Class 7 Science
Fill in the blanks:
Answer: (a) vegetative propagation, (b) unisexual flower, (c) pollination, (d) fertilization, (e) wind, water, animal
Question 1: Describe the different methods of asexual reproduction. Give examples.
Answer: There are following methods of asexual reproduction:
Question 2: Explain what you understand by sexual reproduction.
Answer: When two parents are involved in reproduction, this method is called sexual reproduction. Formation of male and female gametes is the first step of sexual reproduction. The male and female gametes fuse during fertilization to produce zygote. The zygote subsequently develops into an embryo which further develops into a new individual.
Question 3: State the main difference between asexual and sexual reproduction.
Answer: Some difference between asexual and sexual reproduction are as follows:
A single parent is involved in asexual reproduction, while two parents are involved in sexual reproduction.
Gamete formation is an important part of sexual reproduction, but this does not take place during asexual reproduction.
Question 4: Sketch the reproductive parts of a flower.
Question 5: Explain the difference between self-pollination and cross-pollination.
Answer: Following are the main differences between self pollination and cross pollination:
In self pollination, pollen grains are transferred to the stigma of the same flower, while in cross pollination; pollen grains are transferred to the stigma of different flower.
In self pollination, flowers do not need assistance from external agents, but such assistance is required in case of cross pollination.
Question 6: How does the process of fertilisation take place in flowers?
Answer: Once pollen grain lands on the stigma, it produces a pollen tube. This process is called germination of pollen grain. The pollen tube penetrates the style and reaches the ovary. Male nucleus is transferred through this pollen tube. Finally, fusion of male and female nuclei takes place inside the ovary. This step is called fertilization.
Question 7: Describe the various ways by which seeds are dispersed.
Answer: Following are the various methods of seed dispersal:
Dispersal by Wind: Seeds of some plants are light-weight and some hair-like or wing-like structures are present on them. Such seeds float on air and are thus dispersed by wind. Example: Dandelion, maple, drumstick, etc.
Dispersal by Water: Dispersal by water takes place in some aquatic plants and in some which grow near a water body. Seeds of water lily float and thus dispersed by water. The coconut seed has a tough fibrous covering which has plenty of air inside. This helps the coconut seeds in floating on water.
Dispersal by Animals: Some seeds have spine like structures on them. They get stuck to the fur of animals and thus get spread to different places. Examples: Beggar tick, Xanthium, Urena, etc. Some seeds are swallowed by birds and animals along with fruits. These seeds get dispersed with bird or animal droppings.
Dispersal by Bursting: Some fruits burst open when they mature. The force of bursting is enough to spread the seeds. Examples: Ladyfinger, castor, balsam, etc.
Dispersal by Humans: Human beings also help in dispersal of seeds, especially during farming.
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