CBSE Class 10 Science • Ecosystems and Environmental Awareness
Our Environment Class 10 Worksheet with Answers
How does energy move through a food chain? Why do some pollutants become more concentrated in predators? Use the Our Environment Class 10 worksheet with answers to revise ecosystems, trophic levels, decomposers, biological magnification, ozone depletion and waste management.
Our Environment connects living organisms with their surroundings. Plants, animals and microorganisms interact with sunlight, water, air and soil. Understanding these relationships helps you explain how changes in one part of an ecosystem can affect other parts.
Attempt the worksheet independently before checking the answers. The Our Environment Class 10 short notes, examples and practice questions below support concept revision and preparation for a chapter test.
Our Environment Class 10 Summary
| Concept | Key idea | Example |
|---|---|---|
| Ecosystem | Organisms interact with one another and their physical surroundings. | A pond, forest or garden. |
| Food chain | A feeding pathway through which matter and energy pass. | Grass → grasshopper → frog → snake. |
| Trophic level | A feeding position in a food chain. | Producers occupy the first level. |
| Decomposition | Breakdown of dead organic matter and wastes. | Bacteria and fungi acting on fallen leaves. |
| Biological magnification | Increasing concentration of certain pollutants across trophic levels. | Persistent pesticides accumulating in predators. |
| Ozone protection | Stratospheric ozone absorbs harmful ultraviolet radiation. | Protection from much of the Sun’s UV radiation. |
Ecosystem: Biotic and Abiotic Components
Biotic components are living organisms, including plants, animals and microorganisms. Abiotic components are non-living factors such as light, temperature, water, air and soil conditions. Together, they influence how an ecosystem functions.
Producers
Producers make organic food from inorganic materials. In familiar ecosystems, green plants and algae use sunlight through photosynthesis. They provide the starting point for most food chains studied at this level.
Consumers
Consumers obtain food from other organisms. Herbivores feeding on producers are primary consumers. Animals feeding on primary consumers are secondary consumers. Higher consumers occupy later feeding levels.
Decomposers
Many bacteria and fungi break down dead organisms and organic wastes. They help return nutrients to the surroundings, where producers can use them again. Decomposers act on material originating from different trophic levels.
Nutrients Cycle, but Energy Flows
Decomposers recycle nutrients. They do not recycle energy back into sunlight. Energy moves through the ecosystem and is progressively dissipated as heat.
Food Chains and Food Webs Class 10
A food chain shows a sequence of feeding relationships. Its arrows point from the organism being eaten towards the organism that eats it, indicating the direction of energy transfer.
Example: Identify the Trophic Levels
Grass → grasshopper → frog → snake
Grass: producer, first trophic level.
Grasshopper: primary consumer, second level.
Frog: secondary consumer, third level.
Snake: tertiary consumer, fourth level.
A food web connects several food chains. Most organisms have more than one food source or predator, so a web represents feeding relationships more realistically than a single chain. An omnivore may occupy different trophic positions depending on what it eats.
The 10 Percent Law of Energy Transfer
The textbook 10 percent rule estimates that about one-tenth of the energy available at one trophic level becomes available at the next. The actual efficiency varies between ecosystems. Organisms use much of their energy in life processes, and not all biomass is eaten or assimilated.
Worked Example: Energy in a Food Chain
Producers contain 20,000 J of available energy. Estimate the energy at each following level using the 10 percent rule.
Primary consumers = 20,000 × 10/100
Primary consumers = 2,000 J
Secondary consumers = 2,000 × 10/100
Secondary consumers = 200 J
Tertiary consumers = 200 × 10/100
Tertiary consumers = 20 J
Answer: 2,000 J, 200 J and 20 J respectively. Declining energy availability limits the number of feeding levels that can be supported.
Check Where the Given Energy Starts
Energy arriving as sunlight is different from energy already stored in producers. Apply the 10 percent rule between trophic levels, not automatically between sunlight and plants.
Biological Magnification Class 10
Biological magnification, also called biomagnification, is an increase in the concentration of certain persistent pollutants at successive trophic levels. A predator can consume many contaminated prey, allowing pollutants that are retained in tissues to become more concentrated.
For example, a persistent pesticide may enter water, accumulate in small organisms and pass to fish and fish-eating birds. The highest concentration may occur in organisms at the top of that food chain.
Biomagnification and Bioaccumulation
Bioaccumulation: a substance builds up within an organism over time.
Biomagnification: its concentration increases across trophic levels.
Not every pollutant biomagnifies. Persistence and the organism’s ability to absorb, break down and eliminate the substance matter.
Biodegradable and Non-Biodegradable Waste
| Feature | Biodegradable waste | Non-biodegradable waste |
|---|---|---|
| Biological breakdown | Can be broken down by organisms under suitable conditions. | Does not readily undergo biological breakdown. |
| Examples | Vegetable peels, food scraps and untreated plant material. | Many conventional plastics, glass and metal items. |
| Management | Suitable organic waste can be composted. | Reduce use, reuse and recycle suitable materials. |
| Important caution | Large quantities can still cause pollution. | Persistence does not mean every item biomagnifies. |
Segregating waste helps keep compostable material separate from recyclable and hazardous items. Reducing unnecessary consumption and reusing products can prevent waste before disposal becomes necessary.
