NEW SPEC UNIT 5 (TOPIC 8)

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Salters-Nuffield Advanced Biology Resources

Activity 8.1 Student Sheet

THE PUPIL REFLEX

Purpose

 To observe the pupil reflex and explain what is happening to bring about the change in size with varying light intensity.

 To understand the nerve pathway of the pupil reflex.

YOU NEED

● Room that can be blacked out ● Small torch or mobile phone

Observing pupil diameter

The diameter of the pupil varies with changing light intensity. In this activity you will observe the pupil diameter in the light and the dark.

SAFETY

Take care when working in the dark. Minimise movement by getting your teacher to black out the room once everyone is seated.

Only use a small source of light to prevent discomfort.

Procedure

1 Black out the room and allow a few minutes for your eyes to adjust. If it is difficult to black out the room, close your eyes before being exposed to the torch light. This will reduce the effects of any remaining ambient light.

2 Working in pairs, one person is the experimenter and the other the subject. The subject covers one eye.

3 Slowly bring the light source in from the side to within 5–10 cm of the subject’s face. Remove the light if the subject feels any discomfort.

4 Describe any changes in pupil diameter observed.

5 Use Student Book 2 to help you explain in detail how the changes in the pupil diameter are brought about.

Questions

Q1 Accurate measurements of pupil diameters have been made.

a Use the data below to calculate the percentage change of the pupil diameters in response to light.

Diameter of pupil in

dark/mm Diameter of pupil in light/mm

7.240 3.100 7.737 3.050 7.440 2.973

b Calculate the mean percentage change.

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THE PUPIL REFLEX

Purpose

 To observe the pupil reflex and explain what is happening to bring about the change in size with varying light intensity.

 To understand the nerve pathway of the pupil reflex.

Observing pupil diameter

Students need to understand how the nervous systems of organisms can cause effectors to respond as exemplified by pupil dilation and contraction. The effect of light intensity on pupil diameter can be demonstrated with the eye covered or lights off, and then uncovered or lights on. Students who wear spectacles should remove them. Contact lenses do not need to be removed.

SAFETY

Ensure only small sources of light are used to prevent discomfort. If the light shone into the eye is too bright it will lead to ‘after images’ but will not damage the eye. Leave the student in a dimly lit room until the ‘after images’ fade.

Minimise movement by the students in the dark. Seat everyone down before blacking out the room.

Notes on the procedure

In the activity students are asked to write a detailed explanation of how the changes in the pupil diameter are brought about. They should include details of the reflex arc, including the receptors, nerve pathway and effectors involved. Student Book 2 describes the reflex in detail.

If it is difficult to black out the room, students should close their eyes before being exposed to the torch light. This will reduce the effects of any remaining ambient light.

Answers

Q1 a

Diameter of pupil in dark/mm Diameter of pupil in light/mm Percentage change 7.240 3.100 (4.14/7.24) × 100 = 57.18 7.737 3.050 (4.687/7.737) × 100 = 60.60 7.440 2.973 (4.467/7.440) × 100 = 60.04

b Mean percentage change = 59.27

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Salters-Nuffield Advanced Biology Resources

Activity 8.1 Technician Sheet

THE PUPIL REFLEX

Purpose

 To observe the pupil reflex and explain what is happening to bring about the change in size with varying light intensity.

 To understand the nerve pathway of the pupil reflex.

SAFETY

Provide small torches to ensure that the light source is not so bright that it causes discomfort.

Requirements per student or

group of students Notes

Access to a room that can be blacked out

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NERVE IMPULSE

Purpose

 To explain the formation of a nerve impulse (action potential) in terms of changes in membrane permeability to sodium and potassium ions.

Generating an action potential

Use the interactive tutorial that accompanies this activity and Student Book 2 to gain an overview before you attempt this worksheet. You may also wish to use the animation to review the topic after you have completed the worksheet.

The bubble writing in this activity forms a key. You shade the bubble writing and the corresponding part of the diagram in the same colour.

What is a resting potential?

On both sides of the cell surface membrane of living cells there are dilute solutions: the cytoplasm inside the cell and intercellular fluids on the other side. Most inorganic molecules are in the form of ions when in solution.

The following ion concentrations were measured in a neurone of a marine invertebrate:

Concentration of

K+ /mM Concentration of Na+ /mM Concentration of Cl/mM

Intercellular fluid outside axon 6 337 340

Cytoplasm of axon 168 50 41

Q1 Explain why this distribution of ions can only be achieved with expenditure of ATP.

Q2 Colour the words in the key in Figure 1. Use the same colour to shade in the parts of the diagram referred to by the key. (Work out which ion is which from the table above.)

Figure 1 Na+/K+ pumps produce an uneven distribution of Na+ and K+ across the membrane. They do not create

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Activity 8.2 Student Sheet

Q3 The axon membrane in Figure 2 has a K+ channel. K+ ions move through the channel down

their diffusion gradient. Explain why K+ cannot cross the membrane through the lipid bilayer. Q4 a Use the same colours as you used in the first diagram to colour in Figure 2. Use

additional colours for the K+ channel and movement of K+.

Figure 2 K+ diffusion produces a potential difference across the membrane. The membrane is polarised.

Membrane potentials are measured by connecting electrodes placed on either side of the membrane. The electrodes are connected to a sensitive meter (galvanometer). The potential difference across the membrane is a measure of the difference in the voltage between one side and the other.

The meter in Figure 2 shows a negative potential difference across the membrane. This is due to positively charged K+ moving down their concentration gradient. Movement of K+ produces a higher

concentration of positive ions on the outer side of the membrane compared with the inner side.

b Add positive signs on one side of the membrane and negative signs on the other to show the difference in charge across the polarised membrane.

c Add another arrow to Figure 2 and label it to show the pull on K+ ions due to the potential

difference across the membrane. This is the electrical gradient for K+.

The movement of the K+ reaches equilibrium as the opposing pulls of the diffusion gradient and the

electrical gradient balance out at around –70 mV. This is called the resting potential.

Q5 Put the correct resting potential (mV) value onto the meter in Figure 2.

Excitable cells

All cells have a resting potential. However, the membranes of nerve and muscle cells have a special property – they are excitable. The potential difference across the membrane can change. The normal state of these cells is to have a resting potential across the membrane. The membrane can be described as polarised. When the membrane becomes depolarised by a stimulus, voltage-dependent Na+ channels open. Na+ move down their diffusion gradient through the channels.

Q6 a Colour the key and diagram in Figure 3 showing depolarisation of the membrane. The membrane becomes more depolarised as Na+ ions move into the axon (the inside is more positive than the outside). More voltage-dependent Na+ channels open due to this depolarisation, producing a rush of Na+ ions. The voltage-dependent Na+ channels close after a fraction of a millisecond, but in this time the potential difference across the membrane changes to +40 mV.

