Punjab State Board PSEB 12th Class Biology Important Questions Chapter 14 Ecosystem Important Questions and Answers.
PSEB 12th Class Biology Important Questions Chapter 14 Ecosystem
Very Short Answer Type Questions
Question 1.
How is ‘stratification’ represented in a forest ecosystem?
Answer:
Stratification is the vertical distribution of species at different levels. Trees occupy top vertical strata or layer, shrubs the second layer and herbs/grasses occupy the bottom layers.
Question 2.
Write a difference between net primary productivity and gross primary productivity.
Answer:
Gross primary productivity (GPP) is the rate of production of organic matter during photosynthesis. Net primary productivity (NPP) is the available biomass for the consumption by heterotrophs.
GPP – R = NPP.
Question 3.
Why is the rate of assimilation of energy at the herbivore level called secondary productivity? [NCERT Exemplar]
Answer:
It is because the biomass available to the consumer for consumption is a resultant of the primary productivity from plants.
Question 4.
Why is an earthworm called a detritivore?
Answer:
This is because earthworm breaks down detritus into smaller particles.
Question 5.
Justify the pitcher plant as a producer. [NCERT Exemplar]
Answer:
Pitcher plant is chlorophyllous and is thus capable of photosynthesis and act as producer.
Question 6.
Name any two organisms which occupy more than one trophic level in an ecosystem? [NCERT Exemplar]
Answer:
Man and sparrow.
Question 7.
What is common to earthworm, mushroom, soil mites, and dung beetle in an ecosystem? [NCERT Exemplar]
Answer:
They are all detritivores, i.e., decomposing organisms which feed on dead remains of plants and animals.
Question 8.
“Man can be a primary as well as a secondary consumer.” Justify this statement.
Answer:
Man has a varied diet. When on a vegetarian diet, they are primary consumers, and when on a non-vegetarian diet, they are secondary consumers.
Question 9.
Name an omnivore which occurs in both grazing food chain and the decomposer food chain. [NCERT Exemplar]
Answer:
Sparrow/crow.
Question 10.
Differentiate between standing state and standing crop in an ecosystem.
Answer:
In an ecosystem, standing crop is the mass of living material in each trophic level at a particular time. Whereas standing state refers to the amount- of nutrients in the soil at any given time.
Question 11.
Under what conditions would a particular stage in the process of succession revert back to an earlier stage? [NCERT Exemplar]
Answer:
Natural or human-induced disturbances like fire, deforestation, etc.
Question 12.
Climax stage is achieved quickly in secondary succession as compared to primary succession. Why? [NCERT Exemplar]
Answer:
The rate of succession is much faster in secondary succession as the substratum (soil) is already present as compared to primary succession where the process starts from a bare area (rock).
Short answer type questions
Question 1.
What is an incomplete ecosystem? Explain with the help of a suitable example. [NCERT Exemplar]
Answer:
An ecosystem is a functional unit with biotic and abiotic factors interacting with one another resulting in a physical structure. Absence of any component will make an ecosystem incomplete as it will hinder the functioning of the ecosystem. Examples of such an ecosystem can be a fish tank or deep aphotic zone of the oceans where producers are absent.
Question 2.
Justify the importance of decomposers in an ecosystem.
Answer:
Decomposers which are heterotrophic organisms, mainly fungi and bacteria break down complex organic matter into inorganic substances like carbon dioxide, water, and nutrients. They meet their energy and nutrient requirements by degrading dead organic matter or detritus. These are also known as saprotrophs. Decomposers secrete digestive enzymes that break down dead and waste into simple, inorganic materials, which are subsequently absorbed by them.
Question 3.
“In a food chain, a trophic level represents a functional level, not a species.” Explain.
Answer:
Trophic level in a food chain is a level at which organisms obtain their food. Each trophic level has a specific mode of obtaining food. Thus, trophic level represents the mode of obtaining food and not the species. The species has no significance in the food chain. In the food chain, there are generally four trophic levels-producers or autotrophs, the first trophic level; primary consumer/herbivore secondary trophic level; secondary consumer/carnivore third trophic level and finally tertiary consumers (top carnivores) representing fourth trophic level. Thus, in a food chain, trophic levels represent a functional level and which species represent the trophic level, does not matter.
