questions with their answers, prepared for Class 12 CHSE Biology students, covering the chapter "Ecology and Environment."
Chapter: Ecology and Environment
Multiple Choice Questions (MCQ)
1. The specific functional role or position of a species in an ecosystem is called its:
a) Habitat
b) Niche
c) Biome
d) Territory
Answer: b) Niche
2. Which of the following population interactions benefits one species and harms the other?
a) Mutualism
b) Commensalism
c) Predation
d) Competition
Answer: c) Predation
3. If a population of 100 individuals has 5 births and 3 deaths in a year, what is its birth rate?
a) 5 per 1000
b) 0.05 per individual
c) 0.03 per individual
d) 2 per 100
Answer: b) 0.05 per individual
4. The rate of biomass production per unit area over a period by plants during photosynthesis is called:
a) Secondary productivity
b) Gross primary productivity
c) Net primary productivity
d) Decomposition rate
Answer: b) Gross primary productivity
5. Which ecological pyramid is always upright?
a) Pyramid of number
b) Pyramid of biomass
c) Pyramid of energy
d) Both a and b
Answer: c) Pyramid of energy
6. The largest reservoir of carbon on Earth is:
a) Atmosphere
b) Oceans
c) Forests
d) Fossil fuels
Answer: b) Oceans
7. Ecological succession starting on bare rock is called:
a) Hydrarch succession
b) Xerarch succession
c) Climax succession
d) Secondary succession
Answer: b) Xerarch succession
8. The term "Biodiversity Hotspots" refers to regions with:
a) High levels of endemism and high threat of habitat loss
b) Low species diversity but unique ecosystems
c) Areas suitable for establishing national parks
d) Regions with high pollution levels
Answer: a) High levels of endemism and high threat of habitat loss
9. Which of the following is an in situ conservation strategy for biodiversity?
a) Botanical garden
b) Seed bank
c) National Park
d) Zoological park
Answer: c) National Park
10. The phenomenon where an increase in the concentration of a toxic substance occurs at successive trophic levels is called:
a) Eutrophication
b) Biomagnification
c) Bioremediation
d) Deforestation
Answer: b) Biomagnification
11. The major cause of stratospheric ozone depletion is:
a) Carbon dioxide
b) Methane
c) Chlorofluorocarbons (CFCs)
d) Sulphur dioxide
Answer: c) Chlorofluorocarbons (CFCs)
12. Which gas is NOT considered a greenhouse gas?
a) Methane
b) Carbon dioxide
c) Oxygen
d) Nitrous oxide
Answer: c) Oxygen
13. "Bad ozone" is found in the:
a) Stratosphere
b) Troposphere
c) Mesosphere
d) Thermosphere
Answer: b) Troposphere
14. What does the term "eutrophication" refer to?
a) Increase in dissolved oxygen in water bodies
b) Natural aging of a lake by nutrient enrichment
c) Accumulation of toxic substances in the food chain
d) Reduction in primary productivity of an ecosystem
Answer: b) Natural aging of a lake by nutrient enrichment
15. The "Chipko Movement" is a success story related to the conservation of:
a) Water
b) Air
c) Forests
d) Wildlife
Answer: c) Forests
Short Answer Questions (2-3 marks)
1. Differentiate between habitat and niche.Answer:
* Habitat: The specific physical place or environment where an organism lives. It's like the organism's "address."
* Niche: The specific functional role or position of an organism in its ecosystem, including its interactions with biotic and abiotic factors. It's like the organism's "profession" or "role."
2. What is mutualism? Give an example.
Answer: Mutualism is a type of population interaction between two different species where both interacting species benefit. Example: Lichens (symbiotic association between fungi and algae), Mycorrhizae (association between fungi and plant roots), Pollinators (bees) and flowering plants.
3. Define birth rate and death rate for a population.
Answer:
* Birth Rate (Natality): The number of births per unit of population per unit of time.
* Death Rate (Mortality): The number of deaths per unit of population per unit of time.
4. What is primary productivity? Differentiate between GPP and NPP.
Answer: Primary productivity is the rate at which producers (autotrophs) convert light energy into organic matter through photosynthesis or chemosynthesis.
* Gross Primary Productivity (GPP): The total rate of photosynthesis or energy assimilated by producers in an ecosystem.
* Net Primary Productivity (NPP): The amount of organic matter remaining after producers have met their own energetic needs (respiration). NPP = GPP - Respiration (R).