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Figure 3 Movement of Na+ into the axon causes depolarisation of the membrane.

Q7 Explain why Na+ ions move into the axon when voltage-dependent Na+ channels open.

Q8 Explain why the opening of voltage-dependent Na+ channels is described as ‘positive

feedback’.

As voltage-dependent Na+ channels close, voltage-dependent K+ channels open and K+ ions move out of the cell causing repolarisation of the membrane.

Q9 Colour Figure 4 using the colour key from previous diagrams.

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Activity 8.2 Student Sheet

Q10 Add labelled arrows to Figure 4 to show:

 the diffusion gradient for K+

 the electrical gradient across the membrane for positive ions

 movement of K+ through the voltage-dependent channels.

The rush of K+ out of the cell produces an ‘overshoot’ in the potential difference across the membrane;

it is hyperpolarised. The potential difference drops below −70 mV. The membrane is insensitive to stimulation and cannot depolarise again until all the voltage-dependent K+ gates have closed and the resting potential is restored.

Q11 The change in potential difference across the membrane is an ‘action potential’, or an impulse. An action potential can be detected by a galvanometer. Giant axons from squids or earthworms are often used for this type of experiment. One electrode is inserted into the axon and the other is in the surrounding fluid. An electric current stimulates the axon. A galvanometer trace showing an action potential is shown in Figure 5 below. Add label lines and annotations to the trace in Figure 5 with a description of the events that cause the changes in potential difference recorded.

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NERVE IMPULSE

Purpose

 To explain the formation of a nerve impulse (action potential) in terms of changes in membrane permeability to sodium and potassium ions.

Generating an action potential

The interactive that accompanies this activity provides a tutorial on nerve impulses. Using this interactive activity gives an overview of the nerve impulse. This can be used before attempting this worksheet, or as a review afterwards.

The bubble writing in this activity forms a key. Students should shade the bubble writing and the corresponding part of the diagram in the same colour.

Answers

Q1 Energy is needed to move ions against their concentration gradient. This is called active transport.

Q2

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Activity 8.2 Teacher Sheet

Q4 and Q5

Q6

Q7 The diffusion and electrical gradient for Na+ both favour movement of sodium ions into the axon.

Q8 Opening of Na+ channels causes depolarisation of the membrane, which in turn causes more

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Q9 and Q10

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Activity 8.3 Student Sheet

NERVE IMPULSE PROPAGATION

Purpose

 To explain the role of Schwann cells and myelination in saltatory conduction.

 To show how nerve impulses are propagated along axons.

Along the axon

Work through the interactive tutorial that accompanies this activity or use Student Book 2 to see how a nerve impulse is propagated (passes along the axon). Then read the notes below and answer the questions that follow.

Schwann cells and myelin

Myelinated neurones have special cells growing around the axon (Figure 1). The lipid membranes of these Schwann cells form a fatty sheath around the axon.

This fatty (myelin) sheath insulates the axon from electrical activity in nearby cells, which speeds up the nerve impulse. The biggest effect on the speed of a nerve impulse is due to saltatory conduction.

Figure 1 Schwann cells.

Saltatory conduction

The insulating myelin sheath prevents currents from passing through the membrane, except in the gaps between the Schwann cells. The gaps, known as nodes of Ranvier, are the only areas of membrane that become depolarised (Figure 2). This forces the current to travel down the axon to the next gap. Action potentials jump from one gap to the next. Saltatory conduction means ‘jumping’ conduction (from the Latin saltus meaning leap).

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Figure 3 shows how local currents flow between the gaps in the myelin sheath of an axon membrane.

Figure 3 Saltatory conduction.

Q1 Explain why depolarisation causes local currents to flow in an axon membrane.

Q2 Why does the current only flow in one direction, away from the area of depolarisation?

Q3 Fill in the currents for stages 2 and 3 in the sequence in Figure 3 to show the movement of an action potential in a myelinated axon.

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Activity 8.3 Student Sheet

Q5 Different neurones have different speeds of conduction. Use the data below to rank the speeds from lowest (1) to highest (5).

Name of

neurone Speed of impulse (m s–1) Rank of speed How many times faster the impulse travels compared to neurone A

A 0.25

B 88.50 C 15.30 D 98.70 E 85.92

Q6 According to this data, the slowest impulse was travelling along neurone A and was recorded as 0.25 m s–1. For each of the other four neurones, calculate how many times faster their

impulses travel compared with neurone A.

Q7 Which of these five neurones are likely to be myelinated? Use the manipulated data to justify your answer.

Q8 Myelination is one factor that affects the speed of impulse along an axon. Suggest what other factor(s) may affect speed of an impulse.

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NERVE IMPULSE PROPAGATION

Purpose

 To explain the role of Schwann cells and myelination in saltatory conduction.

 To show how nerve impulses are propagated along axons.

Along the axon

The interactive tutorial that accompanies this activity shows how a nerve impulse is propagated. Students can use this tutorial or Student Book 2 to answer the questions on the worksheet.

An alternative approach would be to make a presentation. Choose the same slide layout for each slide, so that when you add a picture it will be in exactly the same position on each slide. Draw a sequence of diagrams similar to those on this worksheet, showing six to eight stages of saltatory conduction. Once your diagrams are placed in the same position on each of a series of slides, select ‘Slide

Transition’ from the slideshow menu. Select to advance slide automatically, after 1 second, and apply this to all slides. From the slideshow menu, select ‘Set Up Show’, then tick ‘Loop continuously until “Esc”’. Now view your show. A non-ICT approach could be used, for example, making a flick-book.

Answers

Q1 Currents flow due to the potential difference between an area of depolarised membrane and the adjacent membrane.

Q2 The area of membrane that has just had an action potential is insensitive to stimulus because it is in its refractory period. The membrane is hyperpolarised. The resting potential is restored during the refractory period. This ensures that impulses only travel in one direction along an axon.

Q3

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Activity 8.3 Teacher Sheet

Q5/Q6

Name of neurone Speed of impulse

(m/s) Rank of speed How many times the impulse is faster than neurone A

A 0.25 1

B 88.50 4 354

C 15.30 2 61

D 98.70 5 395

E 85.92 3 344

Q7 Neurones B, D and E are likely to be myelinated due to the much faster speed of impulse. Students must use their manipulated data to justify their choice.

Q8 The other main factor is diameter of the axon, with larger diameters having faster speeds of impulse. Age, nerve damage and several medical conditions have been shown to affect speed of nerve conduction.

