Board Exam 2025
1 Mark
Q16. Identify from the following a group
containing all non-biodegradable substances.
Analysis:
(A) Leather is biodegradable. (Glass/Plastic are non-bio).
(B) Cotton, Wood are biodegradable. Nylon is non-bio.
(C) DDT, Polyester, Glass. All are synthetic/inorganic and Non-biodegradable.
(D) Leather, Silk, Wool are all natural and biodegradable.
Correct Option: (C)
(A) Leather is biodegradable. (Glass/Plastic are non-bio).
(B) Cotton, Wood are biodegradable. Nylon is non-bio.
(C) DDT, Polyester, Glass. All are synthetic/inorganic and Non-biodegradable.
(D) Leather, Silk, Wool are all natural and biodegradable.
Correct Option: (C)
1 Mark
Q11. The organism occupying the fourth
trophic level in a food chain operating in grassland is :
Food Chain:
T1: Green Plants (Producers)
T2: Grasshopper (Primary Consumer)
T3: Frog (Secondary Consumer)
T4: Snake (Tertiary Consumer/Top Carnivore)
Correct Option: (D)
T1: Green Plants (Producers)
T2: Grasshopper (Primary Consumer)
T3: Frog (Secondary Consumer)
T4: Snake (Tertiary Consumer/Top Carnivore)
Correct Option: (D)
1 Mark
Q16. In an ecosystem, 10% of energy available
for transfer from one trophic level to the next in a food chain is in the form of :
Energy transfer in food chains occurs via food, which stores energy as
chemical energy (biomass). The 10% transferred is this chemical energy.
Correct Option: (B)
Correct Option: (B)
3 Marks
Q32. (a) Define the term biological
magnification.
(b) In the given aquatic food chain, which trophic level will have highest effect of biological magnification and why ?
Phytoplankton \(\rightarrow\) Zooplankton \(\rightarrow\) Fishes \(\rightarrow\) Human
(b) In the given aquatic food chain, which trophic level will have highest effect of biological magnification and why ?
Phytoplankton \(\rightarrow\) Zooplankton \(\rightarrow\) Fishes \(\rightarrow\) Human
(a) Biological Magnification: The phenomenon where the
concentration
of harmful non-biodegradable chemicals (like pesticides) increases at each successive trophic level
in a
food chain.
(b) Highest Effect: Human.
Reason: Humans are at the top trophic level. Since these chemicals accumulate and are
(b) Highest Effect: Human.
Reason: Humans are at the top trophic level. Since these chemicals accumulate and are
Q7. Which one of the following statements is
incorrect about ozone ?
Analysis:
(A) True. Shields from harmful UV.
(B) True. At ground level, it is a poison.
(C) False. Formation of ozone is by UV radiations (\(\text{O}_2 \xrightarrow{UV} \text{O} + \text{O}\), then \(\text{O} + \text{O}_2 \rightarrow \text{O}_3\)). Decomposition involves Chlorofluorocarbons (CFCs), not just UV alone (though UV splits O3 in equilibrium, the statement "Ozone gets decomposed by UV" implies the breakdown process. Wait. UV both produces and breaks down ozone in a dynamic balance. But usually, the "Incorrect" statement is targeted at a specific misconception).
Let's look at (D). True (\(\text{O}_3\)).
Comparing (C): "Ozone gets decomposed by UV". Actually, \(\text{O}_3 \xrightarrow{UV} \text{O}_2 + \text{O}\) is part of the cycle (photodissociation). So it is technically true.
Is there a trick? "Dealing with ozone is essential because it is a deadly poison." This refers to ground level ozone management. But context is usually stratospheric layer.
However, UV is *essential* for its formation. Breakdown is often attributed to CFCs in the context of "Depletion".
But strictly speaking, UV radiation splits molecular oxygen, AND UV radiation splits Ozone. Both happen.
But option (C) might be the intended answer if it implies "Ozone governs UV" rather than "UV destroys Ozone".
Actually, deeper check: High energy UV splits \(\text{O}_2\). Lower energy UV splits \(\text{O}_3\). So (C) is factually correct.
Let's re-read (B). "Dealing with ozone is essential because it is a deadly poison." This sentence is from NCERT: "Ozone is a deadly poison. However, at the higher levels...".
Maybe (C) is correct?
Let's reconsider. Maybe (A) "Shields from UV". True.
Is there any option that is *blatantly* false?
If (C) means "Ozone layer is destroyed by UV", that's false. It absorbs UV.
