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Class 12 Ecosystem worksheet
CBSE Biology. Productivity, decomposition, the 10 per cent law, trophic levels and ecological pyramids. Every sheet has 20 questions in three sections and an answer key, and the numbers change every time.
Sample questions
Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.
Section A · multiple choice
- 1.
The rate of biomass production per unit area over a period is called:
- biomass
- decomposition
- standing crop
- productivity
Answer
(d) productivity
- 2.
Producers in an ecosystem fix 20,000 kJ of energy. By the 10 per cent law, how much energy reaches the fourth trophic level?
- 20 kJ
- 2 kJ
- 200 kJ
- 666.667 kJ
Answer
(a) 20 kJ
20,000 × (1/10)³
- 3.
The gross primary productivity of a grassland is 5,800 kJ m⁻² yr⁻¹, and respiration uses 2,900 kJ m⁻² yr⁻¹. The net primary productivity is:
- 8,700 kJ m⁻² yr⁻¹
- 5,800 kJ m⁻² yr⁻¹
- 2,900 kJ m⁻² yr⁻¹
- 580 kJ m⁻² yr⁻¹
Answer
(c) 2,900 kJ m⁻² yr⁻¹
NPP = GPP − R
Section B · short answer
- 4.
Distinguish between gross and net primary productivity.
Answer
GPP is the rate of production of organic matter during photosynthesis. NPP is GPP minus the energy used in respiration (R); it is the biomass available to heterotrophs.
- 5.
In the food chain grass → grasshopper → frog → snake → hawk, the producers fix 5,000,000 J. How much energy reaches each of the other organisms, by the 10 per cent law?
Answer
grasshopper: 500,000 J; frog: 50,000 J; snake: 5,000 J; hawk: 500 J
only about 10% passes to the next level
Section C · long answer
- 6.
Describe the process of decomposition.
Answer
Decomposers break down complex organic matter into inorganic substances such as CO₂, water and nutrients. Fragmentation: detritivores such as earthworms break detritus into small pieces. Leaching: water-soluble nutrients go down into the soil and are precipitated as salts. Catabolism: bacterial and fungal enzymes degrade detritus into simpler inorganic substances. Humification produces humus, and mineralisation breaks humus down further, releasing inorganic nutrients.
Fresh sheets for your child
In the app, every Ecosystem sheet is new: the app remembers the questions your child has already had and leaves them out. Print the sheet as a PDF, or use notebook mode and write the answers in a notebook.
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