Class 7 Science Chapter 8 Notes Reproduction in Plants
→ A sexual reproduction : It is the type of reproduction in which new individuals are formed without the fusion of male and female gametes. Examples : Layering, cutting etc.
→ Budding : It is a form of asexual reproduction in which you need a new organism develops from an outgrowth or bud due to cell division at one particular site.
→ Embryo : The zygote formed after fertilisation divides many times to form a multicellular structure called an embryo inside the seed. Embryo germinates to form a plant.
→ Fertilisation : The process of fusion of male and female gametes to form a zygote is called fertilisation.
→ Fragmentation : A type of asexual reproduction process, in which an organism breaks up into two or more fragments or pieces that can grow into new individuals is called fragmentation.
→ Gametes : The male and female reproductive cells are called gametes.
→ Hypha : Any of the thread – like filamentous structure in fungus is called hypha.
→ Ovule : It is a structure inside the ovary which contain female gamete inside it.
→ Pollen grain : It is a male productive cell which produce male gametes.
→ Pollen tube : It is a tubular outgrowth that forms from the intine (the inner layer of pollen), when the germpore of exine degenerates.
→ Pollination : The transfer of pollen grains from the anther of a stamen to the stigma of a pistil is called pollination.
→ Reproduction : The process of producing a new organism from the existing organism (or the parent) of the same species is called reproduction.
→ Seed dispersal : The transport of seeds to different places is called seed dispersal.
→ Sexual reproduction : It is the type of reproduction in which new individuals are formed due to the fusion of male and female gametes.
→ Spore : The spore is an asexual reproductive body which is covered , by a hard protective coat to resist unfavourable conditions, such as high temperature and low humidity.
→ Sporangium : It is an enclosure in which spores are formed.
→ Vegetative propagation : When new plants are formed from vegetative parts i.e; the roots, stem, leaves and buds of the plants, it is known as vegetative propagation.
→ Zygote : In sexual reproduction, the cell form from the fusion of male and female gametes is called a zygote.
→ Reproduction helps a species to reproduce its offspring and therefore, continue its species.
→ Offsprings produced by asexual reproduction are genetically identical to their parents.
→ In sexual reproduction, offsprings have a mixture of genes inherited from both the parents.
→ In a sexual reproduction, offsprings are genetically identical to the parent. A population of genetically identical individuals is called clone.
→ Plants can reproduce both asexually and sexually.
→ In strawberry plants and grasses, vegetative propagation or reproduction takes place through side shoots which develop from the main plant. Side shoots have buds that grow into new plants.
→ Corms are short and swollen stems in gladiolus plants, which store food and can separate from each other to form new plants.
→ Runner arises as an axillary bud,that creeps horizontally away from the mother plant, grows out roots and develops into a new plant.
→ Artificial propagation: Vegetative reproduction of plants by artificial methods.
→ Grafting : It is an artificial method of vegetative propagation where stem with bud of one plant is placed over the cut stem of another plant and tied together.
- Scion is the stem with bud of a plant cut for grafting.
- Stock is the cut stem with roots on which a scion is tied during grafting. It supplies the essential nutrients to the scion.
- Grafting helps to develop new varieties of plants by combining the features of both the plants from which scion and stocks are collected. For example: Disease resistant variety may be combined with a high-yielding variety. New varieties of mangoes have been developed by this method. Rose is also grown by this method.
→ Layering : In this method, young branch of a plant is bend towards the ground and covered by moist soil. After some time roots develop from the covered part. When roots arise from the branch, it is cut and made to grow into a new plant.
- Plants such its jasmine and Bougainvillea are grown by this method.
→ Meristematic tissue : A specific tissue found in plants which contain cells that can divide. Growth occurs only at places containing such a tissue.
→ Tissue culture is a method of artificial propagation where a piece of tissue (called explant) is cut from the growing tip of a plant and kept in a nutrient medium containing hormones that make the cells divide to form a group of cells. This unorganised cell mass is called callus.
When roots develop, the callus is transferred to a new medium containing hormones. The cells of callus in this nutrient medium divide and differentiate into roots and shoot and form a new plantlet. The plantlets so formed can now be grown in pots filled with soil. This method of growing plants is also referred to micropropagation.
- Plants like Chrysanthemum, orchids, Asparagus, etc., are grown by this method.
→ Flowers are called reproductive pdrts of sexually reproducing plants.
→ Bisexual flowers are also called complete flowers. They are hermaphrodites. Examples: Hibiscus
→ Unisexual flowers are also called incomplete flowers. Example : Watermelon
→ Insects are attracted by the colour and scent of flowers and help during cross-pollination.
→ Nectar is a sweet liquid present in flowers. Pollen grains stick to the body of insects when they sit on the flowers for collecting nectar.
→ Stigma of a flower produces a sugar containing liquid which is specific to its pollen grains.
- When pollen falls into the stigma, a sugary liquid stimulates the germination of pollen tube from the pollen grain.
- Pollen tube containing the male gamete, grows until it reaches the ovules.
- After reaching the ovule, the tip of the tube bursts, releasing the male gamete. The male gamete fuses with the fenrale gamete present in the ovule to form zygote.
- After fertilisation, only the ovaiy remains and all other parts of the flower i.e., petals, sepals, stamens, fall off. Style and stigma also fall off.
→ Ovules contain nutrients that help the zygote to grow and develop into an embryo.
→ Ovules grow into seeds that encloses a baby plant called embryo. The embryo contains one or two cotyledons with stored food. They are covered by hard protective seed coat.
→ Ovary of a flower develops and becomes a fruit.
→ Inside tire seed, embryo remains in a renting stage and can grow only under favourable conditions such as presence of moisture and oxygen. Seeds also need warmth for growth.
→ Under favourable conditions, seeds begin to grow. This early growth of seeds under favourable conditions is called germination.
→ When a seed germinates, the seed coat splits, a tiny root grows downward and a shoot grows upwards. This produces a seedling of the plant.
- During seed germination, the enzymes stored in the seeds become functioning as they receive water. The soluble enzyme, thus, act on the embryo to grow into a small plantlet.
→ Wind, water and insect pollination are agents for cross-pollination.