Required Practicals - Reaction Time (7) & Plant Responses (8)

Describe the ruler-drop method for investigating reaction time.

One person holds a ruler vertically with the 0 cm mark level with the participant's thumb and finger. The ruler is released without warning and the participant catches it. Record the distance fallen, repeat several times and calculate a mean. Use a conversion table/equation if required to determine reaction time.

What is the independent variable? - Reaction Time

The factor deliberately changed, e.g. caffeine intake or distraction.

What is the dependent variable? - Reaction Time

Reaction time, measured using the distance the ruler falls before being caught.

Give suitable control variables. - Reaction Time

Keep constant factors such as the same person, same hand, same ruler, same starting position and same method of release.

Why repeat the measurements?

To identify anomalous results and calculate a mean, increasing reliability.

How could reliability be improved?

Take more repeat measurements and calculate a mean.

What is Required Practical 8? - Plant Responses

Investigate the effect of light or gravity on the growth of newly germinated seedlings.

How could you investigate phototropism?

Grow newly germinated seedlings with light coming from one direction, keeping other variables constant. Measure/record their growth and direction before and after a set time and compare with an appropriate control.

Give control variables. - Plant Responses

Plant species/age, temperature, water, time allowed for growth, light intensity where appropriate, and starting conditions.

Why use several seedlings?

To account for biological variation, identify anomalies and allow calculation of a mean, making results more reliable.

What would you expect with light from one side?

Shoots show positive phototropism and grow/bend towards the light.