Reproduction in Plants

Binary fission

Rhizopus (Bread Mould)

Bryophyllum

Rose

Gynoecium

Zygote

Sexual reproduction can be defined as the production of offspring due to fusion of male and female sex cells.

Advantages of sexual reproduction in plants

1. The offsprings show variations from the parent plants.
2. They do not lose their vigour after many generations.
3. They show more resistance to diseases as compared to vegetatively reproduced plants.
4. Their seeds are dispersed and hence do not cause overcrowding.

The different types of asexual reproduction in plants are:

1. Binary fission and Multiple fission — Euglena and Chlorella
2. Budding — yeast
3. Fragmentation — Spirogyra
4. Spore formation — Rhizopus
5. Vegetative propagation by natural methods
   1. By underground stem — Potato
   2. By aerial stem — Strawberry
   3. By root — Dahlia
   4. By leaves — Bryophyllum
6. Vegetative propagation by artificial methods
   1. Cutting — Sugarcane
   2. Layering — Rose
   3. Grafting — Mango
   4. Tissue Culture — Orchids

The advantages of vegetative propagation are:

1. Vegetative propagation is faster method of growing plants than growing them from seeds.
2. Plants produced by vegetative propagation bear flowers earlier than those produced from seeds
3. Vegetative propagation is extremely useful for production of seedless plants such as banana, grapes and sugarcane.
4. New plants produced via vegetative propagation are exactly the same as the parent plant and survive even in unfavourable conditions.

Pollination can be either Natural or Artificial.

Natural Pollination
Natural Pollination is of two types —

1. Self pollination — The process of transfer of pollen grains from the anthers to the stigma of the same flower, or another flower of the same plant is called self pollination.
2. Cross pollination — The process of transfer of pollen grains from the anthers of a flower to the stigma of a flower of another plane of the same species is called cross pollination. Depending on the external agents involved, cross pollination is classified as Pollination by insects(entomophily), Pollination by wind(anemophily), pollination by water(hydrophilly) and Pollination by animals.

Artificial Pollination
Artificial pollination is performed by experts to produce new varieties of plants having desired characteristics. In this process two different varieties of a plant are selected and artificially pollinated to get a hybrid variety of that species. This is called hybridization.

Following are the features of a flower pollinated by wind:

1. Most wind-pollinated flowers are small.
2. They have dry and light pollen grains which can be easily carried by wind.
3. Pollen grains are produced in very large quantities so that at least some have a chance to reach the stigma.
4. The style projects out and has a large, feathery stigma so that the pollen flying in the wind can be easily received.

The process of hybridization is used to produce new varieties of plants with desired characteristics. In this process two different varieties of a crop plant with the desired characteristics are selected. After selection of these varieties, cross-breeding is done by artificial pollination to get a variety of plants which has both the desired characteristics from the parent varieties. This is called hybridization. The new variety formed is called a hybrid.

The process of reproduction in unicellular organisms by division of their cell into two daughter cells of roughly equal size is called binary fission.

Short, branched, underground stem which has distinct nodes and internodes bearing buds are called rhizome.

Bryophyllum propagates by vegetative propagation in their leaves. They produce adventitious buds at the margin of their leaves. These buds develop into small plantlets under suitable conditions.

Two disadvantages of vegetative propagation are:

1. All offsprings from the same parent have the same features. So, they are all prone to the same infections, which can result in the destruction of an entire crop.
2. Over a period of time, newer generations of plants produced via vegetative propagation lose their vigour.

The method of growing plants artificially in a test tube under laboratory conditions is known as Tissue culture.

The changes that occur in a flower after fertilization are:

1. The sepals, petals and stamens fall off.
2. The stigma and style wither away.
3. The ovary containing the ovule continues to grow.
4. Fertilized ovule becomes seed and ovary forms fruit.

The reproductive sex cells are known as gametes.

Multiple fission occurs in certain algae such as Chlorella and Chlamydomonas.

Vegetative propagation takes place in plants which do not produce seeds.

Eyes are the organs of vegetative propagation in potato.

Sugarcane and pineapple plants are grown by Cutting method.

In grafting, a stem cutting called Scion from one plant is attached and tied to the rooted stem called Stock of another plant.

Tissue Culture is also called micropropagation.

Calyx (sepal) protects the flower in the bud stage.

The male reproductive part of a flower is called Androecium.

Complete flowers are also called bisexual or hermaphrodite flowers.

The single cell formed after fertilization is called Zygote.

