INTRODUCTION — UNDERSTANDING OUR ENVIRONMENT
We hear the word environment almost everywhere — on
television, in newspapers, in climate discussions and even in daily life. The
environment includes everything around us that affects life.
It includes:
- Air
- Water
- Soil
- Plants
- Animals
- Microorganisms
- Human
beings
All these components interact with each other and maintain
balance in nature.
Human activities also influence the environment. Sometimes
these activities disturb ecological balance and create environmental problems.
This chapter helps us understand:
- Ecosystems
- Food
chains and food webs
- Energy
flow
- Ozone
depletion
- Waste
disposal
- Environmental
protection
13.1 ECOSYSTEM — WHAT ARE ITS COMPONENTS?
ECOSYSTEM
An ecosystem is formed when living organisms interact with
each other and with their surroundings.
Definition:
Ecosystem
A system formed by interaction between biotic and abiotic
components of the environment.
COMPONENTS OF ECOSYSTEM
Two major components:
|
Component |
Meaning |
|
Biotic components |
Living organisms |
|
Abiotic components |
Non-living surroundings |
BIOTIC COMPONENTS
These include:
- Plants
- Animals
- Bacteria
- Fungi
- Human
beings
ABIOTIC COMPONENTS
These include:
- Air
- Water
- Soil
- Temperature
- Minerals
- Rainfall
- Sunlight
- Wind
EXAMPLES OF ECOSYSTEMS
Natural Ecosystems
- Forest
- Pond
- Lake
Artificial (Human-made) Ecosystems
- Aquarium
- Garden
- Crop
field
EXAMPLE — GARDEN AS AN ECOSYSTEM
A garden contains:
- Grasses
- Trees
- Flowering
plants like rose, sunflower and jasmine
- Insects
- Frogs
- Birds
These living organisms interact with each other and with
abiotic factors like sunlight, water and soil.
Thus:
Garden is an ecosystem.
ACTIVITY 13.1 — AQUARIUM
The chapter discusses how an aquarium can become a
self-sustaining ecosystem.
Things needed:
- Water
- Oxygen
- Fish
food
- Aquatic
plants
- Fish
- Space
for swimming
Oxygen can be supplied using:
- Aerator
(oxygen pump)
Aquatic plants help by:
- Producing
oxygen
- Maintaining
balance
Important question from NCERT:
Why do aquariums need cleaning while ponds usually do not?
Reason:
- Natural
ecosystems have balanced decomposers and nutrient cycling.
- Artificial
ecosystems require human maintenance.
TYPES OF ORGANISMS IN ECOSYSTEM
Organisms are divided into three groups:
- Producers
- Consumers
- Decomposers
PRODUCERS (AUTOTROPHS)
Organisms that prepare food using sunlight are called:
Producers
Examples:
- Green
plants
- Photosynthetic
bacteria
Process used:
Photosynthesis
They convert:
- Solar
energy → Chemical energy
CONSUMERS (HETEROTROPHS)
Organisms that depend on producers directly or indirectly
for food are called:
Consumers
Types of consumers:
|
Type |
Example |
|
Herbivores |
Deer, goat |
|
Carnivores |
Lion, tiger |
|
Omnivores |
Human beings |
|
Parasites |
Lice, leech |
DECOMPOSERS
Microorganisms that break down dead plants and animals are
called:
Decomposers
Examples:
- Bacteria
- Fungi
Functions:
- Break
complex organic matter
- Convert
it into simple substances
- Return
nutrients to soil
Without decomposers:
- Garbage
would accumulate
- Dead
organisms would not decompose
- Soil
fertility would decrease
ACTIVITY 13.2 — DEPENDENCE OF ORGANISMS
NCERT asks students to:
- Discuss
interdependence among organisms
- Create
food chains
- Understand
ecological balance
Important idea:
Every organism is important in ecosystem.
13.1.1 FOOD CHAINS AND FOOD WEBS
FOOD CHAIN
A sequence of organisms in which one organism feeds on
another is called:
Food Chain
Examples from textbook:
Forest food chain
Plants → Deer → Tiger
Grassland food chain
Grass → Insect → Frog → Snake → Hawk
Pond food chain
Aquatic plants → Small fish → Large fish → Bird
TROPHIC LEVELS
Each step in a food chain is called:
Trophic Level
DIFFERENT TROPHIC LEVELS
|
Trophic Level |
Organism Type |
|
First trophic level |
Producers |
|
Second trophic level |
Herbivores |
|
Third trophic level |
Small carnivores |
|
Fourth trophic level |
Large carnivores |
FLOW OF ENERGY IN ECOSYSTEM
Energy enters ecosystem through:
Sunlight
Green plants capture only about:
1% of solar energy
and convert it into food energy.
TEN PERCENT LAW
Only about:
10% of energy
is transferred from one trophic level to next.
The remaining energy is:
- Lost
as heat
- Used
in digestion
- Used
for movement and body activities
WHY FOOD CHAINS ARE SHORT
Because energy decreases at every trophic level:
- Very
little usable energy remains after 3–4 levels.
Thus food chains are generally short.
IMPORTANT FEATURES OF ENERGY FLOW
- Energy
flow is:
Unidirectional
- Energy
does not return to previous trophic level.
- Energy
decreases progressively at each level.
FOOD WEB
In nature, organisms usually feed on more than one organism.
Interconnected food chains form:
Food Web
Food webs help maintain ecological stability.
BIOLOGICAL MAGNIFICATION
Some harmful chemicals:
- Pesticides
- Insecticides
enter soil and water.