Ozone Layer and Ozone Depletion
Ozone is a form of oxygen with formula O₃. In the stratosphere, it absorbs harmful ultraviolet radiation. This protective role differs from ozone near ground level, where it is an air pollutant.
Ultraviolet radiation can split oxygen molecules into oxygen atoms. These atoms can combine with oxygen molecules to form ozone. Certain ozone-depleting substances, including chlorofluorocarbons, release reactive species in the stratosphere that destroy ozone.
Ozone Depletion Is Different from Global Warming
Ozone depletion concerns loss of protective stratospheric ozone. Global warming concerns an increase in Earth’s average temperature associated with changes in the energy balance, including increased greenhouse gases.
Our Environment Class 10 MCQs with Answers
1. Which organism occupies the first trophic level?
A. Grass
B. Grasshopper
C. Frog
D. Snake
Answer: A. Grass. Producers occupy the first trophic level.
2. Which organisms commonly act as decomposers?
A. Only large herbivores
B. Many bacteria and fungi
C. Only green plants
D. Only predators
Answer: B. Many bacteria and fungi break down dead organic matter.
3. If producers contain 10,000 J, how much reaches secondary consumers under the 10 percent rule?
A. 10,000 J
B. 1,000 J
C. 100 J
D. 10 J
Answer: C. 100 J. Primary consumers receive about 1,000 J, followed by about 100 J at the secondary-consumer level.
Assertion–Reason Practice
Assertion: Energy available generally decreases at successive trophic levels.
Reason: Organisms use energy in life processes, and only part becomes available to the next feeding level.
Answer: Both statements are true, and the reason correctly explains the assertion.
Our Environment Class 10 Case-Based Questions
Case Study: A Pollutant in a Pond
A persistent pesticide enters a pond. It is absorbed by small organisms, which are eaten by fish. Birds then feed on the fish. Testing finds a higher pesticide concentration in the birds’ tissues.
Question 1: Name the phenomenon.
Biological magnification.
Question 2: Why can concentration increase?
Predators consume contaminated prey, and a retained
pollutant builds up faster than it is eliminated.
Question 3: Does this mean energy also increases
towards the top?
No. Available energy generally decreases across
successive trophic levels.
Question 4: Suggest a way to reduce this problem.
Prevent harmful persistent pollutants from entering
water bodies and manage chemical waste appropriately.
Our Environment Class 10 Important Questions
- Define an ecosystem and identify its biotic and abiotic components.
- Distinguish producers, consumers and decomposers.
- Construct a food chain and identify its trophic levels.
- Explain how a food web differs from a food chain.
- Apply the 10 percent rule to an energy-transfer calculation.
- Explain why energy flow is unidirectional.
- Describe biological magnification with an example.
- Compare biodegradable and non-biodegradable wastes.
- Explain the protective role of stratospheric ozone.
- Suggest practical methods to reduce and manage waste.
How to Use the Worksheet as a Chapter Test
Attempt the worksheet without consulting the answers. For food-chain questions, check arrow direction and count producers as the first trophic level. For energy questions, identify the starting level before calculating.
Review errors under definitions, feeding relationships, energy transfer, pollutants or waste. Practise explaining each answer with a suitable example.
Frequently Asked Questions
Why are producers placed at the first trophic level?
They make organic food that supports consumers. In familiar ecosystems, they capture solar energy through photosynthesis.
Which direction should a food-chain arrow point?
It points from food to consumer, showing energy transfer. For example, grass → rabbit means the rabbit eats grass.
Can an organism occupy more than one trophic level?
Yes. An omnivore can occupy different levels depending on whether it eats producers or other consumers.
Do decomposers act only at the end of a food chain?
No. They break down dead material and wastes originating from different trophic levels throughout the ecosystem.
Is exactly 10 percent of energy transferred every time?
No. Ten percent is a useful textbook approximation. Actual transfer efficiency varies with organisms and ecological conditions.
Does every non-biodegradable material biomagnify?
No. Biomagnification depends on properties such as persistence, uptake and retention. A discarded glass bottle does not biomagnify simply because it persists.
Is biodegradable waste always harmless?
No. Excess organic waste can cause odour, support pests and deplete oxygen during decomposition in water. Proper management remains necessary.
Why is ozone useful high in the atmosphere but harmful near the ground?
Stratospheric ozone absorbs harmful ultraviolet radiation. Ground-level ozone can harm living tissues and is a component of air pollution.
Are ozone depletion and the greenhouse effect the same?
No. Ozone depletion reduces UV protection. The greenhouse effect concerns the absorption and emission of infrared radiation by atmospheric gases.
How can I prepare Our Environment Class 10 extra questions?
Practise food chains, trophic-level identification, energy calculations and explanations of environmental problems. Use precise definitions and relevant examples.
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