The fruit is ripened ovary that contains one or more seeds.

Water, a suitable temperature and Oxygen are required for seeds to germinate.

1. The pollen grain is deposited on the stigma.
2. The pollen grain begins to grow a pollen tube.
3. The pollen tube grows down through the style to the ovary.
4. The nucleus of pollen tube divides to form male gametes.
5. A male gamete travels down each pollen tube.
6. The fusion of the male gamete with the female gamete occurs inside an ovule.

Multiple Fission — The process of asexual reproduction in which the cell divides repeatedly inside the cyst to produce many daughter cells is called Multiple fission. It is found in unicellular algae such as Chlorella and Chlamydomonas.

Budding — The process of asexual reproduction in which a small bulb-like outgrowth called bud appears on the body of an organism, develops into a new organism and finally detaches from the parent to lead an independent life is called Budding. Budding is seen in yeast (fungus).

Gynoecium — The female part of a flower consisting of stigma, Style and ovary is called gynoecium.

Vegetative propagation — Reproduction in plants wherein a new plant can arise from a vegetative part such as root, stem or leaf without the help of any reproductive organ is called vegetative propagation.

Self pollination — The process of transfer of pollen grains from the anthers to the stigma of the same flower, or another flower of the same plant is called self pollination.

Cross pollination — The process of transfer of pollen grains from the anthers to the stigma of a flower of another plant of the same species is called cross pollination.

Fertilization — The process of fusion of the male gamete with the female gamete is called fertilization.

Germination — The process by which a sleeping or dormant embryo becomes active and grows into a new plant is known as germination.

During unfavourable conditions, some organisms develop a thick protective covering called Cyst around themselves.

The small outgrowth arising from the yeast cell is called a bud

The gynoecium consists of Stigma, Style and Ovary .

Pollination taking place between two flowers present on two separate parents plants is called Cross pollination.

The process by which a dormant embryo becomes active and grows into a new plant is known as Germination.

1. The parts labelled a to e are:
   a → Petal (corolla)
   b → Stigma
   c → Anther
   d → Ovules
   e → Thalamus
2. Anther produce pollen grains.
3. Stigma receives pollen grains for pollination.

The below labelled diagram shows the process of fertilization in plants:

In artificial pollination, two different varieties of a crop plant with the desired characteristics are selected. For example, one variety may be high-yielding (higher-grain producing) and the other variety may be disease resistant. After selection of these varieties, cross-breeding is done by artificial pollination to get a variety of plant which has both the desired characteristics from the parent varieties.

Most insect-pollinated flowers produce nectar and are sweet-smelling to attract insects. Insects such as bees and butterflies visit different flowers for their food (nectar) and in this process pollen grains get stuck to their body. When they visit another flower, the pollen grains get transferred to the stigma of flowers. Thus, to facilitate pollination by insects (entomophily), most flowers produce nectar and are sweet-smelling.

In wind-pollinated flowers, pollen grains are produced in very large quantities so that at least some have a chance to reach the stigma.

binary fission

Reason — Binary fission is the simple division of an organism into two smaller daughter cells of roughly equal size.

rose

Reason — By the method of Grafting, rose plant can be reproduced by its stem. It is one of the Artificial Vegetative Propogation methods.

staminate flower

Reason — Androecium is the male part of the flower. A unisexual flower with only male part is called staminate flower.

complete flowers

Reason — Flowers having all the four whorls i.e., Calyx (sepals), Corolla (petals), Androecium and Gynoecium are called complete flowers.

grafting

Reason — Grafting is an artificial method of vegetative propagation.

flower of another plant of same species

Reason — The process of transfer of pollen grains from the anthers to the stigma of a flower of another plant of the same species is called cross pollination.

style

Reason — When a pollen grain reaches the stigma, it begins to grow a pollen tube that travels down through the style to reach the ovules inside the ovary.

ovules

Reason — A seed is a fertilized and mature ovule.

ovule

Reason — When a pollen grain reaches the stigma, it begins to grow a pollen tube that travels down through the style to reach the ovules inside the ovary. A male gamete or male sex cell travels down each pollen tube and fuses with the egg cell (or a female gamete) inside an ovule.

cotyledons and embryonal axis

Reason — After fertilization, the zygote (fertilized egg) divides and grows into an embryo which has two cotyledons and an embryonal axis.

True

False

Correct Statement — The development of a new plant from the vegetative part of a flowering plant is called asexual reproduction.

True

False

Correct Statement — Cutting and layering are artificial methods of asexual reproduction.

True