What this chapter is about
This chapter explores how living organisms interact with each other and with their physical surroundings. A Class 10 student learns about ecosystems, the flow of energy through food chains and food webs, and how matter cycles through nature. Understanding these connections helps explain why balance in nature matters.
The chapter also addresses environmental problems caused by human activities. Students study how waste materials affect ecosystems, why some substances refuse to break down, and how certain chemicals accumulate in living tissues. This knowledge is essential because environmental awareness shapes responsible citizenship.
After studying this chapter, students should be able to trace energy flow in any ecosystem, explain why shorter food chains transfer energy more efficiently, distinguish between biodegradable and non-biodegradable waste, and describe the harmful effects of ozone layer depletion.
Key ideas
- An ecosystem includes all living organisms (biotic components) and non-living factors like air, water, soil, sunlight and temperature (abiotic components) in a given area, functioning together as a unit.
- Producers are green plants and certain bacteria that make their own food through photosynthesis; consumers are organisms that depend on others for food; decomposers like bacteria and fungi break down dead matter and release nutrients back into soil.
- A food chain shows a single pathway of energy transfer: producer → primary consumer → secondary consumer → tertiary consumer. Energy decreases at each step.
- Only about 10 per cent of energy available at one trophic level passes to the next level; the rest is lost as heat during life processes.
- Biological magnification occurs when non-biodegradable chemicals like pesticides become more concentrated at higher trophic levels of a food chain.
- Biodegradable substances (vegetable peels, paper, cotton) can be broken down by microorganisms; non-biodegradable substances (plastic, glass, certain pesticides) cannot be decomposed naturally and persist in the environment.
- The ozone layer in the stratosphere absorbs harmful ultraviolet radiation from the sun; chlorofluorocarbons (CFCs) from refrigerators and aerosols destroy ozone molecules.
- Proper waste management—reducing, reusing and recycling—helps protect ecosystems from pollution.
Formulas and facts to remember
- 10 per cent law: Only about 10% of energy is transferred from one trophic level to the next; the rest is used in metabolism or lost as heat.
- Trophic levels: Producer (first) → Primary consumer (second) → Secondary consumer (third) → Tertiary consumer (fourth).
- Ozone formation: O₂ → O + O (UV splits oxygen); O + O₂ → O₃ (ozone forms).
- Ozone depletion: CFCs release chlorine atoms in the stratosphere; each chlorine atom can destroy thousands of ozone molecules.
- Biodegradable waste: Broken down by bacteria and fungi within weeks or months.
- Non-biodegradable waste: Persists in the environment for decades or centuries; examples include polythene bags, aluminium cans, DDT.
- Biological magnification: Concentration of pesticides increases as we move up the food chain—highest in top predators.
Worked examples
Example 1: Energy transfer in a food chain
In a grassland, grass receives 10,000 joules of solar energy and stores it through photosynthesis. A grasshopper eats the grass. A frog eats the grasshopper. A snake eats the frog. Calculate the energy available at each trophic level.
Solution:
- Grass (producer): 10,000 J
- Grasshopper (primary consumer): 10% of 10,000 = 1,000 J
- Frog (secondary consumer): 10% of 1,000 = 100 J
- Snake (tertiary consumer): 10% of 100 = 10 J
Only 10 J reaches the snake from the original 10,000 J stored by plants.
Example 2: Biological magnification
A pesticide is sprayed on crops at 0.02 parts per million (ppm). Small insects feeding on crops have 0.2 ppm. Fish eating these insects have 2 ppm. A kingfisher eating fish has 20 ppm. Explain the pattern.
Solution: Each consumer accumulates pesticide from all the prey it eats over its lifetime. The pesticide does not break down and is stored in fatty tissues. Moving up each trophic level, concentration increases roughly 10 times. The kingfisher at the top has 1,000 times the concentration found in crops. This explains why top predators suffer most from pesticide poisoning.
Example 3: Classifying waste
Ravi's family produces these items daily: banana peels, old newspapers, empty plastic bottles, leftover rice, broken glass bangles. Classify them as biodegradable or non-biodegradable.
Solution:
- Biodegradable: banana peels, old newspapers, leftover rice (microorganisms can decompose these).
- Non-biodegradable: empty plastic bottles, broken glass bangles (these persist in the environment and need recycling or proper disposal).
The family should compost biodegradable waste and send non-biodegradable items for recycling.
Common mistakes
- Thinking energy increases or stays constant as it moves up a food chain → Energy decreases; only 10% transfers to each higher level.
- Confusing food chain with food web → A food chain is a single linear pathway; a food web is an interconnected network of many food chains.
- Believing all waste eventually decomposes → Non-biodegradable materials like plastic do not break down naturally and accumulate.
- Assuming biological magnification affects all substances equally → Only non-biodegradable, fat-soluble chemicals like DDT magnify up the food chain.
- Thinking ozone in the upper atmosphere is harmful → Stratospheric ozone protects us; ground-level ozone is the pollutant.
Quick revision
- Ecosystem = biotic (living) + abiotic (non-living) components interacting together.
- Energy flow: Sun → Producers → Consumers → Decomposers; only 10% passes to each next level.
- Shorter food chains mean more energy available to top consumers.
- Biological magnification: pesticide concentration rises at higher trophic levels.
- Biodegradable waste decomposes; non-biodegradable waste persists—reduce, reuse, recycle.
- CFCs destroy ozone; ozone loss increases UV radiation reaching Earth, causing health and ecological harm.