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Our Environment: Class 10 Science answers, notes
Get summaries, questions, answers, solutions, notes, extras, PDF and guides for Chapter 13 Our Environment: Class 10 Science textbook, which is part of the syllabus for students studying under SEBA (Assam Board), NBSE (Nagaland Board), TBSE (Tripura Board), CBSE (Central Board), MBOSE (Meghalaya Board), BSEM (Manipur Board), WBBSE (West Bengal Board), and all other boards following the NCERT books. These solutions, however, should only be treated as references and can be modified/changed.
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Summary
Our environment is everything that surrounds us. It includes living things like plants, animals, and tiny microorganisms. It also includes non-living things such as air, water, soil, and sunlight. All these parts interact in an area, forming an ecosystem. A forest is a natural ecosystem, while a garden is human-made. In any ecosystem, all parts are connected and depend on each other.
Living things in an ecosystem get energy in different ways. Plants are producers because they make their own food using sunlight. Animals are consumers because they eat other organisms. Herbivores eat plants. Carnivores eat other animals. Omnivores eat both. When plants and animals die, decomposers like bacteria and fungi break them down. This returns nutrients to the soil, which plants use to grow. This cycle is vital for a healthy ecosystem.
Energy moves through an ecosystem in a food chain, showing who eats whom. For example, grass is a producer. A grasshopper eats the grass, a frog eats the grasshopper, and a snake might eat the frog. Each step is a trophic level. When energy moves from one level to the next, only about 10% is passed on. The rest is used or lost as heat. This energy loss means food chains are usually short, with few levels. Many interconnected food chains form a food web.
Human activities can introduce harmful chemicals, like pesticides, into the environment. These chemicals can enter food chains. They are not easily broken down and build up in organisms at each higher trophic level. This is called biological magnification. Animals at the top of the food chain, including humans, can end up with the highest amount of these harmful substances.
Our actions also affect the Earth’s atmosphere. The ozone layer, high in the atmosphere, shields us from the sun’s harmful ultraviolet (UV) radiation. Certain man-made chemicals, like CFCs once used in refrigerators, have damaged this protective layer. Global efforts are reducing these chemicals to help the ozone layer heal.
We generate a lot of waste. Some waste, like fruit peels, is biodegradable. Decomposers can break it down naturally. Other materials, like plastics, are non-biodegradable. They do not break down easily and can pollute the environment for a long time, harming wildlife. It is important to manage waste by reducing, reusing, and recycling to protect our environment.
Textbook solutions
Intext Questions and Answers I
1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer: Each step or level of the food chain forms a trophic level. An example of a food chain, stating the different trophic levels, is as follows:
- The autotrophs or the producers are at the first trophic level.
- The herbivores or the primary consumers come at the second trophic level.
- Small carnivores or the secondary consumers are at the third trophic level.
- Larger carnivores or the tertiary consumers form the fourth trophic level.
2. What is the role of decomposers in the ecosystem?
Answer: The role of decomposers in the ecosystem is that microorganisms, comprising bacteria and fungi, break down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants. This action ensures the natural replenishment of the soil.
Intext Questions and Answers II
1. Why are some substances biodegradable and some non-biodegradable?
Answer: Some substances are biodegradable because they are broken down by biological processes. Enzymes are specific in their action, and specific enzymes are needed for the break-down of a particular substance. Substances that are not broken down in this manner are said to be non-biodegradable. Because of this specificity of enzymes, many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes; these materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time.
2. Give any two ways in which biodegradable substances would affect the environment.
Answer: Two ways in which biodegradable substances would affect the environment are:
(i) When acted upon by microorganisms like bacteria and fungi, biodegradable substances such as dead remains and waste products of organisms are broken down into simple inorganic substances that go into the soil and are used up once more by the plants, contributing to the natural replenishment of the soil.
(ii) The breakdown of biodegradable substances by decomposers helps in clearing dead remains and waste products of organisms, preventing their accumulation in the environment.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer: Two ways in which non-biodegradable substances would affect the environment are:
(i) These substances may be inert and simply persist in the environment for a long time.
(ii) These substances may harm the various members of the eco-system.
Intext Questions and Answers III
1. What is ozone and how does it affect any ecosystem?
Answer: Ozone (O3) is a molecule formed by three atoms of oxygen. While ozone is a deadly poison, at the higher levels of the atmosphere, it performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Since the ozone layer protects against the ultraviolet radiation from the Sun, its presence is crucial for ecosystems, and damage to this layer could damage the environment.
