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Ecosystem & Environmental Management — Homi Bhabha Class 9 Biology MCQs with Solutions
Free Homi Bhabha Class 9 Biology Ecosystem & Environmental Management MCQs with step-by-step solutions covering Food Chains & Energy Flow, Biogeochemical Cycles, Pollution (Air, Water, Soil), Waste Management, Climate Change. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Food Chains & Energy Flow · easy · theory
In a food chain, green plants that trap sunlight and make their own food are called:
A. Primary consumers
B. Secondary consumers
C. Decomposers
D. Producers ✓ Correct
Solution: Green plants are producers (autotrophs). They capture solar energy and convert it into chemical energy through photosynthesis, forming the first trophic level of every food chain.
Q2 — Biogeochemical Cycles · easy · theory
The conversion of atmospheric nitrogen gas into usable nitrogen compounds by bacteria in the root nodules of legumes is called:
A. Transpiration
B. Denitrification
C. Nitrogen fixation ✓ Correct
D. Condensation
Solution: Nitrogen fixation is the process by which nitrogen-fixing bacteria (such as Rhizobium in root nodules) convert inert atmospheric N2 into nitrogen compounds that plants can use.
Q3 — Biogeochemical Cycles · easy · theory
In the water cycle, the process by which plants release water vapour into the atmosphere from their leaves is called:
A. Evaporation
B. Precipitation
C. Transpiration ✓ Correct
D. Infiltration
Solution: Transpiration is the loss of water vapour from plant leaves through tiny pores called stomata. Evaporation refers to water lost from open surfaces like oceans and lakes.
Q4 — Pollution (Air, Water, Soil) · easy · theory
Which gas released from vehicle exhaust binds tightly with haemoglobin in blood and reduces the transport of oxygen?
A. Carbon monoxide ✓ Correct
B. Oxygen
C. Nitrogen
D. Carbon dioxide
Solution: Carbon monoxide (CO) combines with haemoglobin far more strongly than oxygen does, forming carboxyhaemoglobin and lowering the ability of blood to carry oxygen.
Q5 — Waste Management · easy · theory
Which of the following is a biodegradable waste?
A. Aluminium can
B. Plastic bottle
C. Glass piece
D. Vegetable peels ✓ Correct
Solution: Vegetable peels are organic matter that decomposer microorganisms can break down naturally. Plastic, glass, and aluminium are non-biodegradable and persist for a very long time.
Q6 — Waste Management · easy · theory
In the common two-bin waste segregation system used in India, wet or biodegradable kitchen waste should be put in the bin of colour:
A. Blue
B. Green ✓ Correct
C. Black
D. Red
Solution: Green bins are meant for wet, biodegradable waste (like food scraps), while blue bins are for dry, recyclable waste such as paper, plastic, and metal.
Q7 — Climate Change · easy · theory
Which of the following is a greenhouse gas that contributes to global warming?
A. Oxygen
B. Carbon dioxide ✓ Correct
C. Nitrogen
D. Argon
Solution: Carbon dioxide is a major greenhouse gas that traps heat in the atmosphere. Nitrogen, oxygen, and argon make up most of the air but do not trap heat significantly.
Q8 — Food Chains & Energy Flow · hard · theory
The flow of energy in a food chain is:
A. circular
B. unidirectional (one-way) ✓ Correct
C. zero
D. in both directions
Solution: Energy flows one way — from the Sun to producers to consumers — and is lost as heat at each level.
Q9 — Food Chains & Energy Flow · hard · theory
According to the ten-percent law, the energy passed on to the next trophic level is about:
A. 100%
B. 50%
C. 10% of the energy at the previous level ✓ Correct
D. 90%
Solution: Only about 10% of the energy at one level is transferred to the next; the rest is used up or lost as heat.
Q10 — Food Chains & Energy Flow · hard · theory
A network of many interconnected food chains in an ecosystem is called a:
A. food pyramid only
B. food web ✓ Correct
C. trophic level
D. biome
Solution: A food web is formed by the interlinking of several food chains.
