CBSE Class 7 Science Advanced Biology Our Ecosystem MCQs Set 01

Answer: (c) Desert

Explanation:
1. A region that gets very little rain stays dry and arid.
2. Such a dry land with sparse life is the desert ecosystem.
3. Terrestrial is the whole land group, mountains are defined by height, and steppes are dry grass plains that still get enough rain for short grass.

Teacher's Note:
1. Link each ecosystem to its key climate clue: low rain means desert.
2. Do not confuse the general term terrestrial with one specific type.

Answer: (b) Prairies

Explanation:
1. Flat, fertile, grass-dominated land with little soil erosion describes the prairies of North America.
2. Steppes are drier plains, savannah mixes woodland with grass, and tundra is a cold biome.
3. So the answer is Prairies.

Teacher's Note:
1. Remember each grassland with its continent: prairies in North America, pampas in South America, steppes in Eurasia, savannah in Africa.
2. Fertile and flat are the clue words for prairies.

Answer: (a) coastal desert

Explanation:
1. Hot and dry deserts are very hot in summer and cold at night.
2. Semi-arid deserts have long dry summers, and cold deserts have snowy winters.
3. Moderately cold winters with longer warm summers belong to the coastal desert, for example the Atacama in Chile.

Teacher's Note:
1. Make a small table of the four desert types with their climate and an example.
2. Coastal desert plants store water in fleshy leaves or stems.

Answer: (d) tundra

Explanation:
1. A rainforest is warm and a freshwater ecosystem is a water body.
2. Deserts can be hot or cold but are not the coldest biome.
3. The biome with the lowest temperatures, frozen soil and very few plants is the tundra.

Teacher's Note:
1. The word tundra goes with frost, permafrost and short plants.
2. Arctic and alpine are its two types.

Answer: (b) grassland ecosystem

Explanation:
1. Prairies are flat lands covered mainly with grasses.
2. Any ecosystem dominated by grasses is a grassland.
3. So prairies belong to the grassland ecosystem.

Teacher's Note:
1. Prairies, pampas, steppes and savannah are all grasslands.
2. First decide the dominant vegetation, then name the ecosystem.

Answer: (a) desert ecosystem

Explanation:
1. Cactus has thick stems that store water and thorns instead of leaves.
2. These features let it survive where rain is scarce.
3. So it is found in the desert ecosystem.

Teacher's Note:
1. Adaptation clues: thorns, fleshy stems and deep roots point to deserts.
2. Use the plant to guess the habitat.

Answer: (b) food web

Explanation:
1. A single line of who eats whom is a food chain.
2. Many food chains that cross and join each other form a food web.
3. A trophic level is just one step in a chain.

Teacher's Note:
1. In nature, most animals eat more than one kind of food, so webs are more realistic than chains.
2. Draw a small web to remember this.

Answer: (c) Herbivores

Explanation:
1. Producers form the first trophic level.
2. The organisms that eat producers are the primary consumers, which are herbivores.
3. So the second level is occupied by herbivores.

Teacher's Note:
1. Count the levels from the plants upward: producer, herbivore, carnivore, top carnivore.
2. Primary consumer and herbivore mean the same here.

Answer: (d) Afforestation

Explanation:
1. Commercial exploitation, deforestation and urbanization all remove forest cover.
2. Afforestation means creating new forest by planting trees, so it helps forests.
3. So afforestation is not a threat.

Teacher's Note:
1. Read NOT questions carefully; three options are harmful and one is helpful.
2. Afforestation and reforestation are remedies.

Answer: (b) photosynthesis

Explanation:
1. Respiration, decomposition and burning fuels all release CO₂ into the air.
2. Green plants take CO₂ from the air and use it to make food in photosynthesis.
3. Through the food chain this carbon then reaches animals.

Teacher's Note:
1. The carbon cycle has two directions: removal from air (photosynthesis) and return to air (respiration, decay, burning).
2. Check the direction of movement in the question.

Answer: (c) Reforestation

Explanation:
1. Deforestation is cutting trees, so (a) is wrong.
2. Afforestation makes a new forest where none existed, so (b) does not fit.
3. Planting trees again in the place where they were cut is reforestation; (d) is wrong as (a) is wrong.

Teacher's Note:
1. Re means again: re-forestation is planting again.
2. Af means towards: afforestation creates a new forest.