Food security: what limits yield and what it costs to raise it · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

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Science · Organisms & Life Processes · ages 15-16
Name ______________________   Date ____________

  1. In a model with 10% transfer from crop feed to edible animal tissue, what share of the feed energy is stored in that tissue?

    • Nine tenths of the energy in the feed
    • One half of the energy in the feed
    • One tenth of the energy in the feed

  2. What does food security mean?

    • A country produces a large harvest regardless of who can obtain it
    • Everyone can reliably obtain enough safe, nutritious food
    • Food prices stay low even when households cannot reach the shops

  3. Fertiliser can raise crop yield when nutrients limit growth, but dissolved nutrients can be carried into rivers.

    Circle one:   True   False

  4. Winters in a region become warmer. A crop pest that used to die in winter now survives. How can this affect food supply?

    • More pests may survive to damage crops and reduce harvests
    • More pests must survive to increase every crop's nutrient supply
    • More pests cannot reduce harvests when summers are unchanged

  5. Animals eat grain containing 1600 energy units. Assume 10% becomes edible animal tissue. How many energy units are stored in that edible tissue?

    • 1440 units
    • 1600 units
    • 160 units

  6. Grain people can eat contains 2500 energy units. If it is fed to animals, assume 10% becomes edible tissue. How many fewer food-energy units are available as animal tissue than as grain?

    Answer: ______________

  7. A farmer says repeated use of one pesticide has no costs because it kills pests. Which reply best evaluates this claim?

    • It may protect yield, but only the cost of buying it matters because pest survival cannot affect later crops
    • It may protect yield, but resistant survivors may reproduce and non-target species may be harmed
    • It may protect yield, but resistance develops only if every pest dies before any can reproduce

  8. Cattle eat only grass that people cannot eat. A planner uses the grain-to-meat calculation to claim this grass could feed people directly. Which evaluation fits?

    • The calculation assumes feed people can eat, so it does not show that grass could feed people directly.
    • The calculation proves the grass could feed people directly because all plants provide the same usable food.
    • The calculation shows that cattle store all the energy in grass, so feeding them cannot reduce food energy.
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Answer key

For grown-ups. Fold this page away before handing over the rest.

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  1. One tenth of the energy in the feed · Ten percent means 10 out of 100, which is one tenth. This is the stated model, not a fixed efficiency for every animal.
  2. Everyone can reliably obtain enough safe, nutritious food · Food security requires reliable access to enough safe, nutritious food. Harvest size or low prices alone cannot provide that access.
  3. True · Fertiliser can supply limiting nutrients. Water can also carry dissolved nutrients from fields into rivers, where they may contribute to eutrophication.
  4. More pests may survive to damage crops and reduce harvests · Survival through winter can leave more pests able to damage crops. This can reduce harvests; it does not mean every pest increases in every region.
  5. 160 units · Ten percent of 1600 is 1600 ÷ 10 = 160 units. The calculation concerns edible animal tissue, before people eat it.
  6. 2250 · The edible animal tissue contains 2500 ÷ 10 = 250 units. The difference is 2500 - 250 = 2250 food-energy units.
  7. It may protect yield, but resistant survivors may reproduce and non-target species may be harmed · Pesticides can reduce crop damage. Repeated use can favour resistant pests, and exposure can harm other species. These possible costs remain even when spraying protects yield.
  8. The calculation assumes feed people can eat, so it does not show that grass could feed people directly. · The grain comparison requires feed people could eat instead. Grass does not meet that condition because people cannot eat it. This calculation alone cannot show how many human meals a grass-only system replaces.
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