A student wanted to investigate the effect of caffeine on the pulse rate of the aquatic worm Lumbriculus variegatus (commonly known as the blackworm).

She placed a blackworm on a groove slide with a few drops of pond water.
Under a stereomicroscope, she counted the contractions of the dorsal blood vessel in 20 seconds.
She repeated this procedure for 10 individual blackworms.
She then repeated the experiment using another 10 blackworms in a 0.1% caffeine solution.

Her results are shown in the table below:

Blackworm	Contractions in 20 seconds in Pond Water	Contractions in 20 seconds in Caffeine solution
1	30	42
2	32	45
3	29	40
4	31	43
5	32	41
6	28	39
7	30	44
8	31	41
9	29	42
10	28	43

Name the independent variable in this investigation.

Identify one variable that the student must control to ensure a valid investigation.

Calculate the mean contraction rate (in contractions per minute) of the blackworms in pond water. Show your working.

Describe the effect of caffeine on the pulse rate of Lumbriculus variegatus.

Explain why repeating the measurement on 10 blackworms is better than using only one.

A student wanted to investigate the effect of caffeine on the pulse rate of the aquatic worm Lumbriculus variegatus (commonly known as the blackworm).

She placed a blackworm on a groove slide with a few drops of pond water.
Under a stereomicroscope, she counted the contractions of the dorsal blood vessel in 20 seconds.
She repeated this procedure for 10 individual blackworms.
She then repeated the experiment using another 10 blackworms in a 0.1% caffeine solution.

Her results are shown in the table below:

Blackworm	Contractions in 20 seconds in Pond Water	Contractions in 20 seconds in Caffeine solution
1	30	42
2	32	45
3	29	40
4	31	43
5	32	41
6	28	39
7	30	44
8	31	41
9	29	42
10	28	43

Name the independent variable in this investigation.

Identify one variable that the student must control to ensure a valid investigation.

Calculate the mean contraction rate (in contractions per minute) of the blackworms in pond water. Show your working.

Describe the effect of caffeine on the pulse rate of Lumbriculus variegatus.

Explain why repeating the measurement on 10 blackworms is better than using only one.

Co-ordination and response

Question 17

Markscheme

Co-ordination and response

Question 17

Markscheme

Co-ordination and response

Question 17

Co-ordination and response Questions

Co-ordination and response

Question 17

Co-ordination and response Questions