Class 12 VBQs Biology Ecosystem

VBQs For Class 12

Short Answer Type Questions

Question. Name the two type of nutrient cycles existing in nature. Where are their reservoirs present ? State the functions of the reservoirs.
Answer :
The nutrients are never lost from an ecosystem but are recycled time to time and again indefinitely.
Nutrient cycles are of two types :
(i) Gaseous cycles :
The reservoir for gaseous cycles exists in the atmosphere e.g. carbon cycle, nitrogen cycle.
(ii) Sedimentary cycles : The reservoir for sedimentary cycles exists in the earth’s crust e.g phosphorus cycle, sulphur cycle.
The function of the reservoir is to meet with the deficit, which occurs due to imbalance in the rate of influx and efflux. 

Question. State the function of a reservoir in a nutrient cycle.
Explain the simplified model of carbon cycle in nature. 
Answer : Function :
To meet the deficit which occurs due to imbalance in the rate of influx and efflux. 
Carbon cycle :

Class 12 VBQs Biology Ecosystem

Detailed Answer :
Function of reservoir : To make up for the imbalance caused (deficit) due to loss of balance in the efflux and influx of minerals. 
Carbon Cycle : The carbon cycle is a gaseous cycle with its source and sink as the atmosphere and the oceans.
The carbon is present in atmosphere as carbon dioxide which is released by :
(i) Respiration by plants, animals and other living beings.
(ii) Burning of fossil fuels.
The fixation of carbon dioxide is carried out by plants (photosynthesis) so deforestation hampers cycle.
Carbon is also present in nature as calcareous sediments, on oceans (usually) and land (nutrients). 

Question. (i) Healthy ecosystems are the base of wide range of (ecosystem) services. Justify.
(ii) Explain the difference and the similarities between hydrarch and xerarch successions of plants.
Answer :
(i) Healthy ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services. The products of ecosystem processes are named as ecosystem services. For examples, healthy forest ecosystem purifies air and water, minimize droughts and floods, cycle nutrients, generates fertile soils, provides wildlife habitat, maintains biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values. Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a healthy price tag.
(ii) Based on the nature of the habitat – whether it is water (or very wet areas) or it is on very dry areas – succession of plants is called hydrarch or xerarch, respectively.
Differences : Hydrarch succession takes placein wetter areas and the successional series progress from hydric to mesic conditions. Asagainst this, xerarch succession takes place indry areas and the series progress from xeric tomesic conditions.
Similarity : Both hydrarch and xerarch successions lead to medium water conditions (mesic), neither too dry (xeric) nor too wet (hydric). 

Long Answer Type Questions

Question. (i) Name the specific cellular components
where phosphorus is in abundance in living organisms.
(ii) Name the natural reservoir of phosphorus.
(iii) Explain the phosphorus cycle.
Answer :
(i) Phosphorus in living systems occur in biological membranes / nucleic acids / cellular energy transfer system / bones, teeth / in animal shells.
(ii) The natural reservoir of phosphorus is rock which contains it in the form of phosphates. 
(iii) Phosphorus cycle : The phosphates dissolved in soil solution are absorbed by the roots of higher plants. The dead organic remains of animals and plants are decomposed by microorganism like bacteria to release phosphorus again in the soil from where it is again absorbed by plants.
For diagram:

Class 12 VBQs Biology Ecosystem