A thousand orchids from one plant
315 words over 28 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.
A thousand orchids from one plant
Orchids are among the most popular house plants in the world, yet
growing them from seed is slow and unreliable. Their seeds are as fine
as dust and contain almost no stored food. A grower who finds an
orchid with unusually large or brightly coloured flowers wants to
produce thousands of plants exactly like it.
In a plant laboratory, a technician cuts a tiny piece from the tip of
a young shoot. This piece is called an explant. She dips it in a
dilute bleach solution to kill any bacteria or fungi on its surface,
then rinses it in sterile water. Working in a cabinet with a flow of
filtered air, she places the explant on a jelly called agar in a
sterile glass jar. The agar contains sugar, mineral ions and plant
hormones.
The cells of the explant divide by mitosis and form a small cluster of
shoots. Every four weeks the technician cuts each cluster into four
pieces and moves each piece to a jar of fresh agar. The number of
plantlets produced from one explant is shown in Figure 1.
When there are enough plantlets, the agar is changed to one containing
a different balance of hormones, so that roots form. The young plants
are then moved into compost in a greenhouse. At first they are kept in
very humid air, because their leaves lose water easily. Over several
weeks the humidity is gradually lowered.
All the plants produced in this way are clones. They have the same
genes as the parent plant, so they all have the same flower colour and
flower at the same time, which makes them easy to sell. However, if a
new disease attacks one plant, it is likely to attack them all.
The same method is used to produce bananas, strawberries and potatoes
free from viruses, and to save rare plants that produce very few
seeds.
Figure 1 Number of plantlets produced from one explant
| Time / weeks | Number of plantlets |
|---|---|
| 0 | 1 |
| 4 | 4 |
| 8 | 16 |
| 12 | 64 |
| 16 | 256 |
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 clone.
(1)Explain why all the plantlets have the same flower colour as the parent plant.
(2)Use Figure 1 to calculate the number of plantlets that would be produced from one explant after 24 weeks.
(2)Explain why the technician uses aseptic technique when setting up the jars.
(3)Explain why the young plants are kept in very humid air when they are first moved into compost.
(2)Suggest why a new disease is likely to affect all the plants produced by micropropagation.
(2)Total for this question: 12 marks
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