Chapter 13: Our Environment
[IMAGE PLACEHOLDER: Ecosystem Components & Energy Flow]
1-Mark Questions & Solutions
Q1 | 1 Mark
Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer: (a), (c), and (d) (All components in grass, flowers, leather, fruit-peels, cake, lime-juice, wood are organic and decomposed by micro-organisms; plastic in (b) is non-biodegradable).
Q2 | 1 Mark
Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer: (b) Grass $\rightarrow$ Goat $\rightarrow$ Human
Q3 | 1 Mark
Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer: (d) All of the above
Q4 | 1 Mark
What will happen if we kill all the organisms in one trophic level?
(a) Population of organisms in next trophic level increases
(b) Population of organisms in preceding trophic level decreases
(c) The transfer of food energy to next level stops and ecosystem balance is disturbed
(d) Ecosystem remains stable
(a) Population of organisms in next trophic level increases
(b) Population of organisms in preceding trophic level decreases
(c) The transfer of food energy to next level stops and ecosystem balance is disturbed
(d) Ecosystem remains stable
Answer: (c) The transfer of food energy to next level stops, leading to overpopulation in preceding level and starvation in higher level, causing severe ecological imbalance.
Q5 | 1 Mark
Ozone depletion in the upper atmosphere ($ stratosphere $) is mainly caused by:
(a) $ CO_2 $ (b) $ CFCs $ (Chlorofluorocarbons) (c) $ CH_4 $ (d) $ SO_2 $
(a) $ CO_2 $ (b) $ CFCs $ (Chlorofluorocarbons) (c) $ CH_4 $ (d) $ SO_2 $
Answer: (b) $ CFCs $ (Chlorofluorocarbons)
Q6 | 1 Mark
Which chemicals are responsible for forming ozone gas in the presence of UV radiation?
Equation: $$ O_2 \xrightarrow{\text{UV}} O + O \quad \text{and} \quad O + O_2 \rightarrow O_3 $$
(a) Oxygen molecules and oxygen atoms
(b) Carbon dioxide and water
(c) Methane and nitrogen
(d) Hydrogen and oxygen
Equation: $$ O_2 \xrightarrow{\text{UV}} O + O \quad \text{and} \quad O + O_2 \rightarrow O_3 $$
(a) Oxygen molecules and oxygen atoms
(b) Carbon dioxide and water
(c) Methane and nitrogen
(d) Hydrogen and oxygen
Answer: (a) High-energy UV radiation splits molecular oxygen ($ O_2 $) into free oxygen atoms ($ O $), which combine with $ O_2 $ to form ozone ($ O_3 $).
Q7 | 1 Mark
In an ecosystem, the flow of energy is always:
(a) Unidirectional (b) Bidirectional (c) Multidirectional (d) Cyclic
(a) Unidirectional (b) Bidirectional (c) Multidirectional (d) Cyclic
Answer: (a) Unidirectional (Energy flows progressively from producers to consumers and cannot revert back to lower trophic levels or sunlight).
Q8 | 1 Mark
If $ 10,000\text{ J} $ of solar energy falls on green plants in a terrestrial ecosystem, how much energy is captured as food energy?
(a) $ 10,000\text{ J} $ (b) $ 1,000\text{ J} $ (c) $ 100\text{ J} $ (d) $ 10\text{ J} $
(a) $ 10,000\text{ J} $ (b) $ 1,000\text{ J} $ (c) $ 100\text{ J} $ (d) $ 10\text{ J} $
Answer: (c) $ 100\text{ J} $
Calculation: Producers capture approximately $ 1\% $ of the solar energy reaching their leaves: $$ \text{Captured Energy} = 1\% \text{ of } 10,000\text{ J} = 0.01 \times 10,000 = 100\text{ J} $$
Calculation: Producers capture approximately $ 1\% $ of the solar energy reaching their leaves: $$ \text{Captured Energy} = 1\% \text{ of } 10,000\text{ J} = 0.01 \times 10,000 = 100\text{ J} $$
Q9 | 1 Mark
According to Lindeman's 10% law, if $ 1000\text{ J} $ of energy is available at the producer level, how much energy will be transferred to the primary consumer?
