Q4. A sparrow eats seeds in the morning and insects in the evening. At which trophic levels does it function, and what does this tell you about trophic levels?
It is a primary consumer (second level) when it eats seeds, fruits and peas, and a secondary consumer (third level) when it eats insects and worms. A trophic level is a functional level, not a species as such; one species can occupy more than one level in the same ecosystem at the same time (NCERT page 213).
Q5. List the limitations of ecological pyramids.
They do not take into account the same species belonging to two or more trophic levels; they assume a simple food chain, which almost never exists in nature, and do not accommodate a food web; and saprophytes are given no place in them, although they play a vital role in the ecosystem (NCERT page 214).
Q6. Why can the pyramid of energy never be inverted, although the pyramids of number and biomass sometimes are?
When energy flows from one trophic level to the next, some energy is always lost as heat at each step, so a higher level can never hold more energy than the one below it. Numbers and biomass are counts and masses at one time, which depend on the size and life span of the organisms, so they can be larger at a higher level, as on a big tree or in the sea (NCERT pages 211 and 213).
Q7. An ideal pyramid of energy has 25 000 J in its producers. Following NCERT’s ideal pyramid, how much reaches each of the three consumer levels, and how much sunlight did the producers receive if they converted 1 per cent of it into NPP?
Primary consumers 2500 J, secondary consumers 250 J, tertiary consumers 25 J; sunlight = 25 000 ÷ 0.01 = 2 500 000 J (NCERT Figure 12.4 (d), page 213; our arithmetic).
Q8. In NCERT’s grassland pyramid of numbers, work out the ratio of each level to the one below. Does the number pyramid follow the 10 per cent law?
PC ÷ P = 708 000 ÷ 5 842 000 ≈ 0.12; SC ÷ PC = 354 000 ÷ 708 000 = 0.5; TC ÷ SC = 3 ÷ 354 000 ≈ 8 × 10. No: the 10 per cent law describes the transfer of energy between levels (page 211), not numbers of individuals, which also depend on the size of the organisms at each level (our arithmetic from NCERT Figure 12.4 (a), page 212).
Q9. What does each bar of an energy pyramid represent?
The amount of energy present at that trophic level in a given time, or annually per unit area (NCERT page 213).