2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer: You can help in reducing the problem of waste disposal through methods such as:
(i) Carrying cloth-bags to put purchases in while shopping. This is an environment-friendly practice that helps reduce waste, particularly plastic waste.
(ii) Reducing the generation of waste material by changing attitudes towards the use of disposable items. Improvements in life-style have resulted in greater amounts of waste material generation, and changes in attitude have a role to play, as more and more things we use are becoming disposable, contributing to the problem.
Exercise Questions and Answers
1. 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
Answer: Substances that are broken down by biological processes are said to be biodegradable. Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. Therefore, the groups from the options provided that contain only biodegradable items are:
(a) Grass, flowers and leather
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Group (b) is not included because plastic is a non-biodegradable material.
2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
Answer: A food chain is a series of organisms in which each organism is eaten by the next, showing the flow of energy from producers to consumers.
Option (a) lists grass, wheat, and mango, which are all producers and do not show a sequence of one organism eating another.
Option (b) Grass, goat and human, constitutes a food-chain because grass (a producer) is eaten by a goat (a primary consumer), which in turn is eaten by a human (a secondary consumer). This represents a sequence of organisms feeding on one another. Thus, the group that constitutes a food-chain is (b) Grass, goat and human.
3. 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
Answer: (d) All of the above
4. What will happen if we kill all the organisms in one trophic level?
Answer: If all the organisms in one trophic level are killed, it will disrupt the entire food chain. The organisms in the next higher level will lose their food source and may die, while those in the level below may increase in number due to the absence of predators or consumers. This imbalance can lead to the collapse of the ecosystem, affecting energy flow and nutrient cycling.
5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer: Yes, the impact of removing a trophic level differs depending on which level is removed, but no level can be eliminated without harming the ecosystem. If producers are removed, energy flow stops and all other organisms eventually die. Removing herbivores leads to overgrowth of plants and starvation of carnivores. If carnivores are removed, herbivore populations may grow unchecked and damage vegetation. Without decomposers, waste accumulates and nutrients are not recycled. Every trophic level is essential for maintaining balance in the ecosystem.
6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: Biological magnification is the phenomenon where harmful chemicals that are not degradable get accumulated progressively at each trophic level in a food chain. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in their bodies.
Yes, the levels of this magnification will be different at different levels of the ecosystem because these chemicals get accumulated progressively at each trophic level, with the maximum concentration of these chemicals accumulating in organisms at the top level.
7. What are the problems caused by the non-biodegradable wastes that we generate?
Answer: The problems caused by the non-biodegradable wastes that we generate are that these substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system. The disposal of the waste we generate is causing serious environmental problems.
8. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer: Even biodegradable waste can affect the environment if not properly managed. Biodegradable substances are broken down by biological processes, but large quantities can overwhelm natural systems. For example, excessive biodegradable waste can lead to the depletion of oxygen in water bodies during decomposition, harming aquatic life. It can also cause bad odours and attract pests. So, even though biodegradable waste eventually breaks down, improper disposal can still damage the environment.
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer: Damage to the ozone layer is a cause for concern because ozone at the higher levels of the atmosphere performs an essential function: it shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms; for example, it is known to cause skin cancer in human beings. Since the ozone layer protects against ultraviolet radiation from the Sun, damage to it could damage the environment.
The steps being taken to limit this damage include an agreement forged by the United Nations Environment Programme (UNEP) in 1987 to freeze CFC production at 1986 levels. It is now mandatory for all manufacturing companies to make CFC-free refrigerators throughout the world.
Extras
Additional MCQs (Knowledge Based)
1. What are the non-living constituents, such as temperature, rainfall, and soil, in an environment called?
A. Biotic components
B. Abiotic components
C. Ecological components
D. Physical components
Answer: B. Abiotic components
2. Which of the following is an example of a human-made ecosystem?
A. Forest
B. Pond
C. Garden
D. Lake
Answer: C. Garden
3. Organisms that can produce their own food from inorganic substances using sunlight are known as _____________.
A. Consumers
B. Decomposers
C. Producers
D. Heterotrophs
Answer: C. Producers
4. Microorganisms like bacteria and fungi, which break down dead organic matter, are classified as _____________.
A. Producers
B. Consumers
C. Scavengers
D. Decomposers
Answer: D. Decomposers
5. Each step or level in a food chain where energy transfer occurs is called a _____________.
A. Food web
B. Trophic level
C. Energy pyramid
D. Biomass level
Answer: B. Trophic level
6. In a typical terrestrial ecosystem, approximately what percentage of the sun’s energy falling on leaves is captured by green plants and converted into food energy?