(a) $ 1000\text{ J} $ (b) $ 100\text{ J} $ (c) $ 10\text{ J} $ (d) $ 1\text{ J} $
(a) $ 1000\text{ J} $ (b) $ 100\text{ J} $ (c) $ 10\text{ J} $ (d) $ 1\text{ J} $
Answer: (b) $ 100\text{ J} $
Calculation: $$ E_{\text{Primary Consumer}} = 10\% \text{ of } 1000\text{ J} = 0.10 \times 1000 = 100\text{ J} $$
Calculation: $$ E_{\text{Primary Consumer}} = 10\% \text{ of } 1000\text{ J} = 0.10 \times 1000 = 100\text{ J} $$
Q10 | 1 Mark
Accumulation of non-biodegradable pesticides at highest levels of a food chain is known as:
(a) Eutrophication (b) Biological Magnification (c) Bio-accumulation (d) Pollution
(a) Eutrophication (b) Biological Magnification (c) Bio-accumulation (d) Pollution
Answer: (b) Biological Magnification
[IMAGE PLACEHOLDER: Pyramid of Trophic Levels & 10% Law]
Q11 - Q15 | Additional 1-Mark MCQs
• Q11: Organisms which synthesize organic compounds from inorganic substances using solar energy $\rightarrow$ (c) Autotrophs / Producers.
• Q12: Decomposers in an ecosystem $\rightarrow$ (b) Convert organic material to inorganic forms.
• Q13: Maximum concentration of harmful chemicals like DDT is found in $\rightarrow$ (d) Human beings (top carnivore level).
• Q14: UNEP reached an agreement in 1987 to freeze CFC production at $\rightarrow$ (b) 1986 levels.
• Q15: Disposal of disposable paper cups over plastic cups in trains is better because $\rightarrow$ (a) Paper is biodegradable and eco-friendly.
• Q11: Organisms which synthesize organic compounds from inorganic substances using solar energy $\rightarrow$ (c) Autotrophs / Producers.
• Q12: Decomposers in an ecosystem $\rightarrow$ (b) Convert organic material to inorganic forms.
• Q13: Maximum concentration of harmful chemicals like DDT is found in $\rightarrow$ (d) Human beings (top carnivore level).
• Q14: UNEP reached an agreement in 1987 to freeze CFC production at $\rightarrow$ (b) 1986 levels.
• Q15: Disposal of disposable paper cups over plastic cups in trains is better because $\rightarrow$ (a) Paper is biodegradable and eco-friendly.
2-Mark Questions & Solutions
Q16 | 2 Marks
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer:
• Trophic Levels: The various steps or levels in a food chain where transfer of food energy takes place.
• Example Food Chain: $$\text{Grass (T1)} \longrightarrow \text{Deer (T2)} \longrightarrow \text{Lion (T3)}$$
1) $ T_1 $ (First Trophic Level): Grass (Producers)
2) $ T_2 $ (Second Trophic Level): Deer (Primary Consumers / Herbivores)
3) $ T_3 $ (Third Trophic Level): Lion (Secondary Consumers / Top Carnivores)
• Trophic Levels: The various steps or levels in a food chain where transfer of food energy takes place.
• Example Food Chain: $$\text{Grass (T1)} \longrightarrow \text{Deer (T2)} \longrightarrow \text{Lion (T3)}$$
1) $ T_1 $ (First Trophic Level): Grass (Producers)
2) $ T_2 $ (Second Trophic Level): Deer (Primary Consumers / Herbivores)
3) $ T_3 $ (Third Trophic Level): Lion (Secondary Consumers / Top Carnivores)
Q17 | 2 Marks
What is the role of decomposers in the ecosystem?
Answer:
1) Decomposers (bacteria and fungi) breakdown complex organic substances of dead plants and animals into simple inorganic nutrients.
2) They replenish essential nutrients back into the soil, keeping the ecosystem clean and enabling natural nutrient recycling.
