15.1 Control & Coordination in Mammals

Table 1 shows the speed of impulse transmission in neurones of different type and diameter.

Table 1

Calculate the percentage increase in impulse transmission speed in myelinated neurones when the axon diameter is increased from 7 μm to 16 μm.

Describe the effect of myelination on neurones shown in Table 1

Explain the following from Table 1:

The effect of myelination on speed of nerve impulse transmission.

[3]

(ii)

The effect of axon diameter on speed of nerve impulse transmission.

[1]

Scientists investigated the relationship between myelin in brain tissue and the different types of dementia.

The scientists measured the mean myelin content in brain tissue samples from 3 different groups:

• A control group of 15 people without dementia
• 22 people with vascular dementia (VD)
• 18 people with Alzheimer's dementia (AD)

Their results are shown in Fig. 1 below. The smaller vertical bars represent standard deviation.

Fig. 1

A research assistant reviewing Fig. 1 concluded that there was a relationship between the concentration of myelin present in an individual’s brain and the likelihood of dementia.

Evaluate this conclusion.

A group of six students carried out an experiment to determine their reaction times using a ruler.

Fig. 1 shows the basic procedure used for the experiment.

Fig. 1

The students worked in pairs.

• Student A rested their hand on a bench.
• Student B then dropped a ruler from a set height.
• Student A had to catch the ruler as quickly as possible.
• The distance the ruler had dropped was measured and recorded.
• The students calculated their reaction times.

The formula for calculating reaction time in seconds is shown in Fig. 2.

Fig. 2

Table 1 shows the results for the six students.

Table 1

[1]

(ii)

Predict what would happen to the reaction time if the ruler was held higher than the original set height.

There was some background noise in the classroom when the students carried out their experiment. The students thought that this noise might have affected their reaction times. They decided to modify their original experiment to find out if the presence or absence of background noise affects reaction time.

(ii)

Using the procedure shown in Fig. 1, describe a method that the students could use to find out if the presence or absence of background noise affects reaction time.

Your method should be set out in a logical order and be detailed enough for another person to follow.

Fig. 3 shows some results for a reaction time test that the students found on the internet.

Fig. 3

State why a bar chart is a suitable way to show the data.

Suggest one conclusion the students could have made based on these results.

[1]

(ii)

The students decided to carry out a t-test to find out if the difference in reaction time was significant.

State why a t-test is suitable for these data.

(iii)

State a null hypothesis for this test.

Table 2 shows some probability values of t.

Table 2

The students used 16 degrees of freedom and calculated t = 2.05.

State and explain what the value of t indicates about the difference in mean reaction times shown in Fig. 3.

Another student, when carrying out the ruler experiment shown in Fig. 1, noticed that the more repetitions carried out, the faster the reaction time became.

The student decided to carry out a different experiment to investigate the effect of repetition on the accuracy of carrying out a task.

Five students, V, W, X, Y and Z were tested.

• Each student was given a picture of a star, as shown in Fig. 4.
• Each student sat at a desk so that the star was only visible in a mirror, as shown in Fig. 5.
• Each student was asked to draw between the double lines of the star when looking at it only in the mirror. Fig. 6 shows a star diagram completed by a student.
• The students recorded the number of times their lines went outside the double line of the star.

Fig. 4

Fig. 5

Fig. 6

Each student repeated the task nine times on the same day. The results are shown in Table 3.

Table 3

Identify the independent variable in this experiment.

[1]

(ii)

Suggest the hypothesis that was tested in this experiment.

[1]

(iii)

A person walked into the room and started talking to one of the students who was carrying out the test.

Circle the result in Table 3 that was affected by this.

[1]

(iv)

One of the students had previously carried out a similar task.

Identify this student and give a reason for your answer.

State two conclusions based on the data in Table 3.

Fig. 1 shows an electron microscope image of a synapse.

Fig. 1

Name cell A in Fig. 1.

[1]

Give a reason for your answer to part (i).

[1]

Give one feature that would be found on the cell surface membrane of cell B in Fig. 1.

[1]

Explain why this feature is not visible in Fig. 1.

[2]

Structure C in Fig. 1 is a mitochondrion.

Suggest the roles of structure C within cell A in Fig. 1.

Describe the role of calcium ions at a synapse.

Muscle contraction is stimulated by a series of events taking place at a neuromuscular junction.

Compare the structures and processes of a normal cholinergic synapse with those of a neuromuscular junction.

Fig. 1 shows a section of skeletal muscle under an electron microscope.

Fig. 1

Identify structures A, B and C in Fig. 1.

Skeletal muscle, as shown in Fig. 1, is also known as striated muscle due to its striped appearance.

Use your knowledge of the protein filaments in muscle tissue to explain the striped appearance of skeletal muscle shown in Fig. 1

Several different drugs exist that reduce the contraction of skeletal muscles. Two of these drugs are described in Table 1 below.

Table 1

Explain how each of the drugs in Table 1 reduces the contraction of skeletal muscles.

Outline the roles of sensory receptor cells in the mammalian nervous system.

Fig. 1

State which of the letters C, D and E on Fig. 1 corresponds to each of these events. You may use each of the letters C, D or E once, more than once or not at all.

• The Na⁺ /K⁺ pump is operating

• The voltage‐gated Na⁺ channels are open

• The voltage‐gated K⁺ channels are open

[3]

(ii)

Explain why stimulus A did not result in an action potential being produced whereas stimulus B did.

[2]

(iii)

Describe the importance of the refractory period in the transmission of action potentials.

[2]

Describe how action potentials are transmitted along a myelinated axon.

[4]

Explain how a cholinergic synapse functions.

Fig. 1 shows a transmission electron micrograph of a section through striated muscle.

Fig. 1

Complete Table 1, using the letters A, B or C, to show the location of proteins associated with striated muscle structure.

You may use each letter once, more than once, or not at all.

      Table 1

Explain the role of ATP in the contraction of striated muscle.

Describe how a spinal reflex arc functions and explain why it is an advantage to a mammal.

Explain the importance of the myelin sheath in determining the speed of nerve impulses.