1. Explain the advantage to an organism of simple reflexes.
Answer
To protect the organisms from being harmed or damaged.
2. The heart muscle is described as being myogenic. What does this mean ?
Answer
It has the ability to contract on its own without any nerve impulses from the brain (or CNS).
3. A student investigated the behaviour of blowfly larvae. He set up Petri dishes with filter paper lining the bottom. The filter paper was divided into sections as shown in the figure below. This figure shows how the Petri dish was labelled with L for light, N for neutral and D for dark.
The Petri dish was positioned 10 cm away from the lamp. The lamp was set up to shine directly at the same level as the Petri dish, as shown in the figure below.
The larvae were placed one at a time in the centre of the Petri dish. The larva's position was noted every 2 seconds until it touched the edge of the Petri dish. The markings were then used to measure the distance from the lamp at each interval, and the position of the larva when it touched the edge of the Petri dish was also noted. Each larva was only used once. The filter paper was replaced after each trial. Explain why each larva was placed in exactly the same position in the Petri dish with its front end nearest the direction of light.
Answer
So all results could be compared. No larva was placed closer or further from light.
4. Explain why each larva was only used once in this investigation.
Answer
To ensure that the behaviour was not learned.
5. Explain why the filter paper was replaced after each trial.
Answer
So that the next larva was not influenced by any trace of the previous larva. Replacing the filter paper removes any chemical traces that might be present.
6. The student's results can be seen in the table below. Determine what the data suggest about the response of the larvae to light.
Answer
Larvae tend to move away from light.
7. The student thought that the larvae were showing taxis but another student thought this was a kinesis. Explain how they could test whether this behaviour is a kinesis.
Answer
Measure the rate or direction of movement. Record the distance moved every 2 seconds, or plot the movement to determine whether it is directional or random. If it is kinesis, the rate of movement will slow down in darker areas; if it is taxis, the movement will be directional (away from the light).
8. The students thought that the larvae were responding to light. They decided to carry out a chi-squared test on their data. Suggest the null hypothesis they used.
Answer
Larvae have no preference for light or dark conditions.
9. Complete the table below showing their results.
Answer
10. The students looked up the critical value of chi-squared (χ2) on a table. How many degrees of freedom should they have used?
Answer
2 degree of freedom.
11. The value of chi-squared (χ2) that the students calculated was higher than the critical value at p < 0.05. What does this mean ?
Answer
The probability of obtaining these results by chance is less than 5% (or 0.05). The null hypothesis must be rejected.