Components and Structure of an Ecosystem: Quick Revision

A brief note on Components and Structure of an Ecosystem. Read it before a test. Try each question at the end before you open its answer.

Components

• Ecosystem: a functional unit of nature where living organisms interact with each other and with the physical environment.
• Types: terrestrial (forest, grassland, desert), aquatic (pond, lake, wetland, river, estuary), man-made (crop field, aquarium).
• Abiotic: water, light, temperature, soil, nutrients.
• Biotic: producers, consumers (primary, secondary, tertiary) and decomposers.
• Functions: productivity, decomposition, energy flow, nutrient cycling. Nutrient cycling is not in the NEET syllabus.
• Structure: species composition and stratification (trees, shrubs, herbs).

Food chains and trophic levels

• Grazing food chain: starts with a green plant. Detritus food chain: starts with dead organic matter.
• Decomposers: fungi and bacteria, saprotrophs. Detritivores: such as the earthworm, which fragment detritus.
• Aquatic ecosystem: the grazing chain is the major route. Terrestrial ecosystem: the detritus chain carries a much larger part.
• Trophic levels: T1 producers, T2 primary consumers, T3 secondary consumers, T4 tertiary consumers.
• Food web: joined food chains. An omnivore can sit on more than one level.
• Standing crop: biomass or number in a unit area at a time. Dry weight is more accurate than fresh weight.

A worked example

A plot has 600 g of fresh grass in a square metre, and 70 per cent of it is water. What is the dry mass?

1. The dry part is the share that is not water, $1 - 0.70 = 0.30$.
2. $600 \times 0.30 = 180$ g in each square metre.

Practice with new numbers

A program to try

The program names the job of four living things.

Mistakes to avoid

• Counting the Sun as a producer. It is abiotic.
• Giving the grazing chain to a forest as the larger one. On land the detritus chain is larger.
• Calling an earthworm a decomposer. It is a detritivore. Fungi and bacteria are the decomposers.
• Numbering herbivores T1. Producers are T1.

Check yourself

1. With what does a detritus food chain begin?

2. Which chain is the major route of energy in a lake?

3. What is stratification?

4. Why is dry weight preferred for the standing crop?

Sources

• NCERT (2023). Biology, Textbook for Class XII, chapter 12, Ecosystem.
• OpenStax Biology 2e (2018), chapter 46, Ecosystems.
• Campbell Biology, 12th edition (2021), Pearson, chapter 55, Ecosystems and Energy.