Seaweed for the herd
315 words over 29 numbered lines, then 6 parts worth 12 marks (Modular Unit 2 (4WBI2) style, 12–13 marks). Read the article, answer each part, then open its mark scheme and set your mark.
Illustrative article written for Scholar Lab, not a Pearson text. The biology is real; the studies, people and figures are invented or rounded for practice unless a source is named.
Seaweed for the herd
A cow belches several hundred litres of gas every day. Much of it is
methane, made by microorganisms that live in the cow’s stomach and
break down the grass and grain it eats. Across the world, cattle and
other farm animals that chew the cud release a large share of all the
methane produced by human activities.
Methane is a greenhouse gas. The Sun warms the surface of the Earth,
and the warm surface gives off infrared radiation. Greenhouse gases in
the atmosphere absorb some of this radiation and give it out again in
all directions, so some of the heat stays in the lower atmosphere.
Other greenhouse gases include carbon dioxide, water vapour, nitrous
oxide and CFCs. Rising concentrations of these gases are linked to
global warming.
Methane is present in much lower concentrations than carbon dioxide,
but each molecule traps far more heat. It also breaks down in the
atmosphere within about twelve years, so cutting methane emissions
could slow warming fairly quickly.
Scientists have found that a red seaweed contains a substance that
stops the stomach microorganisms from making methane. In one trial,
young beef cattle were split at random into three groups. The control
group ate a normal diet. The other two groups ate the same diet with a
small amount of dried seaweed added. The scientists measured the
methane in the breath of each animal for five months. Illustrative
results are shown in Figure 1.
The cattle given seaweed grew just as well as the control group, and
taste testers could not tell the difference in the meat. However,
there is not yet enough seaweed to feed every cow, and scientists are
now learning how to farm it in the sea. Others want longer trials, to
check that the seaweed is safe for the animals over many years and
that none of its active substance passes into meat or milk.
Figure 1 Methane released by cattle given three diets
Based on Roque B M et al. (2021) PLoS ONE 16(3): e0247820. The values in Figure 1 and the article text are illustrative and rounded.
Read the article and study the figure. Use the information in the article and your own knowledge to answer the questions. The lines in brackets show where to look; select them to highlight the text.
Use the information in the article and your own knowledge to answer the questions. The lines in brackets show you where to look; select them to highlight the text.
State what is meant by the term greenhouse gas.
(1)Name two greenhouse gases other than methane, and give one human activity that releases each one.
(2)Explain how an increase in the concentration of methane in the atmosphere may lead to global warming.
(3)Use Figure 1 to calculate the percentage decrease in methane released by cattle on the 0.5% seaweed diet, compared with the control group.
(2)Give two control variables in this trial.
(2)Suggest two reasons why farmers may not yet add seaweed to the diet of their cattle.
(2)Total for this question: 12 marks
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