Maarg Manthan · Topic 2.2

Structure/Components of an Ecosystem: Abiotic and Biotic Components

Environment & Ecology › Ecosystem Structure and Function · Topic 2.2

An ecosystem has two kinds of components. The abiotic components are the non-living physical and chemical factors: solar radiation, temperature, water, air, soil, minerals, nutrients, pH and topography. They include inorganic substances such as carbon dioxide and water, organic compounds such as proteins and humus, and climatic factors. The biotic components are the living parts, grouped by function into producers, consumers and decomposers. Producers or autotrophs, mainly green plants, algae and some bacteria, make food by photosynthesis or chemosynthesis. Consumers or heterotrophs depend on others for food and include primary consumers or herbivores, secondary and tertiary consumers or carnivores, and omnivores. Decomposers, such as bacteria and fungi, break down dead matter and return nutrients, and detritivores like earthworms feed on dead debris.

5 min read · UPSC Prelims · Environment & Ecology · Ecosystem Structure and Function

At a Glance

Non-living Abiotic: light, soil, water
Food makers Producers
Food users Consumers
Recyclers Decomposers
Dead debris eaters Detritivores
Exam link UPSC Prelims, Environment & Ecology: Ecosystem Structure and Function

Where Does It Fit?

This topic follows the definition of an ecosystem. It lists the parts that make up the system, which the next topics on energy flow and trophic levels arrange into chains. Previous topic: homeostasis Stability…">Definition, Functions and Properties of an Ecosystem. Next topic: Flow of Energy in an Ecosystem.

What Are the Abiotic Components?

Group	Examples and role
Climatic factors	Sunlight, temperature, rainfall, humidity and wind. Light drives photosynthesis and sets the zones in water
Edaphic factors	Soil texture, minerals, humus, pH, moisture and air in the soil. They decide what plants grow
Topographic factors	Altitude, slope and aspect affect local climate
Inorganic substances	Water, carbon dioxide, oxygen, nitrogen, phosphorus, sulphur and minerals taken in by organisms
Organic compounds	Proteins, carbohydrates, lipids and humus that link the living and non-living parts
Water factors	Salinity, dissolved oxygen, turbidity and currents in aquatic ecosystems
Fire and pressure	Fire in grasslands and pressure at depth in oceans act as physical factors

What Are the Biotic Components?

Producers (autotrophs): make organic food from inorganic matter using light (photosynthesis) or chemical energy (chemosynthesis). Green plants, algae, cyanobacteria and phytoplankton
Chemosynthetic bacteria: produce food from chemicals, as around deep sea hydrothermal vents
Primary consumers: herbivores that eat producers, such as deer, cattle, rabbits and zooplankton
Secondary consumers: carnivores that eat herbivores, such as frogs, small fishes and foxes
Tertiary consumers: top carnivores that eat other carnivores, such as tigers, lions, eagles and large fish
Omnivores: eat both plants and animals, such as humans, bears and crows
Decomposers (saprotrophs): bacteria and fungi that digest dead matter outside the body and absorb nutrients
Detritivores: animals that eat dead organic debris, such as earthworms, millipedes, vultures (scavengers) and dung beetles

What Else Should You Remember?

Parasites: consumers that live on a host and feed on it
Scavengers: animals like vultures and hyenas that feed on dead animals
Saprotrophs: organisms feeding on dead matter by external digestion
Autotroph types: photoautotrophs use light and chemoautotrophs use chemical energy
Heterotroph types: herbivores, carnivores, omnivores, detritivores
Microconsumers: another name for decomposers
Macroconsumers: animals that eat organic matter
Symbionts: organisms in close association, as in lichens and mycorrhiza
Humus: dark organic part of soil formed by decay
Detritus food chain: starts with dead matter
Grazing food chain: starts with living plants
Producers in oceans: phytoplankton produce about half of the oxygen on Earth
Light zones: the euphotic zone gets enough light for photosynthesis
Mycorrhiza: association of fungus and plant root that helps nutrient uptake
Nitrogen fixers: Rhizobium in root nodules of legumes
Vultures decline: diclofenac in cattle drugs poisoned Indian vultures, harming scavenging
Soil organisms: bacteria, fungi, earthworms and mites form a rich community in soil
Edaphic factors: soil types of India include alluvial, black, red and laterite
Link: how energy moves among them is in Flow of Energy in an Ecosystem
Link to trophic levels: see Trophic Levels, Food Chain and Its Types and Significance
Caution: an animal can belong to different consumer levels in different chains
Role of light: light intensity and quality control the depth to which algae can grow in water
Role of temperature: sets rates of metabolism and decides distribution of species
Role of soil: provides anchorage, water and minerals, and hosts decomposers
Role of fire: in grasslands and some forests fire recycles nutrients and keeps open habitat
Mixed feeders: some plants such as the pitcher plant trap insects to get nitrogen
Autotrophs in numbers: producers form the largest biomass in most ecosystems, except in oceans where phytoplankton have small biomass but high turnover
Scavenging value: vultures and other scavengers clean carcasses and reduce disease
Link to trophic levels: each consumer class forms a trophic level in the food chain

