Theory question 103
Feeding Relationships and Energy Flow(a)(i) State the second law of thermodynamics.
(ii) Use the second law of thermodynamics to explain the flow of energy across different trophic levels in a food chain.
(b)(i) State three factors that can likely limit the size of human populations.
(ii) Outline two ways each by which humans can overcome the factors named in 3(b)(i).
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(a)(i) Whenever energy is changed from one form to another, some of it is lost (degraded) as heat, so no transfer is 100% efficient.
(ii) Producers trap light energy and store part of it as chemical energy; when a herbivore eats the plant only part of that energy is passed on, the rest being lost as heat in respiration, movement and waste; the same happens at each higher level; so energy decreases along the chain (about 10% passes on), energy flow is one-way, and food chains are short.
(b)(i) Any three: food shortage/famine; disease; shortage of water; lack of space/housing; war; natural disasters.
(ii) e.g. Food shortage — mechanised farming, use of fertilisers and improved varieties, irrigation, food storage. Disease — vaccination, good hygiene and sanitation, better health care. Space — building high-rise houses, planning towns, family planning. Water — boreholes, dams and water treatment.
Link the law directly to heat loss at each trophic level.