These chemicals:
- Are
absorbed by plants
- Enter
food chains
- Accumulate
at higher trophic levels
This phenomenon is called:
Biological Magnification
IMPORTANT POINT
Humans generally occupy top trophic level.
Therefore:
Maximum concentration of harmful chemicals accumulates in
human body.
Examples:
- Pesticide
residues in wheat
- Rice
- Fruits
- Vegetables
- Meat
ACTIVITY 13.3 — PESTICIDES IN FOOD
NCERT discusses:
- Pesticide
residues in ready-made foods
- Health
concerns
- Need
to reduce pesticide intake
Methods to reduce intake:
- Wash
vegetables properly
- Reduce
pesticide use
- Prefer
organic farming
QUESTIONS FROM NCERT
1. What are trophic levels?
Different feeding levels in food chain.
2. Role of decomposers?
They recycle nutrients back into environment.
13.2 HOW DO OUR ACTIVITIES AFFECT THE ENVIRONMENT?
Human activities directly affect environment.
Main environmental problems discussed:
- Ozone
layer depletion
- Waste
disposal
13.2.1 OZONE LAYER AND ITS DEPLETION
OZONE
Ozone is a molecule containing:
Three oxygen atoms
Chemical formula:
Normal oxygen:
IMPORTANCE OF OZONE LAYER
The ozone layer protects Earth from:
Harmful ultraviolet (UV) radiation
UV rays can cause:
- Skin
cancer
- Damage
to living organisms
FORMATION OF OZONE
High-energy UV rays split oxygen molecules.
Free oxygen atoms combine with oxygen molecules:
OZONE LAYER DEPLETION
Ozone layer started decreasing sharply during:
1980s
Main cause:
Chlorofluorocarbons (CFCs)
Used in:
- Refrigerators
- Fire
extinguishers
- Aerosol
sprays
UNEP AGREEMENT
In 1987:
United Nations Environment Programme (UNEP)
agreed to control CFC production.
Now:
- CFC-free
refrigerators are encouraged worldwide.
ACTIVITY 13.4
Students are asked to:
- Find
chemicals responsible for ozone depletion
- Study
ozone hole changes
13.2.2 MANAGING THE GARBAGE WE PRODUCE
Daily human activities generate:
Garbage and waste materials
Examples:
- Kitchen
waste
- Plastic
packets
- Paper
- Old
clothes
- Bottles
- Wrappers
ACTIVITY 13.5 — BURYING WASTE
Students bury different wastes and observe changes.
Observation:
- Some
materials decompose quickly
- Some
remain unchanged for long time
BIODEGRADABLE SUBSTANCES
Substances broken down by microorganisms are called:
Biodegradable Substances
Examples:
- Vegetable
peels
- Paper
- Cotton
- Food
waste
NON-BIODEGRADABLE SUBSTANCES
Substances not broken down naturally are called:
Non-biodegradable Substances
Examples:
- Plastic
- Glass
- Metals
- Polythene
WHY PLASTICS DO NOT DECOMPOSE
Enzymes are highly specific.
Microorganisms cannot break down many human-made substances
like:
- Plastics
Therefore plastics remain in environment for long periods.
EFFECTS OF BIODEGRADABLE WASTE
✔ Recycles nutrients
✔ Produces manure
✔ Maintains ecological balance
However excessive biodegradable waste may:
- Produce
foul smell
- Release
harmful gases
EFFECTS OF NON-BIODEGRADABLE WASTE
✔ Soil pollution
✔ Water pollution
✔ Harm to animals
✔ Biological magnification
✔ Environmental damage
ACTIVITY 13.6
Students explore:
- Decomposition
time of materials
- Biodegradable
plastics
- Environmental
effects
WASTE MANAGEMENT
Ways to reduce waste problems:
1. Reduce
Use fewer disposable products.
2. Reuse
Reuse materials whenever possible.
3. Recycle
Recycle paper, plastic, glass and metals.
ACTIVITY 13.7
Students study:
- Local
waste collection
- Biodegradable
waste
- Classroom
waste management
SEWAGE AND INDUSTRIAL WASTE
Untreated sewage and industrial waste can pollute:
- Water
- Soil
Thus proper treatment is necessary.
THINK IT OVER — DISPOSABLE CUPS
NCERT discusses:
- Plastic
cups
- Clay
cups (kulhads)
- Paper
cups
Conclusion:
Paper cups are environmentally safer than plastic cups.
Reason:
- Paper
is biodegradable.
ELECTRONIC WASTE (E-WASTE)
Electronic items contain hazardous materials.
Examples:
- Lead
- Mercury
- Toxic
chemicals
Improper disposal harms environment.
ACTIVITY 13.9
Students study:
- E-waste
hazards
- Plastic
recycling
- Environmental
effects of recycling
IMPORTANT DEFINITIONS
|
Term |
Definition |
|
Ecosystem |
Interaction of living and non-living components |
|
Producers |
Organisms preparing food |
|
Consumers |
Organisms depending on others for food |
|
Decomposers |
Organisms breaking down dead matter |
|
Food chain |
Sequence of feeding |
|
Food web |
Interconnected food chains |
|
Trophic level |
Feeding level in food chain |
|
Biological magnification |
Increase of harmful chemicals along food chain |
|
Biodegradable |
Can be decomposed naturally |
|
Non-biodegradable |
Cannot be decomposed naturally |
IMPORTANT EXAMPLES FROM NCERT
✔ Garden ecosystem
✔ Aquarium ecosystem
✔ Forest food chain
✔ Pond food chain
✔ Pesticide accumulation
✔ Ozone depletion by CFCs
✔ Disposable cups in trains
