18. Ecosystems
Complete solutions to the Exercises. Maharashtra State Board (Balbharati), Grade Eight General Science.
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Exercises
(a) Air, water, minerals, soil are physical factors of an ecosystem.
(b) River, ponds, ocean are aquatic ecosystems.
(c) Man is consumer in an ecosystem.
| Producers | Ecosystem |
|---|---|
| a. Cactus | 4. Desert |
| b. Aquatic plants | 3. Aquatic |
| c. Mangroves | 2. Creek |
| d. Pine | 1. Forest |
(a) Ecosystem
The biotic factors, the abiotic factors and their interactions together make an ecosystem. Examples: Forest, pond, grassland.
Components of an ecosystem.
(b) Biome
A very large ecosystem with the same climate over a vast area is called a biome.
- Land biomes: Grasslands, forests, deserts.
- Aquatic biomes: Fresh water and marine ecosystems.
(c) Food web
Many food chains in an ecosystem are joined to one another. This network of food chains is called a food web. It keeps the ecosystem stable.
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(a) Plants in an ecosystem are called producers.
Green plants make their own food by photosynthesis. All other organisms depend on this food. Hence, plants are called producers.
The textbook prints ‘consumers’ in this question. It is a misprint for ‘producers’.
(b) Large dams destroy ecosystems.
A large dam holds water over a large area. Forests and grasslands go under water. Plants and animals lose their habitat. The flow of the river below the dam also reduces. Hence, large dams destroy ecosystems.
(c) Rhinos were restored in Dudhwa forest.
Rhinos became extinct in Dudhwa forest due to hunting. This disturbed the ecosystem. So rhinos were restored there on 1st April 1984 to balance the ecosystem.
(a) What are the effects of increased population on ecosystems?
- Natural resources are used on a large scale.
- Forests are cut for houses, farms and roads.
- Organisms lose their habitat.
- More waste is produced. It causes pollution.
- Ecosystems change or get destroyed.
(b) How is urbanization responsible for destruction of ecosystems?
Cities grow continuously. Farms, forests, grasslands and wetlands are used for buildings and roads. Plants and animals lose their habitat. Cities also produce sewage and garbage. Hence, ecosystems are destroyed.
(c) What are the reasons for war?
Wars occur due to competition for land, water and minerals. Economic and political reasons also cause wars.
(d) Explain the interactions among the factors of an ecosystem.
Interactions among the factors of an ecosystem.
- Abiotic factors decide which organisms can live in a place.
- Plants use sunlight, water and carbon dioxide to make food.
- Herbivores eat plants. Carnivores eat herbivores.
- Decomposers break down dead bodies. Minerals go back to the soil.
- Plants use these minerals again.
(e) Differentiate between evergreen forests and grasslands.
| Evergreen forests | Grasslands |
|---|---|
| They get heavy rainfall. | They get less rainfall. |
| They have tall and dense trees. | They have grass and a few trees. |
| They have a great variety of organisms. | They have less variety of organisms. |
| They remain green throughout the year. | Grass dries in summer. |
(1) A desert ecosystem
- Abiotic factors: Sand, less water, high temperature.
- Producers: Cactus and thorny plants.
- Consumers: Camel, lizards, snakes, scorpions.
- Organisms here are adapted to save water.
(2) A wetland (fresh water) ecosystem beside a forest
- Abiotic factors: Water, mud, sunlight.
- Producers: Aquatic plants and trees.
- Consumers: Insects, fishes, frogs, birds, crocodile, tiger.
- Decomposers: Bacteria and fungi.