Q9 Active transport is required to re-establish the resting potential following action potentials. Therefore, if less surface area of the neurone membrane actually becomes depolarised, the Na+/K+ pumps will be used less frequently so in a given time less ATP will have to be

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CROSSING A SYNAPSE

Purpose

 To understand the structure and function of synapses in nerve impulse transmission, including the role of neurotransmitters.

Neurotransmitters bridge the gap

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Activity 8.4 Student Sheet

Figure 1 How a nerve impulse crosses the synapse.

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CROSSING A SYNAPSE

Purpose

 To understand the structure and function of synapses in nerve impulse transmission, including the role of neurotransmitters.

Neurotransmitters bridge the gap

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Activity 8.5 Student Sheet

DO PLANTS HAVE HORMONES?

Purpose

 To explain how phototropism is controlled.

 To investigate how IAA affects plant growth response to light.

YOU NEED

● Germinating wheat grain

● Syringe mounting for coleoptile ● Rubber bands or adhesive tack

● Microscope with a stage that can be angled ● Eyepiece graticule scale

SAFETY

Never use a microscope with a daylight mirror in a place where sunlight could strike the mirror. Your retina could be permanently damaged.

Phototropism

Leave a plant on a window ledge and you often see the shoots start growing in a curve towards the light. How does this happen? How is it controlled? Find out for yourself by working through the interactive tutorial accompanying this activity and by completing the experiments.

Measuring phototropism

The coleoptiles of grasses and cereals have been used extensively for studying phototropism – their simple shape makes it possible to observe the response to light and measure it. In this experiment you can do both.

Follow the procedure below to investigate how the coleoptile responds to light.

Procedure

1 Select a germinating wheat grain with only the coleoptile visible, i.e. no leaves should have broken through the sheath. Place it inside a syringe, as shown in Figure 1.

2 Fit a graticule into the eyepiece of a microscope.

3 Position the microscope so that light from a window or lamp strikes it from one side. Arrange the microscope so that the stage is angled vertically, as shown in Figure 2.

4 Fix the coleoptile mount on to the microscope stage using rubber bands or adhesive tack.

5 Focus the low-power objective on the coleoptile. Adjust the mount to line up the tip of the

coleoptile with the mid-point of the graticule scale.

6 Note the time and start a stopclock. After 2

minutes, note the position of the tip of the coleoptile on the scale. Looking through a monocular

microscope, the movement appears to be reversed; the movement seems to be away from

the light.

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7 Take further readings of the coleoptile position at 1- or 2-minute intervals. Do this for about 10 minutes, or until a regular movement has been recorded.

8 Note the time and rotate the mounted coleoptile through 180°on its vertical axis. Reset the coleoptile tip on the centre of the scale. Repeat the measurements in steps 6 and 7.

9 Plot the positions of the coleoptile tip on graph paper.

10 If possible, leave the coleoptile in position for an hour or more and observe its final position.

Figure 2 Microscope turned to make stage vertical. (Note that some microscopes cannot be turned in this way.)

Questions

Q1 Describe the response of the coleoptile to light that you observed in this experiment.

Remember the reversing of the image down the microscope. Did the whole coleoptile respond?

Q2 Describe the effect of rotating the coleoptile through 180°. How can you account for any delay observed in the change of response on reversal?

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Activity 8.5 Student Sheet

The effect of IAA on growth of seedlings

Auxins are a group of chemicals found in plants; they are involved in the growth and development of plant tissues. Traditionally, these chemicals have been called ‘plant hormones’. This is because they are produced in one area of the plant and are transported to, and have effects on, different parts of the plant. The term ‘auxin’ is derived from the Greek word auxein, which means to grow. One of the most important auxins is indole-3-acetic acid (IAA). IAA is synthesised naturally by the plant from the amino acid tryptophan and is made in rapidly growing tissues in the plant, especially the tip of the shoot. In this practical you will investigate the effect of different concentrations of IAA on the growth of roots and shoots.

SAFETY

Indole-3-acetic acid (IAA) may cause skin irritation and eye irritation. Wear eye protection and gloves.

YOU NEED

● 60 germinated cress seedlings ● 6 Petri dishes

● Filter paper

● Fine forceps (to remove seedlings) ● Graph paper or ruler

● Distilled water

● Syringes or graduated pipettes (5 cm3)

● 1.0, 10–1, 10–2, 10–3 and 10–4 IAA solutions

● Access to an incubator

Scientific questions and information research

Before completing the following experiment, complete the interactive tutorial and read the key biological principle section on coordination in plants in Topic 8. Read through the procedure below and predict what you think the effect of IAA will be on the growth of shoots and the growth of roots.

Questions

Q1 Identify the dependent and independent variables, and the variables that should be controlled in this experiment.

Q2 Consider the following features of the experimental design. In each case, explain why this feature is important.

 Several hundred seeds were germinated from which you make your selection.

 Each Petri dish contains ten seedlings.

 The Petri dishes are incubated in the dark.

 The increase in shoot length and root length for several seedlings is measured at each concentration.

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Procedure

1 Line six Petri dishes with filter paper or folded paper towel. You will need several layers.

2 Select ten similar-sized cress seedlings. These will have been germinated for you by placing seeds in an incubator at 28–30 °C for two days. They will have been kept in the dark, as light destroys IAA.

3 Measure and record the length of the root and shoot of each seedling. The easiest way of

measuring is to place the seedling on graph paper. You will be shown how to distinguish the root and shoot.

4 Measure 5 cm3 of distilled water, using a syringe or graduated pipette. Soak the filter paper. It

should be wet, but without excess liquid on the top.

5 Repeat steps 2 to 4 using a range of IAA solutions. Your teacher may ask you to make up the range of IAA solutions from a stock solution of 1000 ppm. Alternatively, they may be supplied for you. The concentrations of IAA required are shown in Table 1. Prepare the dishes in order from the least concentrated IAA to the most concentrated.

IAA concentration/ppm

0 (control) 10–4 10–3 10–2 10–1 1

Table 1 Concentrations of IAA.

6 Place the Petri dishes in an incubator in the dark at about 25 °C for two days.

7 Measure and record the length of each root and shoot after two days.

Analysis and interpretation data

Calculate the mean increase in shoot length and root length for each concentration compared with the control, and the percentage increase in length of shoot and root compared with the control.

Draw an appropriate graph to represent your results.

Discuss the effect of IAA on the growth of shoots and roots with reference to your results. Do they support your original prediction?

Conclusion and evaluation

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Activity 8.5 Student Sheet

How auxins regulate growth

Questions

Q1 Use the information on pages 213 and 214 in Student Book 2 to draw a flow chart that summarises the information explaining how auxins such as IAA regulate cell expansion. Remember that a ‘correct’ flow chart may look quite different from someone else’s ‘correct’ flow chart.

