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?

______

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 shows
a 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?

______

______

7 Use your results to predict what would happen if you used water instead of a sugar solution.

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