A. 10%
B. 50%
C. 1%
D. 0.1%
Answer: C. 1%
7. What is the average percentage of organic matter present at one trophic level that is transferred to the next higher trophic level?
A. 1%
B. 10%
C. 50%
D. 100%
Answer: B. 10%
8. A complex network of interconnected food chains within an ecological community is referred to as a _____________.
A. Trophic system
B. Energy cycle
C. Food web
D. Ecological pyramid
Answer: C. Food web
9. The flow of energy through different trophic levels in an ecosystem is best described as:
A. Cyclic
B. Bidirectional
C. Multidirectional
D. Unidirectional
Answer: D. Unidirectional
10. What is the term for the phenomenon where the concentration of certain harmful, non-degradable chemicals increases progressively at each trophic level in a food chain?
A. Bioaccumulation
B. Eutrophication
C. Biological magnification
D. Biodegradation
Answer: C. Biological magnification
11. How many oxygen atoms combine to form a single molecule of ozone?
A. One
B. Two
C. Three
D. Four
Answer: C. Three
12. What essential protective function does the ozone layer perform in the higher levels of the atmosphere?
A. Traps greenhouse gases
B. Shields Earth from UV radiation
C. Regulates atmospheric temperature
D. Produces oxygen for breathing
Answer: B. Shields Earth from UV radiation
13. Which group of synthetic chemicals, widely used as refrigerants and in fire extinguishers, has been primarily implicated in the depletion of the ozone layer?
A. Polychlorinated biphenyls (PCBs)
B. Dichlorodiphenyltrichloroethane (DDT)
C. Chlorofluorocarbons (CFCs)
D. Sulphur dioxides (SO₂)
Answer: C. Chlorofluorocarbons (CFCs)
14. In which year did the United Nations Environment Programme (UNEP) succeed in forging an agreement to freeze the production of CFCs at 1986 levels?
A. 1977
B. 1987
C. 1997
D. 2007
Answer: B. 1987
15. Substances that can be broken down into simpler, harmless substances by the action of microorganisms are known as:
A. Non-biodegradable
B. Inert substances
C. Toxic substances
D. Biodegradable
Answer: D. Biodegradable
16. Given below are descriptions of different materials. Select the one that is typically non-biodegradable.
| Material | Description |
| W | Fruit peels |
| X | Cotton cloth |
| Y | Plastic cup |
| Z | Paper bag |
A. W
B. X
C. Y
D. Z
Answer: C. Y
17. With reference to ecological roles, complete the following: Grass: Producer :: Fungi: _____________.
A. Consumer
B. Decomposer
C. Herbivore
D. Autotroph
Answer: B. Decomposer
18. Which category of organisms forms the first trophic level in all food chains?
A. Herbivores
B. Carnivores
C. Decomposers
D. Producers
Answer: D. Producers
19. This molecule is essential for all aerobic forms of life, while its allotrope, ozone, is a deadly poison at ground level. Identify this essential molecule.
A. Nitrogen (N₂)
B. Oxygen (O₂)
C. Carbon dioxide (CO₂)
D. Hydrogen (H₂)
Answer: B. Oxygen (O₂)