Wait. Absorption *is* the decomposition (absorption of photon energy breaks the bond).
Let's assume the question implies the *cause of depletion*. The cause is CFCs, not UV.
Thus (C) is likely the "Incorrect" one in the context of "What is wrong with the Ozone Layer context".
Correct Option: (C)
(A) True. Shields from harmful UV.
(B) True. At ground level, it is a poison.
(C) False. Formation of ozone is by UV radiations (\(\text{O}_2 \xrightarrow{UV} \text{O} + \text{O}\), then \(\text{O} + \text{O}_2 \rightarrow \text{O}_3\)). Decomposition involves Chlorofluorocarbons (CFCs), not just UV alone (though UV splits O3 in equilibrium, the statement "Ozone gets decomposed by UV" implies the breakdown process. Wait. UV both produces and breaks down ozone in a dynamic balance. But usually, the "Incorrect" statement is targeted at a specific misconception).
Let's look at (D). True (\(\text{O}_3\)).
Comparing (C): "Ozone gets decomposed by UV". Actually, \(\text{O}_3 \xrightarrow{UV} \text{O}_2 + \text{O}\) is part of the cycle (photodissociation). So it is technically true.
Is there a trick? "Dealing with ozone is essential because it is a deadly poison." This refers to ground level ozone management. But context is usually stratospheric layer.
However, UV is *essential* for its formation. Breakdown is often attributed to CFCs in the context of "Depletion".
But strictly speaking, UV radiation splits molecular oxygen, AND UV radiation splits Ozone. Both happen.
But option (C) might be the intended answer if it implies "Ozone governs UV" rather than "UV destroys Ozone".
Actually, deeper check: High energy UV splits \(\text{O}_2\). Lower energy UV splits \(\text{O}_3\). So (C) is factually correct.
Let's re-read (B). "Dealing with ozone is essential because it is a deadly poison." This sentence is from NCERT: "Ozone is a deadly poison. However, at the higher levels...".
Maybe (C) is correct?
Let's reconsider. Maybe (A) "Shields from UV". True.
Is there any option that is *blatantly* false?
If (C) means "Ozone layer is destroyed by UV", that's false. It absorbs UV.
Wait. Absorption *is* the decomposition (absorption of photon energy breaks the bond).
Let's assume the question implies the *cause of depletion*. The cause is CFCs, not UV.
Thus (C) is likely the "Incorrect" one in the context of "What is wrong with the Ozone Layer context".
Correct Option: (C)
1 Mark
Q18. Assertion (A): In a food
chain, the first trophic level is occupied by autotrophs.
Reason (R): Autotrophs can fix solar energy to make it available for consumers.
Reason (R): Autotrophs can fix solar energy to make it available for consumers.
Assertion (A): True. Producers (Autotrophs) are always at the base
(First Trophic Level).
Reason (R): True. They convert solar energy into chemical energy (food).
Reason correctly explains why they are the first level (because they bring energy into the system).
Correct Option: (A) Both A and R are true and R is correct explanation.
Reason (R): True. They convert solar energy into chemical energy (food).
Reason correctly explains why they are the first level (because they bring energy into the system).
Correct Option: (A) Both A and R are true and R is correct explanation.
2 Marks
Q24. Differentiate between biodegradable and
non-biodegradable wastes. Give one example of each.
Differences:
Biodegradable
Non-biodegradable
Substances that can be broken down by biological processes (microorganisms).
Substances that cannot be broken down by biological processes.
Example: Vegetable peels, Paper.
Example: Plastic bottles, Glass.
5 Marks
Q34. (a) (i) What is meant by biological
magnification ?
(ii) "The energy flow in a food chain is unidirectional." Justify this statement.
(iii) Construct a food chain of four trophic levels comprising the following :
Hawk, Snake, Plants, Rat
OR
(b) (i) Suggest any two methods of waste disposal for the proper safety of the environment.
(ii) Explain how ozone is formed in the upper atmosphere. Why is damage to ozone layer a cause of concern to us ?
(ii) "The energy flow in a food chain is unidirectional." Justify this statement.
(iii) Construct a food chain of four trophic levels comprising the following :
Hawk, Snake, Plants, Rat
OR
(b) (i) Suggest any two methods of waste disposal for the proper safety of the environment.
(ii) Explain how ozone is formed in the upper atmosphere. Why is damage to ozone layer a cause of concern to us ?
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(a) (i) Biological Magnification: The phenomenon of progressive
increase in the concentration of harmful non-biodegradable chemicals (pesticides) at each successive
trophic level in a food chain.
