CHAPTER 14: ECOSYSTEM
Comprehensive Class 12 Biology Study Document | NCERT Based
1. 🌱 Introduction to Ecosystem
An ecosystem is a functional unit of nature, where living organisms (biotic) interact
among themselves and also with the surrounding physical environment (abiotic).
The entire biosphere is regarded as a Global Ecosystem. Since it is too big to be studied
as a whole, it is divided into two main categories:
• Terrestrial Ecosystems: Examples include Forest, Grassland, and Desert.
• Aquatic Ecosystems: Examples include Pond, Lake, Wetland, River, and Estuary.
Note: Man-made (Anthropogenic) ecosystems include Crop fields and Aquariums.
2. 🧩 Ecosystem – Structure and Function
Interaction of biotic and abiotic components results in a physical structure. Two key
structural features are:
1. Species Composition: Identification and enumeration of plant and animal species of
an ecosystem.
2. Stratification: Vertical distribution of different species occupying different levels.
Example: In a forest, trees occupy top vertical strata, shrubs the second, and herbs/
grasses the bottom layers.
Biology Class 12: Ecosystem | Page 1
, 📌 The Pond as a Self-Sustaining Unit
Producers (Phytoplankton/Algae)
Consumers (Fish/Zooplankton)
Decomposers (Bacteria/Fungi in soil)
Figure 1: Functional Components of a Pond Ecosystem
A pond ecosystem performs all major functions: Productivity, Decomposition, Energy
Flow, and Nutrient Cycling.
3. 🌾 Productivity
A constant input of solar energy is the basic requirement for any ecosystem to function.
Productivity is the rate of biomass production per unit area over a time period.
Primary Productivity
The amount of biomass produced per unit area over a time period by plants during
photosynthesis.
• Gross Primary Productivity (GPP): Rate of production of organic matter during
photosynthesis.
• Net Primary Productivity (NPP): The available biomass for the consumption to
heterotrophs.
NPP = GPP – R
(Where R = Respiration losses)
Secondary Productivity: Rate of formation of new organic matter by consumers.
Biology Class 12: Ecosystem | Page 2
Comprehensive Class 12 Biology Study Document | NCERT Based
1. 🌱 Introduction to Ecosystem
An ecosystem is a functional unit of nature, where living organisms (biotic) interact
among themselves and also with the surrounding physical environment (abiotic).
The entire biosphere is regarded as a Global Ecosystem. Since it is too big to be studied
as a whole, it is divided into two main categories:
• Terrestrial Ecosystems: Examples include Forest, Grassland, and Desert.
• Aquatic Ecosystems: Examples include Pond, Lake, Wetland, River, and Estuary.
Note: Man-made (Anthropogenic) ecosystems include Crop fields and Aquariums.
2. 🧩 Ecosystem – Structure and Function
Interaction of biotic and abiotic components results in a physical structure. Two key
structural features are:
1. Species Composition: Identification and enumeration of plant and animal species of
an ecosystem.
2. Stratification: Vertical distribution of different species occupying different levels.
Example: In a forest, trees occupy top vertical strata, shrubs the second, and herbs/
grasses the bottom layers.
Biology Class 12: Ecosystem | Page 1
, 📌 The Pond as a Self-Sustaining Unit
Producers (Phytoplankton/Algae)
Consumers (Fish/Zooplankton)
Decomposers (Bacteria/Fungi in soil)
Figure 1: Functional Components of a Pond Ecosystem
A pond ecosystem performs all major functions: Productivity, Decomposition, Energy
Flow, and Nutrient Cycling.
3. 🌾 Productivity
A constant input of solar energy is the basic requirement for any ecosystem to function.
Productivity is the rate of biomass production per unit area over a time period.
Primary Productivity
The amount of biomass produced per unit area over a time period by plants during
photosynthesis.
• Gross Primary Productivity (GPP): Rate of production of organic matter during
photosynthesis.
• Net Primary Productivity (NPP): The available biomass for the consumption to
heterotrophs.
NPP = GPP – R
(Where R = Respiration losses)
Secondary Productivity: Rate of formation of new organic matter by consumers.
Biology Class 12: Ecosystem | Page 2