20. Identify the odd one out from the following abiotic components of an ecosystem.
A. Sunlight
B. Wind
C. Microorganisms
D. Rainfall
Answer: C. Microorganisms
21. Identify the biotic components of an ecosystem:
P. Soil
Q. Plants
R. Minerals
S. Animals
A. P and R
B. Q and S
C. P and Q
D. R and S
Answer: B. Q and S
22. Which of the following is NOT a primary role of producers in an ecosystem?
A. Fixing solar energy
B. Converting light to chemical energy
C. Consuming other organisms
D. Forming the food chain base
Answer: C. Consuming other organisms
23. What are the living organisms within an ecosystem collectively termed?
A. Abiotic factors
B. Physical factors
C. Biotic components
D. Chemical factors
Answer: C. Biotic components
24. Crop-fields represent what kind of ecosystem?
A. Natural aquatic
B. Human-made terrestrial
C. Natural terrestrial
D. Human-made aquatic
Answer: B. Human-made terrestrial
25. What is the ultimate source of energy for the vast majority of ecosystems on Earth?
A. Geothermal heat
B. Chemical bonds
C. Moonlight
D. Sunlight
Answer: D. Sunlight
26. What is the chemical formula representing ozone?
A. O
B. O₂
C. O₃
D. O₄
Answer: C. O₃
27. Which international protocol or agreement specifically addressed the issue of ozone-depleting substances like CFCs?
A. Kyoto Protocol
B. Paris Agreement
C. Montreal Protocol (implied by UNEP agreement)
D. Rio Declaration
Answer: C. Montreal Protocol (implied by UNEP agreement)
28. Materials like plastics, which are not broken down by microorganisms, are classified as:
A. Biodegradable
B. Organic
C. Non-biodegradable
D. Compostable
Answer: C. Non-biodegradable
29. What material were ‘kulhads’, once suggested as an alternative to plastic cups for serving beverages, traditionally made from?
A. Glass
B. Metal
C. Clay
D. Paper
Answer: C. Clay
30. Which of the following groups contains only biodegradable items?
A. Grass, flowers, glass
B. Grass, wood, plastic
C. Fruit-peels, cake, lime-juice
D. Cake, wood, glass
Answer: C. Fruit-peels, cake, lime-juice
31. Which of the following correctly represents a food chain?
A. Grass → wheat → mango
B. Grass → goat → human
C. Goat → cow → elephant
D. Grass → fish → goat
Answer: B. Grass → goat → human
32. The primary reason for the limited number of trophic levels (usually 3-4) in a food chain is:
A. Limited food availability
B. Scarcity of top carnivores
C. Significant loss of energy at each step
D. Slow reproduction rates
Answer: C. Significant loss of energy at each step
33. An aquarium, if set up with fish, aquatic plants, an aerator, and food, can be considered a self-sustaining system and is an example of a:
A. Natural pond ecosystem
B. Human-made ecosystem
C. Complex food web
D. Biome
Answer: B. Human-made ecosystem
34. Organisms that feed directly on producers are known as:
A. Secondary consumers
B. Decomposers
C. Primary consumers
D. Tertiary consumers
Answer: C. Primary consumers
35. The process by which UV radiation splits molecular oxygen (O₂) into free oxygen atoms (O), which then combine with other O₂ molecules to form ozone (O₃), occurs in the:
A. Lower atmosphere
B. Higher levels of the atmosphere
C. Earth’s core
D. Hydrosphere
Answer: B. Higher levels of the atmosphere
Additional MCQs (Competency Based)
1. Assertion (A): The ozone layer in the upper atmosphere is crucial for life on Earth.
Reason (R): Ozone (O₃) is formed from oxygen (O₂) by the action of UV radiation and it absorbs harmful UV rays from the sun.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
2. A remote village relies on a local lake for fishing. After a new agricultural practice involving extensive pesticide use was adopted in the surrounding farms, the villagers noticed a significant decline in the fish population, and the larger predatory fish seemed more affected than smaller fish. Which of the following is the LEAST plausible explanation for the decline in the overall fish population?
(a) Direct toxicity of pesticides to fish.
(b) Biological magnification of pesticides affecting predatory fish more severely.
(c) Reduction in food sources (e.g., aquatic insects) for fish due to pesticides.
(d) A sudden, unrelated outbreak of a fish disease that coincided with pesticide use.
Answer: (d) A sudden, unrelated outbreak of a fish disease that coincided with pesticide use.
3. Match the items in Column A with their most appropriate description in Column B.
| Column A | Column B |
| (i) Producers | 1. Break down dead organic matter |
| (ii) Herbivores | 2. Feed on primary consumers |
| (iii) Decomposers | 3. Convert solar energy into chemical energy |
| (iv) Carnivores (Secondary) | 4. Feed directly on producers |
Select the correct option:
(a) (i)-3, (ii)-4, (iii)-1, (iv)-2
(b) (i)-3, (ii)-1, (iii)-4, (iv)-2
(c) (i)-4, (ii)-3, (iii)-2, (iv)-1
(d) (i)-2, (ii)-4, (iii)-1, (iv)-3
Answer: (a) (i)-3, (ii)-4, (iii)-1, (iv)-2
4. Arrange the following trophic levels in the correct order from the base to the top of an energy pyramid in a typical ecosystem:
(i) Tertiary Consumers
(ii) Producers
(iii) Primary Consumers
(iv) Secondary Consumers
(a) (ii) → (iv) → (iii) → (i)
(b) (ii) → (iii) → (iv) → (i)
(c) (i) → (iv) → (iii) → (ii)
(d) (iii) → (ii) → (i) → (iv)
Answer: (b) (ii) → (iii) → (iv) → (i)
5. If the producers in a food chain capture 10,000 Joules of solar energy to convert into food energy, approximately how much energy will be available to the secondary consumers in that food chain, assuming the 10% energy transfer rule at each trophic level?
