Class 10 Science — Chapter 13: Our Environment
Quality Revision Notes
1. Ecosystem
An ecosystem is a system in which living organisms interact with one another and with the non-living conditions around them.
It has two major components:
- Biotic components: Living organisms such as plants, animals, microorganisms and humans.
- Abiotic components: Non-living factors such as temperature, rainfall, wind, soil and minerals.
Examples
- Natural ecosystems: forests, ponds and lakes.
- Artificial ecosystems: gardens, crop fields and aquariums.
2. Producers, Consumers and Decomposers
Producers
Green plants and certain bacteria that prepare food through photosynthesis are called producers. They convert solar energy into chemical energy stored in food.
Consumers
Organisms that obtain food directly or indirectly from producers are consumers.
They include:
- Herbivores — feed mainly on plants.
- Carnivores — feed on other animals.
- Omnivores — obtain food from both plant and animal sources.
- Parasites — obtain nourishment from other organisms.
Decomposers
Bacteria and fungi break down dead organisms and waste materials into simpler substances.
Importance: Decomposers return simple inorganic substances to the environment, allowing nutrients to become available again to plants. They therefore help maintain the natural recycling of materials.
3. Food Chain
A food chain shows the sequence in which organisms obtain food from one another.
Example:
Grass → Grasshopper → Frog → Snake
Each position in a food chain is called a trophic level.
Trophic levels
| Trophic level | Organisms |
|---|---|
| 1st | Producers |
| 2nd | Primary consumers / herbivores |
| 3rd | Secondary consumers |
| 4th | Tertiary consumers |
The producers occupy the first trophic level because they introduce energy from sunlight into the ecosystem.
4. Flow of Energy in an Ecosystem
Energy enters most ecosystems through sunlight.
Sun → Producers → Herbivores → Carnivores → Higher consumers
Important points:
- Green plants capture only a small fraction of the sunlight reaching their leaves.
- On average, only about 10% of the organic matter/energy available at one trophic level becomes available to the next level.
- Much energy is lost during life processes and as heat.
- Therefore, food chains normally contain only a few trophic levels.
- The amount of available energy decreases as we move upward through trophic levels.
Key concept: Unidirectional energy flow
Energy moves in one direction through an ecosystem. It does not return from higher trophic levels to lower ones.
Remember:
Energy flow = one-way
Energy available = decreases at successive trophic levels
5. Food Web
A single organism may be eaten by more than one type of organism and may itself feed on different organisms.
Therefore, several interconnected food chains form a food web.
Food chain: A single feeding pathway.
Food web: A network of interconnected feeding pathways.
6. Biological Magnification
Some harmful chemicals, such as certain pesticides, can enter food chains through contaminated soil or water.
These substances may not be easily broken down and can become increasingly concentrated at higher trophic levels.
This increase in concentration of harmful, non-degradable chemicals along successive trophic levels is called biological magnification.
Why is it important?
- Chemicals can enter plants from contaminated soil or water.
- Herbivores consume the plants.
- Carnivores consume herbivores.
- The concentration can increase at successive trophic levels.
- Humans, often occupying a high trophic position, may receive a relatively high concentration.
7. Ozone Layer
Ozone (O₃) consists of three oxygen atoms.
Ozone has different effects depending on where it is present:
- At higher levels of the atmosphere, it performs an important protective function.
- It absorbs harmful ultraviolet (UV) radiation from the Sun.
- Excessive exposure to UV radiation can damage living organisms and is associated with health problems such as skin cancer.
Ozone formation
UV radiation can split some oxygen molecules (O₂) into individual oxygen atoms. These atoms can then combine with oxygen molecules to form ozone (O₃).
Ozone depletion
The amount of atmospheric ozone began decreasing sharply during the 1980s. This was linked to synthetic chemicals such as chlorofluorocarbons (CFCs), which were used in applications including refrigeration.
International action was taken to control CFC production and reduce damage to the ozone layer.
Exam point:
Damage to the ozone layer is dangerous because it reduces protection from harmful UV radiation.
8. Waste and Its Management
Human activities generate many kinds of waste. The increasing use of disposable products and non-biodegradable packaging has increased the waste problem.
Biodegradable substances
Materials that can be broken down through biological processes are called biodegradable substances.
Examples include many materials of plant and animal origin.
Non-biodegradable substances
Materials that cannot be broken down easily by biological processes are called non-biodegradable substances.
Many such materials can remain in the environment for long periods and may harm organisms or disturb ecosystems. Plastics are an important example.
Quick comparison
| Biodegradable | Non-biodegradable |
|---|---|
| Broken down biologically | Not easily broken down biologically |
| Usually decomposed by microorganisms | May persist for long periods |
| Can be returned to natural cycles more readily | Can accumulate and create environmental problems |
9. Why Waste Disposal Is a Problem
Poor waste management can lead to:
- accumulation of garbage,
- pollution of soil and water,
- harm to organisms,
- persistence of non-biodegradable materials,
- environmental problems caused by increasing disposable waste.
Even biodegradable waste needs proper management when produced in very large quantities.
10. Human Activities and the Environment
Humans are a part of the environment, so environmental changes affect us, while our activities also alter the environment.
Major concerns discussed in this chapter include:
- Disruption of ecosystems
- Energy loss through trophic levels
- Biological magnification
- Ozone-layer depletion
- Waste accumulation and disposal
The chapter emphasizes that ecosystem components are interdependent, so disturbing one part can affect other parts as well.
Must-Know Definitions
Ecosystem: A system formed by interactions among living organisms and their physical surroundings.
Producer: An organism, such as a green plant, that makes its own food.
Consumer: An organism that obtains food from producers or other consumers.
Decomposer: An organism such as a bacterium or fungus that breaks down dead matter and wastes.
Food chain: A sequence showing feeding relationships among organisms.
Trophic level: Each feeding position occupied by an organism in a food chain.
Food web: A network formed by several interconnected food chains.
Biological magnification: Progressive increase in the concentration of certain harmful, non-degradable chemicals at successive trophic levels.
Biodegradable: Capable of being broken down by biological processes.
Non-biodegradable: Not readily broken down by biological processes.
⭐ Exam-Focused Takeaways
- Ecosystem = Biotic + Abiotic components
- Producers form the first trophic level.
- Energy flow is unidirectional.
- Only about 10% of the available organic matter/energy is transferred to the next trophic level on average.
- Food chains generally have only a few trophic levels because energy decreases at each step.
- Several interconnected food chains form a food web.
- Biological magnification is associated with harmful, non-degradable chemicals.
- The ozone layer protects Earth from harmful UV radiation.
- CFCs have been linked with ozone depletion.
- Biodegradable and non-biodegradable wastes require appropriate management.
- All components of an ecosystem are interdependent.
- Human activities can significantly affect environmental balance.
One-Line Revision
Ecosystem → Producers → Food chain → Trophic levels → Energy loss → Food web → Biological magnification → Ozone protection → Waste management