Characteristics, Classification & Features of Organisms (Cambridge (CIE) IGCSE Biology)

Woodlice were used to investigate their sensitivity to different conditions. A choice chamber was set up with four different compartments: light and dry, light and moist, dark and dry, dark and moist.

A student placed 15 woodlice into the choice chamber and then recorded the number of woodlice in each compartment after a period of 10 minutes. They then removed all the woodlice and repeated the experiment twice more. 

Choice chambers allow us to know what environmental conditions animals prefer when looking for suitable habitats.

Fig. 1 shows the experimental set up of the choice chamber used. 

Fig. 1

(i)

Explain why the student left the woodlice in the choice chamber for 10 minutes before counting the woodlice in each chamber.

[1]

(ii)

State two variables that should be kept constant throughout the investigation. 

[2]

(iii)

For one of the variables stated in part (ii), describe how to keep this constant. 

[1]

(i)

Identify one possible hazard associated with carrying out the experiment. 

[1]

(ii)

Describe the safety precautions associated with the hazard identified in part (i).

[1]

(iii)

Describe the ethical considerations when using living organisms such as woodlice. 

[2]

Create a table in which the student could record their results

Describe how you could adapt this experiment to investigate the sensitivity of woodlice to temperature changes.

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

Fig. 1 shows part of their experimental set up.

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.

(i)

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

[1]

(ii)

Suggest how the student could make the test more 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

(i)

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

[1]

(ii)

Describe a source of error associated with the student's experiment.

[1]

(iii)

Explain improvements that could be made to overcome the source of error.

[1]

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