(a) (ii) Unidirectional Energy Flow:
Energy captured by autotrophs does not revert back to the sun. Energy passed to herbivores does not come back to autotrophs. At each step, energy is lost as heat and potential energy decreases.
(a) (iii) Food Chain:
Plants \(\rightarrow\) Rat \(\rightarrow\) Snake \(\rightarrow\) Hawk.
(b) (i) Waste Disposal Methods:
1. Recycling: Processing waste materials (paper, glass, metal) to make new products.
2. Composting: Burying biodegradable waste in pits to form manure.
(b) (ii) Ozone Formation:
- High energy UV radiates split molecular oxygen (\(\text{O}_2\)) into free oxygen atoms (\(\text{O}\)).
- \(\text{O}_2 \xrightarrow{UV} \text{O} + \text{O}\)
- These free atoms combine with molecular oxygen to form Ozone (\(\text{O}_3\)).
- \(\text{O} + \text{O}_2 \rightarrow \text{O}_3\)
Concern: Damage to ozone layer leads to depletion, allowing harmful UV radiations to reach earth, causing skin cancer, cataracts, and damage to crops.
(a) (ii) Unidirectional Energy Flow:
Energy captured by autotrophs does not revert back to the sun. Energy passed to herbivores does not come back to autotrophs. At each step, energy is lost as heat and potential energy decreases.
(a) (iii) Food Chain:
Plants \(\rightarrow\) Rat \(\rightarrow\) Snake \(\rightarrow\) Hawk.
(b) (i) Waste Disposal Methods:
1. Recycling: Processing waste materials (paper, glass, metal) to make new products.
2. Composting: Burying biodegradable waste in pits to form manure.
(b) (ii) Ozone Formation:
- High energy UV radiates split molecular oxygen (\(\text{O}_2\)) into free oxygen atoms (\(\text{O}\)).
- \(\text{O}_2 \xrightarrow{UV} \text{O} + \text{O}\)
- These free atoms combine with molecular oxygen to form Ozone (\(\text{O}_3\)).
- \(\text{O} + \text{O}_2 \rightarrow \text{O}_3\)
Concern: Damage to ozone layer leads to depletion, allowing harmful UV radiations to reach earth, causing skin cancer, cataracts, and damage to crops.
1 Mark
Q5. Which of the following is biodegradable ?
Biodegradable: Substances broken down by biological processes.
(A) Plastic - Non-bio.
(B) Leather - Biodegradable (Animal product).
(C) Silver foil - Non-bio (Metal).
(D) Iron nail - Non-bio (Metal).
Correct Option: (B)
(A) Plastic - Non-bio.
(B) Leather - Biodegradable (Animal product).
(C) Silver foil - Non-bio (Metal).
(D) Iron nail - Non-bio (Metal).
Correct Option: (B)
1 Mark
Q16. Other than the abiotic components, which of
the given biotic components are not required to make an aquarium with small herbivorous
fishes a self-sustaining system ?
- Aquatic plants and aquatic animals
- Terrestrial plants and terrestrial animals
- Decomposers as bacteria and fungi
- Consumers as clown fishes and sea urchins
Analysis:
To be self-sustaining, an aquarium needs: - Producers (Aquatic plants) for Oxygen and Food.
- Consumers (the fishes already present).
- Decomposers (Bacteria/Fungie) to recycle waste.
It does not need:
(ii) Terrestrial plants/animals (Not suitable for aquarium).
(iv) Additional Consumers like Clown fishes/Sea urchins (Not required for the *system* to function if basic herbivorous fishes are there).
Correct Option: (D) (ii) and (iv).
To be self-sustaining, an aquarium needs: - Producers (Aquatic plants) for Oxygen and Food.
- Consumers (the fishes already present).
- Decomposers (Bacteria/Fungie) to recycle waste.
It does not need:
(ii) Terrestrial plants/animals (Not suitable for aquarium).
(iv) Additional Consumers like Clown fishes/Sea urchins (Not required for the *system* to function if basic herbivorous fishes are there).
Correct Option: (D) (ii) and (iv).
1 Mark
Q18. Assertion (A): Use of jute
bags for shopping reduces pollution.
Reason (R): Jute is biodegradable and its bag may be reused as and when needed.
Reason (R): Jute is biodegradable and its bag may be reused as and when needed.
Assertion (A): True. Reduces use of plastic bags.
Reason (R): True. Being biodegradable means it doesn't persist as pollutant. Reuse reduces overall waste.