(a) 1000 Joules
(b) 100 Joules
(c) 10 Joules
(d) 1 Joule
Answer: (b) 100 Joules
6. Consider the following simplified food web:
Grass → Grasshopper → Frog → Snake
Grass → Rabbit → Fox
Which statement is accurate based on this food web?
(a) The frog and rabbit occupy the same trophic level.
(b) The snake is a primary consumer.
(c) If the grasshopper population decreases, the frog population is likely to be unaffected.
(d) Grass is the producer in both food chains.
Answer: (d) Grass is the producer in both food chains.
7. A student sets up two identical aquariums. Aquarium A contains fish, aquatic plants, and an aerator. Aquarium B contains only fish and an aerator. After a few weeks, the fish in Aquarium B appear less healthy and the water requires more frequent cleaning than Aquarium A. The primary reason for this difference is:
(a) The plants in Aquarium A consume excess fish food.
(b) The plants in Aquarium A provide shelter for the fish.
(c) The plants in Aquarium A contribute to oxygen production and nutrient cycling.
(d) The fish in Aquarium B are more susceptible to diseases.
Answer: (c) The plants in Aquarium A contribute to oxygen production and nutrient cycling.
8. Assertion (A): Non-biodegradable wastes like plastics pose a serious environmental threat.
Reason (R): Microorganisms can easily decompose plastics into harmless substances, returning them to the soil.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (c) A is true but R is false.
9. Match the environmental concern in Column A with its primary cause or characteristic in Column B.
| Column A | Column B |
| (i) Ozone layer depletion | 1. Accumulation of toxins in food chains |
| (ii) Biological magnification | 2. Breakdown by microorganisms |
| (iii) Biodegradable waste | 3. Release of Chlorofluorocarbons (CFCs) |
| (iv) Artificial ecosystem | 4. Human-made and managed, like a crop field |
Select the correct option:
(a) (i)-1, (ii)-3, (iii)-2, (iv)-4
(b) (i)-3, (ii)-1, (iii)-4, (iv)-2
(c) (i)-3, (ii)-1, (iii)-2, (iv)-4
(d) (i)-2, (ii)-4, (iii)-1, (iv)-3
Answer: (c) (i)-3, (ii)-1, (iii)-2, (iv)-4
10. Arrange the steps of energy flow in a terrestrial ecosystem, starting from the initial energy source:
(i) Energy transfer to primary consumers
(ii) Solar energy captured by producers
(iii) Energy transfer to secondary consumers
(iv) Conversion of solar energy to chemical energy by producers
(a) (ii) → (i) → (iv) → (iii)
(b) (ii) → (iv) → (i) → (iii)
(c) (iv) → (ii) → (i) → (iii)
(d) (i) → (ii) → (iii) → (iv)
Answer: (b) (ii) → (iv) → (i) → (iii)
11. If green plants in a terrestrial ecosystem capture approximately 1% of the energy of sunlight that falls on their leaves, and the total sunlight energy falling on the leaves of plants in a specific area is 500,000 kJ, how much energy is converted into food energy by these plants?
(a) 50 kJ
(b) 500 kJ
(c) 5,000 kJ
(d) 50,000 kJ
Answer: (c) 5,000 kJ
12. “The interactions among various components of the environment involve flow of energy from one component of the system to another. From autotrophs, the energy goes to the heterotrophs and decomposers. However, when one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again.”
This statement implies that:
(a) Energy transfer between trophic levels is 100% efficient.
(b) Energy is recycled within an ecosystem, similar to nutrients.
(c) The amount of usable energy decreases at each successive trophic level.
(d) Decomposers create new energy for the ecosystem.
Answer: (c) The amount of usable energy decreases at each successive trophic level.
13. In a garden ecosystem, if a new, highly effective pesticide is introduced that eliminates all insect species, which of the following is LEAST likely to be an immediate consequence?
(a) A decline in the population of insectivorous birds.
(b) A decrease in pollination for some flowering plants.
(c) An initial surge in plant growth due to reduced herbivory by insects.
(d) An immediate increase in the soil decomposer population.
Answer: (d) An immediate increase in the soil decomposer population.