Q2 Recall how in Topic 3 you discovered the different stages of mitosis in a root tip squash. Look at Figure 3 below and describe what will be happening in each of the four areas highlighted as the root grows.

Figure 3 Cross section of a growing root tip.

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DO PLANTS HAVE HORMONES?

Purpose

 To explain how phototropism is controlled.

 To investigate how IAA affects plant growth response to light.

There are four parts to this activity. There is an interactive tutorial, two practical procedures described on the Student Sheet and summary questions. How much of the practical work is completed will depend on the time available.

Interactive tutorial

The interactive tutorial accompanying this activity adopts an investigative approach to the role of plant growth substances in the control of growth, as exemplified by phototropism. This could be completed outside of class time.

Measuring phototropism

SAFETY

Students should be made aware of the hazard of using microscopes where direct sunlight may strike the mirror.

The first experiment allows phototropism to be observed and measured. If a microscope that can be angled is not available, it may be possible to complete the practical as a demonstration using a flexicam.

Although not described on the Student Sheet, it is also possible to investigate which part of the coleoptile is sensitive to light. To do this, use a pot of coleoptiles, making sure that the first leaves have not broken through the surrounding sheaths. Place small aluminium caps over the top 3 mm of one third of the coleoptiles. Place aluminium sleeves covering all but the top 3 mm on a third of the coleoptiles. Leave the remaining third of the coleoptiles uncovered. Place the pot in a box with light entering from one side. Leave it for 3–4 hours and then observe.

The effect of IAA on growth of seedlings

SAFETY

Indole-3-acetic acid (IAA) may cause skin irritation and eye irritation. Ensure eye protection and gloves are worn throughout.

Exercise appropriate precautions to minimise direct contact with skin or eyes. Avoid inhalation of IAA powder when making up stock solution.

The second experiment is a practical investigation into the effect of IAA on growth of cress seedlings. The seedlings are grown on filter paper and their fragile roots may be damaged when students remove them. It is therefore advisable to over-estimate the number of seeds that need to be germinated and to sow very thinly indeed. One possible solution is sowing on filter paper on which you have already drawn pencilled lines, so that groups of seedlings can be cut out. Digital photography could be used at the measurement stage, allowing photographs to be taken quickly and then the length of the seedlings to be measured on the photographs later, without damaging the seedlings.

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Activity 8.5 Teacher Sheet

Students may need help in interpreting their results. Very low concentrations of IAA tend to stimulate roots, but do not affect shoots. Higher concentrations stimulate shoots. These higher concentrations of IAA seem to inhibit roots. Students will only see these patterns by comparison with the control. The students’ graphs should show % stimulation and % inhibition on the y axis and IAA concentration in ppm on the x axis.

Answers

Measuring phototropism

Q1 The coleoptile will move towards the light (positive phototropism). The bending occurs in a region a few millimetres behind the tip where maximum elongation occurs. (Some students may become confused by the inversion of the image when using a microscope.)

Q2 Rotating the coleoptile through 180° reverses the direction of the stimulus so that the movement of the coleoptile is reversed. There is a delay due to the delay in transmitting the chemical signal.

Q3 The slow bending response and the delay when the stimulus is reversed suggest that a chemical signal is transmitted to the region of cell elongation.

The effect of IAA on growth of seedlings

Q1 Dependent variables are shoot and root length. Independent variable is IAA concentration. Variables that should be controlled in this experiment are light, temperature, water and initial size of seedlings.

Q2  Several hundred seeds were germinated from which you made your selection – this allowed seedlings of approximately equal size to be selected.

 Each Petri dish contained ten seedlings – this allowed average increase in shoot length and root length for each concentration to be determined, increasing the validity.

 The Petri dishes were incubated in the dark – to prevent destruction of the IAA.

 Measured the increase in shoot length and root length for several seedlings at each concentration – to allow a mean value to be calculated.

 All factors kept constant except concentration of IAA – to improve the validity of the results.

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How auxins regulate growth

Q1 Suggested flow chart to show action of auxins:

Q2 A − root cap: function − protective cells that prevent damage to the apical meristem; B −

apical meristem, the cells undergoing very rapid mitosis; C − zone of elongation, the cells that lengthen and push the root cap and apical meristem through the soil; D − zone of

differentiation or maturation, an area where the elongated cells differentiate into tissues such as phloem, xylem, epidermis, cortex, etc.

Q3 Students will need to recall the structure of the cell wall from Topic 4. They will realise that cell wall building, from the stage of glucose subunits to the creation of a network of cellulose microfibrils embedded in pectins and hemicelluloses that make up the wall matrix, is a complex process. Therefore they should realise that enzymesare critically important in the process. As cellulose is needed for cell elongation, students might suggest that enzymes such as cellulose synthase would be needed. Several classes of enzymes also modify the structure of the pectins and hemicelluloses in the cell wall. The switching on of the genes for these

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Activity 8.5 Technician Sheet

DO PLANTS HAVE HORMONES?

Purpose

 To explain how phototropism is controlled.

 To investigate how IAA affects plant growth response to light.

Measuring phototropism

SAFETY

Do not place daylight illumination microscopes on benches that will catch the direct rays of the Sun.

Requirements per student or

group of students Notes

Germinating wheat grain The coleoptile should be intact, i.e. the first leaf must not have broken through the sheath.

Syringe mounting for coleoptile The wheat grain is placed within a syringe with the coleoptile protruding from the nozzle – see the diagram on the Student Sheet. Rubber bands or adhesive tack To hold the syringe mounting on the microscope stage.

Microscope with a stage that can be angled

See the photograph on the Student Sheet for the position that the microscope must be put in.

Eyepiece graticule scale Glass and plastic graticule scales can be purchased that fit inside the eyepiece. If it is not possible to put one inside, it will be

necessary to hold it in place on the outside. This can be done using a piece of wire around the edge. This may be unsatisfactory as it will not be in focus at the same time as the plant stem.

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The effect of IAA on growth of seedlings

SAFETY

Indole-3-acetic acid (IAA) may cause skin irritation and eye irritation. Wear eye protection and gloves.

Exercise appropriate precautions to minimise direct contact with skin or eyes. Avoid inhalation of IAA powder when making up stock solution.

Requirements per student or group of students

Notes

60 germinated cress seedlings Several hundred seeds will need to be germinated two or three days before the experiment, on filter paper or folded paper towel. This will allow for variation in germination rate and allow students to select 60 of a similar size.

Seeds will need to be sown very thinly. The teacher/lecturer may prefer seeds to be sown in groups, so that they can be cut from the paper and placed on the Petri dish. The recommended temperature is 28–30 °C, but there is a great deal of natural variation in cress seeds and it is worth testing in advance.