Explanation: R correctly explains why it reduces pollution (biodegradability + reusability).
Correct Option: (A) Both A and R are true and R is correct explanation.
Reason (R): True. Being biodegradable means it doesn't persist as pollutant. Reuse reduces overall waste.
Explanation: R correctly explains why it reduces pollution (biodegradability + reusability).
Correct Option: (A) Both A and R are true and R is correct explanation.
3 Marks
Q33. (a) "In a food chain energy flow is
unidirectional." Give two reasons for the given statement.
(b) If 10,000 J energy is available at the producer level, how much energy will be available to the secondary consumers ? Give reason to justify your answer.
(b) If 10,000 J energy is available at the producer level, how much energy will be available to the secondary consumers ? Give reason to justify your answer.
(a) Unidirectional Flow:
1. Energy captured from the sun by autotrophs does not revert back to the sun.
2. Energy passed to the herbivores does not come back to autotrophs. It moves progressively through trophic levels and is lost as heat, never reused.
(b) Energy Calculation:
Producer Level = 10,000 J.
10% Law: Only 10% of energy is transferred to the next trophic level.
First Consumer (Primary) = \(10\%\) of \(10,000\) = \(1,000\) J.
Second Consumer (Secondary) = \(10\%\) of \(1,000\) = \(100\) J.
Answer: 100 J.
1. Energy captured from the sun by autotrophs does not revert back to the sun.
2. Energy passed to the herbivores does not come back to autotrophs. It moves progressively through trophic levels and is lost as heat, never reused.
(b) Energy Calculation:
Producer Level = 10,000 J.
10% Law: Only 10% of energy is transferred to the next trophic level.
First Consumer (Primary) = \(10\%\) of \(10,000\) = \(1,000\) J.
Second Consumer (Secondary) = \(10\%\) of \(1,000\) = \(100\) J.
Answer: 100 J.
1 Mark
Q1. Which one of the following gets biomagnified
at different levels in a food chain ?
Biomagnification: Accumulation of toxic substances at higher
trophic levels.
DDT is non-biodegradable and accumulates.
Correct Option: (c)
DDT is non-biodegradable and accumulates.
Correct Option: (c)
1 Mark
Q2. In the food chains given below. Select the
most efficient food chain in terms of energy :
Efficiency: Shortest food chain has highest energy transfer (10%
law).
(c) Plants (\rightarrow) Man (2 steps) is the shortest.
Correct Option: (c)
(c) Plants (\rightarrow) Man (2 steps) is the shortest.
Correct Option: (c)
3 Marks
Q31. What are decomposers? Give two examples.
State how they maintain a balance in an ecosystem.
Decomposers: Organisms that break down complex organic matter
(dead plants/animals) into simple inorganic substances.
Examples: Bacteria, Fungi.
Role in Balance:
1. They recycle nutrients (N, P, K) back into the soil for plants to reuse.
2. They clean the environment by removing dead decaying matter.
Examples: Bacteria, Fungi.
Role in Balance:
1. They recycle nutrients (N, P, K) back into the soil for plants to reuse.
2. They clean the environment by removing dead decaying matter.
1 Mark
Q13. Human activities that are affecting the
environment are :
Analysis:
The question likely implies "negatively affecting" or "causing pollution".
(A), (C), (D) are positive/eco-friendly actions.
(B) Excessive use of disposables creates waste/pollution.
Correct Option: (B)
The question likely implies "negatively affecting" or "causing pollution".
(A), (C), (D) are positive/eco-friendly actions.
(B) Excessive use of disposables creates waste/pollution.
Correct Option: (B)
1 Mark
Q14. The examples of natural and manmade
(artificial) ecosystems are respectively
Examples:
Natural: Forest, Lake, Pond.
Artificial: Crop field, Garden, Aquarium.
Req: Natural first, then Artificial.
(A) Forest (Nat), Pond (Nat). (No).
(B) Crop (Art). NO.
(C) Lake (Nat), Garden (Art). Matches.
(D) Crop (Art). NO.
Correct Option: (C)
Natural: Forest, Lake, Pond.
Artificial: Crop field, Garden, Aquarium.
Req: Natural first, then Artificial.
(A) Forest (Nat), Pond (Nat). (No).
(B) Crop (Art). NO.
(C) Lake (Nat), Garden (Art). Matches.
(D) Crop (Art). NO.
Correct Option: (C)
2 Marks
Q25. Study the food web given below :
(a) Identify the food chain(s) in which the eagle receives the highest energy from the producers.
