Our Environment
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📖 Chapter Roadmap
1. Environment
2. Ecosystem
3. Biotic and Abiotic Components
4. Producers, Consumers and Decomposers
5. Food Chain
6. Food Web
7. Trophic Levels
8. 10 Percent Law
9. Flow of Energy
10. Ecological Pyramids
11. Role of Decomposers
12. Biodegradable and Non-Biodegradable Waste
13. Ozone Layer and Its Depletion
14. Waste Management
15. Important Board Questions
16. Final 96%-Target Revision
17. Practice Corner
High-score rule: Learn ecosystem components, food chains, food webs, trophic levels, the 10% law, energy flow, decomposers, biodegradable/non-biodegradable waste, ozone layer and waste management. For board answers use definition → explanation → example/diagram → conclusion.
1. Environment
Environment includes all the living and non-living surroundings that affect an organism.
Main Parts of Environment
Biotic Components
Living components such as plants, animals, microorganisms and other organisms.Abiotic Components
Non-living components such as air, water, soil, sunlight, temperature and minerals.Why Is the Environment Important?
- It provides air, water and other resources needed for life.
- It provides living organisms with suitable conditions for survival.
- Organisms interact with one another and with physical factors.
- Changes in the environment can affect the balance of ecosystems.
Memory: “Biotic = living; Abiotic = non-living.”
2. Ecosystem
An ecosystem is a functional unit in which living organisms interact with one another and with the non-living components of their surroundings.
Examples of Ecosystems
- Forest ecosystem
- Pond ecosystem
- Grassland ecosystem
- Lake ecosystem
- Garden ecosystem
How Does an Ecosystem Work?
Plants capture solar energy and make food. Animals obtain energy by eating plants or other animals. Decomposers break down dead organisms and wastes and return nutrients to the environment.
Board point: An ecosystem contains both biotic and abiotic components and their interactions.
3. Biotic and Abiotic Components
Biotic Components
These are the living parts of an ecosystem.
| Group | Role | Example |
|---|---|---|
| Producers | Make food | Green plants |
| Consumers | Obtain food from other organisms | Animals |
| Decomposers | Break down dead matter and wastes | Bacteria and fungi |
Abiotic Components
These include sunlight, air, water, soil, temperature, minerals and other physical conditions.
Interaction Between Components
Plants need sunlight, water, carbon dioxide and minerals to make food. Animals depend directly or indirectly on plants for food and oxygen. Decomposers recycle nutrients back into the environment.
4. Producers, Consumers and Decomposers
Different organisms have different roles in the transfer of energy and nutrients through an ecosystem.
Producers
Green plants are called producers because they prepare their own food by photosynthesis using sunlight.
\[\boxed{\text{Carbon dioxide}+\text{Water}\xrightarrow{\text{sunlight, chlorophyll}}\text{Glucose}+\text{Oxygen}}\]
Consumers
- Primary consumers: Usually herbivores that eat plants.
- Secondary consumers: Eat primary consumers.
- Tertiary consumers: May eat secondary consumers.
Decomposers
Bacteria and fungi break down complex organic matter from dead plants, animals and wastes into simpler substances. This helps recycle nutrients.
Memory: “Producers make → Consumers eat → Decomposers recycle.”
5. Food Chain
A food chain is a sequence of organisms in which food and energy pass from one organism to another.
Example
\[\boxed{\text{Grass}\rightarrow\text{Grasshopper}\rightarrow\text{Frog}\rightarrow\text{Snake}\rightarrow\text{Eagle}}\]
How to Read a Food Chain
The arrow shows the direction of transfer of food and energy. It should be read as “is eaten by” when moving from left to right in the example above.
Important Features
- A food chain normally starts with a producer.
- Energy passes from one trophic level to the next.
- Only a small part of energy is transferred to the next trophic level.
- Food chains are usually limited in length because available energy decreases at higher levels.
Board point: Draw arrows carefully. The arrow represents the flow of food/energy, not movement of the animal.
6. Food Web
A food web is a network of interconnected food chains in an ecosystem.
Why Are Food Webs Important?
An organism may eat more than one type of food and may also be eaten by different organisms. Therefore, many food chains can become interconnected to form a food web.
Food Chain vs Food Web
| Food Chain | Food Web |
|---|---|
| Usually shows one feeding pathway. | Shows many interconnected feeding pathways. |
| Simple representation. | More complex and realistic representation. |
| Less flexible if one link changes. | Alternative feeding paths may exist. |
Memory: “One path = food chain; many connected paths = food web.”
