Chapter 13: Our Environment
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Chapter 13 – Our Environment
Introduction
The environment includes everything
around us—living (biotic) and non-living (abiotic) components. Humans depend on
the environment for survival but also impact it significantly. This chapter
studies ecosystems, energy flow, waste generation, and the impact of human
activities.
1.
Ecosystem, Types and Its Components
Ecosystem
: An ecosystem is a functional unit of nature where living organisms
interact with each other and the physical environment.
Types:
a) Natural Ecosystem : An ecosystem which exits in nature on its own without any
human interference is called natural ecosystem. E.g – desert, grassland,
forest, ponds, lakes, estuaries, rivers and oceans.
b) Artificial Ecosystem: An ecosystem which is created and maintained by humans is
called artificial ecosystem. E.g : Aquariums, botanical gardens, parks, field
crops, etc are artificial ecosystem.
Components
of an Ecosystem
1.
Biotic Components (Living
things): These includes all the living
organisms present in the ecosystem i.e plants, animals including human and
microorganisms. It is classified into:
a)
Producers
(Autotrophs): Plants, algae, etc are known as
producers as they can prepare food by
photosynthesis. They absorb radiant energy of the sun and convert it into
chemical energy to produce organic compounds (i.e carbohydrates).
b)
Consumers
(Heterotrophs): Animals & humans are the
consumers as they depend on others for food.
§ Primary Consumers:
Herbivores (e.g., deer)
§ Secondary Consumers:
Carnivores (e.g., frog)
§ Tertiary Consumers:
Top carnivores (e.g., tiger)
c)
Decomposers: Bacteria, fungi –These are the microorganisms
that feed upon the dead and decaying organic matter. They break down dead
organisms & return nutrients to soil.
Importance of decomposers:
- They help is decomposing waste from the ecosystem.
- They help in recycling of materials, cleaning of waste and creating space for the growth of new organisms.
2. Abiotic Components (Non-living things): These are the non-living components on which the living organisms depend. They are air, water, soil, temperature, light, etc.
2.
Food Chain and Food Web
- Food Chain:
It is a linear network of living organisms in a community through which
energy is transferred in the form of food. It is a linear sequence of
organisms showing “who eats whom.”
a)Terrestrial
food chain :
- Example: Grass → Grasshopper → Frog → Snake → Hawk
b) Aquatic food chain:
Example:
Phytoplankton →Zooplankton → Fish →
Shark
- Food Web:
It is defined as the interconnection of different food chains, which correlate
at various trophic levels operating in an ecosystem.
- Trophic levels:
The transfer of food or energy takes place through various steps or levels
in the food chain known as trophic levels. They are:
a)
First trophic level (T1)-
Producers are present here. They fix solar energy, making it available for
consumers.
b)
Second trophic level(T2) –
The herbivores or primary consumers are found here.
c)
Third trophic level (T3) – Small carnivores or secondary consumers
are found here.
d)
Fourth trophic level (T4) – Larger carnivores or the tertiary
consumers forms this level.
3.
Energy Flow in an Ecosystem
- Energy Transfer:
- Sun → Producers → Consumers → Decomposers
- The green plants in a terrestrial ecosystem capture about 1% of the energy from sunlight and convert it into food.
- Only 10% energy passes from one trophic level
to the next (10% law by Lindeman).
- Trophic Levels:
Steps in a food chain (Producer = 1st level, herbivore = 2nd, carnivore =
3rd, etc.)
- Energy flow is unidirectional (cannot be
reused)
10% Law: According to this law, an average of 10% of the energy of
food eaten by an organism is turned back into its own body and made available
for the next level of consumers.
Numerical Question on 10% Law
Question:
In a grassland ecosystem, plants (producers) capture 10,000 Joules of energy from the sun. Using the 10% law, calculate:
a) Energy available to herbivores (primary consumers)
b) Energy available to primary carnivores (secondary consumers)
c) Energy available to top carnivores (tertiary consumers)
Solution:
According to the 10% law, only 10% of energy is transferred from one trophic level to the next.
Answer:
a) Herbivores = 1,000 J
b) Primary Carnivores = 100 J
c) Top Carnivores = 10 J
4.
