Control and Coordination

Describe the events that cause each of the potential differences at points X, Y and Z.

Suggest how one action potential causes an action potential in an adjacent section of the axon of an unmyelinated neurone.

Vertebrate animals generally have a myelin sheath around the axons of motor neurones.

Explain why the presence of a myelin sheath around a motor neurone axon is an advantage.

An axon membrane is described as being at its resting potential when an action potential is not occurring.

Describe and explain how a resting potential of an axon membrane is maintained.

With reference to Fig. 7.1 and Fig. 7.2, describe the differences between a normal action potential and an action potential of a person with hypokalaemia.

Suggest how hypokalaemia may affect nervous coordination.

Most carnivorous mammals need to move to hunt their prey.

Outline why a carnivorous mammal makes more use of its nervous system, rather than its endocrine system, when it hunts.

Fig. 9.1 is a diagram of a motor neurone.

On Fig. 9.1, add label lines and the letters R, S and T to label a part of the neurone that:

• can become depolarised – use the letter R
• contains many mitochondria – use the letter S
• acts as an insulator – use the letter T.

Suggest an explanation for the shape of the curve that shows changes in the width of the sarcomere.

Suggest an explanation for the curve that shows changes in calcium ion concentration.

Fig. 8.1 is a transmission electron micrograph of striated muscle.

On Fig. 8.1:

• use the letter P with a label line to show a region containing only actin
• use the letter Q with a label line to show a region containing only myosin
• use the letter R with a label line to show a region containing both actin and myosin.

Striated muscle contraction is explained by the sliding filament model.

Outline the role of the proteins troponin and tropomyosin in the sliding filament model.

Striated muscles can sometimes become less efficient at contracting if they have been active for a long time. This is called muscle fatigue.

Suggest why muscles may become fatigued.

Complete Table 5.1 to show the features of three cell-signalling molecules of the endocrine system: antidiuretic hormone (ADH), glucagon and insulin.

Use a tick ($\checkmark$) if the molecule has the feature and a cross ($\times$) if the molecule does not have the feature.

Put a tick ($\checkmark$) or a cross ($\times$) in every box.

Table 5.1

The endocrine system has a slower transmission speed than the nervous system.

Describe other ways in which the endocrine system and the nervous system differ.

State the letter on Fig. 5.1 that indicates the length of a sarcomere.

State the letter on Fig. 5.1 that indicates a region where actin and myosin overlap.

Describe and explain how the region labelled D on Fig. 5.1 changes during muscle contraction.

Suggest a reason why the Venus fly trap needs to capture insects, even though it carries out photosynthesis.

The leaves are specialised to form 2 lobes. The lobes are red on the upper surface.

Suggest why the lobes are red.

The lobes have sensory hairs. Touching 1 sensory hair will not cause a response by the leaf. At least 2 sensory hairs need to be touched within 20 seconds to cause a response in the leaves.

State the advantage to the plant of producing a response only when 2 sensory hairs are touched within 20 seconds.

When an insect has been trapped, the leaves have to remain closed for a number of days.

Suggest why this needs to happen.

Action potentials are produced by the Venus fly trap during the closure of a leaf. Each action potential is also associated with a refractory period. This is similar to the action potential and refractory period observed in a mammalian neurone during nerve impulse transmission.

Explain the role played by the refractory period in the transmission of an impulse in a mammalian neurone.

Nerve impulses can be transmitted along a myelinated motor neurone to a neuromuscular junction at fast speeds of up to $100\ \text{m s}^{-1}$.

Outline how a transmission speed of $100\ \text{m s}^{-1}$ is achieved by the neurone.

When a nerve impulse reaches the neuromuscular junction, acetylcholine is released and diffuses to the sarcolemma.

Describe how the release of acetylcholine can result in the binding of calcium ions to troponin in the sarcomere.

Muscle contraction can be affected by a low blood glucose concentration.

Suggest how a low blood glucose concentration would affect the functioning of the sarcomere.

Complete Table 5.1 to show the features of three cell-signalling molecules of the endocrine system: antidiuretic hormone (ADH), glucagon and insulin.

Use a tick (✓) if the molecule has the feature and a cross (✗) if the molecule does not have the feature.

Put a tick (✓) or a cross (✗) in every box.

Table 5.1

The endocrine system has a slower transmission speed than the nervous system.

Describe other ways in which the endocrine system and the nervous system differ.

State the letter on Fig. 5.1 that indicates the length of a sarcomere.

State the letter on Fig. 5.1 that indicates a region where actin and myosin overlap.

Describe and explain how the region labelled D on Fig. 5.1 changes during muscle contraction.

Fig. 1.1 is a diagram of a sensory neurone.

Use the letters A–F in Fig. 1.1 to identify:

a receptor cell ______

an area where dendron membrane depolarisation occurs ______

a structure that forms a synapse with an intermediate neurone ______

a structure that allows rapid transmission of impulses ______

Opioid drugs can bind to opioid receptors in the presynaptic membrane of a cholinergic synapse.

Fig. 1.2 is a diagram of a presynaptic membrane with an opioid receptor.

Opioid drugs have an effect on the normal events that occur at a cholinergic synapse.

Suggest and explain the effect that an opioid drug will have on the normal events that occur at a cholinergic synapse.

An investigation was carried out to study the effect of different intensities of blue light on the percentage germination of barley seeds. Barley seeds were exposed to blue light for a period of seven days. All other variables were kept constant.

The results are shown in Table 9.1.

Table 9.1

The effect of blue light on the concentration of abscisic acid (ABA) was also investigated. ABA concentration was measured at intervals over seven days in barley seeds exposed to blue light at an intensity of 57 arbitrary units.

The results are shown in Table 9.2.

Table 9.2

For comparison, in the dark the concentration of ABA in barley seeds fell from $100\,\text{au}$ at the start (day 0) to $45\,\text{au}$ on day 1 and did not increase from day 1 to day 7.

ABA is thought to affect gibberellin synthesis or activity.

Using the information in Table 9.1 and Table 9.2, describe the effect of blue light on the germination of barley seeds and suggest an explanation for this effect.

After germination, auxin is important in the growth of barley plants.

Describe and explain the role of auxin in cell elongation.