Class 7 Science
Reproduction
The process by which a living being produces its offspring is called reproduction.
Types of Reproduction:
Asexual Reproduction:
When a single parent is involved in the process, it is called asexual reproduction. Following means of asexual reproduction are used by plants:
(a) Budding: This method is used by unicellular plants; like yeast. Yeast is a fungus and fungi are also known as non-green plants. The yeast cell produces a bud which gets its own nucleus. The bud develops to certain size and detaches from the mother cell to produce the new yeast.
(b)Fragmentation: In some simple plants, the plant body is divided into smaller fragments. Each fragment then develops into a new plant. Example: Spirogyra.
(c) Spore Formation: Special spore-bearing organs are present in some plants; especially in fungi and algae. These are called sporangiophores. The sporangiophore bears spores. The spores germinate to develop a new plant.
(d) Vegetative Propagation: When a new plant is developed by a vegetative part; such as root, stem or leaf; it is known as vegetative propagation. For example: when the tuber of potato is cut into several pieces and each piece bears an ‘eye’; each piece produces a new plant. The stems of moneyplant, rose, mango, etc. can produce new plants when they are inserted in soil. The leaf of bryophyllum produces new plants through its notches.
Review Questions:
Give an example of an organism which reproduces by budding.
Answer: Yeast
How many parents are involved in asexual reproduction?
Answer: Only one
Sexual Reproduction:
When two parents are involved in the process, it is called sexual reproduction. Two gametes, viz. male and female gametes, are formed. The fusion of male and female gametes is called fertilization. Zygote is formed after fertilization. The zygote develops into an embryo and finally into a new individual.
Flower: Flower is a special organ of flowering plants (angiosperms) which works as the reproductive system. A flower is composed of four distinct whorls.
- Calyx: The outermost whorl is called calyx. It is composed of green leaf-like structures; called sepals.
- Corolla: The second whorl is called corolla. It is composed of colourful structures; called petals. Petals are colourful so that insects and other animals can be attracted towards them. This is necessary for pollination.
- Androecium: The third whorl is called androecium. It is composed of stamens. Stamen has two main parts. The tube-like portion is called filament. The capsule like structure at the top is called anther. The anther produces pollen grains; which are the male gametes.
- Gynoecium: The whorl at the center is called gynoecium. It has a swollen base; called ovary and a tube-like structure; called style. The top of the tube is somewhat flattened and is called stigma. Ovary produces the eggs or female gametes.
Review Questions
What is the benefit of colourful petals for plants?
Answer: Colourful petals attract insects, birds and other animals. It helps in cross pollination.
What is the name of the male gamete in a flowering plant?
Answer: Pollen grain