Beetroot cells contain a red pigment that cannot normally escape from the cells through the cell surface membrane. A student carried out an investigation into the effect of temperature on the permeability of the cell surface membrane of beetroot cells.




She measured permeability by using a colorimeter to measure the absorbance of green light by the solutions in which samples of beetroot had been immersed. The greater the absorbance, the more red pigment had leaked out of the beetroot cells. The graph above shows her results.

(a) With reference to the graph, describe the effect of temperature on the absorbance of light in the colorimeter.

Candidate A

(a) Between 0 and 30 the absorbance goes up very slightly . ü Above 40°C it goes up
very quickly. û Then it starts to level out at about 70°C .ü

* The student has correctly identified the three main regions of the graph, stating where changes in gradient occur. However, he or she has used the term 'quickly', which is not correct because the graph does not show anything about time. He or she could also have gained a third mark by quoting some figures from the graph. 2/3

(b) High temperatures damage the proteins in the membrane . ü They become denatured, so they leave holes ü in the membrane that the beetroot pigment can get through.

~ This is a good answer as far as it goes, clearly expressed. However, it is not enough to store a full set of marks. 2/4

Candidate B

(a) The general trend is that the higher the temperature, the greater the absorbance. Between 0 and 30°C, the absorbance increases very slightlyü from about 16 to 18 arbitrary units. Above 40°C it increases much more steeply, ü  levelling off at about 70°C .ü The maximum absorbance is 98 arbitrary units.

*A good answer. However, although the candidate has quoted some figures from the graph, he or she has not manipulated them in any way - for example, he or she could have calculated the increase in absorbance between 0 and 30°C.3/3

(b) As temperature increases, the phospholipids and protein molecules in the membrane move about faster ü  and with more energy. This leaves gaps in the membrane, so the beetroot pigment molecules can get through ü  and escape from the cell. The protein molecules start to lose their shape at high temperatures ü because their hydrogen bonds break, ü so the protein pores get wider ü which increases permeability.

*An excellent answer. 4/4

The diagram below shows pressure changes in the left atrium and left ventricle of
the heart and the aorta during the cardiac cycle.





(a) Calculate how many heart beats there will be in one minute.
(b) (i) On the diagram, indicate the point at which the semilunar valves in the aorta snap shut.
     (ii) Explain what causes the semilunar valves to shut at this point in the cardiac cycle.
     (iii) On the diagram, indicate the period when the left ventricle is contracting.
    (iv) On the diagram, draw a line to show the changes in pressure in the right ventricle.

(c) After the blood leaves the heart, it passes into the arteries. The blood pressure gradually reduces and becomes more steady as the blood passes through the arteries. Explain what causes this reduction and steadying of the blood pressure.
Candidate A

(a) 1 cycle in 0.75 seconds ü so in 60 seconds there will be 60 x 0.75 û - 45 beats

* The student has read the length of one cycle correctly, but the calculation is wrong. 1/2

(b) (i)

   * Correct. 1/1

   (ii) The valves shut when the ventricle starts to relax . ü

   *  Correct as far as it goes, but it needs to give more information in order to get the second mark. 1/2

   (iii) See diagram.

    * Correct. 1/1

   (iv) See diagram

    *  Partly correct. The pressure in the right ventricle is correctly shown as less than that in the left ventricle, but it should be contracting and relaxing at exactly the same times as the left ventricle. 1/2

(c) The pressure gets less as the blood gets further away from the heart. ü The muscle in the walls of the arteries contracts û and relaxes to push the blood along, and it does this in between heart beats so the pulse gets evened out.

* The first statement is correct, but does not really tell us any more than is in the question. However, it is not correct that the muscles in the artery wall contract and relax to push the blood along. 1/2


Candidate B

(a) 60/0.75ü = 80 beats per minute .ü
    * Correct. 2/2

(b) (i)

* Correct. 1/1

   (ii) They close when the pressure of the blood inside the arteries is higher than inside the ventricles ü - the blood therefore pushes down on the valves and makes them shut. ü
       * Correct. 2/2

(iii) Seediagram.
     * Correct. 1/1
(iv) Seediagram.
     * Correct. 2/2

(c) As the blood is forced into the artery as the ventricle contracts, ü it pushes outwards on the artery wall, making the elastic tissue stretch . ü In between heart beats, the pressure of the blood inside the artery falls, and the elastic tissue recoils . üSo the wall keeps expanding and springing back. When it springs back it pushes on the blood in between üheart beats, so this levels up the pressure changes.

