Photosynthesis Experiments

Question 1

destarched leaf iodine solution experiment method?

Answer 1

1. take a leaf
2. heat in boiling water for 1 min
3. turn off the Bunsen burner - transfer the leaf to a test tube containing ethanol and place in the hot water
4. soften the leaf by transferring it to the beaker of hot water
5. place the leaf on a white tile and cover in iodine solution

• the leaves need to be destarched by placing in the dark for 24 hours so that they are free from starch at the start of the experiment - this means that any starch in the leaf you test was produced from the glucose made in photosynthesis during your experiment

Question 2

as this experiment shows the conditions needed for photosynthesis, how can we show that light is required?

Answer 2

• one part of the leaf is covered so only one part of the leaf is exposed to light, which will produce starch and turn black

Question 3

as this experiment shows the conditions needed for photosynthesis, how can we show that chlorophyll is required?

Answer 3

• a variegated leaf, in which the white parts of the leaf lacks chlorophyll, is used and starch is only produced in the areas that were green

Question 4

as this experiment shows the conditions needed for photosynthesis, how can we show that carbon dioxide is required?

Answer 4

• one leaf of a plant is enclosed in a conical flask (or plastic bag) containing soda lime to absorb the carbon dioxide and this leaf is compared to another enclosed in a flask but without the soda lime
• only the leaf that had access to carbon dioxide produces starch

Question 5

factors affecting the rate of photosynthesis Elodea pondweed experiment?

Answer 5

1. a length of the pondweed Elodea is put in a beaker of water and the number of bubbles released from the stalk in one minute is counted
2. the distance of a bench lamp can be moved to vary the light intesity, or differing masses of sodium bicarbonate to vary the carbon dioxide concentration

Question 6

how can we improve the accuracy of the Elodea experiment?

Answer 6

• putting the Elodea into a boiling tube of water and this can then be placed in a beaker, with a thermometer, to act as water bath - this reduces the temperature change during the experiment.
• collecting the gas in an inverted measuring cylinder and measure the volume of oxygen evolved per unit time.
• adding a fixed mass of sodium bicarbonate to the water, to provide a higher (constant) concentration of carbon dioxide.