REPRODUCTION IN PLANTS

 NOTES

Different organisms reproduce in a different way. In plants, there are two different methods of reproduction:

1. Asexual reproduction
2. Sexual reproduction

The term ‘sexual’ means involving the fusion of sex cells or gametes while ‘asexual’ means without involving the fusion of gametes.

Asexual Reproduction
The process in which only one parent is involved in the production of new individuals of the same kind is called asexual reproduction. In plants, asexual reproduction results in the formation of offsprings or new plants without seeds or spores.
Asexual reproduction in plants occurs through the following methods:

1. Vegetative propagation
2. Budding
3. Fragmentation
4. Spore formation

Types of Flower
On the basis of the type of reproductive organs present in a flower, the flowers are of following types:
(i) Unisexual flower: The flower which contains only one reproductive organ (i.e. either male or female) are called unisexual flowers. These are also called as an incomplete flower, e.g. papaya, watermelon, corn, cucumber, etc.

(ii) Bisexual flower: The flower that contains both reproductive parts (i.e. male and female) in a single flower are called a bisexual flower. These are also termed as hermaphrodites or complete flower, e.g. rose, mustard, Hibiscus, etc.

Function of a Flower
The function of a flower is to make male and female gametes and also to ensure that fertilisation would take place for the seed formation. During sexual reproduction male and female gametes fuse to form the zygote.

Pollination
The transfer of pollen grains from the anther of a stamen to the stigma of a pistil is called pollination. Pollination takes place in two different ways:
(i) Self-pollination: When the pollen grain from the anther of one flower reaches to the stigma of the same ‘ flower, it is called self-pollination. Self-pollination generally occurs in a bisexual flower.

(ii) Cross-pollination: When the pollen grains from the anther of a flower or of a plant are transferred to the stigma of a flower of the same plant or that of a different plant of the same kind the process is called cross-pollination. This transfer to another plant is mediated by insects, wind, water, animals, birds, etc.

Agents of Pollination
The process of pollination is carried out by some external agencies like wind, water, insects, birds, etc. These are called agents of pollination.

Fertilisation
The process in which the male gamete fuses with the female gamete to form a new cell (called zygote) is called fertilisation.

When the pollens are deposited on the stigma of the pistol, it begins to germinate. After some time, a long pollen tube is developed from the pollen grain which passes through the style towards the female gametes in the ovary. The male gametes move down the pollen tube and the tube enters the ovule present inside the ovary.

The tip of pollen tube bursts and the male gamete comes out of the pollen tube. Inside the ovary, the male gametes fuse with the female gametes present in the ovule to form a fertilised egg cell which is called zygote.
The zygote develops into an embryo which is a part of a seed that develops into a new plant.

Fruit and Seed Formation
After the fertilisation, the ovary grows into the fruit and the ovule develops into the seeds

Seed Dispersal
Seeds are developed from the ovule. Seeds contain an embryo enclosed in a protective seed coat. Plants produce a large number of seeds. When these seeds fall down, they start growing. If a large number of seeds falls on the same place, they will not get enough space for water and light, and will not develop into a healthy plant. Thus, the seeds are moved away by some external agencies to far off places.

The process by which the seeds are scattered to different places (far and wide from their parents) is called dispersal. The seeds and fruits are dispersed away through various agencies like wind, water, birds and some animals. Sometime seed dispersal takes place naturally by the explosion or bursting of fruits.

Exercise Questions
1. Fill in the blanks:
(a) Production of new individuals from the vegetative part of parent is called_____________.
(b) A flower may have either male or female reproductive parts. Such a flower is called_____________.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________.
(d) The fusion of male and female gametes is termed as _____________.
(e) Seed dispersal takes place by means of _____________, _____________ and _____________.
Solution:
(a) Production of new individuals from the vegetative part of parent is called vegetative propogation.
(b) A flower may have either male or female reproductive parts. Such a flower is called unisexual.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as Pollination.
(d) The fusion of male and female gametes is termed as fertilisation.
(e) Seed dispersal takes place by means of wind, water and animals.
2. Describe the different methods of asexual reproduction. Give examples.
Solution:
Asexual modes of reproduction are as follows
Vegetative propagation:
A plant can produce new plants from vegetative parts of the plant like roots, stems.
Budding:
It involves the formation of a new individual from a bulb-like projection called a bud.
Fragmentation:
New organisms are formed from the fragments of the parent body.
Spore formation:
Plants reproduce by the formation of spores.
3. Explain what you understand by sexual reproduction.
Solution:
Sexual reproduction is a method where male and female gametes fuse to form a new individual. In plants, stamens and pistils are male and female reproductive organs which bear the anthers and ovary respectively.
4. State the main difference between asexual and sexual reproduction.
Solution:

Asexual reproduction	Sexual reproduction
It requires only one parents	Requires a male and female parent
Daughter cells formed are identical to parents and to each other.	Newly formed offsprings show variations in comparision to the parents.
Special reproductive organs are not required	Special reproductive organs are required
Ex: Yeast, rose, jasmine	Ex: Insects, animals

5. Sketch the reproductive parts of a flower.
Solution:

6. Explain the difference between self-pollination and cross-pollination.
Solution:

Self-pollination	Cross-pollination
It involves the transfer of pollen from the stamen to the pistil of the same flower.	It involves the transfer of pollen from the stamen of one flower to the pistil of another flower.
Self-pollination occurs only in bi-sexual flowers	It occurs in both unisexual and bisexual flowers

7. How does the process of fertilisation take place in flowers?
Solution:
The process of fusion of male and female gametes (to form a zygote) is called fertilisation. The zygote develops into an embryo and embryo undergoes mitotic cell division to form seeds.
8. Describe the various ways by which seeds are dispersed.
Solution:
Seeds and fruits of plants are carried away by wind, water and animals. Winged seeds such as those of drumstick and maple, light seeds of grasses or hairy seeds of aak (Madar) and hairy fruit of sunflower, get blown off with the wind to faraway places. Some seeds are dispersed by water. These fruits or seeds usually develop floating ability in the form of spongy or fibrous outer coat as in coconut. Some seeds are dispersed by animals, especially spiny seeds with hooks which get attached to the bodies of animals and are carried to distant places. Examples are Xanthium and Urena. Some seeds are dispersed when the fruits burst with sudden jerks. The seeds are scattered far from the parent plant. This happens in the case of castor and balsam.
9. Match items in Column I with those in Column II: Column I Column II

Column-I	Column-II
(a) Bud	(i) Maple
(b) Eyes	(ii) Spirogyra
(c) Fragmentation	(iii) Yeast
(d) Wings	(iv) Bread mould
(e) Spores	(v) Potato
	(vi) Rose

Solution:

Column-I	Column-II
(a) Bud	(iii) Yeast
(b) Eyes	(v) Potato
(c) Fragmentation	(ii) Spirogyra
(d) Wings	(i) Maple
(e) Spores	(iv) Bread mould

10. Tick the correct answer:
(a) The reproductive part of a plant is the
(i) leaf (ii) stem (iii) root (iv) flower
(b) The process of fusion of the male and the female gametes is called
(i) fertilisation (ii) pollination (iii) reproduction (iv) seed formation
(c) Mature ovary forms the
(i) seed (ii) stamen (iii) pistil (iv) fruit
(d) A spore-producing organism is
(i) rose (ii) bread mould (iii) potato (iv) ginger
(e) Bryophyllum can reproduce by its
(i) stem (ii) leaves (iii) roots (iv) flower
Solution:
a) (iv) flower
b) (i) fertilization
c) (iv) fruit
d) (ii) bread mould
e) (ii) leaves