Q11 — Biogeochemical Cycles · hard · theory
The conversion of atmospheric nitrogen into compounds usable by plants is called:
A. nitrogen fixation ✓ Correct
B. denitrification
C. respiration
D. nitrification only
Solution: Nitrogen fixation converts inert N₂ into usable nitrogen compounds, often by bacteria.
Q12 — Biogeochemical Cycles · hard · theory
Bacteria that live in the root nodules of leguminous plants and fix nitrogen are:
A. Plasmodium
B. yeast
C. Lactobacillus
D. Rhizobium ✓ Correct
Solution: Rhizobium bacteria in legume root nodules fix atmospheric nitrogen.
Q13 — Biogeochemical Cycles · hard · theory
Biogeochemical cycles are important because they:
A. recycle essential nutrients so that life can continue ✓ Correct
B. only occur in oceans
C. destroy nutrients permanently
D. stop energy flow
Solution: These cycles continuously recycle nutrients (carbon, nitrogen, water) between living things and the environment.
Q14 — Pollution (Air, Water, Soil) · hard · theory
Acid rain is caused mainly by the release of ______ into the atmosphere:
A. sulphur dioxide and nitrogen oxides ✓ Correct
B. oxygen and nitrogen
C. water vapour
D. carbon dioxide only
Solution: SO₂ and NOₓ from burning fuels dissolve in rain to form acids, causing acid rain.
Q15 — Pollution (Air, Water, Soil) · hard · theory
The excessive use of chemical pesticides and plastics mainly causes:
A. oxygen pollution
B. noise pollution
C. soil pollution ✓ Correct
D. sound pollution
Solution: Pesticides and non-degradable plastics accumulate in the soil, causing soil pollution.
Q16 — Pollution (Air, Water, Soil) · hard · theory
Which practice would help REDUCE air pollution?
A. Using more diesel vehicles
B. Using public transport and clean energy ✓ Correct
C. Cutting down forests
D. Burning more coal
Solution: Public transport and clean (renewable) energy reduce the emission of pollutants.
Q17 — Waste Management · hard · theory
Which of the following is a NON-biodegradable waste?
A. Cotton cloth
B. Vegetable peels
C. Plastic bag ✓ Correct
D. Paper
Solution: Plastics are not broken down by microbes and persist in the environment.
Q18 — Waste Management · hard · theory
The "three Rs" recommended for managing waste are:
A. Reduce, Reuse, Recycle ✓ Correct
B. Run, Rest, Repeat
C. Read, Write, Recite
D. Reduce, Remove, Reject
Solution: Reduce, Reuse and Recycle help minimise waste and conserve resources.
Q19 — Waste Management · hard · theory
Recycling of materials like paper and metal is beneficial because it:
A. wastes energy
B. increases pollution
C. uses more raw material
D. saves natural resources and reduces waste ✓ Correct
Solution: Recycling conserves resources, saves energy and reduces the amount of waste dumped.
Q20 — Climate Change · hard · theory
The gradual rise in the average temperature of the Earth is called:
A. condensation
B. global warming ✓ Correct
C. acid rain
D. eutrophication
Solution: Global warming is the increase in Earth's average temperature due to greenhouse gases.
Q21 — Climate Change · hard · theory
The depletion of the ozone layer is caused mainly by:
A. chlorofluorocarbons (CFCs) ✓ Correct
B. oxygen
C. water vapour
D. carbon dioxide
Solution: CFCs released from refrigerants and sprays break down ozone in the stratosphere.
Q22 — Climate Change · hard · theory
Which of the following would help to REDUCE global warming?
A. Increasing use of CFCs
B. Planting more trees and using renewable energy ✓ Correct
C. Burning more fossil fuels
D. Cutting down forests
Solution: Afforestation absorbs CO₂ and clean energy cuts emissions, both reducing global warming.