14. Assertion (A): An aquarium, if set up with only fish and water, requires regular cleaning and addition of food.
Reason (R): In such a setup, there are no producers to generate food or decomposers to break down waste effectively.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
15. Match the term in Column A with its correct definition or example in Column B.
| Column A | Column B |
| (i) Abiotic component | 1. A food chain showing who eats whom |
| (ii) Trophic level | 2. Organisms like bacteria and fungi |
| (iii) Decomposers | 3. Non-living factors like temperature, soil |
| (iv) Food web | 4. Each step in a food chain |
Select the correct option:
(a) (i)-3, (ii)-4, (iii)-2, (iv)-1
(b) (i)-2, (ii)-1, (iii)-3, (iv)-4
(c) (i)-3, (ii)-1, (iii)-2, (iv)-4
(d) (i)-4, (ii)-3, (iii)-1, (iv)-2
Answer: (a) (i)-3, (ii)-4, (iii)-2, (iv)-1
16. Consider the process of biological magnification of a pesticide. Arrange the following organisms in the order of increasing concentration of the pesticide in their bodies, starting from the lowest concentration.
(i) Large predatory fish
(ii) Phytoplankton (producers)
(iii) Small fish (primary consumers)
(iv) Zooplankton (herbivores feeding on phytoplankton)
(a) (ii) → (iv) → (iii) → (i)
(b) (i) → (iii) → (iv) → (ii)
(c) (ii) → (iii) → (iv) → (i)
(d) (iv) → (ii) → (i) → (iii)
Answer: (a) (ii) → (iv) → (iii) → (i)
17. A food chain consists of: Phytoplankton → Zooplankton → Small Fish → Large Fish.
If the concentration of a non-degradable pesticide in Phytoplankton is 0.01 ppm, and biological magnification causes a 10-fold increase in concentration at each successive trophic level, what would be the approximate pesticide concentration in Large Fish?
(a) 0.01 ppm
(b) 0.1 ppm
(c) 1 ppm
(d) 10 ppm
Answer: (d) 10 ppm
18. “Chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers, have been linked to the depletion of the ozone layer. In 1987, an international agreement aimed to freeze CFC production.”
What is the primary environmental service provided by the ozone layer that CFCs threaten?
(a) Regulating global temperatures.
(b) Shielding the Earth from harmful ultraviolet (UV) radiation.
(c) Producing oxygen for respiration.
(d) Facilitating cloud formation.
Answer: (b) Shielding the Earth from harmful ultraviolet (UV) radiation.
19. A community decides to manage its organic waste by creating a large compost pit. They add kitchen scraps, yard trimmings, and paper. Which group of organisms is primarily responsible for breaking down this organic matter into nutrient-rich compost?
(a) Producers like algae and moss.
(b) Primary consumers like earthworms and millipedes.
(c) Decomposers like bacteria and fungi.
(d) Secondary consumers like birds that might visit the pit.
Answer: (c) Decomposers like bacteria and fungi.
20. Assertion (A): The choice between disposable paper cups and plastic cups involves considering different environmental impacts for each.
Reason (R): Paper cup production can contribute to deforestation, while plastic cups are non-biodegradable and persist in the environment.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
21. Match the activity in Column A with its potential environmental consequence in Column B.
| Column A | Column B |
| (i) Excessive use of pesticides in agriculture | 1. Depletion of the stratospheric ozone layer |
| (ii) Release of CFCs from old refrigerators | 2. Accumulation of non-biodegradable waste |
| (iii) Disposing of plastic packaging | 3. Biological magnification in food webs |
| (iv) Setting up a large-scale kulhad production | 4. Loss of fertile top-soil |
Select the correct option:
(a) (i)-2, (ii)-1, (iii)-4, (iv)-3
(b) (i)-3, (ii)-1, (iii)-2, (iv)-4
(c) (i)-1, (ii)-3, (iii)-2, (iv)-4
(d) (i)-3, (ii)-4, (iii)-1, (iv)-2
Answer: (b) (i)-3, (ii)-1, (iii)-2, (iv)-4
22. The formation of ozone in the upper atmosphere involves the following steps. Arrange them in the correct sequence:
(i) Free oxygen atoms (O) combine with molecular oxygen (O₂)
(ii) UV radiation splits molecular oxygen (O₂)
(iii) Ozone (O₃) is formed
(a) (i) → (ii) → (iii)
(b) (ii) → (iii) → (i)
(c) (ii) → (i) → (iii)
(d) (iii) → (ii) → (i)
Answer: (c) (ii) → (i) → (iii)
23. In an ecosystem, producers have 20,000 kJ of energy. According to the 10% law of energy transfer, how much energy is transferred from primary consumers to secondary consumers?
