Ecology & Environment
Short Notes (2025 Edition)
1. Introduction to Ecology
Ecology is the branch of biology that studies how living
organisms interact with each other and with their physical
surroundings. The term “ecology” comes from the Greek
words oikos (home) and logos (study), meaning “the study of
the home environment.”
Ecology focuses on understanding relationships at different
levels — from small populations of organisms to the global
biosphere. It helps us answer questions like:
How do species survive in their natural habitats?
What factors control the population of plants and animals?
How do energy and nutrients move through the
environment?
The main goal of ecology is to maintain a balance between
living things and the natural world, ensuring long-term
sustainability.
2. Levels of Ecological Organization
Ecologists study nature at different levels of organization,
each showing a unique interaction between living and non-
living components:
1. Organism – A single living being (e.g., a frog or a tree).
, 2. Population – A group of organisms of the same species in
one area.
3. Community – All living species in a particular area (plants,
animals, microbes).
4. Ecosystem – The community plus its physical environment
(air, soil, water, climate).
5. Biome – A large region with similar climate, plants, and
animals (e.g., desert, rainforest).
6. Biosphere – The entire zone of life on Earth, including land,
water, and air.
Each level interacts closely with others. For example, if a
population of bees decreases, it affects the entire community
of plants that depend on pollination.
3. Components of an Ecosystem
Every ecosystem has two main components:
A. Abiotic Components (Non-living)
These are physical and chemical elements like:
Sunlight
Temperature
Water
Soil and minerals
Air (oxygen, carbon dioxide, nitrogen)
These factors directly influence the survival and reproduction
of living organisms.
B. Biotic Components (Living)
These include all living organisms, divided into three groups:
Short Notes (2025 Edition)
1. Introduction to Ecology
Ecology is the branch of biology that studies how living
organisms interact with each other and with their physical
surroundings. The term “ecology” comes from the Greek
words oikos (home) and logos (study), meaning “the study of
the home environment.”
Ecology focuses on understanding relationships at different
levels — from small populations of organisms to the global
biosphere. It helps us answer questions like:
How do species survive in their natural habitats?
What factors control the population of plants and animals?
How do energy and nutrients move through the
environment?
The main goal of ecology is to maintain a balance between
living things and the natural world, ensuring long-term
sustainability.
2. Levels of Ecological Organization
Ecologists study nature at different levels of organization,
each showing a unique interaction between living and non-
living components:
1. Organism – A single living being (e.g., a frog or a tree).
, 2. Population – A group of organisms of the same species in
one area.
3. Community – All living species in a particular area (plants,
animals, microbes).
4. Ecosystem – The community plus its physical environment
(air, soil, water, climate).
5. Biome – A large region with similar climate, plants, and
animals (e.g., desert, rainforest).
6. Biosphere – The entire zone of life on Earth, including land,
water, and air.
Each level interacts closely with others. For example, if a
population of bees decreases, it affects the entire community
of plants that depend on pollination.
3. Components of an Ecosystem
Every ecosystem has two main components:
A. Abiotic Components (Non-living)
These are physical and chemical elements like:
Sunlight
Temperature
Water
Soil and minerals
Air (oxygen, carbon dioxide, nitrogen)
These factors directly influence the survival and reproduction
of living organisms.
B. Biotic Components (Living)
These include all living organisms, divided into three groups:
