Farming upwards
374 words over 33 numbered lines, then 8 parts worth 17 marks (Linear Paper 2 (4BI1/2B) style, 14–18 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 surveys, people and figures are invented or rounded for practice.
Farming upwards
In a warehouse on the edge of a city, lettuces are growing in trays
stacked twelve layers high. There is no soil and no sunlight. Workers
move between the layers on lifts, and robots carry the trays to the
packing room. This is a vertical farm, and supporters say that farms
like it could help to feed growing cities while using much less land
and water.
The plants grow with their roots in a flowing solution of water and
mineral ions, a method called hydroponics. The solution contains
nitrate ions, magnesium ions and other ions the plants need, and any
solution the roots do not take up is collected and used again.
Overall, the farm uses about 95 per cent less water than a field
growing the same crop. Sensors measure the pH and the concentration of
each ion every few minutes, and a computer adds more ions whenever the
concentration falls.
Light comes from LED lamps that give out mainly red and blue light,
the colours that chlorophyll absorbs best. The lamps stay on for about
16 hours a day. The concentration of carbon dioxide in the air is kept
at about three times the normal concentration, and the temperature is
kept at about 22 °C all year round.
The air entering the farm is filtered, and workers wear clean
overalls. Because there are no insects and no soil, the lettuces are
grown without pesticides. In an illustrative year, a farm with a floor
area of 1 000 m² produced 82 tonnes of lettuce. A field of the same
area outdoors produced about 3.9 kg of lettuce per m² in a year.
There are drawbacks. The LED lamps, pumps and air conditioning use
large amounts of electricity, which is expensive and may be generated
by burning fossil fuels. Only some crops, such as salad leaves and
herbs, can be grown profitably in this way. Staple crops such as wheat
and rice need too much space and light. The buildings and equipment
cost millions to set up, and several vertical farm companies have
closed. Supporters reply that falling prices for solar and wind
electricity will make indoor farms cheaper to run in future, and that
fresh food grown close to cities needs less transport.
Read the article. 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.
The concentration of carbon dioxide may limit the rate of photosynthesis. State what is meant by the term limiting factor.
(1)The LED lamps give out red and blue light. Which colours of light are absorbed least by chlorophyll?
(1)Explain why the solution contains nitrate ions and magnesium ions.
(2)Explain why increasing the concentration of carbon dioxide increases the yield of lettuce.
(3)Calculate how many times more lettuce was produced per m² of floor area in the vertical farm than in the field. Give your answer to 2 significant figures.
(2)Suggest why the lettuces can be grown without pesticides.
(2)Explain why the temperature is controlled.
(3)Suggest why vertical farms are unlikely to replace most outdoor farming.
(3)Total for this question: 17 marks
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