CBSE Class 10 Science Our Environment Notes

2. Key Concepts and Components

2.1 Biotic Components

Biotic components are the living parts of the ecosystem. They are classified based on their mode of nutrition:

•         Producers (Autotrophs): Green plants, algae, and cyanobacteria that prepare their own food through photosynthesis. They form the base of all food chains.

•         Consumers (Heterotrophs): Organisms that depend on producers or other consumers for food. Classified as Primary, Secondary, and Tertiary consumers.

•         Decomposers (Saprotrophs): Bacteria and fungi that break down dead organic matter into simple inorganic substances, returning nutrients to the soil.

2.2 Abiotic Components

Abiotic components are the non-living physical and chemical factors of the environment:

•         Climatic factors: Temperature, rainfall, humidity, wind, light

•         Edaphic factors: Soil type, pH, mineral content

•         Topographic factors: Altitude, slope, aspect

•         Aquatic factors: Water pH, salinity, dissolved oxygen

2.3 Food Chain

Food chain is a linear sequence showing the transfer of food energy from one organism to another. Energy flows from producers to consumers in a unidirectional manner.

Grass --> Grasshopper --> Frog --> Snake --> Eagle

Each level in a food chain is called a Trophic Level. Producers occupy the 1st trophic level, herbivores the 2nd, carnivores the 3rd, and so on.

2.4 Food Web

Food web is a network of interconnected food chains in an ecosystem. It represents more realistic feeding relationships. Food webs provide stability to ecosystems - if one species is removed, others can compensate.

2.5 Biodegradable and Non-biodegradable Wastes

•         Biodegradable waste: Materials that can be broken down by microorganisms (bacteria, fungi). Example: vegetable peels, paper, cotton, wood, animal waste

•         Non-biodegradable waste: Materials that cannot be broken down by microorganisms and persist in the environment. Example: plastics, synthetic fibers, metals, glass, nuclear waste

2.6 Biological Magnification (Biomagnification)

Biological magnification is the progressive increase in the concentration of harmful chemicals (like DDT, pesticides) as they move up through the food chain. Since these substances are not easily metabolized, they accumulate in fatty tissues.

Organisms at higher trophic levels accumulate greater concentrations of these toxins, a phenomenon called biomagnification. Top predators and humans at the apex are most severely affected.

3. Core Concepts with Derivations

3.1 Ten Percent Law of Energy Transfer

Ten Percent Law (proposed by Lindeman, 1942): Only 10% of the energy available at one trophic level is transferred to the next trophic level. The remaining 90% is lost as heat during metabolic activities.

Energy at next trophic level = 10% of Energy at current trophic level

Derivation and Explanation:

When producers capture solar energy through photosynthesis, a large portion is used for their own metabolism (respiration). Only a fraction is stored as biomass. When consumers eat producers, they absorb this stored energy but again use most for their own metabolism. This continues at each level.

If producers have 10,000 J --> Herbivores get 1,000 J --> Carnivores get 100 J --> Top carnivores get 10 J

This law explains why food chains are limited to 3-4 trophic levels - very little energy remains beyond that level to sustain a population.

3.2 Ecological Pyramid

Ecological pyramid is a graphical representation of the number, biomass, or energy at successive trophic levels.

•         Pyramid of Numbers: Shows the number of organisms at each trophic level - usually upright (decreasing numbers)

•         Pyramid of Biomass: Shows the total dry weight of organisms - usually upright in terrestrial, inverted in aquatic

•         Pyramid of Energy: Always upright - energy decreases at each successive trophic level

Efficiency (%) = (Energy at higher trophic level / Energy at lower trophic level) x 100

4. Solved Examples

Example 1: Energy Calculation

Question: If 10,000 J of energy is available at the producer level, how much energy is available at the tertiary consumer level?

Solution:

•         Producers: 10,000 J

•         Primary consumers (10%): 10,000 x 10/100 = 1,000 J

•         Secondary consumers (10%): 1,000 x 10/100 = 100 J

•         Tertiary consumers (10%): 100 x 10/100 = 10 J

Answer: Only 10 J of energy is available at the tertiary consumer level.

