Download Std. VII

Std. VII
Science – Reproduction in Plants-2014
Answer the following:
Q.1 What is the difference between asexual and sexual reproduction?
Asexual Reproduction
Sexual Reproduction
Reproduction takes place without involvement Reproduction takes place with the
Of seeds or spores.
involvement of seeds or spores.
The organism reproduces on its own without
the help of other organism.
A male and female are needed to give rise to
a new individual.
There is only a single parent.
There are two parents.
Q.2 State the difference between unisexual and bisexual flower.
Unisexual flower
Bisexual flower
Flower which has either male or female sex
organ is called unisexual flower.
Flower with both male and female sex organs is
called bisexual flower.
Ex. : Papaya and mulberry plant
Ex. : China rose, sweet pea and mustard
Q.3 Explain the methods of asexual reproduction.
The methods of asexual reproduction are as follows:
 Spore formation
 Fragmentation
 Budding
 Vegetative reproduction (Natural and artificial)
 Tissue culture
 Spore formation is seen in plants like ferns. They have special leaves that bear spore-bearing
structures called sori. The spores are tiny, single-celled asexual reproductive units. They are
surrounded by a tough coat for protection. When these spores mature, the sori burst and release
1
them into the air. Whenever the spores come in contact with suitable environment, they germinate
to give rise to young plants. Ex.: Bread mould
Fern leaf
Bread Mould
Fragmentation:
Fragmentation is seen in Spirogyra. A green algae Spirogyra reproduces by breaking its filamentous body
into two or more parts after a certain period of growth. Each fragment then grows into a new plant. This
form of asexual reproduction is called fragmentation.
Spirogyra
Budding:
In some unicellular organisms like yeast, a small bud-like projection starts growing from the body.
Slowly it grows in size till a complete cell similar to the parent cell is formed which gets detached from
the parent body. In this way, a chain of these buds may be formed giving rise to a number of new
individuals. This process of multiplying with the formation of buds is called budding.
Yeast Budding
2
Vegetative reproduction:
When a new plant is produced from the vegetative parts of a plant such as roots, stem and leaves, it is
called as vegetative reproduction.
It is of two types.
 Natural vegetative reproduction.
 Artificial vegetative reproduction.
Natural vegetative reproduction:
Vegetative part
By Roots
Examples
Sweet Potato, Asparagus and Dahlia
Description
These roots have buds on them.
When these swollen roots are
planted in the soil, they grow into
new plants.
Bryophyllum
By leaves
A leaf can reproduce by growing
some plantlets from the notches
at the end of the leaf margins.
These plantlets fall on the soil
and grow into new plants.
3
By Stem
Potato tuber
Tuber :
Potato tuber has buds or eyes that
grow into a new plant.
Onion bulb
Bulbs :
Bulbs consist of thick, succulent
leaves. These bulbs produce new
bulb with help of buds.
E.g. onion.
Amorphophallus
Corms :
In plants like Colocasia,
reproduction takes place with the
help of swollen stems called
corms.eg. Amorphophallus
Ginger
Rhizomes :
Rhizomes are stems which grow
horizontally under the ground. It
also has scales, leaves and buds
which reproduce. E.g. ginger
Strawberry
Runner:
Runners are also horizontal stems
growing from the parent plant,
but they grow above ground.
Eg. Strawberry
4
Artificial vegetative reproduction:
The process of growing plants through artificial methods by farmers is known as artificial vegetative
reproduction.
Advantages: To grow plants with desirable characters
a) Cutting: In plants which have nodes and internodes, the stem is obliquely cut and planted in the
soil. This stem then grows into a new plant.
b) Grafting :
This method is used to get the combined features of two plants, the stem of a healthy plant is cut
(scion) and inserted over the cut stem of another plant. (Stock) which is rooted in the soil and
then both of them are tied together at the joint. After a few days, the plant starts giving out new
branches and shows combined features of both the plants.
c) Layering: In this method, the branch of a plant is bent down to touch the ground which is then
covered with soil. After some time, roots start growing from the covered part which is then
separated from the original plant. Ex. : jasmine, climbing rose
Tissue culture: It is a method of propagating plants under sterile conditions, where exact copies
of plants with desired qualities are produced.
5
Q.4 Describe a well-labelled diagram of a typical flower and explain its parts.
A flower has male and female gametes in it, thus flowering plants show sexual mode of
reproduction.
A flower consists of four whorls (parts).
Sepals : Sepals form the outermost whorl of the flower. They are green in colour.
Petals : Petals are brightly coloured and they form second whorl of the flower.
Stamen : It is the third whorl of the flower which has male sex organ.
The stamen consists of a filament and an anther. The anther has yellow coloured powdery
substance known as pollen grains. A pollen grain contatins a male gamete.
Pistil : It forms the innermost whorl of the flower and it has the female sex organ.
The pistil has three parts- ovary, style and stigma. One or more ovules are present inside an
ovary. These ovules contain egg cell or female gamete.
Q.5 Explain ‘Bisexual flower’ and ‘Unisexual flower’.
Flowers that have both sex organs are called Bisexual flowers.
As they have all parts of the flower, they are also called complete flowers.
Ex. : China rose, sweet pea, mustard
Flowers that have either male or female sex organ are called unisexual flowers.
As these flowers lack one of the sex organs, they are also called incomplete flowers.
Ex.: Papaya, Mulberry plants
Q.6 What is fertilization?
When male gamete fuses with a female gamete, a single celled structure called zygote is
formed, this process is known as fertilization.
6
Q.7 State the advantages of Vegetative Propagation.
a)
b)
c)
d)
Plants that do not produce seeds can be grown by this method.
Vegetative plants grow faster than the ones produced by seeds.
This method is helpful for farmers as they get the exact copies of the required plant.
These plants need less attention.
******************
7