5. Briefly describe the role of decomposers in an ecosystem.
Answer: Decomposers (bacteria and fungi) break down complex organic matter from dead organisms (detritus) into simpler inorganic substances. This process, called decomposition, releases nutrients back into the ecosystem, making them available for producers, thus completing the nutrient cycling.
6. Draw a typical pyramid of energy. Why is it always upright?
Answer: (Diagram not possible in text, but should show broad base representing producers, tapering upwards through successive trophic levels, with decreasing energy at each level).Reason for Upright Pyramid of Energy: According to the 10% law, only about 10% of the energy from one trophic level is transferred to the next trophic level, with the rest being lost as heat during metabolic activities. Thus, there is always less energy at higher trophic levels, making the pyramid of energy always upright.
7. Name the two main nutrient cycles discussed in ecology. What are their primary reservoirs?
Answer:
* Carbon Cycle: Primary reservoir is the ocean (in dissolved form, like carbonates and bicarbonates), also significant reservoirs in the atmosphere (CO2), biomass, and fossil fuels.
* Phosphorus Cycle: Primary reservoir is the Earth's crust (in rocks).
8. What is ecological succession? Differentiate between primary and secondary succession
.Answer: Ecological succession is the gradual and predictable change in the species composition of an area over time.
* Primary Succession: Begins in an area where no soil exists (e.g., bare rock, newly cooled lava, newly formed sand dunes). It is a very slow process.
* Secondary Succession: Begins in an area where a community has been disturbed or destroyed but where soil or substrate remains (e.g., abandoned farmlands, deforested areas, areas after fire or flood). It is generally faster than primary succession.
9. What is biodiversity? Name two patterns of biodiversity.
Answer: Biodiversity (or biological diversity) refers to the variety of life on Earth at all levels, from genes to species to ecosystems. Two patterns of biodiversity are:
* Latitudinal Gradients: Species diversity generally decreases as one moves from the equator towards the poles.
* Species-Area Relationship: Within a region, species richness increases with increasing explored area, up to a certain limit.
10. What are biodiversity hotspots? Name two biodiversity hotspots in India.
Answer: Biodiversity hotspots are regions characterized by very high levels of species richness (endemism) and are also facing severe threats of habitat destruction. They are priority areas for conservation. Examples in India: Western Ghats and Sri Lanka, Indo-Burma, Himalayas, Sundaland. (Any two from the four)
11. Define endangered organisms and extinction.
Answer:
* Endangered Organisms: Species that are at a very high risk of extinction in the wild in the near future due to significant population decline or habitat loss.
* Extinction: The complete disappearance of a species from Earth (or a specific region) when the last individual of that species dies.
12. What is the greenhouse effect? Name two major greenhouse gases
.Answer: The greenhouse effect is a naturally occurring phenomenon where certain gases in the Earth's atmosphere trap outgoing longwave (infrared) radiation from the Earth's surface, warming the planet. This natural effect is essential for life on Earth. Major Greenhouse Gases: Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), Chlorofluorocarbons (CFCs).
13. What is ozone depletion? Where does it occur, and what causes it?
Answer: Ozone depletion refers to the thinning of the ozone layer in the stratosphere. It primarily occurs over the Antarctic region (forming the 'ozone hole'). It is mainly caused by the release of human-made chemicals, especially chlorofluorocarbons (CFCs), which act as catalysts to break down ozone molecules.
14. What are 'e-wastes'? How can they be managed?
Answer: 'E-wastes' (electronic wastes) are discarded electronic devices and appliances (e.g., old computers, mobile phones, TVs). They are managed primarily through recycling, which involves dismantling the waste to recover valuable metals (copper, iron, gold, etc.) and other components. Proper disposal is crucial to prevent environmental pollution from toxic substances.
15. Mention any two benefits of ecological services.
Answer:
* Oxygen Release: Forests and phytoplankton release oxygen into the atmosphere through photosynthesis, essential for aerobic respiration.
* Pollination: Animals (insects, birds, bats) pollinate crops and wild plants, vital for reproduction and food production.
* Carbon Fixation/Sequestration: Plants absorb atmospheric CO2 through photosynthesis, helping to regulate the Earth's climate.
* Water Purification: Ecosystems (e.g., wetlands) naturally filter and purify water.
* Soil Formation and Erosion Control: Microbes, plants, and animals contribute to soil formation and stability.
