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How can you measure the rate of photosynthesis

By Kimberly Hudson,2014-08-09 05:15
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How can you measure the rate of photosynthesis

    How can you measure the B9.2

    rate of photosynthesis? Light affects the rate of photosynthesis. You are going to investigate the rate of photosynthesis

    under different lighting conditions.

     Method

     Apparatus ; stop clock 3 ; 10 cmsyringe ; strong source of light ; cress seedlings ; eye protection ; scalpel or sharp scissors

    ; sodium hydrogencarbonate solution

    (a source of carbon dioxide)

    A Take two leaves from a cress seedling. Cut each one in half using a scalpel or a pair of sharp scissors.

    B Do this over a sink. Take the plunger out of the syringe. 3 Hold your thumb over the end and pour in 10 cmof sodium hydrogencarbonate solution.

    C Drop your half cress leaves into the syringe.

D Put the plunger back in and turn the syringe so that it points

    upwards.

    E Push in the plunger so that all the air is removed. Do not lose

    any of the liquid.

F Place a finger on top of the syringe and pull down the

    plunger. Bubbles will appear on the leaves.

    G Tap the side of the syringe hard so that all the bubbles rise

    to the top.

    H Repeat steps EG until the leaves sink to the plunger end of

    the syringe. (Steps EG get rid of any air bubbles that were

    trapped in the leaves.)

    I Stand the syringe on its plunger near a bright light. Start

    your stop clock and record the time each leaf takes to float

    off the plunger.

    J Repeat steps EI but this time place the syringe near

    a dimmer light.

? Pearson Education Limited 2001 Adapted from Longman Foundation Science for GCSE 1

B9.2 How can you measure the rate of photosynthesis?

    Prediction

    1 What do you think will happen and why?

    Results

    2 Draw a table of your results, like this.

    Condition the Time taken Time taken Time taken Time taken Average (mean)

    leaves were for the 1st leaf for the 2nd for the 3rd for the 4th time for the

    placed in to float leaf to float leaf to float leaf to float leaves to float

     Bright light

     Dimmer light

    3 Work out the mean (average) time it took for the leaves to start to float. 4 The leaves floated because they produced a gas. What was this gas? 5 Why were the leaves put in sodium hydrogen carbonate solution? 6 Explain why the leaves floated more quickly in bright light. 7 What do you think would happen to the time it took for the leaves to float if the following changes

    were made to the experiment?

     a) The syringe was put in darkness.

     b) A lower concentration (strength) of sodium hydrogen carbonate was used.

     c) The syringe was put under the same brightness of lamp as in the experiment, but the temperature

     was lower.

    ? Pearson Education Limited 2001 Adapted from Longman Foundation Science for GCSE 1

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