Chapter 13: Our Environment

1. Introduction

The environment is everything that surrounds us — the air we breathe, the water we drink, the soil we grow crops in, and all living organisms that share this planet with us. It consists of biotic components (living things like plants, animals, and microorganisms) and abiotic components (non-living things like air, water, and sunlight).

All these elements are closely connected. Any change in one component affects others. For example, cutting down trees can reduce rainfall, increase pollution, and disturb the balance of nature.

This natural balance of all living and non-living things that supports life on Earth is called ecological balance.

2. Ecosystem

An ecosystem is a system formed by the interaction between living organisms and their physical surroundings.

Each ecosystem has both biotic (living) and abiotic (non-living) components.

Abiotic Components

These are non-living elements such as:

  • Air
  • Water
  • Soil
  • Temperature
  • Light

They provide the basic conditions necessary for life.

Biotic Components

These include all living organisms, grouped into:

Producers (Autotrophs):

  • Green plants and algae.
  • They make food using sunlight through photosynthesis.
  • Example: Grass, phytoplankton.

Consumers (Heterotrophs):

  • They depend directly or indirectly on producers for food.
  • Types:
    • Primary consumers: Eat plants (e.g., deer, cow, rabbit).
    • Secondary consumers: Eat herbivores (e.g., frog, cat).
    • Tertiary consumers: Eat other carnivores (e.g., lion, tiger).

Decomposers (Saprotrophs):

  • Fungi and bacteria that feed on dead plants and animals.
  • They break down complex organic matter into simple substances, returning nutrients to the soil.

3. Types of Ecosystems

Natural Ecosystems:

  • Found naturally in the environment.
  • Example: Forests, ponds, lakes, oceans, deserts.

Artificial Ecosystems:

  • Made and maintained by humans.
  • Example: Crop fields, aquariums.

4. Food Chain

A food chain is the sequence by which energy and nutrients are passed from one organism to another.

Example:

🌿 Grass → 🐇 Deer → 🐅 Tiger

Here:

  • Grass is the producer.
  • Deer is the primary consumer (herbivore).
  • Tiger is the secondary or tertiary consumer (carnivore).

Energy Flow:
 Sun → Plants → Herbivores → Carnivores → Decomposers

Energy always flows in one direction — from the sun to producers and then to consumers.

5. Food Web

In nature, food chains are interconnected. When several food chains combine, they form a food web.

Example: Grass → Grasshopper → Frog → Snake
 Grass → Rabbit → Fox

The food web shows how energy moves in many directions and how organisms depend on more than one food source.

6. Flow of Energy in Ecosystem

The Source of All Energy

The Sun is the ultimate source of energy for all living organisms.

  • Green plants trap solar energy through photosynthesis.
  • This energy is transferred through the food chain.
 Law of Energy Flow (10% Law)

When energy is transferred from one trophic level to another, only 10% of the energy is passed on; the rest is lost as heat.

Example: If plants have 10,000 J energy → Herbivores get 1,000 J → Carnivores get 100 J → Top carnivores get 10 J.

This is known as the 10% law, given by Raymond Lindeman.

7. Trophic Levels

Each step in a food chain is called a trophic level.

Example:
 🌿 Plants → 🐇 Herbivores → 🐍 Carnivores → 🦅 Top carnivores

Trophic Level

Organisms

Example

1st

Producers

Plants

2nd

Primary consumers

Herbivores

3rd

Secondary consumers

Carnivores

4th

Tertiary consumers

Top predators

8. Decomposition and Recycling of Nutrients

Decomposers such as bacteria and fungi break down dead organisms into simple compounds like carbon dioxide, water, and minerals.
 These nutrients are then reused by plants.

This process maintains the nutrient cycle and keeps the environment clean.

9. Biological Magnification

Definition:
 The increase in the concentration of harmful, non-biodegradable substances (like pesticides) in organisms at each higher trophic level of a food chain is called biological magnification.

Example: Spraying pesticides on crops → eaten by insects → eaten by frogs → eaten by snakes → eaten by hawks.
 At each level, the amount of pesticide increases.

Result:

  • Top consumers accumulate the highest concentration of toxins.
  • Harmful effects include health issues and reproductive problems.

10. Ozone Layer and Its Importance

Ozone (O₃):
  • A molecule made up of three oxygen atoms.
  • Found in the stratosphere (about 16–60 km above Earth).
  • It forms the ozone layer, which absorbs harmful ultraviolet (UV) rays from the sun.
Importance:
  • Protects living organisms from UV radiation.
  • Prevents skin cancer, cataracts, and damage to crops.
Ozone Depletion:
  • Caused by chlorofluorocarbons (CFCs) used in refrigerators, air conditioners, and aerosols.
  • CFCs break down ozone molecules, thinning the ozone layer.
Solution:
  • Reduce use of CFCs.
  • Use eco-friendly cooling devices.
  • Follow the Montreal Protocol (1987) – an international agreement to protect the ozone layer.

11. Waste Management

Human activities produce two types of waste:

  1. Biodegradable Waste:

     

  • Can be decomposed by microorganisms.
  • Example: Vegetable peels, paper, sewage.
  1. Non-biodegradable Waste:

     

  • Cannot be broken down by microorganisms.
  • Example: Plastics, glass, metals, pesticides.
Problems with Non-biodegradable Waste:
  • Accumulate in the environment.
  • Cause land and water pollution.
  • Enter food chains and cause biological magnification.
  • Harmful to wildlife and humans.

12. Managing Our Garbage

Three Rs – Reduce, Reuse, Recycle

Reduce:

  • Use less of things that cause pollution.
  • Example: Avoid plastic bags, save electricity and water.

Reuse:

  • Use items again instead of throwing them away.
  • Example: Use glass bottles multiple times.

Recycle:

  • Convert waste materials into useful products.
  • Example: Recycling paper saves trees.
Segregation of Waste:
  • Green bins: For biodegradable waste.
  • Blue bins: For non-biodegradable waste.

13. Ecosystem Disturbance and Balance

Human interference like deforestation, pollution, and excessive resource use leads to ecological imbalance.

Effects:
  • Loss of biodiversity.
  • Climate change and global warming.
  • Soil erosion and water scarcity.
  • Increased pollution and health problems.
How to Maintain Balance:
  • Plant more trees.
  • Control pollution.
  • Save electricity and fuel.
  • Use eco-friendly products.

14. Key Terms Summary

Term

Meaning

Ecosystem

Interaction between living and non-living components

Producer

Green plants that make food using sunlight

Consumer

Organisms that depend on producers or other consumers

Decomposer

Organisms that break down dead matter

Food Chain

Sequence of energy transfer in an ecosystem

Food Web

Interconnected food chains

Trophic Level

Each step in a food chain

10% Law

Only 10% energy passes to next trophic level

Ozone Layer

Protects Earth from UV radiation

Biological Magnification

Increase of toxins along the food chain

15. Summary

  • The ecosystem maintains the natural balance of life.
  • Energy flows in one direction — from sun to producers to consumers to decomposers.
  • Decomposers are vital for recycling nutrients.
  • Ozone layer protects life from harmful UV rays.
  • Human waste and pollution threaten this balance.
  • Practicing Reduce, Reuse, Recycle helps preserve the environment.
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