Gardening without gravity
313 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.
Gardening without gravity
Astronauts on the International Space Station have grown lettuce,
radishes and even flowers. Fresh food is good for their diet, and many
astronauts say that looking after plants makes them feel better. But
growing plants in space raises an interesting question: how does a
seedling know which way to grow?
On Earth, shoots grow towards light and away from gravity, while roots
grow towards gravity. These growth responses are called tropisms. A
response towards light is phototropism, and a response to gravity is
geotropism. They help a young plant to reach light for photosynthesis
and to anchor itself in the soil, where it can take up water and
mineral ions.
Tropisms are controlled by a plant hormone called auxin, which is made
in the tip of the shoot. When light comes from one side, auxin moves
to the shaded side of the shoot. There, it makes the cells elongate
more than the cells on the lit side. The shoot therefore bends towards
the light.
In an illustrative experiment, students grew cress seedlings in the
dark for three days. They then placed one group in a box lit from one
side only. A second group was placed on a slowly rotating turntable in
the same box, so that light reached them evenly from all sides. Every
two hours, the students measured the angle of the shoots from the
vertical. Their mean results are shown in Figure 1.
In orbit, everything in the space station is in free fall, so plants
experience almost no gravity. Roots of seedlings grown there in the
dark spread out in many directions. When a lamp is placed above them,
the shoots still grow towards the light, and the roots tend to grow
away from it. Engineers are now testing which colours of light give
the best growth, because every lamp on the station uses electricity
from its solar panels.
Figure 1 Angle of cress shoots from the vertical
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 phototropism.
(1)Explain how auxin causes a shoot to bend towards light.
(3)Use Figure 1 to calculate the mean rate of bending of the shoots lit from one side between 2 and 8 hours. Give the unit.
(2)Explain why the students included a control group of seedlings on a rotating turntable.
(2)Suggest why the roots of seedlings grown in the dark on the space station spread out in many directions.
(2)Suggest how positive phototropism helps a seedling to survive.
(2)Total for this question: 12 marks
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