1.0, 10–1, 10–2, 10–3 and 10–4 IAA

solutions

Prepare a stock solution of 1000 ppm IAA by dissolving 1 g of IAA in 1 dm3 of distilled water. Keep the IAA solution in the dark – the use of aluminium foil is recommended. This is because IAA breaks down in the light.

6 Petri dishes Filter paper

Fine forceps (to remove seedlings)

5 cm3 syringes or graduated pipettes One for each dilution.

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Activity 8.6 Student Sheet

EYE QUIZ

Purpose

 To recall the structure and function of the eye.

How the eye works

The aim is to locate the parts of the eye, in particular the iris, pupil, retina and optic nerve. You should also refresh your memory of how the eye works to aid understanding of the more detailed

consideration of the function of the retina that appears later in the topic.

Figure 1 The eye.

Q1 Label the following parts of the eye in Figure 1:

cornea lens conjunctiva ciliary muscle suspensory ligament

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Q2 Fill in the names of the appropriate parts of the eye in the sentences below.

a The eye is covered in a tough outer layer called the __________________. The section at

the front of the eye is transparent and allows light to pass through. Light rays are

refracted as they pass through this layer.

b The __________________ is a thin membrane containing blood vessels that covers the

cornea. It can become inflamed, resulting in ‘red eye’.

c Muscles in the __________________ control the amount of light passing into the eye.

These relax and contract to alter the size of the __________________.

d Light is focused on the retina both by the __________________, at the front of the eye,

and the __________________ behind the pupil. The latter is held in place by the

____________________________________. The shape of the lens is altered by the

____________________________________. When this contracts it allows the lens to

become more rounded. When it relaxes the lens is pulled flat.

e The __________________ contains sensory cells called rods and cones. These generate

impulses that travel to the brain along the ____________________________________.

Q3 Cross out the wrong answers to complete the following table showing what happens in the eye when light from nearby or distant objects is focused on the retina. Take care, as not all possible answers are used. It might help to sketch the path of light entering the eye onto the diagram on the previous page.

Focusing on near object Focusing on distant object

Light rays entering eye are divergent/nearly parallel divergent/nearly parallel

Cornea refracts light/does not refract light refracts light/does not refract light

Lens round/flat round/flat

Suspensory ligaments slack/taut slack/taut

Ciliary muscle contracted/relaxed contracted/relaxed

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Salters-Nuffield Advanced Biology Resources

Activity 8.6 Teacher Sheet

EYE QUIZ

Purpose

 To recall the structure and function of the eye.

How the eye works

This is a simple revision exercise to remind students about the structures and functions of the eye. This is only required at GCSE level and does not form a separate learning outcome in the specification. The aim is to locate the parts of the eye, in particular the iris, pupil, retina and optic nerve, and refresh their memory of how the eye works. This is to aid understanding of the more detailed consideration of the function of the pupil reflex and retina that appears later in the topic.

Answers

Q1 a Conjunctiva

b Cornea

c Lens

d Iris

e Suspensory ligament

f Retina

g Optic nerve

h Sclera

i Ciliary muscle

Q2 a Sclera

b Conjunctiva

c Iris, pupil

d Cornea, lens, suspensory ligaments, ciliary muscle

e Retina, optic nerve

Q3

Focusing on near object Focusing on distant object Light rays entering eye are divergent nearly parallel

Cornea refracts light refracts light

Lens round flat Suspensory ligaments slack taut

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DARK ADAPTATION

Purpose

 To explain how rods in the retina help us to see in dim light.

SAFETY

Take care when working in the dark. Minimise movement, or get someone to guide your movements.

Adjusting to dim light

Enter a dimly lit room from a bright corridor and you can end up falling over the furniture until your eyes get used to the dark. This adjustment is known as dark adaptation and it occurs as a result of the way that the rods work in the retina.

Demonstrating dark adaptation

You can demonstrate dark adaptation by placing a blindfold carefully over one eye and fixing it in place. After about half an hour turn off the lights or go into a darkened room.

Take off the blindfold and shut each eye in turn to compare their performance. You should find that at first the eye that has been covered will work better than the one that has not been covered. Gradually the function of the eye that has been exposed will improve.

What is happening in the rods?

Q1 Label the diagram of the rod in Figure 1 to show the locations and functions of the outer and inner segments, vesicles containing rhodopsin, sodium ion pumps and non-specific cation channels.

Figure 1 A rod cell.

Q2 Annotate the diagram to show what happens in a rod cell in the light to allow an action potential to be generated in the neurone of the optic nerve.

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Salters-Nuffield Advanced Biology Resources

Activity 8.7 Teacher Sheet

DARK ADAPTATION

Purpose

 To explain how rods in the retina help us to see in dim light.

SAFETY

Take care when working in the dark. Minimise movement by the students by guiding their movements in the dark.

Adjusting to dim light

In this activity dark adaptation is used to show how rods work. The practical activity described could be completed to demonstrate dark adaptation. Students are then required to annotate a diagram to show what is happening in the rods when stimulated by light. This will allow them to describe how the nervous systems of organisms can detect stimuli with reference to rods in the retina of mammals. They are then asked to explain what is happening in dark adaptation, which should confirm their

understanding of the ideas covered.

Answers

Q1 and Q2

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THE EFFECT OF LIGHT ON GERMINATION OF

SEEDS

Purpose

 To investigate the effect of light on the germination of seeds.

Seed germination

It has been observed experimentally that light has a significant role in controlling the growth and development of plants. The seeds of some plant species need light for germination, whereas others do not. In this activity you will investigate the effect of white, red and far-red light on the germination of light-sensitive species.

Scientific questions and information research

Read through the procedure provided and write a question you will be answering or a hypothesis you will be investigating using this procedure. Then write a null hypothesis you can test.

Make sure that you can support your ideas with relevant biological knowledge.

Planning and experimental design

Complete a risk assessment for the procedure provided. Decide on a statistical test that you can use to test your null hypothesis.

YOU NEED

● 200 light-sensitive seeds ● 4 Petri dishes with lids ● Filter paper

● Graduated pipette or 5 cm3 measuring cylinder ● Distilled water

● Access to a very dark area or aluminium foil

● White light source ● Red light source ● Far-red light source ● Stopclock

● Pen for labelling Petri dishes

SAFETY

Complete a risk assessment for the procedure listed below. Consider how you might modify your experimental design to address safety issues.

Discuss your findings with your teacher prior to starting the practical. Wash your hands thoroughly after handling seeds.

Procedure

1 Line four Petri dish bases with filter paper.

2 Label the dishes on the base: 1 darkness, 2 white light, 3 red light, 4 far-red light (if available).

3 Count out 50 seeds into the lid of each Petri dish.

4 Measure 5 cm3 distilled water into each dish. Remove any air bubbles. 5 Spread the 50 seeds evenly over the surface of the wet filter paper.