Biological Magnification
- It is the defined as the phenomenon of progressive
increase in the concentration of harmful non-biodegradable toxicants in
the bodies of organisms at each successive levels,
Or
It is the
process where harmful non-biodegradable chemicals (like pesticides, DDT)
increase in concentration at each trophic level.
- Top consumers (humans) are most affected.
- It is also known as bioconcentration.
Causes of Biological Magnification
1.
Excessive use of
pesticides and insecticides like DDT in agriculture.
2.
Industrial
discharge of harmful chemicals such as mercury, lead, and arsenic into
water bodies.
3.
Agricultural
run-off carrying pesticides and fertilizers into rivers and lakes.
4.
Improper disposal
of non-biodegradable waste including plastics and chemicals.
5.
Mining and chemical
industry waste contaminating soil and water.
5.
Waste and Its Types
Human activities produce waste,
classified into:
· Biodegradable Substances: Substances
that can be broken down into simpler, harmless forms by the action of
microorganisms such as bacteria and fungi are called biodegradable
substances.
Examples: Vegetable peels, paper, wood, cotton, animal waste.
· Non-Biodegradable Substances :Substances
that cannot be broken down by natural organisms and persist in
the environment for a long time are called non-biodegradable substances.
Examples: Plastics, metals, glass, pesticides, polythene bags.
Effects of Biodegradable Substances
1. Cause bad odour when decomposing in large amounts.
2. Lead to water pollution if dumped in water bodies.
3. Release methane gas during decomposition, contributing to global warming.
4. Spread of diseases due to growth of harmful microbes in waste.
5. Can clog drains and cause unhygienic conditions when not managed properly.
Effects of Non-Biodegradable Substances
1. Soil and water pollution as they do not break down easily.
2. Harm to animals when ingested (e.g., plastic bags swallowed by cows).
3. Biological magnification of toxic chemicals like DDT in food chains.
4. Blockage of sewage and drainage systems, causing floods and sanitation issues.
5. Long-term environmental damage as they persist for hundreds of years.
6. Release of toxic fumes when burned (e.g., burning plastics produces harmful gases).
6.
Ozone Layer and Its Depletion
- Ozone Layer: It is the protective layer in the stratosphere that
absorbs harmful UV radiation. It consists of 3 atoms of oxygen i.e O3
and found 20 – 30 km above earth.
- Depletion Causes: Use
of CFCs (Chlorofluorocarbons) in refrigerators, ACs, aerosol
sprays.
- Effects: Skin cancer, eye problems, reduced crop yield.
- Solution: In 1987, the United Nations Environment Programme (UNEP) succeeded in forming an agreement to freeze CFC’s production under Montreal Protocol (1987).
- Methods of Waste Disposal
-
The various methods of waste disposal are:
1. Landfills
- Waste is buried in designated sites.
- Advantages:
Simple, cost-effective.
- Disadvantages:
Requires large land areas, risk of soil and water pollution, produces
methane gas.
2. Incineration
- Waste is burned at high temperatures to reduce its
volume.
- Advantages:
Reduces waste volume, can generate energy.
- Disadvantages:
Produces toxic gases, expensive setup.
3. Composting
- Organic waste (food, leaves) is decomposed by
microorganisms to produce manure.
- Advantages:
Eco-friendly, produces useful compost for agriculture.
- Disadvantages:
Slow process, requires space and maintenance.
4. Recycling
- Converting waste materials (plastic, paper, glass,
metal) into new products.
- Advantages:
Conserves resources, reduces pollution.
- Disadvantages:
Requires segregation and processing facilities.
5. Vermicomposting
- Using earthworms to decompose organic waste into
nutrient-rich compost.
- Advantages:
Produces high-quality fertilizer, eco-friendly.
- Disadvantages:
Needs controlled conditions.
6. Waste-to-Energy (Biogas & Energy Recovery)
- Organic waste is broken down anaerobically to produce
biogas or converted into electricity/heat.
- Advantages:
Produces energy, reduces landfill use.
- Disadvantages:
Requires technology and investment.
- Waste is buried in designated sites.
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