1) Decomposers (bacteria and fungi) breakdown complex organic substances of dead plants and animals into simple inorganic nutrients.
2) They replenish essential nutrients back into the soil, keeping the ecosystem clean and enabling natural nutrient recycling.
Q18 | 2 Marks
Why are plastic bags considered a threat to the environment? Suggest two alternatives.
Answer:
• Plastic bags are **non-biodegradable**; they cannot be decomposed by microbes, leading to soil degradation, choking of sewage drains, and toxicity to animals if ingested.
• Alternatives: (1) Cloth bags, (2) Jute bags or paper bags.
• Plastic bags are **non-biodegradable**; they cannot be decomposed by microbes, leading to soil degradation, choking of sewage drains, and toxicity to animals if ingested.
• Alternatives: (1) Cloth bags, (2) Jute bags or paper bags.
Q19 | 2 Marks
How is ozone formed in the upper atmosphere? Write the relevant balanced chemical equations.
Answer:
Ozone ($ O_3 $) is formed in the stratosphere when high-energy Ultraviolet (UV) radiation splits molecular oxygen ($ O_2 $) into free oxygen atoms ($ O $), which then react with $ O_2 $: $$ O_2 \xrightarrow{\text{UV Radiation}} O + O $$ $$ O + O_2 \longrightarrow O_3 \text{ (Ozone)} $$
Ozone ($ O_3 $) is formed in the stratosphere when high-energy Ultraviolet (UV) radiation splits molecular oxygen ($ O_2 $) into free oxygen atoms ($ O $), which then react with $ O_2 $: $$ O_2 \xrightarrow{\text{UV Radiation}} O + O $$ $$ O + O_2 \longrightarrow O_3 \text{ (Ozone)} $$
[IMAGE PLACEHOLDER: Ozone Shield & UV Ray Absorption]
3-Mark Questions & Solutions
Q20 | 3 Marks
Explain Lindeman's 10% law of energy transfer with a calculation example.
Answer:
• 10% Law: Only $ 10\% $ of the energy entering a particular trophic level is available for transfer to the next higher trophic level; $ 90\% $ is lost as heat in metabolic processes (respiration, movement, digestion).
• Calculation Example: $$\text{Plants (Producers)} = 10,000\text{ J}$$ $$\text{Herbivores (Primary Consumers)} = 10\% \text{ of } 10,000\text{ J} = 1000\text{ J}$$ $$\text{Carnivores (Secondary Consumers)} = 10\% \text{ of } 1000\text{ J} = 100\text{ J}$$ $$\text{Top Carnivores (Tertiary Consumers)} = 10\% \text{ of } 100\text{ J} = 10\text{ J}$$
• 10% Law: Only $ 10\% $ of the energy entering a particular trophic level is available for transfer to the next higher trophic level; $ 90\% $ is lost as heat in metabolic processes (respiration, movement, digestion).
• Calculation Example: $$\text{Plants (Producers)} = 10,000\text{ J}$$ $$\text{Herbivores (Primary Consumers)} = 10\% \text{ of } 10,000\text{ J} = 1000\text{ J}$$ $$\text{Carnivores (Secondary Consumers)} = 10\% \text{ of } 1000\text{ J} = 100\text{ J}$$ $$\text{Top Carnivores (Tertiary Consumers)} = 10\% \text{ of } 100\text{ J} = 10\text{ J}$$
Q21 | 3 Marks
What is biological magnification? Explain with the help of an example. Why is its concentration maximum in human beings?
Answer:
• Biological Magnification: The progressive increase in the concentration of non-biodegradable toxic chemicals (e.g., pesticides like DDT) at each successive trophic level in a food chain.
• Example: Pesticides sprayed on crops enter soil/water $\rightarrow$ absorbed by aquatic plants $\rightarrow$ eaten by small fish $\rightarrow$ eaten by large fish $\rightarrow$ consumed by humans.
• Maximum in Humans: Humans occupy the top position (highest trophic level) in most food chains, resulting in maximum accumulated chemical dosage.