Why Does It Matter for the Exam?

Abiotic groups: climatic, edaphic, topographic
Biotic groups: producers, consumers, decomposers
Consumers: primary, secondary, tertiary
Current affairs link: vulture conservation
Common errors: calling fungi producers or decomposers detritivores

As an analytical point, every ecosystem needs all three biotic groups: producers to capture energy, consumers to pass it on, and decomposers to recycle nutrients. Loss of any group, such as vultures, disrupts the whole system.

Why Is This Topic Important?

Abiotic Physical base
Biotic Three groups
Roles Make, use, recycle

What Came Next?

The next topic covers the flow of energy in an ecosystem. Next topic: Flow of Energy in an Ecosystem.

Key People and Terms

Autotroph Self-feeder
Heterotroph Depends on others for food
Saprotroph Feeds on dead matter
Detritivore Eats dead debris
Omnivore Eats plants and animals
Chemosynthesis Food from chemical energy

Exam Corner

Points to Remember

Producers: autotrophs.
Decomposers: bacteria and fungi.
Detritivores: earthworms, millipedes.
Vents have chemosynthetic producers.
Humans are omnivores.

Do Not Confuse With

Decomposer and detritivore External digestion versus eating debris
Scavenger and predator Eats dead versus kills
Photosynthesis and chemosynthesis Light versus chemical energy

Memory Hook

Abiotic sets the stage; producers make, consumers eat, decomposers recycle.

Mains Angle

Questions ask for classification with examples. These points help.

Parts Components
Roles Functions
Loss Vultures

A Question You May Face

An original practice question, not a past paper question.

“Describe the abiotic and biotic components of an ecosystem and explain the role of each group in ecosystem functioning.”

How to Answer

Abiotic Factors.
Biotic Three groups.
Roles Make, use, recycle.
Example Vultures.

GS Relevance

Prelims: components, classes of consumers, decomposers versus detritivores. GS Paper 3: ecology.

Frequently Asked Questions

What are the components of an ecosystem?

An ecosystem has abiotic components, the non-living factors such as sunlight, temperature, water, air and soil minerals, and biotic components, the living organisms. The biotic part is divided by function into producers that make food, consumers that eat other organisms, and decomposers that break down dead matter.

What are producers in an ecosystem?

Producers, or autotrophs, are organisms that make their own food from inorganic substances. Most use sunlight for photosynthesis, like green plants, algae and cyanobacteria, while some bacteria use energy from chemicals in a process called chemosynthesis. They form the base of all food chains and bring energy into the ecosystem.

What is the difference between decomposers and detritivores?

Decomposers such as bacteria and fungi feed on dead matter by secreting enzymes outside their body and absorbing the products, which releases nutrients into the soil or water. Detritivores such as earthworms, millipedes and dung beetles ingest dead debris and break it into smaller pieces, which decomposers then act upon.

What are primary, secondary and tertiary consumers?

Primary consumers are herbivores that feed directly on producers, such as deer and zooplankton. Secondary consumers are carnivores that feed on herbivores, such as frogs and small fishes. Tertiary consumers are top carnivores that feed on other carnivores, like tigers and eagles.

What is chemosynthesis?

Chemosynthesis is the process by which some bacteria make organic food using energy released from chemical reactions of inorganic substances such as hydrogen sulphide, instead of sunlight. It supports ecosystems around deep sea hydrothermal vents, where there is no light and tube worms and other animals depend on such bacteria.

PYQ Practice — Statement Analysis

1 Fungi act as decomposers in an ecosystem.

True

Along with bacteria.

2 Earthworms are decomposers by external digestion.

False

They are detritivores.

3 Chemosynthetic bacteria are producers.