The role of light in photosynthesis practical
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Questions and Answers

What is the purpose of wrapping a part of the leaf with aluminium foil in the experiment?

  • To enhance the light absorption of the leaf.
  • To block exposure to light, acting as a control. (correct)
  • To provide nourishment to the plant.
  • To prevent water loss from the leaf.
  • What is the function of iodine solution in the experiment?

  • To nourish the plant.
  • To measure light intensity.
  • To increase photosynthesis rates.
  • To test for the presence of starch. (correct)
  • What is indicated by the presence of starch in the leaf after the experiment?

  • Photosynthesis occurred where light was available. (correct)
  • The control set-up was affected by external factors.
  • The plant was unhealthy before the experiment.
  • Light was not necessary for photosynthesis.
  • Why is a control set-up important in this experiment?

    <p>It ensures external factors do not affect the results. (A)</p> Signup and view all the answers

    What safety precautions must be taken when using alcohol in the experiment?

    <p>Ensure adequate ventilation and avoid naked flames. (A)</p> Signup and view all the answers

    What is the significance of using a destarched plant in this experiment?

    <p>To provide a clean starting point without stored starch. (D)</p> Signup and view all the answers

    What is the purpose of using a destarched plant from the beginning of this experiment?

    <p>To ensure any starch detected in the experiment is produced by the plant during the experiment.</p> Signup and view all the answers

    What part of the plant is used as a 'control' in this experiment?

    <p>The part of the plant that is wrapped in aluminium foil.</p> Signup and view all the answers

    In this experiment, what is the independent variable?

    <p>Presence of light.</p> Signup and view all the answers

    What are two important factors that are kept constant during this experiment?

    <p>Supply of oxygen (B), Supply of water (D)</p> Signup and view all the answers

    What would you expect to observe when you test the part of the leaf that was exposed to light?

    <p>A blue-black color, indicating the presence of starch (B)</p> Signup and view all the answers

    What would you expect to observe after testing the part of the leaf that was covered with aluminium foil?

    <p>No change in color when tested with iodine (A)</p> Signup and view all the answers

    What would be the expected result, if the experiment was conducted in complete darkness instead of bright light?

    <p>No starch production in any part of the leaf (C)</p> Signup and view all the answers

    What would be a reasonable conclusion to draw from the experiment, if both the covered and uncovered parts of the leaf show the same results?

    <p>The experiment might need to be repeated to investigate why the expected results were not observed.</p> Signup and view all the answers

    If the experiment was repeated with red light, instead of bright white light, what might be the difference in the results?

    <p>Starch production might be less, because red light is not as effective at driving photosynthesis as white light.</p> Signup and view all the answers

    Flashcards

    Photosynthesis

    The process plants use to make food using sunlight, water, and carbon dioxide.

    Control setup

    A setup that is identical to the experimental setup, except that the factor being tested is absent.

    Iodine test

    A test using iodine solution to check for the presence of starch.

    Destarch plant

    A plant that has had its starch removed, often by leaving it in the dark.

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    Experimental setup

    The setup in which the factor being tested is present.

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    Light exposure

    Part of a leaf that is exposed to light.

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    Control set-up procedure

    The procedure to ensure that any results are caused by the tested factor and not other factors.

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    Starch

    A nutrient that plants store as energy.

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    Initial iodine test

    The first iodine test conducted before any light exposure to establish a baseline for starch presence.

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    Light-exposed area

    The part of the leaf directly exposed to bright light in the experiment.

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    Four-hour light exposure

    The duration for which the plant is left in bright light for photosynthesis to occur.

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    Aluminium foil removal

    The step where the foil is removed from the leaf to expose the covered area to light.

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    Final iodine test

    The iodine test performed again after the light exposure to compare starch levels in different parts of the leaf.

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    Starch production in light-exposed areas

    The expected result of starch being present in the light-exposed part of the leaf.

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    Control setup significance

    The control setup helps demonstrate the importance of light in photosynthesis, as it shows no starch production in the covered area.