* This answer explains very well why the blood pressure levels out. However, it does not mention the overall fall in blood pressure. All the same, this is a good answer which gets full marks. 2/2

The diagram below shows a small part of a human lung as it appears through a microscope.



(a) Name the type of blood vessel in which the red blood cell is present.
(b) Describe and explain two ways in which the structure of the alveoli, shown in the diagram, enables gas exchange to take place rapidly.
(c) Explain why large organisms such as mammals need specialised gas exchange surfaces, whereas small organisms such as a single-celled Amoebo do not.

Candidate A

(a) capillary ü
* This is correct. 1/1

(b) They have a large surface area ü
     They are thin, so oxygen can diffuse across quicklyü

* The statement about a large surface area is correct, but the answer also needs to say why this enables gas exchange to take place rapidly (because the question asks you to 'explain'). The second answer is not sufficiently clear - what is thin? It is not the whole alveoli that are thin, but their walls. The second part of this answer does give a clear explanation of why this helps gas exchange to
take place quickly. 2/4

(c) Large organisms have small surface areas compared to their volume,ü so they need extra surface üto be able to get enough oxygen.

* There is a correct and clear statement about surface area to volume ratio, and the answer also lust gets a second mark. However, this isn't really very clear - see candidate B for a better explanation. 2/2

Candidate B

(a) capillary ü
* Correct. 1/1
(b) large surface area ü - so more oxygen and carbon dioxide molecules can diffuse across at the same time  ü
      good supply of oxygen - to maintain a diffusion gradient between the alveoli and the blood

* The first way is correct and well explained. However, the second, although true, does not answer the question which is about the structure of the alveoli. So just 2/04.

(c) They have small surface area to volume ratios, übut an Amoeba has a large surface area to volume ratio. The oxygen that diffuses in across the surface has to supply the whole volume ü of the animal, so in a large animal that is not enough and they have specialised gas exchange surfaces to increase the surface areaü and let more oxygen diffuse in.

* This is a good answer. All the important points are there and it is clearly expressed. 2/2

The diagrams below show five molecules found in living organisms.




(a) Give the letter of one molecule that fits each of these descriptions.

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

   (i) the form in which carbohydrates are transported through phloem tissue in plants
   (ii) the form in which carbohydrates are stored in animals
   (iii) a molecule that is insoluble in water
   (iv) a molecule that links together with others to form a polypeptide
   (v) a molecule that contains ester bonds

(b) Explain how the structure of water molecules makes water a good solvent.
Candidate A

(a) (i) A û
    * A is a glucose molecule, but plants transport sucrose. Even if you did not know what a sucrose molecule looks like, you should know that it is a disaccharide.

   (ii) Cü
   * Correct. 1/1

   (iii) E û
   * Amino acids are soluble. Either C or D would be correct.

   (iv) E ü
    *  Correct. 1/1

  (v) D ü
   *  Correct. 1/1

(b) Water has dipoles and hydrogen bonds,ü which help it to dissolve other substances.

* There are no wrong statements in this answer, but it does not really give an explanation of why water is a good solvent - it just states two facts about water molecules. 1/3

Candidate B

(a) (i) Bü
    *  Correct. 1/1

    (ii) Cü
    *  Correct. 1/1

   (iii) D or Cü
   *  Correct. However, the candidate took an unnecessary risk with (iii),by giving two answers. If the second one had been wrong, it could have negated the first correct one. If you are asked for one answer, it is best to give only one, 1/1

   (iv) E ü
   *  Correct. 1/1

  (v) D ü
   *  Correct. 1/1

(b) In a water molecule, the hydrogen atoms have a tiny positive electrical charge and the oxygen atom has a similar negative charge. üOther atoms or ions with electrical chargesü are attracted ü to these charges on the water molecules. This makes them spread about ü among the water molecules.

* This is a good answer. It really does explain how a substance dissolves in water and relates this clearly to the structure of a water molecule. The candidate has actually earned four possible marking points, but there is a maximum of three marks available in total. 3/3

(a) The diagrams show a cell in various stages ofthe mitotic cell cycle.

