Science STD 7 Chapter 8: Reproduction in Plants - Exercises
1. Fill in the blanks:
- (a) Production of new individuals from the vegetative part of parent is called vegetative propagation.
- (b) A flower may have either male or female reproductive parts. Such a flower is called unisexual.
- (c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as pollination.
- (d) The fusion of male and female gametes is termed as fertilisation.
- (e) Seed dispersal takes place by means of wind, water and animals.
2. Describe the different methods of asexual reproduction. Give examples.
The different methods of asexual reproduction in plants are:
- Vegetative Propagation: New plants are produced from vegetative parts like roots, stems, leaves, and buds. For example, a new rose plant can be grown from a stem cutting, and a potato plant can be grown from the eyes on its stem.
- Budding: A small bulb-like projection, called a bud, grows on the parent cell, detaches, and develops into a new individual. This is common in single-celled organisms like yeast.
- Fragmentation: A filamentous alga breaks up into two or more pieces or fragments. These fragments grow into new individuals. This is how algae like Spirogyra reproduce.
- Spore Formation: Spores are asexual reproductive bodies that can withstand unfavourable conditions. Under favourable conditions, a spore germinates and develops into a new individual. This method is common in fungi, moss, and ferns.
3. Explain what you understand by sexual reproduction.
Sexual reproduction is the process of reproduction that involves the fusion of male and female gametes to form a new individual. In flowering plants, the male gamete is found in the pollen grain, and the female gamete is in the ovule. The fusion of these two gametes forms a zygote, which develops into an embryo. The new plants produced through sexual reproduction have the characteristics of both parents.
4. State the main difference between asexual and sexual reproduction.
| Asexual Reproduction | Sexual Reproduction |
|---|---|
| Involves only a single parent. | Involves two parents (male and female). |
| New plants are produced without seeds. | New plants are obtained from seeds. |
| The new plant is an exact copy of the parent. | The new plant has characteristics of both parents. |
| Examples: Budding, fragmentation, spore formation. | Examples: Plants reproducing through flowers and seeds. |
5. Sketch the reproductive parts of a flower.
A typical flower contains both male and female reproductive parts. The male part is the stamen, consisting of an anther and a filament. The female part is the pistil, which includes the stigma, style, and ovary containing ovules.
[Image of the reproductive parts of a flower]
6. Explain the difference between self-pollination and cross-pollination.
| Self-Pollination | Cross-Pollination |
|---|---|
| The transfer of pollen grains occurs from the anther to the stigma of the same flower or another flower on the same plant. | The transfer of pollen grains occurs from the anther of one flower to the stigma of a flower on a different plant of the same kind. |
| It does not require external agents like wind, water, or animals. | It requires external agents like wind, water, or animals (insects) to carry pollen. |
7. How does the process of fertilisation take place in flowers?
The process of fertilisation begins with pollination, where a pollen grain lands on the stigma of a flower. The pollen grain then germinates and grows a tube, called the pollen tube, which travels down the style to the ovary. The male gamete from the pollen grain fuses with the female gamete (or egg) present in the ovule. This fusion of gametes is called fertilisation, and the resulting cell is a zygote, which then develops into an embryo.
8. Describe the various ways by which seeds are dispersed.
Seeds are dispersed in various ways to prevent overcrowding and competition for resources, helping plants to grow in new habitats. The main methods of seed dispersal are:
- By Wind: Seeds of some plants are light and may have wings or hairy structures that help them to be carried away by the wind. Examples include seeds of drumstick, maple, and aak (Madar).
- By Water: Seeds of plants that grow near water bodies often have floating ability, such as a spongy or fibrous outer coat, which helps them to be carried by water currents. A classic example is the coconut.
- By Animals: Some seeds have hooks or spiny structures that get attached to the bodies of animals and are carried to distant places. Other seeds are dispersed when animals eat fruits and excrete the seeds in a new location. Examples include Xanthium and Urena.
- By Explosion: In some plants, the fruits burst with a sudden jerk, scattering the seeds far from the parent plant. This occurs in plants like castor and balsam.
9. Match items in Column I with those in Column II:
| Column I | Column II |
|---|---|
| (a) Bud | (iii) Yeast |
| (b) Eyes | (v) Potato |
| (c) Fragmentation | (ii) Spirogyra |
| (d) Wings | (i) Maple |
| (e) Spores | (iv) Bread mould |
10. Tick (✓) the correct answer:
- (a) The reproductive part of a plant is the
- leaf
- stem
- root
- flower
- (b) The process of fusion of the male and the female gametes is called
- fertilisation
- pollination
- reproduction
- seed formation
- (c) Mature ovary forms the
- seed
- stamen
- pistil
- fruit
- (d) A spore producing organism is
- rose
- bread mould
- potato
- ginger
- (e) Bryophyllum can reproduce by its
- stem
- leaves
- roots
- flower
Suggested Activities and Projects
1. Make your own cactus garden by collecting pieces cut from different kinds of cacti. Grow the variety in one single flat container or in separate pots.
Outline: This is a hands-on activity to learn about vegetative propagation. You would collect different types of cacti cuttings and plant them in a container. By observing them grow, you would understand that new plants can be grown from the detached parts of the parent plant without the need for seeds.
2. Visit a fruit market and collect as many local fruits as possible. If many fruits are not available, you can collect tomatoes and cucumbers (these are fruits, though we use them as vegetables). Make drawings of the different fruits. Split the fruits and examine the seeds within. Look for any special characteristics in the fruits and their seeds. You can visit a library also to learn about this.
Outline: This activity is about observing the diversity of fruits and seeds. You would collect different fruits, draw them, and then examine their seeds. You would note characteristics like the number of seeds, their size, shape, and any protective outer layers. This helps in understanding that a fruit is a mature ovary that protects the seed within it.
3. Think of ten different fruit-bearing plants. Remember that many vegetables are also fruits of the plants. Discuss with your teacher, parents, farmers, fruit growers and agricultural experts (if available nearby) and find out the manner of their dispersal. Present your data in the form of a table as shown below:
Outline: This project focuses on researching seed dispersal methods. You would list ten plants and, with the help of teachers, parents, and experts, identify how their seeds are dispersed (e.g., by wind, water, animals, or explosion). You would then create a table to present the data, which includes the plant name, the agent of dispersal, and the part that aids in dispersal (e.g., wings, hooks, fibrous coat).
4. Suppose there is one member of a particular kind of organism in a culture dish, which doubles itself in one hour through asexual reproduction. Work out the number of members of that kind of organism which will be present in the culture dish after ten hours. Such a colony of individuals arising from one parent is called a "clone".
Outline: This is a mathematical problem to demonstrate the rapid reproduction rate in asexual reproduction. Since the organism doubles itself every hour, you would calculate the number of organisms after 10 hours as follows: 1 → 2 → 4 → 8 → 16 → 32 → 64 → 128 → 256 → 512 → 1024. After ten hours, there would be 1024 organisms, which is a significant increase from a single parent due to asexual reproduction.