6 Allow the seeds to soak for one hour in complete darkness. The seeds are not sensitive to light until after they have taken up water.

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Salters-Nuffield Advanced Biology Resources

Activity 8.8 Student Sheet

8 Examine the seeds after two or three days and record the percentage germination in each dish. Depending on the species used, you may have to leave the seeds for longer before recording percentage germination. Lettuce, for instance, is expected to germinate in seven days, while

Coleus takes 21 days. A seed is considered to have germinated if the radicle projects 1 mm or more from the seed coat.

Analysis and interpretation of data

Present your results in the most appropriate way in order to show the effect of light on germination. Complete appropriate statistical analysis.

Conclusion and evaluation

Discuss your findings with reference to your question or problem.

State a clear, valid conclusion to your work, summarising what you have found. Support your statements with evidence from your results, your statistical analysis and relevant biological knowledge.

Comment on any systematic or random errors in the data.

Evaluate your experimental apparatus and methods, commenting on the accuracy and precision of your results.

Propose any changes to the procedure that would improve the quality of the results.

Q1 Experiments have shown that one wavelength of light seems to inhibit germination. Suggest a reason why light-sensitive seeds will germinate in white light (this contains all wavelengths).

Q2 Which form of phytochrome is required for germination by light-sensitive seeds, such as

Coleus, lettuce and feverfew?

Q3 Suggest a reason why light-sensitive seeds are almost always very tiny and conversely why seeds needing darkness (such as peas) are usually larger.

Q4 Why do you think that seed packets recommend specific planting depths for seeds?

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THE EFFECT OF LIGHT ON GERMINATION OF

SEEDS

Purpose

 To investigate the effect of light on the germination of seeds.

SAFETY

Review the students’ risk assessments and discuss any safety considerations. Ensure students wash their hands thoroughly after handling seeds.

Seed germination

The experiment investigates the effect of light on the germination of light-sensitive seeds, such as lettuce, feverfew, Nicotiana, Achillea and Coleus. Experiments with seeds of such species indicate that a flash of red light will trigger germination, but that germination is inhibited if followed by a flash of far-red light. The final flash of light is the decisive factor. This suggests that the effects of red light and far-red light are reversible.

Students follow the procedure provided while focusing on hypothesis-testing. In preparation for completing the practical work they come up with a question or hypothesis that the procedure is testing and write the matching null hypothesis. For a question they may say something like: what effect will white, red and far-red light have on germination of light-sensitive seeds? Or a hypothesis such as ‘Light-sensitive seeds are likely to germinate in white or red light and not in darkness or with far-red light, which will inhibit germination’. The null hypothesis would be that there is no difference in the frequency of germination of type x seeds when exposed to the different light conditions – darkness, white, red or far-red light.

The appropriate statistical test to use in this experiment would be a chi-squared test. The frequency of germination in each light would be recorded, the total calculated and used to calculate the expected frequencies, those expected given a null hypothesis of no difference.

Notes about the procedure

The seeds that are to have complete darkness must remain in darkness throughout the whole experiment, during soaking and germination.

If a source of far-red light is readily available (for instance, far-red LEDs) then students could use this. If not, a blue and red filter used together will stop transmission of red and blue light, but will allow the transmission of far-red light beyond 720 nm.

Both Coleus and lettuce seeds have been shown to work well, with results from Coleus being

particularly impressive. Coleus requires longer to germinate than lettuce, but there are many varieties of both species and a particular variant may not have this light requirement. Test carefully beforehand. Students may realise that counting 50 seeds into each dish is not absolutely necessary, since they can calculate the percentage of seeds that have germinated. However, having very unequal numbers of seeds in each dish will reduce the validity of results.

Students should find that the seeds germinate to the same extent in the white and red light. Far-red appears to inhibit germination, but there may be low germination in the far-red light and dark. Students need to describe the action of phytochromes. The short burst of red light triggers

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Salters-Nuffield Advanced Biology Resources

Activity 8.8 Teacher Sheet

Answers

Q1 Red light is more effective at converting the phytochrome than far-red light. In white light more Pr is converted to the Pfr form and germination is triggered.

Q2 Pfr.

Q3 Light-sensitive seeds must be close to the surface to receive the light needed to trigger

germination. Therefore they do not require a large food store to grow and reach the soil surface before making their own food by photosynthesis. Seeds that need darkness are often larger. This is because they need to be deeper in the soil and so need greater food reserves in order to produce a long shoot to break the soil surface.

Q4 The planting depth may be related to the degree of light exposure that a seed requires for germination. It may also be linked to temperature; if the seeds are planted early in the year, deeper planting may protect them from frost.

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THE EFFECT OF LIGHT ON GERMINATION OF

SEEDS

Purpose

 To investigate the effect of light on the germination of seeds.

Requirements per student or

group of students Notes

200 light-sensitive seeds Light-sensitive seeds include varieties of lettuce, feverfew, Nicotiana, Achillea and Coleus. In trials, lettuce and Coleus varieties worked well. It is necessary to check that the variety selected is light-sensitive, i.e. if different seeds are placed in light and complete dark, light-sensitive seeds will only germinate successfully in the light. Four Petri dishes with lids

Filter paper Four pieces to line the Petri dishes. Graduated pipette or 5 cm3 measuring

cylinder Distilled water

Access to a very dark area or aluminium foil

A dark incubator allows the seeds to be germinated at the optimum temperature for germination. Aluminium foil is needed to wrap Petri dishes if a place with complete darkness is not available.

White light source Fluorescent lights are not suitable for this experiment. The light produced does not contain sufficient red or far-red light.

Incandescent light bulbs are better. Halogen light bulbs may also be suitable.

Red light source

Far-red light source LED lights are suitable but, if not available, a combination of red and blue filters can be used.

Stopclock Pen For labelling Petri dishes.

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Salters-Nuffield Advanced Biology Resources

Activity 8.9 Student Sheet

HOW DOES LIGHT AFFECT FLOWERING?

Purpose

 To assess understanding of the role of phytochromes in photoperiodism.

Light and flowering

Plants normally flower at the same time every year; some, like chrysanthemums, flower in the autumn whereas others, such as strawberries, bloom in the spring. They flower in response to the length of day (light) and night (dark). Hence the response is known as photoperiodism. Read pages 219–221 of Student Book 2 before you complete the questions below.

Q1 Table 1 shows the length of light and dark required to stimulate flowering in five different plant species. Plants of these five species were subjected to the different regimes of light and dark shown in Table 2. In Table 2 use a tick to show which plants would flower under the conditions shown; use a cross to show if the plants would not flower.

