U3 Bio Leaf disc photosynthesis prac 2025

Research Question

How does the colour of light affect the rate of photosynthesis in spinach leaf discs?

Experimental Groups

Beakers with coloured cellophane (e.g. red, green, blue, yellow).

Control Group

Beaker with clear (uncoloured) cellophane or no filter.

Importance of a Control Group

The control group gives a baseline rate of photosynthesis under normal (white) light. It allows you to compare how coloured light affects the process.

Independent Variable (IV)

Colour of light (controlled using different coloured cellophane).

Dependent Variable (DV)

Time taken for 50% of the discs to float (measured in seconds).

Controlled Variables

Type of leaf, Number and size of discs, Distance from the light source, Volume and concentration of bicarbonate solution, Light intensity (same lamp), Temperature.

Importance of Controlled Variables

Ensures a fair test by making sure that only the colour of light affects the results.

Importance of Repeated Trials

Repeated trials help improve reliability, reduce the impact of anomalies, and make the average result more accurate.

Aim

To investigate the effect of different colours of light on the rate of photosynthesis in spinach leaf discs.

Hypothesis

If the colour of light affects the rate of photosynthesis, then spinach discs under red and blue light will float faster than those under green light.

Quantitative Data

Time taken for 5 discs to float (numerical data in seconds).

Qualitative Data

Colour of light (observational/categorical).

Graph Type

Column graph or line graph.

X-axis

Colour of light (independent variable).

Y-axis

Average time for 5 discs to float (dependent variable, in seconds).

Example Trend

Red and blue light may result in faster floating times (indicating higher photosynthesis rates). Green light may result in slower times (lower rate).

Explanation of Trend

Chlorophyll absorbs red and blue light more efficiently, which increases photosynthesis. It reflects green light, so green is less effective.