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Ecosystem

Question
CBSEENBI12002234
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Which one of the following processes during decomposition is correctly described? 

  • Fragmentation - Carried out by organisms such as earthworm

  • Humification - Leads to the accumulation of a dark coloured substance humus, which undergoes microbial action at a very fast rate

  • Catabolism - Last step in the decomposition under fully anaerobic condition

  • Leaching - Water soluble inorganic nutrients rise to the top layers of soil

Solution

A.

Fragmentation - Carried out by organisms such as earthworm

Fragmentation is one of the steps during decomposition, in which detritus is converted into small fragments. Humification leads to a dark coloured amorphous substance called humus that is highly resistent to microbial action and undergoes decomposition at an extremely slow rate. 
Catabolism is the set of metabolic pathways that breaks down metabolic pathways that break down molecules into smaller units to release energy. Leaching refers to the loss of water-soluble plant nutrients from the soil due to rain and irrigation

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Question
CBSEENBI12002462
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Which one of the following statements for pyramid of energy is incorrect, whereas the remaining three are correct?

  • It shows energy content of different trophic level organisms

  • It is inverted in shape

  • It is upright in shape

  • Its base is broad

Solution

B.

It is inverted in shape

Pyramid of energy is graphic representation of energy per unit area sequence-wise in various rising trophic levels with producers at the base and top carnivores at the apex. Pyramid of energy is upright in all the cases. It is also more accurate than other types of ecological pyramids. 

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Question
CBSEENBI12002457
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Which one of the following statements is correct for secondary succession?

  • It occurs on a deforested site

  • It follows primary succession

  • It is similar to primary succession except that it has a relatively fast pace

  • It begins on a bare rock

Solution

A.

It occurs on a deforested site

Secondary succession or subsere is ecological succession that takes place in a recently denuded area which still contains a lot of organic debris, remains and propagules of previously living organisms. It is a more common and caused by baring of an area due to forest fires, deforestation, excessive overgrazing, landslides, earthquakes, repeated floods, etc. Only 50 to 100 years are required for establishment of a grassland over a recently denuded area. Formation of forest requires 100 to 200 years.

Question
CBSEENBI12002635
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Which one of the following types of organisms occupy more than one trophic level in a pond ecosystem?

  • Phytoplankton 

  • Fish

  • Zoonplankton

  • Frog

Solution

B.

Fish

In a pond ecosystem fishes occupy the more than one trophic levels.

Question
CBSEENBI12046987
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Assertion: A network of food chains existing together in an ecosystem is known as a food web.

Reason: An animal like kite cannot be a part of a food web

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.

Solution

C.

If assertion is true but reason is false

The process of transfer of energy from producers through a series of organisms i.e. from primary consumers to secondary consumers to tertiary consumers by process of eating and being eaten constitute a food chain, eg. grassland ecosystem. Food chains can never occur independently in ecosystem but various food chains are inter-connected with each other forming an interlocked system known as food web. In grassland ecosystem food chains may be-

(i)Grass > Rabbit > Hawk/kite

(ii)Grass > Mouse > Snake > Kite/Hawk

(iii)Grass > Grasshopper > Lizard > Kite/Hawk

So, the food web will include kite.

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