photosynthesis practical

Aim of the practical

To investigate how light intensity affects the rate of photosynthesis

Independent variable

Light intensity (distance of lamp)

Dependant variable

Rate of photosynthesis (bubbles per minute)

Control variable

Temperature

Carbon dioxide concentration

Type and size of pondweed

Results pattern

As light intensity increases, the rate of photosynthesis increases. Eventually it levels off because another factor becomes limiting

Graph for practical

X axis: distance from lamp

Y axis: number of bubbles per minute

Draw smooth curve

3 potential errors

Counting bubbles is inaccurate as oxygen bubbles are different sizes

Temperature may change during experiment (lamp can heat the water changing temperature)

Light intensity may not be measured accurately (using distance as a substitute for light intensity is not exact)

Step 1

Place the pondweed in a beaker of water

Step 2

Add sodium hydrogencarbonate to ensure CO2 is not limiting

Step 3

Place a lamp at a measured distance from the pondweed

Step 4

Turn on the lamp and wait a short time to allow the plant to adjust

Step 5

Count the number of oxygen bubbles produced in one minute

Step 6

Move the lamp closer and repeat

Step 7

Repeat measurements and calculate a mean