
S gma Anther
Style Filament
Sepal
Ovary Receptacle
Parts of a Flower
The female organ has a round base called ovary
from which a tube, called style, leads upwards
to a fla ened top called s gma. The en re
organ is called carpel. The reproduc ve process
starts when the cells of the anther divide to
become powdery pollen grains (male cells). The
cells of the ovary in the female form the egg.
POLLINATION
The transfer of pollen grains from the anther of
one flower to the s gma of the same or
another flower is known as pollina on. It can
be caused by insects, birds, wind, water and
animals including man. These are together
called as pollina ng agents.
They carry male cells (gamete) to the female
egg (s gma). The s gma produces a liquid with
sugar in it. It lets the male cells move down the
tube called style to reach the ovary which has
ovules in it. These ovules have female cells in
them. Thus, the fusion of the male and female
Science-7