(b) Identify the organism in which a non-biodegradable pesticide will be found in maximum concentration. Name the term used for this phenomenon.
(a) Identify the food chain(s) in which the eagle receives the highest energy from the producers.
(b) Identify the organism in which a non-biodegradable pesticide will be found in maximum concentration. Name the term used for this phenomenon.
(a) For highest energy transfer, the food chain length must be shortest (10%
Law).
Possible chains ending in Eagle:
1. Grass \(\rightarrow\) Mouse \(\rightarrow\) Eagle (3 trophic levels).
2. Grass \(\rightarrow\) Grasshopper \(\rightarrow\) Frog \(\rightarrow\) Snake \(\rightarrow\) Eagle (5 levels).
Shortest chain is Grass \(\rightarrow\) Mouse \(\rightarrow\) Eagle. Eagle gets most energy here.
(b) Eagle (Top Carnivore).
Term: Biological Magnification.
Possible chains ending in Eagle:
1. Grass \(\rightarrow\) Mouse \(\rightarrow\) Eagle (3 trophic levels).
2. Grass \(\rightarrow\) Grasshopper \(\rightarrow\) Frog \(\rightarrow\) Snake \(\rightarrow\) Eagle (5 levels).
Shortest chain is Grass \(\rightarrow\) Mouse \(\rightarrow\) Eagle. Eagle gets most energy here.
(b) Eagle (Top Carnivore).
Term: Biological Magnification.
1 Mark
Q15. In the following groups of wastes, which
group contains only non-biodegradable wastes ?
(A) Leather is bio-degradable (takes time but yes).
(B) Empty bottle (Glass?), Milk packet (Plastic), Al Can (Metal). All non-bio.
(C) Tea leaves, Cardboard are Bio.
(D) Newspaper is Bio.
Let's re-evaluate (B). Milk packet (Plastic). Glass Bottle. Aluminium. Yes, all are non-biodegradable.
Correct Option: (B)
(B) Empty bottle (Glass?), Milk packet (Plastic), Al Can (Metal). All non-bio.
(C) Tea leaves, Cardboard are Bio.
(D) Newspaper is Bio.
Let's re-evaluate (B). Milk packet (Plastic). Glass Bottle. Aluminium. Yes, all are non-biodegradable.
Correct Option: (B)
1 Mark
Q16. Consider the following food chain :
\(\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \rightarrow \text{Eagle}\)
If the amount of energy available at third trophic level is 50 kJ, the available energy at the producer level was :
\(\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \rightarrow \text{Eagle}\)
If the amount of energy available at third trophic level is 50 kJ, the available energy at the producer level was :
Tropic Levels:
T1 (Producer): Grass
T2: Grasshopper
T3: Frog (Given 50 kJ)
Backwards calculation (10% Law):
If T3 = 50 kJ (which is 10% of T2). Then T2 = 500 kJ.
If T2 = 500 kJ (which is 10% of T1). Then T1 = 5000 kJ.
Correct Option: (D)
T1 (Producer): Grass
T2: Grasshopper
T3: Frog (Given 50 kJ)
Backwards calculation (10% Law):
If T3 = 50 kJ (which is 10% of T2). Then T2 = 500 kJ.
If T2 = 500 kJ (which is 10% of T1). Then T1 = 5000 kJ.
Correct Option: (D)
1 Mark
Q19. Assertion (A): Food web is
a network of several food chains operating in an ecosystem.
Reason (R): Food web decreases the stability of an ecosystem.
Reason (R): Food web decreases the stability of an ecosystem.
Assertion (A): True. Definition.
Reason (R): False. Food webs increase stability by providing alternative pathways for energy flow.
Correct Option: (C) (A is true, R is false).
Reason (R): False. Food webs increase stability by providing alternative pathways for energy flow.
Correct Option: (C) (A is true, R is false).
2 Marks
Q26. Write the percentage of the energy of
sunlight captured by green plants, to convert it into food energy. Explain the fate of this energy when
green plants are eaten by primary consumers.
Percentage: About 1% of solar energy falling on leaves is
captured.
Fate: When eaten by primary consumers (herbivores), about 10% of this food energy is turned into their own body mass and available for next level. The rest (90%) is lost as heat/digestion/work. (10% Law).
Fate: When eaten by primary consumers (herbivores), about 10% of this food energy is turned into their own body mass and available for next level. The rest (90%) is lost as heat/digestion/work. (10% Law).
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