notebook work for reproduction in plants

Reproduction is the process by which an organism gives birth to young ones of

the same species

Different species have different methods of reproduction.

Reproduction in plants:-

There are certain plants that have 2 different sexes --- either on the sameplant/flower -- ( bisexual) or on different plants/flowers--- ( unisexual )

Some plants do not show any sex discriminated in their structure eg. rose.

Plants produce sexually or asexually.

Asexual reproduction in plants :-

It takes place in the following ways :- 1) Spore formation

2) Fragmentation

3) Vegetative propagation

Spore formation :-- Spores are microscopic reproductive units produced in the sac called the

sporangium

Plants that reproduce by spore formation are the common bread mould orRhizopus, mucor, ferns, penicillium from which the antibiotic penicillin isproduced.

Spores float around in the air and under favourable conditions germinate and give rise to a new plant.

In the beginning the bread mould ig white, but later in a few days it turnsblack.

This is because on germination the spore gives rise to a new fungus plant with thread like branches called Hyphae having a spore sac at its tip. It is white.

As the spores mature the sporangium develops a black colour.

Fragmentation :-

It is the process in which the body of a multicellular plant on maturity breaks into many pieces called fragments and each fragment gives rise to a new plant.

eg. spirogyra

It is different from fission where a unicellular organism gives rise to new organisms.

Vegetative propagation :-

It is the process in which any part of the plant body like the stem, root, leaves give rise to a new plant with the help of the buds on them.

eg. root --- Dahlia

Stem ---- potato, ginger

stem ---- money plant, stolons

leaf ---- bryophyllum

Vegetative propagation can happen either naturally as stated above or artificially as given below.

– a. Cutting :---

It is a process in which one part of the stem with a node is cut off and planted in the soil with favourable conditions. It gives rise to a new plant

eg. rose, sugarcane, banana

b. Layering:-

In this process a branch of the plant is pulled down and pushed under

the soil. It is then layered with soil and after a few days it gives rise to a new plant.

This branch can then be cut off from the parent plant.

eg. strawberry, raspberry, bougainvillea, hibiscus, lemon

c. Grafting :---

In this process stems of 2 different plants are cut and joined together and they grow as a single plant.

The stem that is put into the soil should have the roots to hold it in place and provide for the plant.It is called as the stock. It has a slanting cut made in it.

The stem that fits into it is called the scion which also has a slanting such that fits

into the stock. The joint is coated with manure and the tied together firmly. It is

covered with a protective covering in the form of a polythene bag to protect form infection.

The cambium of the 2 parts which contains the meristematic tissue rapidly

produces new cells and the 2 parts fuse and grow as a single plant having the

desired characteristics of both the plants.

eg. Fruitless trees like the guava, papaya, rose plants with different colour combinations.

Advantages of grafting --- 1. Desired characteristics of plants can be grown

2. A young scion can produce fruits faster. A short plant can bear a lot of fruits

3. A variety of seedless fruits can be grown

4. By grafting scions of different plants, a variety of different flowers with different colours can be grown on the same plant.

5. Plants grown by grafting require less attention.

d. Tissue culture :- Also called Micropropagation

In this method a few cells from the growing part of the plant are placed in a medium containing nutrients in the form of jelly. These help in the growth of the cells into a mass called Callus.

It is transferred to another medium which contains hormones that stimulate the growth of roots.

Lastly it is placed in another medium having hormones to stimulate the growth of the shoot.

The small plantlets formed are then transplanted in pots.

eg. orchids, carnations, chrysanthemum

Advantages :--

1. Many plants can be cultivated in a small area

2. They can be cultivated irrespective of the season, climate, and favourable conditions.

3. Take a short time to grow

4. New plants are disease free.

Sexual reproduction in plants :- This requires the

1. 2 sexes to be present in one flower or on the same plant with one flower having one sex and another one having the other, or on 2 different plants each having all flowers of one sex only.

2. It requires special cells from each sex.

3. These cells are called gametes

4. They fuse to form the Zygote

5. The male gametes called the pollen grains are in the anther lobes at the tip of the filament together called as the Androecium

6. The female gametes called the ovules are found in the ovary found at the end of a tube called the style which has the stigma at its tip on which the pollen grains deposit

7. The stigma, style , and the ovary together form the Gynoecium

8. The nucleus of the pollen grain travels down the style and enters the ovary and fuses with the nucleus of the ovule and fertilization is said to have taken place, which results in the formation of the zygote

9. After fertilsation the ovary turns into a fruit and the ovules develop into the seeds from which new plants grow

10. The carpel is the gynoecium.stigma of the same or different flower

define the following terms

1. Pollination is the process of the deposition of the pollen grains on the

2. Fertilisation is the process in which the nuclei of the male and femalegametes fuse.

3. Germination is the process by which a seed grows into a new plant