Which strength of sugar solution is best for growing pollen tubes?
Once a pollen grain has landed on a stigma, a pollen tube begins to grow. The stigma contains a sugar solution to help the pollen tube grow down the style to the ovary.
Prediction
1 The bar chart shows the results of an experiment with pollen from a plant called blue smokebush.
a Write down which sugar solution you think will be best for growing pollen tubes.
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b Why do you think this?
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Apparatus
• slides • forceps (tweezers) • paintbrush
• sugar solutions • pipette • mounted needle
• coverslips • pollen • microscope
Method
A Use the graph to choose which strengths of sugar solution to use. Write them down.
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B Place a drop of sugar solution onto a slide.
C Using a mounted needle or paintbrush, take some pollen and place it in the sugar solution.
D Carefully lower a coverslip onto the drop using a mounted needle or forceps.
E Repeat steps A–D using a different strength of
sugar solution.
F Look carefully at both slides using a microscope.
You will need to draw what you see.
G Leave the slides in a warm place
for 30 minutes and then
look at them again.
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Recording your results
2 Draw a picture of a pollen grain at the start of your experiment. Draw pictures to show what your pollen grains looked like after 30 minutes.
The drawing showsa pollen grain from a
______flower at the start of the experiment. / The picture shows the pollen grain after 30 minutes in a sugar solution of strength
______. / The picture shows the pollen grain after 30 minutes in a sugar solution of strength
______.
Not all pollen grains will grow tubes.
3 Count 20 pollen grains in each type of sugar solution. Write down how many have grown tubes:
a In the sugar solution of strength ______, ______out of 20 grew tubes.
b In the sugar solution of strength ______, ______out of 20 grew tubes.
Considering your results/conclusions
4 a Why is drawing pollen grains a good way of recording the results of this investigation?
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b How else could you record the results so that people could see what happens?
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5 a Which sugar solution made the pollen tubes grow best? ______
b How do you know this?
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6 Why is it a good idea to count only 20 pollen grains and not all of them?
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7 Use your results to predict what would happen if you used water instead of a sugar solution.
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