Q23 — Food Chains & Energy Flow · hard · numerical
Producers in a grassland fix 20000 kJ of energy. Following the 10% law, how much energy is available at the 4th trophic level?
A. 2000 kJ
B. 2 kJ
C. 20 kJ ✓ Correct
D. 200 kJ
Solution: Each level retains 10% of the level below. Level 1 = 20000, Level 2 = 2000, Level 3 = 200, Level 4 = 20 kJ.
Q24 — Biogeochemical Cycles · hard · theory
Assertion (A): The total amount of carbon on Earth stays roughly constant. Reason (R): Carbon continuously cycles between the atmosphere, living organisms, oceans, and rocks.
A. A is false but R is true
B. A is true but R is false
C. Both A and R are true but R is not the correct explanation of A
D. Both A and R are true and R is the correct explanation of A ✓ Correct
Solution: Carbon is neither created nor destroyed; it merely moves through different reservoirs in the carbon cycle. Because it is recycled rather than lost, the total remains constant, so R correctly explains A.
Q25 — Pollution (Air, Water, Soil) · hard · numerical
A pesticide is present in producers at 0.5 ppm and its concentration increases 10 times at each higher trophic level. What is its concentration in the third-level consumer (three levels above the producer)?
A. 1500 ppm
B. 50 ppm
C. 500 ppm ✓ Correct
D. 5 ppm
Solution: Multiply by 10 for each level up: producer 0.5, first consumer 5, second consumer 50, third consumer 500 ppm.
Q26 — Waste Management · hard · theory
Assertion (A): Dumping large amounts of biodegradable waste in landfills contributes to global warming. Reason (R): Anaerobic decomposition of organic waste in landfills releases methane, a greenhouse gas.
A. A is true but R is false
B. Both A and R are true and R is the correct explanation of A ✓ Correct
C. Both A and R are true but R is not the correct explanation of A
D. A is false but R is true
Solution: Buried organic waste decomposes without oxygen (anaerobically) and releases methane, which is a potent greenhouse gas. This warming effect makes R the correct explanation of A.
Q27 — Climate Change · hard · theory
Assertion (A): The melting of polar ice caps speeds up global warming. Reason (R): Bright ice reflects most sunlight, so when it melts the darker ocean and land absorb more heat.
A. Both A and R are true and R is the correct explanation of A ✓ Correct
B. A is false but R is true
C. Both A and R are true but R is not the correct explanation of A
D. A is true but R is false
Solution: Ice has high albedo and reflects sunlight; the exposed darker surfaces absorb more heat, which melts more ice. This positive feedback (reduced albedo) means R correctly explains A.
Q28 — Climate Change · hard · theory
Which of the following statements correctly distinguishes ozone-layer depletion from global warming?
A. Ozone depletion directly causes global warming and they are the same problem
B. Both are caused by the same gas, carbon dioxide
C. Ozone-layer depletion is caused mainly by CFCs, while global warming is caused mainly by greenhouse gases such as carbon dioxide ✓ Correct
D. Both are caused by a build-up of oxygen in the atmosphere
Solution: They are distinct problems. Ozone depletion is driven mainly by chlorofluorocarbons (CFCs) breaking down ozone in the upper atmosphere, whereas global warming results chiefly from heat-trapping greenhouse gases like CO2.
Q29 — Food Chains & Energy Flow · medium · theory
In a food chain, green plants are called ______ because they make their own food:
A. producers ✓ Correct
B. predators
C. decomposers
D. consumers
Solution: Green plants are producers (autotrophs) and form the base of every food chain.
Q30 — Food Chains & Energy Flow · medium · theory
Animals that eat only plants (herbivores) occupy the level of ______ in a food chain:
A. producers
B. primary consumers ✓ Correct
C. decomposers
D. tertiary consumers
Solution: Herbivores feed directly on producers, so they are primary consumers.