Question 4.
How does primary succession start in water to the climax community? Explain.
Answer:
In primary succession in water, the pioneers are the small phytoplanktons. They are replaced with time by free-floating angiosperms, then by rooted hydrophytes; sedges, grasses, and finally the trees. The climax again would be a forest. With time the water body is converted into land.
Question 5.
Why are nutrient cycles in nature called biogeochemical cycles? [NCERT Exemplar]
Answer:
Nutrient cycles are called biogeochemical cycles because ions/molecules of a nutrient are transferred from the environment (rocks, air and water) to organisms (life) and then brought back to the environment in a cyclic pathway.
The literal meaning of biogeochemical is bio-living organisms and geo-rocks, air, and water.
Question 6.
(a) State any two differences between phosphorus and carbon cycles in nature.
(b) Write the importance of phosphorus in living organisms.
Answer:
(a)
| Phosphorus cycle | Carbon cycle |
| 1. It is a sedimentary cycle. | It is a gaseous cycle. |
| 2. Atmospheric inputs through rainfall are much smaller. | Atmospheric inputs through rainfall are more. |
| 3. Gaseous exchange of phosphorus between organism and environment is nil. | Gaseous exchange of carbon between organism and environment is much more. |
(b) Phosphorus is a major constituent of biological membranes, nucleic acids, and cellular energy transfer systems.
Long answer type questions
Question 1.
Explain succession of plants in xerophytic habitat until it reaches climax community.
Answer:
Xerarch Succession:
- It starts in primary bare, dry area such as rocks or sand dunes, etc.
- The pioneer species on the rock are usually lichens and blue-green algae under humid conditions.
- They secrete acids to dissolve rocks, help in weathering and soil formation.
- Little soil formation makes the way to the appearance of small plants like bryophytes (mosses). They accumulate more soil and organic matter.
- With time, they are succeeded by bigger plants; perennial grasses and shrubs.
- After several more stages, ultimately a stable climax forest community is formed.
- Climax community remains stable as long as environment remains unchanged.
- With time, the xerophytic habitat gets converted into mesic habitat.
Question 2.
Describe the advantages for keeping the ecosystems healthy.
Answer:
An healthy ecosystem is stable and have a functional balance amongst different populations found in ecosystem. Ecosystem advantages are benefits provided by ecosystem processes to environment in its cleaning and maintenance, enhancing aesthetic beauty, maintenance of biodiversity, protection of soil, water and land sources besides providing a habitat to wildlife, tribals and grazing areas. The important advantages are given ahead :
(i) Oxygen Release : (Purify air) Suspended particulate matter is intercepted by vegetation and made to settle down. Air is thus removed of its pollutants. It is further purified by removal of carbon dioxide and release of oxygen during photosynthetic activity of vegetation.
(ii) Water: Most of rainwater is held over the soil by plant litter like a sponge. It slowly percolates down and becomes the source of all springs, rivulets and rivers. The water is clean and fresh.
(iii) Prevention of Floods: As there is little runoff, flood water is not formed.
(iv) Protection of Soil: Maintenance of soil fertility depends upon a good soil cover and optimum nutrient cycling. Soil cover also protects the soil from air and water erosion. Soil particles remain bound together by plant roots. Landslides are rare.
(v) Biodiversity: Natural ecosystems are a source of biodiversity with a variety of genes, gene pools, species and habitats.
(vi) Climate: Ecosystems, especially forests, maintain good climatic conditions by increasing humidity, reducing extremes of temperature and increasing periodicity of rainfall.
(vii) Nutrient Cycling: It is one of the most important ecosystem services which maintains the continuity of life on earth. Through cycling, biogenetic nutrients are made available all the time for absorption.
(viii) Pollination: Insects, especially bees, and birds visit areas around the forests for pollination of crop plants, bushes, and trees.
(ix) Pest Control: In natural ecosystem, pests are kept under control by their natural predators. Maintenance of natural ecosystems will allow the predators to free the nearby areas of pests.
(x) Wildlife: Ecosystems provide habitats to wildlife.
(xi) Aesthetic Value: Ecosystems also provide aesthetic, cultural, and spiritual value.