Photosynthesis

• What is photosynthesis? The process by which plants synthesise glucose using light energy from the Sun
• Describe how you would investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant ● Place cut pondweed in a boiling tube (containing sodium hydrogen carbonate solution) at a fixed distance from a light source ● Count the number of bubbles produced in one minute using stopwatch ● Repeat several times at different distances/light intensities, and calculate a mean for each distance ● Plot a graph of light intensity (x) against rate of photosynthesis (bubbles per minute, y)
• Why is it best to use an LED light source rather than a lamp? A lamp will emit more heat energy than an LED - therefore it may change the temperature of the experiment and affect the rate of photosynthesis
• What is the relationship between the distance from a light source and light intensity? Inverse square law - light intensity∝1 / distance2
• How can the measurement of oxygen production be made more accurate? If the the pondweed is placed under a filter funnel with an inverted measuring cylinder over the spout, the volume of oxygen produced can be determined
• Why is sodium hydrogen carbonate solution used during this experiment? It releases CO2 , which is used by the pondweed during photosynthesis
• Why can the number of bubbles produced be used to calculate the rate of photosynthesis? Oxygen bubbles are formed as a product during photosynthesis. The number of bubbles produced in a given time is proportional to the rate of photosynthesis