The banana that might disappear
304 words over 30 numbered lines, then 7 parts worth 13 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.
The banana that might disappear
Almost every banana sold in supermarkets around the world belongs to a
single variety, the Cavendish. The plants have no seeds. Instead, new
plants are grown from suckers, small shoots that grow from the base of
a parent plant, or from tiny pieces of tissue grown in a laboratory.
Every Cavendish plant is therefore a clone of the others.
Growing clones has advantages for farmers. Every plant produces fruit
of the same size, flavour and colour, and the fruit all ripens at
about the same time. This makes the bananas easy to harvest, transport
and sell.
The same thing has happened before. Until the 1950s, most exported
bananas were of a variety called Gros Michel. A fungus that lives in
the soil, causing a condition called Panama disease, infected the
roots and blocked the xylem vessels. The leaves wilted and the plants
died. Because all the plants were genetically identical, the disease
spread through plantation after plantation.
The Cavendish was resistant to that strain of the fungus, so farmers
replaced their crops. However, a new strain that kills Cavendish
plants appeared in Asia and has now reached Africa and South America.
The fungus can survive in soil for decades, and it is spread on boots,
tools and lorry tyres.
Scientists are trying several solutions. Some are searching wild
banana species, which have seeds and much more variation, for plants
that resist the new strain. In Australia, researchers inserted a
resistance gene from a wild banana into Cavendish plants. In an
illustrative field trial, 2 of 50 modified plants became infected,
compared with 33 of 50 unmodified plants.
Other farmers are protecting their land by washing boots and vehicles
before they enter a farm. Some people argue that the real answer is to
grow many different banana varieties, even if the fruit is less
uniform.
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.
State what is meant by the term clone.
(1)Which type of cell division produces the cells of a sucker?
(1)Explain why blocking the xylem vessels causes the leaves to wilt.
(2)Explain why a disease spreads through a crop of clones faster than through a crop grown from seed.
(3)Calculate the difference between the percentage of unmodified plants and the percentage of modified plants that became infected.
(2)Describe how a resistance gene from a wild banana could be inserted into a Cavendish plant.
(3)Suggest why farmers wash boots and vehicles before they enter a farm.
(1)Total for this question: 13 marks
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