Example 2: Identifying Trophic Levels

Question: In the food chain: Grass --> Rabbit --> Fox --> Lion, identify the trophic level of Fox.

Solution:

•         Grass = Producer (1st Trophic Level)

•         Rabbit = Primary Consumer (2nd Trophic Level)

•         Fox = Secondary Consumer (3rd Trophic Level)

•         Lion = Tertiary Consumer (4th Trophic Level)

Answer: Fox belongs to the 3rd Trophic Level (Secondary Consumer).

Example 3: Biomagnification

Question: Explain why DDT concentration is highest in humans even though they spray it on crops.

Solution: DDT sprayed on crops is absorbed by small amounts by plants (1st trophic level). Insects eating the plants accumulate more DDT (2nd level). Small birds eating insects accumulate even more (3rd level). Large predatory birds and humans at the top consume the most concentrated DDT. Since DDT is fat-soluble and not easily broken down, it accumulates progressively. This is biological magnification. Humans, being at the top of many food chains, accumulate the highest concentration.

Example 4: Ecosystem Components

Question: Identify the biotic and abiotic components in a pond ecosystem.

Solution:

Biotic components:

•         Producers: algae, aquatic plants (lotus, water hyacinth)

•         Consumers: fish, frogs, insects, water birds

•         Decomposers: bacteria, fungi in pond sediment

Abiotic components:

•         Water, sunlight, temperature, dissolved oxygen, CO2, pH, minerals

Example 5: Ozone Layer

Question: What is the ozone layer and why is its depletion harmful?

Solution: The ozone layer is a region in the stratosphere (15-35 km above Earth) with high concentration of ozone (O3) molecules. It absorbs harmful ultraviolet (UV) radiation from the sun before it reaches Earth's surface.

Harmful effects of ozone depletion:

•         Increased UV radiation reaches Earth, causing skin cancer and cataracts

•         Suppression of the immune system in humans and animals

•         Damage to aquatic ecosystems and phytoplankton

•         Disruption of plant photosynthesis reducing crop yields

5. Applications and Special Cases

5.1 The Ozone Layer and CFCs

Chlorofluorocarbons (CFCs) released from refrigerators, air conditioners, aerosol sprays, and fire extinguishers react with ozone molecules in the stratosphere, breaking them down. Each CFC molecule can destroy thousands of ozone molecules.

O3 + UV light --> O2 + O (ozone is broken down)

The Montreal Protocol (1987) was an international treaty to phase out substances that deplete the ozone layer. It has been successful in reducing CFC emissions globally.

5.2 Waste Management Strategies

Proper waste management is critical to maintaining environmental health. Key strategies include:

•         Reduce: Minimize the production of waste at the source

•         Reuse: Use materials multiple times before disposing

•         Recycle: Convert waste materials into reusable products

•         Composting: Biodegradable waste can be composted to make manure

•         Segregation: Separate biodegradable from non-biodegradable waste

5.3 Garbage in Our Towns

Human settlements produce enormous amounts of garbage - both biodegradable and non-biodegradable. Non-biodegradable plastics cause significant problems as they persist in soil and water. Animals often ingest plastic waste, leading to fatal consequences. Chemical pollutants from industrial waste enter food chains through water bodies, causing biomagnification.

6. Formula and Concept Summary

Ten Percent Law:

Energy transferred to next level = 10% of energy at current level

Efficiency of Energy Transfer:

Energy Efficiency = (Energy at higher level / Energy at lower level) x 100

Trophic Level Energy:

Tn = T1 x (0.10)^(n-1)  where T1 = energy at producer level, n = trophic level

Ozone Formation:

3O2 + UV radiation --> 2O3  (Ozone formation in stratosphere)

Ozone Depletion:

2O3 + CFCs --> 3O2 + free radicals  (Ozone breakdown)

7. Key Theorems and Properties

7.1 Lindeman's Ten Percent Law

Statement: Only 10% of the energy available at one trophic level is transferred to the next higher trophic level. This was proposed by Raymond Lindeman in 1942 based on his studies of Cedar Bog Lake.

