CAPE Bio Photosynthesis Lab

Photosynthesis: Objectives: 1. To investigate the effect of light intensity on the rate photosynthesis by measuring oxygen evolved 2. To investigate the effect of carbon dioxide concentration on the rate of photosynthesis Precaution On the day of the experiment, cut 10 cm lengths of Elodea, put a paper-clip on one end to weigh them down and place in a boiling tube of water in a boiling tube rack, near a high intensity lamp, such as a halogen lamp or a fluorescent striplight. Check the Elodea to see if it is bubbling. Sometimes cutting 2–3 mm off the end of the Elodea will induce bubbling from the cut end or change the size of the bubbles being produced There are various set-ups that can be used to measure the rate of photosynthesis, each relies on counting the oxygen produced during the reaction. To improve results, add a pinch of baking soda to the water in the test tube. Cut elodea stems at an angle and use your fingers to crush the end of the stem. The water in the beaker is meant to absorb the heat from the light.

Materials: test tube, Elodea cuttings, sodium bicarbonate (baking soda), beaker, pond water, lamp. Metre rule, digital clock, knife/scissors, analytic balance Method: 1) Cut a segment of the Elodea plant approximately 8cm with scissors. 2) Crush the end of the stem at the site of incision gently. 3) Submerge the plant into a test tube filled with 40mL room temperature water and 1g baking soda. 4) Set the test tube on the test tube rack. 5) Place a light source 50cm away facing the test tube. 6) Turn on the light source and begin taking observations. 7) Count the number of bubbles generated the following intervals:10 second, 30 second, and 60 seconds for each trial. 8) Repeat steps one through seven for the following light distances: 1. 40cm 2. 30cm

3. 20cm 4. 10cm Part B: CO2 Concentration vs Light 1. Set up the apparatus as shown in a darkened room. 2.

Look for a stream of bubbles coming from the cut end of the pondweed.

3. Count the number of bubbles produced in 1 minute. Repeat twice and calculate a mean bubble count – number of bubbles per minute. This is the mean rate of bubble production

4. Add 0.05 g of potassium hydrogencarbonate at a time. The available mass of carbon dioxide increases with each addition. 5. Leave for 2 minutes and then take counts of the number of bubbles produced in one minute. Repeat the count and calculate the mean rate of bubble production as before. 6. Plot data on a line graph. The values for the factor being varied should be on the x-axis, and the mean bubble rate in bubbles / minute should be on the y axis PD Next Week Bring to lab a written PD to carry out investigation on any of the factors below. No two persons must have the same method!!! I’ll give you the problem later on 

Acidity: use buffer solutions to maintain different pHs.

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Colour of light.

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Temperature