Characteristics, Classification & Features of Organisms (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

A student wanted to investigate the sensitivity of the skin to temperature change.

Fig. 1

The students followed the following method:

1. Fill three beakers with water of a different temperatures: one with cold water at 10-15 °C, one with warm water at 25 °C, and one with hot water at 40-50 °C.
2. Place the index finger of the left hand into the cold water and the index finger of the right hand into the hot water. Leave submerged for 2 minutes. 
3. After 2 minutes remove both fingers from the hot and cold water and place them repeatedly, but alternately, into and out of the warm for one second at a time. Do this for 1 minute.
4. Record your observations of the sensations felt.

Identify one variable that needs to be kept constant throughout the experiment.

[1]

Suggest how the student could check that the test is reliable.

[1]

A second student also investigated the sensitivity of the skin. They used a hairpin to determine whether one or two prongs of a hairpin could be felt on different areas of the hand and arm.

1. One student closed their eyes whilst another used the hairpin to gently but firmly touch the skin with either one or two prongs for 1 second.
2. The student with their eyes closed guessed how many prongs were being pressed onto their skin.
3. The test was repeated with increasing gaps of the hair pin prongs on different areas of the hand and arm.

The aim was to determine the most sensitive area of those tested. 

Fig. 2 shows the forearm being tested. 

Fig. 2

Their results are shown in Table 1.

Table 1

Identify the variable that is measured (the dependent variable).

[1]

Describe a possible limitation of the student's experimental method.

[1]

Describe an improvement that could be made to overcome the limitation described in (ii).

[1]

Draw a graph of the students results shown in Table 1.