Implication: Because only 10% of energy is transferred, food chains are short (3-4 levels). The longer the food chain, the less energy is available at the top. This is why large carnivores are rare in nature.

7.2 Pyramid of Energy

Property: The pyramid of energy is always upright regardless of the ecosystem type. This is because energy always decreases from one trophic level to the next, as it is lost as heat during metabolism and respiration.

7.3 Stability of Food Webs

Food webs provide greater ecological stability than simple food chains. If one species in a food web is removed or declines, other species can shift their feeding habits to compensate. This is why more complex ecosystems with diverse food webs are more resilient to disturbances.

7.4 Role of Decomposers

Decomposers play a critical role in nutrient cycling. Without decomposers, dead organic matter would accumulate and nutrients would be locked in dead biomass, making them unavailable to producers. Decomposers complete the cycle by returning nutrients to the soil and water.

8. Common Mistakes and Exam Tips

8.1 Common Mistakes

•         Confusing food chain with food web: A food chain is linear; a food web is a network of multiple interconnected food chains.

•         Misapplying the Ten Percent Law: Remember, only 10% is transferred - NOT 10% is lost. 90% is lost, 10% is transferred.

•         Pyramid of Biomass confusion: In aquatic ecosystems, the pyramid of biomass can be inverted (phytoplankton have less biomass than zooplankton at a given moment).

•         Thinking decomposers are consumers: Decomposers are a separate category. They break down dead matter, not living organisms.

•         CFC sources: Students often miss that fire extinguishers are also a source of CFCs.

8.2 Important Exam Tips

•         Always draw and label diagrams for food chains, food webs, and ecological pyramids.

•         Ten Percent Law calculations are frequently asked - practice calculating energy at each trophic level.

•         Know specific examples of biodegradable and non-biodegradable wastes.

•         Montreal Protocol date (1987) and its purpose is frequently tested.

•         Understand why the pyramid of energy is always upright - examiners test conceptual understanding.

•         Know the difference between producers, consumers, and decomposers with examples.

•         Be able to explain biological magnification with a diagram and examples.

9. Practice Questions

1 Mark Questions (MCQ / Very Short Answer)

Q1. Who coined the term 'Ecosystem'?

Q2. What percentage of energy is transferred from one trophic level to the next according to Lindeman's Law?

Q3. Which of the following is a non-biodegradable substance? (a) Paper (b) Plastic (c) Cotton (d) Wood

Q4. Name the layer that protects Earth from harmful UV radiation.

Q5. What is the role of decomposers in an ecosystem?

Q6. Which gas is responsible for depletion of the ozone layer?

3 Mark Questions (Short Answer)

Q7. What is biological magnification? Explain with an example showing how DDT concentration increases through a food chain.

Q8. Differentiate between biodegradable and non-biodegradable waste. Give two examples of each. Why are non-biodegradable wastes more harmful to the environment?

Q9. What is a food web? How does a food web provide more stability to an ecosystem than a simple food chain? Give one example of a food web.

Q10. State Lindeman's Ten Percent Law. If 20,000 J of energy is available at the grass level in a food chain Grass --> Deer --> Tiger, how much energy reaches the tiger?

Q11. Name three types of ecological pyramids. Which of these is always upright and why?

5 Mark Questions (Long Answer)

Q12. Draw a labelled diagram of a food web in a pond ecosystem. Identify the producers, primary consumers, secondary consumers, and decomposers. Explain how energy flows through this ecosystem using the Ten Percent Law.

Q13. What is the ozone layer? Where is it located? What are the causes of its depletion? What are the harmful effects of ozone layer depletion on living organisms and what measures have been taken to protect it?

Q14. Explain the structure of an ecosystem with its biotic and abiotic components. How do these components interact with each other to maintain ecological balance? Give a suitable example.

Q15. What is meant by biodegradable and non-biodegradable substances? How does the accumulation of non-biodegradable substances in our environment lead to problems? Suggest four methods of proper waste management that can help solve these problems.

Q16. Explain biological magnification in detail. Why does it occur? Give a suitable example showing increasing concentration of a harmful substance through different trophic levels. What measures can be taken to prevent biomagnification?