(a) 20,000 kJ
(b) 2,000 kJ
(c) 200 kJ
(d) 20 kJ
Answer: (c) 200 kJ
24. “An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.”
Which of the following is an example of an interaction between a biotic and an abiotic component in a garden ecosystem?
(a) A bird eating an insect.
(b) A frog hiding under a leaf.
(c) Plants absorbing water and minerals from the soil.
(d) Two bees competing for nectar from the same flower.
Answer: (c) Plants absorbing water and minerals from the soil.
25. Assertion (A): All human-made materials, like plastics, eventually biodegrade naturally in the environment.
Reason (R): Physical processes like heat and pressure can act upon these materials, but under ambient environmental conditions, many persist for a long time.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
Additional Questions and Answers
1. What is an ecosystem?
Answer: All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
2. What are the biotic components of an ecosystem?
Answer: An ecosystem consists of biotic components comprising living organisms.
3. What are the abiotic components of an ecosystem?
Answer: An ecosystem consists of abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.
4. Give two examples of natural ecosystems.
Answer: Two examples of natural ecosystems are forests and ponds.
5. Give two examples of human-made ecosystems.
Answer: Two examples of human-made (artificial) ecosystems are gardens and crop-fields. An aquarium is also an example of a human-made ecosystem.
6. Which organisms produce food by photosynthesis?
Answer: All green plants and certain bacteria which can produce food by photosynthesis are called the producers.
7. What process allows certain organisms to make organic compounds using sunlight?
Answer: Photosynthesis is the process that allows certain organisms, like all green plants and certain bacteria, to make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll.
8. Name the four categories of consumers.
Answer: Consumers can be classed variously as:
(i) Herbivores
(ii) Carnivores
(iii) Omnivores
(iv) Parasites
9. What is a food chain?
Answer: A series of organisms taking part at various biotic levels form a food chain (Fig. 13.1).
10. Define trophic level.
Answer: Each step or level of the food chain forms a trophic level.
11. What is a food web?
Answer: Instead of a straight line food chain, the relationship where each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms can be shown as a series of branching lines called a food web (Fig. 13.3).
12. What percentage of sunlight energy do green plants capture?
Answer: The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.
13. What percentage of energy is transferred from one trophic level to the next?
Answer: An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers.
14. Why are food chains generally limited to three or four trophic levels?
Answer: Food chains generally consist of only three or four steps because so little energy is available for the next level of consumers. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
15. What phenomenon describes the progressive accumulation of non-degradable chemicals at successive trophic levels?
Answer: The phenomenon where non-degradable chemicals get accumulated progressively at each trophic level, resulting in the maximum concentration of these chemicals in human beings who occupy the top level in any food chain, is known as biological magnification.
16. What is the chemical formula of ozone?
Answer: Ozone (O₃) is a molecule formed by three atoms of oxygen.
17. How is ozone formed in the upper atmosphere? (Write the reactions.)
Answer: Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O₂) molecule. The higher energy UV radiations split apart some molecular oxygen (O₂) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown:
O₂ –UV–> O + O
O + O₂ –> O₃ (Ozone)
18. Which synthetic chemicals are responsible for ozone layer depletion?
Answer: The decrease in the amount of ozone in the atmosphere has been linked to synthetic chemicals like chlorofluorocarbons (CFCs).
19. In which year was CFC production frozen at 1986 levels under the United Nations Environment Programme?
Answer: In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.
20. What term describes substances broken down by biological processes?
Answer: Substances that are broken down by biological processes are said to be biodegradable.
21. What term describes substances that persist without being broken down biologically?
Answer: Substances that are not broken down by biological processes are said to be non-biodegradable.
22. Why do plastics persist in the environment under ambient conditions?
Answer: Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time.
23. Name four types of household waste materials.
Answer: Four types of household waste materials could include:
(i) Spoilt food
(ii) Vegetable peels
(iii) Waste paper
(iv) Old and torn clothes
24. What role do aerators play in maintaining an aquarium ecosystem?
Answer: In an aquarium, an oxygen pump (aerator) can provide oxygen.
