practical - Investigating the effect of light intensity on rate of photosynthesis.

how can you identify if a piece of pondweed is photosynthesising

They release oxygen gas that forms visible bubbles in water or solution.

what determines the rate of photosynthesis

The amount of oxygen produced.

how can light intensity be altered

By moving a light source closer or further away from the plant.

how does the distance of the light source affect the light intensity

The greater the distance, the lower the light intensity.

step 1

Place a piece of freshly cut pondweed in a boiling tube filled with sodium hydrogen carbonate solution.  

step 2

Place the boiling tube 10 cm away from a lamp.

step 3

Switch the light on and leave for 5 minutes bubbles should start appearing from the end of the pondweed.

step 4

Start the stopwatch and count and record the number of bubbles produced in 1 minute1 minute.

step 5

Repeat the count at this distance twice more in order to calculate the mean number of bubbles per minute. 

step 6

Repeat the experiment with the boiling tube at different distances from the lamp.

why is it important to ensure the temperature of the solution stays the same throughout the investigation

Increasing the temperature will increase the rate of photosynthesis.

how can the temperature of the solution be kept the same

Using an LED bulb and putting a glass tank full of water between the lamp and plant.

why is it important to control the experiment

the carbon dioxide concentration

how can the carbon dioxide concentration be controlled

Using the same concentration of sodium hydrogen carbonate solution and using the same piece of pondweed/same sized pondweed each time.

how can the oxygen bubbles be collected

Using an inverted funnel and measuring the volume of gas using a syringe.

what can be plotted on

The relationship between the distance from the lamp and the rate of bubble production.

calculating light intensity - Distance and light intensity are actually linked through the - inverse square law:

Light intensity ∝ 1 / Distance²