• Biological Magnification: The progressive increase in the concentration of non-biodegradable toxic chemicals (e.g., pesticides like DDT) at each successive trophic level in a food chain.
• Example: Pesticides sprayed on crops enter soil/water $\rightarrow$ absorbed by aquatic plants $\rightarrow$ eaten by small fish $\rightarrow$ eaten by large fish $\rightarrow$ consumed by humans.
• Maximum in Humans: Humans occupy the top position (highest trophic level) in most food chains, resulting in maximum accumulated chemical dosage.
Q22 | 3 Marks
Differentiate between biodegradable and non-biodegradable wastes with suitable examples.
Answer:
1) Biodegradable Wastes: Substances that can be broken down into simpler non-toxic substances by saprophytic micro-organisms (e.g., vegetable peels, paper, cow dung, wood).
2) Non-Biodegradable Wastes: Substances that cannot be broken down by biological processes and persist in the environment for a long time (e.g., plastics, glass, DDT, heavy metals).
1) Biodegradable Wastes: Substances that can be broken down into simpler non-toxic substances by saprophytic micro-organisms (e.g., vegetable peels, paper, cow dung, wood).
2) Non-Biodegradable Wastes: Substances that cannot be broken down by biological processes and persist in the environment for a long time (e.g., plastics, glass, DDT, heavy metals).
[IMAGE PLACEHOLDER: Food Web Diagrams & Ecological Balance]
4-Mark Passage & 5-Mark Questions & Solutions
Q23 | 4 Marks
Passage on Waste Management and Ecological Balance:
(i) Why are kulhads (disposable clay cups) no longer encouraged in railways?
(ii) Give two methods of waste disposal.
(iii) What are the advantages of composting organic waste?
(i) Why are kulhads (disposable clay cups) no longer encouraged in railways?
(ii) Give two methods of waste disposal.
(iii) What are the advantages of composting organic waste?
Answer:
(i) Making kulhads on a massive scale resulted in the loss of fertile topsoil from agricultural fields.
(ii) Methods: (1) Recycling non-biodegradable materials, (2) Biogas and composting for organic wastes.
(iii) Converts organic waste into nutrient-rich manure, reduces landfill waste, and prevents methane emissions from open dumps.
(i) Making kulhads on a massive scale resulted in the loss of fertile topsoil from agricultural fields.
(ii) Methods: (1) Recycling non-biodegradable materials, (2) Biogas and composting for organic wastes.
(iii) Converts organic waste into nutrient-rich manure, reduces landfill waste, and prevents methane emissions from open dumps.
Q24 | 5 Marks
(a) Why is energy flow in an ecosystem unidirectional?
(b) Why is the length of a food chain generally limited to 3 to 4 trophic levels?
(c) What will happen if all carnivores are removed from a forest ecosystem?
(b) Why is the length of a food chain generally limited to 3 to 4 trophic levels?
(c) What will happen if all carnivores are removed from a forest ecosystem?
Answer:
(a) Energy captured by autotrophs from solar radiation cannot revert back to the sun, and energy passed to herbivores cannot return to autotrophs. It flows strictly in one direction.
(b) According to the $ 10\% $ law, $ 90\% $ energy is lost at each level. After $ 3\text{--}4 $ trophic levels, the amount of available energy becomes too small to support another level of consumers.
(c) Removing carnivores causes:
1) Rapid unchecked increase in herbivore population (e.g., deer).
2) Overgrazing of plants/trees, leading to loss of vegetation, soil erosion, and desertification.
3) Complete breakdown of ecological stability.
(a) Energy captured by autotrophs from solar radiation cannot revert back to the sun, and energy passed to herbivores cannot return to autotrophs. It flows strictly in one direction.
(b) According to the $ 10\% $ law, $ 90\% $ energy is lost at each level. After $ 3\text{--}4 $ trophic levels, the amount of available energy becomes too small to support another level of consumers.
(c) Removing carnivores causes:
1) Rapid unchecked increase in herbivore population (e.g., deer).
2) Overgrazing of plants/trees, leading to loss of vegetation, soil erosion, and desertification.
3) Complete breakdown of ecological stability.
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