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    Experiment duration (four hours)

    The four-hour period allows sufficient time for starch production during photosynthesis.

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    Same leaf used for both areas

    Using the same leaf for the control and experimental setup ensures consistent conditions for all variables except light.

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    Bright light necessity

    Bright light is specified to ensure optimal conditions for photosynthesis to occur.

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    Labelled diagram purpose

    The labelled diagram accurately records the experimental setup by showing the areas of light exposure and non-exposure.

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    Careful foil removal

    Removing the foil carefully avoids damaging the leaf tissue and allows accurate study of the covered area.

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    Final iodine test aim

    The test aims to reveal the presence or absence of starch in different parts of the leaf, demonstrating the effect of light.

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    Blue-black color in exposed area

    The expected result of a blue-black color in the light-exposed area indicates the presence of starch produced during photosynthesis.

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    No color change in covered area

    The expected result of no color change in the covered area indicates the absence of starch due to the lack of light.

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    Comparison of iodine tests

    Comparing the iodine tests before and after light exposure helps demonstrate the effect of light on starch production.

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    Blue-black color in exposed area conclusion

    The observation of blue-black color in the exposed area supports the conclusion that light is essential for photosynthesis.

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    Successful experiment results

    The results are considered successful if they show starch production only in the light-exposed area, supporting the idea that light is necessary for photosynthesis.

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    Experiment in darkness outcome

    Conducting the experiment in complete darkness would result in no starch production in any part of the leaf.

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    Experiment duration variation

    Increasing the duration of light exposure from 4 hours to 8 hours could lead to more pronounced starch presence in the light-exposed areas.

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    Similar results in both areas

    If both covered and uncovered parts of the leaf show the same result after the final iodine test, it indicates a potential error in the experiment.

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    Red light experiment

    Using red light instead of bright white light might result in less starch production, as red light is less effective for photosynthesis.

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    Chlorophyll involvement

    The positive results of the experiment support the idea that chlorophyll plays a role in the light-dependent reactions of photosynthesis.

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    Study Notes

    Aim of Experiment

    • To determine if light is necessary for photosynthesis

    Apparatus and Materials

    • Boiling tube
    • Beaker (250 cm³)
    • Forceps
    • Glass rod
    • Scissors
    • Wire gauze
    • Insulating mat
    • Gas lighter
    • Potted plant with leaves
    • Aluminium foil
    • Paper clip
    • White tile
    • Bunsen burner
    • Table lamp
    • Iodine solution
    • Alcohol (70%)
    • Tripod

    Procedure

    • Obtain a destarched plant and select a leaf.
    • Test the leaf for starch using iodine solution (see Practical 7.3).
    • Cover part of a leaf with aluminium foil.
    • The foil-covered part is the control (not exposed to light).
    • Draw a labeled diagram of the leaf showing the covered and uncovered parts.
    • Place the plant in bright light for 4 hours.
    • Remove the foil from the leaf.
    • Test the leaf for starch using iodine solution.

    Safety Precautions

    • Wear disposable gloves.
    • Avoid contact with iodine, as it is harmful.
    • Use the minimum amount of alcohol possible and ensure the room is well-ventilated.
    • Only use alcohol in the absence of a naked flame.
    • Alcohol is flammable.

    Control Set-up

    • A control set-up is used to ensure that any changes observed are due to the factor under investigation and not other factors.
    • The control setup is identical to the experimental setup except the factor under investigation is absent (no light in this case).

    Variables

    • Independent Variable: Presence of light
    • Dependent Variable: Presence of starch
    • Controlled Variables: Supply of CO2, water, temperature, chlorophyll, the supply of light, and temperature.

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    Related Documents

    Light Experiment Questions PDF

    Description

    Test your understanding of the experiment to determine if light is essential for photosynthesis. This quiz covers the apparatus used, the procedure followed, and important safety precautions. Perfect for reinforcing your knowledge of plant biology.

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