Plant species Requirement

1 at least 13 hours of light 2 at least 12 hours of darkness 3 at least 16 hours of darkness 4 No specific requirement 5 at least 11 hours of darkness

Table 1 Light requirements for flowering of five species.

Dark/light regime

A B C D E F G H Hours of continuous dark 9 10 11 12 13 14 15 16 Hours of continuous light 15 14 13 12 11 10 9 8 Plant species 1

Plant species 2 Plant species 3 Plant species 4 Plant species 5

Table 2 The effect of different light treatments on flowering.

Q2 For each of the plant species, decide which photoperiodic group they belong to. Use the terms ‘short-day’, ‘long-day’ and ‘day-neutral’ in your answer.

Q3 Explain why long-night plants might be a better description than short-day plants. In your answer refer to the role of phytochromes in the control of flowering of short-day plants.

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Q5 A commercial grower wants plant species 3 to flower all year round, so it is available for florists. Which of the treatments shown in Figure 1 below would a grower of plant 3 use to make it flower out of season? Give a reason for your answer.

Time (hours)

Figure1 Different treatments of light and dark.

Q6 Complete the concept map in Figure 2 that summarises the role of phytochromes.

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Salters-Nuffield Advanced Biology Resources

Activity 8.9 Teacher Sheet

HOW DOES LIGHT AFFECT FLOWERING?

Purpose

 To assess understanding of the role of phytochromes in photoperiodism.

Answers

Q1

Dark/light regime

A B C D E F G H Hours of continuous dark 9 10 11 12 13 14 15 16 Hours of continuous light 15 14 13 12 11 10 9 8 Plant species 1         Plant species 2         Plant species 3         Plant species 4         Plant species 5        

Q2 Species 1 are long-day plants; species 2 are short-day plants; species 3 are short-day plants; species 4 are day-neutral plants; species 5 are short-day plants.

Q3 It would be better to call them long-night plants because it is the period of darkness that is critical. Short-day plants flower when the period of darkness is longer than a critical length, the long night giving sufficient time for all the Pfr formed in the light to be converted back into

Pr. If any Pfr remains at the end of the dark period it inhibits flowering. Q4 Plants 2, 3, 4 and 5.

Q5 J, N and P would induce flowering. All these treatments have sufficiently long dark periods. N has a flash of far-red light that would ensure any Pfr was converted back to Pr preventing

inhibition of flowering by Pfr. The flash of red light in treatment P does not prevent flowering

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Q6

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Salters-Nuffield Advanced Biology Resources

Activity 8.10 Student Sheet

STRUCTURE AND FUNCTION OF THE BRAIN

Purpose

 To investigate the structure and function of different regions of the human brain.

The brain

The human brain is a remarkable organ. Over the years it has fascinated scientists and we are gathering more and more evidence about the complexity of its functions.

Work through the interactive tutorial accompanying this activity and answer the questions below.

Q1 Calculate the average surface area to volume ratio for a human brain.

Q2 The average surface area of an African elephant’s brain is 6300 cm2; the average volume is

3890 cm3. Work out the average surface area to volume ratio for an African elephant’s brain. Q3 Use these data to suggest a link between intellectual capacity and surface area to volume ratio.

Q4 It has been suggested that Albert Einstein had a particularly folded cortex in certain areas. Does this provide further evidence to support your answer to Question 3? Give a reason for your answer.

Q5 Albert Einstein’s parietal lobes were approximately 15% larger than average. Using your knowledge of the function of the parietal lobes, suggest what effect this may have had on his intellectual capacity.

Q6 The average mass of an adult male human brain is approximately 1400 g. Surprisingly the mass of Albert Einstein’s brain was about 1200 g. What percentage smaller than average was Albert Einstein’s brain?

Q7 Many textbooks state that there are about 100 billion neurones in the human brain. A group of researchers looking to provide a more accurate figure dissolved the cell membranes within the brain and stained the nuclei of neurones so that they could be counted. They estimated that there are about 86 billion neurones in the brain and about the same number of non-neural cells. It has been estimated that a single neurone can have up to about 10 000 synapses.

a State the number of neurones present in the brain in standard form.

b Calculate how many synapses there could be in the brain using the figures above. Give your answer in standard form.

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STRUCTURE AND FUNCTION OF THE BRAIN

Purpose

 To investigate the structure and function of different regions of the human brain.

The brain

There is an interactive tutorial on brain function accompanying this activity. It takes students through the functions of different regions of the brain. Students then identify the area of the brain injured from the description of symptoms described.

Activity 8.11 contains more examples of symptoms; it can be used after this activity to assess students’ learning about the functions of the brain. Activity 8.12 could be used in a similar way; this uses scans to identify functions.

Answers

Q1 Surface area of human brain 2500 cm2, volume 1400 cm3, thus SA:V is 2500/1400 = 1.79 Q2 6300/3890 = 1.62

Q3 There appears to be a correlation between surface area to volume ratio and intellectual

capacity. Humans have a larger surface area to volume ratio than elephants, suggesting that the highly folded cortex (a high surface area) is linked to a higher intellectual capacity. Students should ‘use their data’ to back up their answer. However, one cannot conclude a causal relationship.

Q4 This does provide further evidence to support the idea that a highly folded cortex/high surface area is linked to higher intellectual capacity. However, students need to realise that one piece of anecdotal information is not enough to prove this. A much more extensive piece of research, with a large sample size, would need to be conducted. Students should also note that Einstein’s brain has been extensively studied; it contained a higher ratio of glial cells to neurones than other brains. Glial cells do not carry impulses, they provide nutrition and support for neurones.

Q5 The parietal lobes have a key role in spatial awareness and mathematical calculation. This may explain his particular strengths in maths and theoretical physics, leading to the development of new theories.

Q6 (200/1400) × 100 = 14.29% smaller.

Q7 a 8.6 × 1010 b 8.6 × 1014 Q8

Region of the cortex Functions

Parietal lobe Orientation, movement, sensation, calculation and some types of recognition. Frontal lobe Higher brain functions, such as decision-making, reasoning, planning and

emotions. It forms associations by processing information and is involved with ideas. It includes the primary motor cortex; this has neurones connected directly to the spinal cord and brain stem, and from there to the muscles. It sends information via motor neurones to muscles to carry out movements, including learned movements.

Occipital lobe Processing information from eyes, including vision, colour, shape recognition and perception.

Temporal lobe Concerned with processing auditory information, that is hearing, sound recognition and speech.

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Salters-Nuffield Advanced Biology Resources

Activity 8.11 Student Sheet

IN THE DOCTOR’S SURGERY

Purpose

 To identify the functions of different areas of the human brain.

Where did the problem occur?