7. Trophic Levels
A trophic level is a step or position of an organism in a food chain according to how it obtains food and energy.
| Trophic Level | Organism | Example |
|---|---|---|
| First | Producers | Grass |
| Second | Primary consumers | Grasshopper |
| Third | Secondary consumers | Frog |
| Fourth | Tertiary consumers | Snake/Eagle depending on chain |
Important Rule
Energy available generally decreases as we move from one trophic level to the next.
\[\boxed{\text{Producer}\rightarrow\text{Primary consumer}\rightarrow\text{Secondary consumer}\rightarrow\text{Higher consumer}}\]
Board point: The first trophic level is occupied by producers.
8. 10 Percent Law
According to the 10% law, only about 10% of the energy available at one trophic level is transferred to the next trophic level.
Example
Suppose producers have \(10,000\,J\) of energy available.
\[\boxed{10,000\,J\rightarrow1,000\,J\rightarrow100\,J\rightarrow10\,J}\]
About \(1,000\,J\) reaches the primary consumers, \(100\,J\) reaches the secondary consumers and \(10\,J\) reaches the next trophic level.
Why Is Energy Lost?
- Organisms use energy for respiration and life processes.
- Energy is released as heat.
- Not all parts of food are eaten or digested.
Memory: “Only about 10% goes forward; most energy is used or lost at each level.”
9. Flow of Energy
Energy in an ecosystem mainly enters through sunlight and flows from producers to consumers and then through higher trophic levels.
Direction of Energy Flow
\[\boxed{\text{Sun}\rightarrow\text{Producers}\rightarrow\text{Consumers}}\]
Why Is Energy Flow Unidirectional?
Energy moves from the Sun to producers and then to consumers. At each transfer, much energy is dissipated as heat. It is not returned to the Sun or recycled through the ecosystem in the same way nutrients are.
Energy vs Nutrients
| Energy | Nutrients |
|---|---|
| Flows through the ecosystem. | Can be recycled. |
| Decreases at higher trophic levels. | Move between organisms and the physical environment. |
| Main source is sunlight for most ecosystems. | Examples include carbon, nitrogen and minerals. |
10. Ecological Pyramids
An ecological pyramid is a graphical representation of the relationship among different trophic levels of an ecosystem.
Energy Pyramid
The energy pyramid represents the amount of energy available at different trophic levels. It becomes narrower towards the top because energy decreases at higher trophic levels.
\[\boxed{\text{Energy decreases}\uparrow\text{ trophic levels}}\]
Why Is the Top Small?
Because only about 10% of the energy is transferred from one trophic level to the next.
Exam point: When asked to draw an energy pyramid, place producers at the base and higher consumers above them.
11. Role of Decomposers
Decomposers break down dead plants, dead animals and organic wastes into simpler substances.
Why Are Decomposers Important?
- Dead organisms and wastes contain complex organic matter.
- Decomposers break this matter into simpler substances.
- Nutrients are returned to the soil and surroundings.
- Plants can use many of these nutrients again.
What If Decomposers Were Absent?
Dead matter and organic wastes would accumulate, and the recycling of nutrients would be seriously disturbed.
Memory: “Decomposers clean dead matter and recycle nutrients.”
12. Biodegradable and Non-Biodegradable Waste
Waste can be grouped according to whether microorganisms can break it down naturally.
| Type | Meaning | Examples |
|---|---|---|
| Biodegradable | Can be broken down by microorganisms through natural processes. | Vegetable waste, paper, leaves |
| Non-biodegradable | Does not break down easily by natural biological processes. | Many plastics, glass and some synthetic materials |
Why Is Non-Biodegradable Waste a Problem?
- It can remain in the environment for long periods.
- It can accumulate and pollute land and water.
- It may enter food chains.
- Some pollutants can show biomagnification, meaning their concentration increases at higher trophic levels.
Biomagnification
Biomagnification is the increase in concentration of certain non-biodegradable harmful substances as they move through successive trophic levels.
Board point: Biomagnification is especially important for persistent pollutants that are not easily broken down.
13. Ozone Layer and Its Depletion
The ozone layer in the upper atmosphere absorbs a large part of the harmful ultraviolet (UV) radiation coming from the Sun.
Why Is Ozone Important?
Excessive exposure to harmful UV radiation can damage living organisms. Therefore, the ozone layer provides important protection.
Ozone Formation and Breakdown
Ozone is represented by \(O_3\). It can be formed from oxygen under the action of ultraviolet radiation.
\[\boxed{O_2+\text{UV}\rightarrow 2O}\]
\[\boxed{O+O_2\rightarrow O_3}\]
Ozone Depletion
Certain chemicals released into the atmosphere can participate in reactions that destroy ozone molecules. Chlorofluorocarbons (CFCs) are an important example of ozone-depleting substances.
How Can We Help?
- Reduce the use and release of ozone-depleting substances.
- Use environmentally safer alternatives where available.
- Follow proper handling and disposal of chemicals and cooling equipment.
Memory: “Ozone \(O_3\) protects us from harmful UV radiation.”
