Sample 1Medium
A flow diagram of decomposition shows: P, detritivores such as earthworms break detritus into smaller particles; Q, water-soluble inorganic nutrients go down into the soil and precipitate as unavailable salts; R, bacterial and fungal enzymes break detritus into simpler inorganic substances; S, a dark amorphous substance highly resistant to microbial action builds up; T, this substance is slowly degraded, releasing inorganic nutrients. Which naming is correct?
- A
P catabolism, Q leaching, R fragmentation, S humification, T mineralisation
- B
P fragmentation, Q leaching, R catabolism, S humification, T mineralisation
- C
P fragmentation, Q mineralisation, R catabolism, S humification, T leaching
- D
P fragmentation, Q leaching, R humification, S catabolism, T mineralisation
Show the answer
The answer is B.Decomposition involves fragmentation by detritivores, leaching of soluble nutrients, catabolism by bacterial and fungal enzymes, humification forming humus, and mineralisation of humus that releases inorganic nutrients.
- A.
Breaking detritus into particles by detritivores is fragmentation; enzymatic breakdown is catabolism.
- C.
Downward loss of soluble nutrients is leaching; release of nutrients from humus is mineralisation.
- D.
Humification forms humus; catabolism is the enzymatic breakdown of detritus.
NCERT: Class 12 Biology, Chapter 12, 12.3
Sample 2NEET level
Consider the following statements: 1. Net primary productivity is gross primary productivity minus the loss by respiration. 2. The annual net primary productivity of the whole biosphere is about 170 billion tons (dry weight) of organic matter. 3. Despite covering about 70 per cent of the surface, the productivity of the oceans is only about 55 billion tons. 4. Decomposition is faster when the detritus is rich in lignin and chitin. Which of the statements above are correct?
- A
1, 2 and 3 only
- B
1 and 2 only
- C
2, 3 and 4 only
- D
1, 3 and 4 only
Show the answer
The answer is A.NPP = GPP − R, the biosphere's annual NPP is about 170 billion tons dry weight, and the oceans contribute only about 55 billion tons of it. Decomposition is slower, not faster, when detritus is rich in lignin and chitin, so statement 4 is false.
- B.
Leaves out statement 3, which correctly gives the oceans' productivity.
- C.
Includes statement 4, which is false, and leaves out the correct statement 1.
- D.
Includes statement 4, which is false, and leaves out the correct statement 2.
NCERT: Class 12 Biology, Chapter 12 (Ecosystem), Productivity and Decomposition