Required Practical 6 - 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