25. Explain the components of an ecosystem and illustrate with examples.
Answer: An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
For example, if you visit a garden you will find different plants, such as grasses, trees; flower bearing plants like rose, jasmine, sunflower; and animals like frogs, insects and birds. All these living organisms interact with each other and their growth, reproduction and other activities are affected by the abiotic components of ecosystem. So a garden is an ecosystem. Other types of ecosystems are forests, ponds and lakes. These are natural ecosystems while gardens and crop-fields are human-made (artificial) ecosystems.
26. Describe the roles of producers, consumers and decomposers in maintaining ecosystem balance.
Answer: Producers, consumers, and decomposers are grouped according to the manner in which they obtain their sustenance from the environment, and their interactions help maintain a balance in nature.
Producers, such as all green plants and certain bacteria which can produce food by photosynthesis, make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll. They fix up the solar energy and make it available for heterotrophs or the consumers.
Consumers are organisms that depend on the producers either directly or indirectly for their sustenance. These organisms consume the food produced, either directly from producers or indirectly by feeding on other consumers. Consumers can be classed variously as herbivores, carnivores, omnivores and parasites.
Decomposers, such as microorganisms comprising bacteria and fungi, break-down the dead remains and waste products of organisms. They break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants. This ensures the natural replenishment of the soil. If decomposers are not there, garbage, and dead animals and plants would not be broken down, and the natural replenishment of the soil would not take place.
27. Discuss the flow of energy through trophic levels, including energy capture by autotrophs and transfer efficiency.
Answer: The interactions among various components of the environment involve flow of energy from one component of the system to another. Autotrophs capture the energy present in sunlight and convert it into chemical energy. This energy supports all the activities of the living world. From autotrophs, the energy goes to the heterotrophs and decomposers.
The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy. When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers. Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers. Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
The flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs. As it moves progressively through the various trophic levels it is no longer available to the previous level. Secondly, the energy available at each trophic level gets diminished progressively due to loss of energy at each level.
28. Compare food chains and food webs in terms of their structure and ecological significance.
Answer: A food chain is a series of organisms feeding on one another, where organisms taking part at various biotic levels form the chain. Each step or level of the food chain forms a trophic level.
The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web. A food web consists of many food chains.
Both food chains and food webs illustrate the flow of energy in an ecosystem. Food chains show a single pathway of energy flow, while food webs show multiple interconnected pathways, representing a more realistic depiction of feeding relationships and energy transfer in an ecosystem.
29. Describe biological magnification and explain its impact on organisms at higher trophic levels.
Answer: Biological magnification is the phenomenon where harmful chemicals, such as pesticides, enter our bodies through the food chain. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This is the reason why our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues.
30. Explain how ozone is formed in the upper atmosphere through photochemical reactions.
Answer: Ozone (O₃) is a molecule formed by three atoms of oxygen. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O₂) molecule. The higher energy UV radiations split apart some molecular oxygen (O₂) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown:
O₂ →(UV) O + O
O + O₂ → O₃ (Ozone)
31. Examine how chlorofluorocarbons contribute to ozone layer depletion and its potential effects on living organisms.
Answer: The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. Ozone performs an essential function at the higher levels of the atmosphere: it shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Depletion of the ozone layer allows more UV radiation to reach the Earth’s surface, increasing these harmful effects.
32. Outline the key provisions and outcomes of the 1987 agreement to control CFC emissions.
Answer: In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world.
33. Differentiate between biodegradable and non-biodegradable substances and discuss their environmental impacts.
Answer: Substances that are broken down by biological processes are said to be biodegradable. Substances that are not broken down in this manner are said to be non-biodegradable.
Biodegradable substances, when disposed of, are acted upon by microorganisms and broken down into simpler, harmless substances, returning nutrients to the ecosystem.
Non-biodegradable substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system. Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time. The disposal of the waste we generate, particularly non-biodegradable waste, is causing serious environmental problems.
34. Explain why plastics persist for long periods in the environment under ambient conditions.
Answer: Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes. Enzymes are specific in their action, specific enzymes are needed for the break-down of a particular substance. Because of this, plastics will not be broken down. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time.
35. Why were disposable cups introduced in trains originally?
Answer: The introduction of disposable cups was hailed as a step forward for reasons of hygiene.
36. Why are some substances biodegradable and others non-biodegradable?
Answer: Substances that are broken down by biological processes are said to be biodegradable. This breakdown is facilitated by enzymes, which are specific in their action; specific enzymes are needed for the break-down of a particular substance. Substances that are not broken down in this manner are said to be non-biodegradable. Many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes because the necessary enzymes to break them down are not present or effective.
