Read the passage below. Use the information in the passage and your own knowledge
to answer the questions that follow.
Snail Farming
The photograph shows a snail that is farmed for its meat.
Farming snails has many benefits. Economically, there are many people prepared to
pay for the luxury of eating snail meat. The meat itself is high in protein. It is also low
in fat, so snail meat is healthy to eat. Also, farming snails helps to conserve natural
5 snail populations which are at risk due to being collected in large numbers in many
places.
In the wild, snails grow fastest in warm temperatures and a humid atmosphere.
Maintaining these conditions on a snail farm creates problems with insect pests
and bacterial infections. Natural predators of the insect pests, such as spiders, are
10 encouraged on farms, as is the constant use of fly swatters and sticky fly traps. To
prevent bacterial infections, disinfectant is added to the water used to clean the
cages.
Snails are herbivores but on a snail farm they are not fed with green vegetables
as might be expected. Green vegetables are not assimilated very well by many
15 organisms. The assimilation efficiency (AE) of an organism is the percentage of total
food eaten that is absorbed into the blood after digestion, and not lost as faeces.
Carnivores tend to have an AE of 80%, while most leaf-eating herbivores have an
AE of about 50%. However, snails have symbiotic microorganisms in their gut that
release the enzyme, cellulase, to digest cellulose into glucose. This boosts their AE to
20 about 75%. Nevertheless, snails on a farm are fed with high quality food containing a
mixture of amino acids, carbohydrates, vitamins and mineral ions.
The production efficiency (PE) of an animal is the proportion of assimilated food
that is turned into new biomass rather than being metabolised. Birds and mammals
have a very low PE of 1 to 2%, but snails have a much higher PE. This is because the
20 metabolic use of assimilated food, particularly glucose, is much reduced in snails.
Selective breeding is used on a snail farm to produce fast-growing snails that
have thin shells and lay lots of eggs. The eggs are put on damp, sterilised soil and
incubated. The young snails that hatch are put in plastic trays that are easy to clean.
Explain why snail meat is healthy to eat (line 4).
(2)
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