14. Waste Management
Waste management means collecting, separating, treating, recycling and safely disposing of waste so that its harmful effects on the environment are reduced.
Best Approach: 3Rs
Reduce
Use fewer resources and avoid unnecessary products and packaging.Reuse
Use an item again instead of throwing it away after one use.Recycle
Process suitable waste materials so that useful materials can be recovered and used again.Waste Segregation
Separate waste at the source into suitable categories. Biodegradable organic waste can often be composted, while recyclable materials such as paper, metals and suitable plastics can be sent for recycling.
Composting
Composting is the controlled biological decomposition of organic waste to produce a nutrient-rich material that can be used to improve soil.
Why Should Plastic Use Be Reduced?
Many plastics are non-biodegradable and can persist in the environment. Reducing unnecessary plastic use, reusing materials and recycling suitable plastics can help lower pollution.
Board point: Write Reduce → Reuse → Recycle in this order when asked about the 3Rs.
15. ⭐ Important Board Exam Questions
1-Mark Questions
Q1. What is an ecosystem?
An ecosystem is a functional unit in which living organisms interact with one another and with non-living components.
An ecosystem is a functional unit in which living organisms interact with one another and with non-living components.
Q2. Who are producers?
Organisms such as green plants that make their own food are called producers.
Organisms such as green plants that make their own food are called producers.
Q3. What is a food chain?
A sequence of organisms through which food and energy pass from one organism to another.
A sequence of organisms through which food and energy pass from one organism to another.
Q4. What is a trophic level?
A position or step of an organism in a food chain based on how it obtains food and energy.
A position or step of an organism in a food chain based on how it obtains food and energy.
Q5. State the 10% law.
Only about 10% of the energy at one trophic level is transferred to the next trophic level.
Only about 10% of the energy at one trophic level is transferred to the next trophic level.
Q6. Name two decomposers.
Bacteria and fungi.
Bacteria and fungi.
Q7. What is biomagnification?
The increase in concentration of certain persistent harmful substances at successive trophic levels.
The increase in concentration of certain persistent harmful substances at successive trophic levels.
Q8. What is the chemical formula of ozone?
\(O_3\).
\(O_3\).
Q9. Name the three Rs.
Reduce, Reuse and Recycle.
Reduce, Reuse and Recycle.
3-Mark Questions
Q. Explain the role of decomposers in an ecosystem.
Answer: Decomposers break down dead organisms and organic wastes into simpler substances. This prevents excessive accumulation of dead matter and helps return nutrients to the environment for reuse by plants.
Answer: Decomposers break down dead organisms and organic wastes into simpler substances. This prevents excessive accumulation of dead matter and helps return nutrients to the environment for reuse by plants.
Q. Differentiate between biodegradable and non-biodegradable waste.
Answer: Biodegradable waste can be broken down naturally by microorganisms, while non-biodegradable waste does not break down easily. Vegetable waste and leaves are examples of biodegradable waste; many plastics and glass are examples of non-biodegradable waste.
Answer: Biodegradable waste can be broken down naturally by microorganisms, while non-biodegradable waste does not break down easily. Vegetable waste and leaves are examples of biodegradable waste; many plastics and glass are examples of non-biodegradable waste.
Q. Why does energy decrease at successive trophic levels?
Answer: Organisms use much of the available energy for respiration, movement, growth and other life processes. Much energy is released as heat, so only a small fraction is transferred to the next trophic level.
Answer: Organisms use much of the available energy for respiration, movement, growth and other life processes. Much energy is released as heat, so only a small fraction is transferred to the next trophic level.
Q. Why is the ozone layer important?
Answer: The ozone layer absorbs a large part of harmful ultraviolet radiation from the Sun and therefore helps protect living organisms from excessive UV exposure.
Answer: The ozone layer absorbs a large part of harmful ultraviolet radiation from the Sun and therefore helps protect living organisms from excessive UV exposure.
5-Mark Questions
Q. Explain a food chain and the flow of energy through trophic levels.
Answer plan: Define food chain → draw example → identify producer → primary/secondary/higher consumers → explain trophic levels → state 10% law → explain energy loss → conclude that energy flow is unidirectional.
Answer plan: Define food chain → draw example → identify producer → primary/secondary/higher consumers → explain trophic levels → state 10% law → explain energy loss → conclude that energy flow is unidirectional.
Q. Explain the harmful effects of non-biodegradable waste and biomagnification.
Answer plan: Define non-biodegradable waste → long persistence → pollution → entry into food chains → definition of biomagnification → concentration increases at higher trophic levels → need for proper waste management.
Answer plan: Define non-biodegradable waste → long persistence → pollution → entry into food chains → definition of biomagnification → concentration increases at higher trophic levels → need for proper waste management.
