Rajasthan Board RBSE Class 8 Science Notes Chapter 6 Reproduction in Plants
Reproduction and its Types:
Reproduction: Every living being which has taken birth on earth, its death is definite whether it is a plant/animal/human being. Hence to continue its existence on earth every living being gives birth to his/her own kind. The process to give birth of own kind is called reproduction. In living being this process goes on from generation to generation, so their existence and continuity remain on earth.
Methods of reproduction in plants are as follows:
1. Vegetative reproduction
2. Asexual reproduction
3. Sexual reproduction
4. Reproduction without fertilization
- Vegetative reproduction-When a new plant grows from a vegetative part of plant rather than seed it is called vegetative reproduction. Seedlings developed from vegetative reproduction have some properties as their parent plant. They are called clones. For example potato, grass, onion, arbi, ginger, chameli etc. In the same manner buds are found in the grooves of Bryophytlum leaf, when these buds fall in the soil, a new plant grows from each bud. In cactus, stem separates from the plant and gives birth to a new plant, while in Dehalia roots gives birth to a new plant.
- Activity: Cut a branch of rose from its inter node. Inter node is that part of the stem from where leaf grows. This 10 -12 cm long branch is called kalam. By cutting it slant, plant inside the soil and water regularly it would grow into a new plant.
- Advantages of vegetative reproduction:
- Through this, plants grow in less time.
- It gives flowers and fruits in less time.
- In this method new plants are obtained from the same parent.
- It gives birth to uniform hereditary plants, which help in keeping the ancestral properties conserved.
- Asexual reproduction: in this the new plant grows from the same parent. In this type of reproduction pairs of chromosomes are not crossed and number of chromosomes remains same. Asexual reproduction takes place in the following methods.
- Budding: Put a pinch of yeast in a beaker containing water, now put a spoon of sugar into it and shake properly. Keep it at warm place. After an hour when a drop of this solution is kept on a slide and seen with a microscope cells of new yeast would be seen. Cell of yeast form a bud, it grows and detach from parent cell and grows into new cell.
- Fragmentation-You might have seen green slippery substance in ponds or stagnant water. This is called algae. They rapidly grow through fragmentation, example: Spirogyra.
- Spore Formation-lf the pieces of bread are kept in moisture. After some time cotton web like fungi are developed. It contains black brown spores. When these spores become free they float in air as they are light in weight spread up to a great distance. Every spore due to adverse conditions like high temperature and moisture forms a hard coat around it. When favorable conditions come it sprouts and develop into new fungi tentacles like mucor and rhizopus. Such reproduction generally occurs in lower organisms like – algae, fungi, mosses, and fern.
- Sexual reproduction – Parts of a flower
- Calyx – outer green leaves like structure.
- Corolla – colored part.
- Stamen – male organ (anther and filament)
- Carpel – female organ (stigma, style and ovary)
- Uni sexual flower: Those flowers in which one of the reproductive organs either male or female is present, example- maize, papaya, cucumber etc.
- Bisexual-Those flowers in which both the organs male and female are present like mustard, rose, pitunia, dhatura etc. In stamen pollen grains are present which they sprout male gametes are developed in them. In ovary of female organ one or more than one eggs (female gamete) are present. Zygote formation takes place in ovule. Pollen grains-Are reached to other places by wind, water, animals and human, it is called dispersal.
By any means of transfer of pollen grains from anther to the stigma of a flower is called pollination.
- Self pollination : When pollens are reached to the stigma of the same flower or other flower of the same plant then it is
- called self pollination, examples – Pea, Tomato etc.
- Cross pollination : When pollens are reached on the flower of other plant of the same species it is called cross pollination, examples – Rose, Poppy etc.
Pollen grains sprout after reaching to stigma of carpel. A pollen tube is developed which reaches to the ovule present inside the ovary through style. Sperm cell present in the pollen tube combined or fuse with the egg cell (ovum) present in the ovary, it is called fertilization. It results in the formation of double zygote which develops into an embryo. After fertilization ovules develop into seeds and ovary into fruit, after the utilization of fruit again seed develop into new plants. This process of plants is called sexual reproduction. In angiosperms zygote is triple zygote.
Development of fruits and seed: After fertilization, ovules develops into seed and ovary into fruit. Seed consists of an embryo, which is responsible for the development of the new plant after sprouting.
Fruits: Mature ovary is called fruit. Its wall develops into fruit wall.
Fruits are mainly of two types-
- Real fruit
- False fruit
Real fruit: if only ovary takes part in the formation of fruit, it is called real fruit, example mango.
False fruit: Some times in place of ovary the other part of flower like thalamus, calyx, etc take part in the fruit formation such fruits are called false fruits; Example: apple, pear (thalamus takes part) in fruit formation. Hence apple and pear are false fruits.
Reproduction without fertilization (apomixis):
When ovary develops into fruit directly without fertilization, then it is called reproduction without fertilization/apomixis. Such fruits do not contains seed in them like – banana, grapes etc.
All fruits can be divided into three categories :
1. Simple fruit
2. Aggregate fruit
3. Composite fruit
- Simple fruit: When ovary of a flower develops into a single fruit like – mango, wheat etc.
- Aggregate fruit: When a multi ovulated ovary of a flower develops into separate fruits but remains in a bunch, it is called aggregate fruit like strawberry.
- Composite fruit: When all flowers of entire inflorescene takes part in a formation of fruit like -mulberry and jack fruit etc.
Every seed produces its own kind of plant and animals also produce their own kind. Such species transfers parental traits from generation to generation. The process by which parental traits are transferred from one generation to next generation is called heredity. First of all Gregor John Mendel experimented heredity on the basis of different properties on pea plant. Due to his great contribution in the field of heredity he is known as the father of heredity or genetics. He used seven characters of pea in pair (opposite characters) carriers of characters are called factors by him, which are named as genes in the present time.
Causes of choosing pea as heredity experiment plant:
- Seven dearly visible opposite characters.
- Short life span or period of pea plant.
Generally self pollination takes place in a pea but cross pollination can be done easily.
Laws of Mendelism:
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment.
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