Your task in this activity is to use the symptoms experienced by each patient to identify where damage may have occurred in their brain. Reading the section of Student Book 2 on regions of the brain (pages 224–226) and having a look at the weblinks that accompany this activity will help.

Patient A had an overwhelming urge to eat. Despite consistent and sincere efforts to control her eating she had become extremely obese by the age of six years.

Paralysis in the left side of patient B’s body.

Patient C reported that she could remember events from her childhood, but could not remember what had happened an hour ago.

Patient D reported problems with thinking and problem-solving. Despite having perfect vision he even showed difficulty in the recognition and identification of common objects on the doctor’s desk.

Patient E was found in a squalid flat. Two dogs were found in a neglected state. Patient E appeared to be unaware of her current situation, apathetic and totally unconcerned about her pets, a change from her previous caring manner.

Patient F could no longer walk in a straight line. His gait involved wide separation of his legs. The timing of his steps was jerky and irregular, causing him to lurch from side to side in an unbalanced manner. By the fifth day after the onset of his symptoms he could no longer stand without assistance, and he began to display rapid and jerky eye movements.

After being knocked out and striking the back of his head on the canvas, a boxer, patient G, experienced vision problems.

Extension

If you have time and access to more detailed resources on the parts of the brain, try these additional patients.

Patient H has a history of impulsive criminal behaviour resulting from a tendency to ignore future consequences and a failure to make meaningful plans.

A post-mortem on a patient I, who had for many years shown the confused thinking characteristic of schizophrenia, revealed a definite abnormality in one area of the brain.

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IN THE DOCTOR’S SURGERY

Purpose

 To identify the functions of different areas of the human brain.

Where did the problem occur?

In this activity students identify possible parts of the brain from the symptoms experienced by patients who have suffered damage to specific areas of the brain.

Answers

A Hypothalamus

B Right motor cortex

C Hippocampus

D Association cortex of the occipital and frontal lobes

E Frontal lobes

F Cerebellum

G Occipital lobes

Extension

H Frontal lobes

I Thalamus or basal ganglia

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Salters-Nuffield Advanced Biology Resources

Activity 8.12 Student Sheet

WHAT HAPPENS WHERE?

Purpose

 To consider the functions of different regions of the brain.

 To understand how positron emission tomography (PET) is used in medical diagnosis, and the investigation of brain structure and function.

Using brain images

Brain-imaging provides a non-invasive technique for studying the functions of different regions of the brain. Watch the video clip accompanying this activity to see a functional MRI scan taking place. The brain image in Figure 1 shows the brain at rest (i.e. not undertaking a particular task). Compare this resting brain with the four sets of brain images that follow (Figures 2 to 5). In each of these figures the active area of the brain is highlighted with an arrowhead. Identify the active area in each figure and place the figure number in the appropriate box on Figure 6. There are more boxes than brain images so you will have to select carefully. Use Student Book 2 to add the name and function of all the parts that are labelled.

The PET images in Figures 1 to 5, 8 and 9 can also be downloaded from the mediabank in SNAB Online.

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Figure 2 Brain image of someone completing a thinking task.

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Salters-Nuffield Advanced Biology Resources

Activity 8.12 Student Sheet

Figure 4 Image of the brain of a person who is performing a motor task, namely hopping up and down on one leg. (Note that the stimulation is higher in the brain than in Figure 5.)

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Figure 6 Regions of the brain.

Deeper inside the brain

Using Student Book 2, label Figure 7 below and annotate it with each part’s functions. Then answer the question that follows.

Figure 7 Functions of the brain regions.

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Salters-Nuffield Advanced Biology Resources

Activity 8.12 Student Sheet

Figure 8 PET image of the brain of someone remembering an image for later recall.

18F-fluorodeoxyglucose (18F-FDG – glucose labelled with radioactive fluorine) is used to measure the

regional cerebral glucose metabolism in µmol/min/100 g. Figure 9 shows 18F-FDG-PET scans of a

normal brain (left) and the brain of a patient with Alzheimer’s disease (right). The red colour indicates high (about 50–60 μmol/min/100 g), yellow indicates medium (about 30–40 μmol/min/100 g) and blue indicates low (10–20 μmol/min/100 g) 18F-FDG uptake by tissue. Black indicates very low uptake of

less than 10 μmol/min/100 g.

Figure 9 PET scans with 18F-FDG showing a normal brain (left) and the brain of a patient with

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Q2 In 18F-fluorodeoxyglucose, radioactive fluorine (18F) is substituted for the normal hydroxyl

group at position 2 in β-glucose. Draw a diagram that shows the structure of this molecule.

Q3 The units used on the PET images above are µmol/min/100 g. Convert 20 µmol/min/100 g into mol/min/100 g.

Q4 Using Figure 9, describe cerebral glucose metabolism changes with Alzheimer’s disease.

Q5 It has been suggested that patients suffering with Alzheimer’s disease have reduced cerebral glucose metabolism due to disrupted glycolysis. Recall your knowledge of respiration to explain the possible effects of disrupted glycolysis in neurones.

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Salters-Nuffield Advanced Biology Resources

Activity 8.12 Teacher Sheet

WHAT HAPPENS WHERE?

Purpose

 To consider the functions of different regions of the brain.

 To understand how positron emission tomography (PET) is used in medical diagnosis, and the investigation of brain structure and function.

Using brain images

The aim of this activity is to encourage students to think about the regions of the brain and their functions in an active way rather than merely as a rote-learning exercise.

Websites with brain images can be found in the weblinks that accompany this activity.

Answers

Looking at the scans, the students should link the scans to the regions on Figure 6 as shown below. The names and functions of these regions of the cortex can be found in Student Book 2.

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Deeper inside the brain

Q1 The hippocampus, because longer-term memories are being laid down.

Q2  

Q3 0.00002 mol/min/100 g or 2.0 × 10–5 mol/min/100 g.

Q4 Evidence for changing cerebral glucose metabolism includes:

 a large increase in the amount of brain tissue with very low glucose metabolism (less than 10 µmol/min/100 g 18F-FDG, shown as areas of black);

 the areas of brain tissue having very high glucose metabolism (50–60 µmol/min/100 g, shown as areas of red) and medium glucose uptake (30–40 μmol/min/100 g) are reduced.

Q5 Glycolysis is the first stage of respiration. If glycolysis is disrupted, then there are likely to be a number of effects, as listed below:

 fewer ATP, reduced NAD and molecules of pyruvate produced in glycolysis;

 link reaction, Krebs cycle and electron transport chains activity will be reduced;

 fewer ATP produced per molecule of glucose;

 metabolic reactions in neurones that require ATP will be negatively affected, for example, synthesis of neurotransmitters, active transport of ions and active uptake of

neurotransmitters.

Figure

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References

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