Q. Explain ozone depletion and measures to protect the ozone layer.
Answer plan: Define ozone → \(O_3\) → UV protection → ozone-depleting substances such as CFCs → depletion → harmful UV exposure → reduce release/use of ozone-depleting substances and adopt safer alternatives.
Answer plan: Define ozone → \(O_3\) → UV protection → ozone-depleting substances such as CFCs → depletion → harmful UV exposure → reduce release/use of ozone-depleting substances and adopt safer alternatives.
Q. Explain waste management and the 3Rs.
Answer plan: Define waste management → segregation → Reduce → Reuse → Recycle → composting of organic waste → safe disposal → environmental benefits.
Answer plan: Define waste management → segregation → Reduce → Reuse → Recycle → composting of organic waste → safe disposal → environmental benefits.
16. ⭐ Final 96%-Target Board Revision
Must Learn Definitions
- Environment
- Ecosystem
- Biotic components
- Abiotic components
- Producer
- Consumer
- Decomposer
- Food chain
- Food web
- Trophic level
- 10% law
- Biodegradable waste
- Non-biodegradable waste
- Biomagnification
- Ozone layer
- Waste management
Must Learn Equations / Key Relations
Energy Transfer
\(\displaystyle E_{\text{next}}\approx0.1E_{\text{previous}}\)10% Example
\(10,000\,J\rightarrow1,000\,J\rightarrow100\,J\rightarrow10\,J\)Ozone
\(O_2+\text{UV}\rightarrow2O\), then \(O+O_2\rightarrow O_3\)Must Learn Memory Lines
\[\text{Biotic}=\text{Living}\qquad \text{Abiotic}=\text{Non-living}\]
\[\text{Producers}\rightarrow\text{Consumers}\rightarrow\text{Decomposers}\]
\[\text{Sun}\rightarrow\text{Producers}\rightarrow\text{Consumers}\]
\[\text{Only about }10\%\text{ energy passes to the next trophic level}\]
\[\text{Food chain}=\text{One feeding pathway}\]
\[\text{Food web}=\text{Many connected food chains}\]
\[\text{Ozone}=O_3\rightarrow\text{Protection from harmful UV radiation}\]
\[\text{3Rs}=\text{Reduce}+\text{Reuse}+\text{Recycle}\]
⚠ Common Board Mistakes
- Do not confuse a food chain with a food web.
- Always start a simple food chain with a producer.
- Read arrows as the direction of transfer of food/energy.
- Do not say that all energy is transferred to the next trophic level; only about 10% is transferred.
- Do not confuse energy flow with nutrient cycling.
- Remember that decomposers help recycle nutrients.
- Do not call all waste biodegradable.
- Biomagnification is related to the increasing concentration of certain persistent harmful substances at higher trophic levels.
- Remember the ozone formula \(O_3\).
- Do not confuse ozone depletion with ordinary air pollution in general; explain the role of ozone-depleting substances.
- Write Reduce → Reuse → Recycle correctly.
📝 Last-Minute Checklist
- ☐ Environment
- ☐ Ecosystem
- ☐ Biotic components
- ☐ Abiotic components
- ☐ Producers
- ☐ Consumers
- ☐ Decomposers
- ☐ Food chain
- ☐ Food web
- ☐ Trophic levels
- ☐ 10% law
- ☐ Energy flow
- ☐ Energy pyramid
- ☐ Role of decomposers
- ☐ Biodegradable waste
- ☐ Non-biodegradable waste
- ☐ Biomagnification
- ☐ Ozone layer
- ☐ Ozone depletion
- ☐ 3Rs
- ☐ Waste segregation
- ☐ Composting
- ☐ Board diagrams
- ☐ Important questions
🎯 96%-type board method: Learn every definition in simple scientific language, practise food-chain and energy-flow diagrams, remember the 10% law, explain ozone protection clearly, and write waste-management answers with practical examples.
17. ✍ Practice Corner
Write these answers without looking at the notes:
- Define environment.
- What is an ecosystem? Give two examples.
- Differentiate between biotic and abiotic components.
- Define producers, consumers and decomposers.
- Draw and explain a simple food chain.
- What is a food web? How is it different from a food chain?
- What are trophic levels?
- State and explain the 10% law.
- Explain the flow of energy in an ecosystem.
- Why is energy flow unidirectional?
- Draw an energy pyramid and label its trophic levels.
- Explain the role of decomposers.
- Differentiate between biodegradable and non-biodegradable waste.
- What is biomagnification?
- Why can non-biodegradable waste be harmful to ecosystems?
- What is the ozone layer?
- Why is ozone important for living organisms?
- What causes ozone depletion?
- Explain the 3Rs of waste management.
- Write five ways to reduce environmental pollution caused by waste.
Final answer tip: For 5 marks, use definition + principle/concept + step-wise explanation + labelled diagram/example + conclusion. For food-chain questions, draw arrows clearly and identify every trophic level.
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