The diagram shows the bacterium Mycobacterium tuberculosis, which causes tuberculosis (TB).




(a) M. tuberculosis is taken up by macrophages and multiplies inside them.
(b) In an experiment to investigate how M tuberculosis avoids destruction by macrophages, bacteria were added to a culture of macrophages obtained from the alveoli of mice. At the same time, a quantity of small glass beads, equivalent in size to the bacteria, were added to the culture. The experiment was repeated using increasing quantities of bacteria and glass beads.

After 4 hours, the macrophages were sampled to find out how many had taken up either glass beads or bacteria. The results are shown in the graph. The x-axis shows the initial ratio of bacteria or glass beads to macrophages in the mixture.


Discuss what these results suggest about the ability of macrophages to take up M. tuberculosis.

(c) When M tuberculosis is present inside a phagosome of a macrophage, it secretes glycolipids that accumulate in lysosomes and prevent the lysosomes fusing with the phagosome.

Explain how this prevents the macrophage from destroying the bacterium.                            (3 marks)

Candidate A

(a) It stops the B cells seeing them, so they don't make antibodies ü against them.

* This is not a very clear answer. B cells do not 'see', so this is not a good term to use. The 'they' in the second half of the sentence could refer to either B cells or the bacteria. 1/3

(b) The macrophages took up more glass beads than bacteria .ü So they are not very good at taking up the bacteria .ü

* Just enough for two marks, although the second sentence is weak. 2/3

(c) tysosornes contain digestive enzymes, ü so if they don't fuse with the phagosome the bacteria won't get digested. ü

* Once again, the candidate has the right ideas, but does not give enough biological detail to get full marks. 2/3

 Candidate B

(a) B cells only become active when they meet the specific antigen ü to which they are able to respond. If the bacteria are inside a macrophage. then the B cell's receptors won't meet the antigen ü on the bacteria. This means that the B cells will not divide to produce plasma cells , üand will not secrete antibodies üagainst the bacteria.

* A good answer. 3/3

(b) The cells only started to take up any bacteria when the particle.macrophage ratio was 1 ü On the other hand, they took up glass beads even when the ratio was above 0.01. üWhen the ratio of particles to macrophages was 10, only about 30% of the macrophages had taken up bacteria, whereas over 75% of them had taken up glass beads. ü This shows the macrophages do take up the bacteria,
but not as well as they take up glass beads. ü

* A good answer, which does attempt to 'discuss' by providing statements relating to the relatively low ability of the macro phages to take up the bacteria, but also stating that they do take them up. In general, it is always a good idea to quote data where they are relevant in your answer. 3/3

(c) Normally, lysosomes fuse with phagosomes and release hydrolytic enzymes üinto them. These enzymes then hydrolyse (digest) whatever is in the phagosome. ü If this doesn't happen, then the bacteria can live inside the phagesome ü without being digested.

* All correct. 3/3

(a) The diagram shows a small part of a cell, as seen using an electron microscope.




      (i) Name the parts labelled A to D.   (2 marks)
      (ii) Describe how part B is involved in the formation of extracellular enzymes. (3 marks)

(b) Give two reasons, other than the presence of part B, why the cell in the diagram cannot be a prokaryotic cell. (2 marks)
Candidate A

(a) (i) A plasma membrane ü
          B  Golggi ü
         C nucleus û
         D phagocyte û

* C is the nuclear envelope (or membrane), not the nucleus itself. A phagocyte is a cell - perhaps the candidate is thinking of a phagocytic vesicle. 1/2

    (ii) First, the enzymes are made by protein synthesis on the ribosomes. Then they go into the endoplasmic reticulum. Then they are taken üto the Golgi where they are packaged. Then they go in vesicles üto the cell membrane where they are sent out byexocytosis.

* This candidate has not really thought about exactly what the question was asking, and has wasted time writing about events that take place before and after the involvement of the Golgi apparatus. There is, however, a mark for the idea that the Golgi apparatus receives proteins that have been in the RER, and another for packaging them into vesicles. 2/3

(b) It has a nucleus. ü And it has Golgi apparatus. û

* The Goigi apparatus is part B, and tilis has been excluded by the question. 1/2

Candidate B

(a) (i) A cell surface membrane ü
          B Golgi apparatus ü
          C nuclear envelope ü
          D vesicle ü

* All correct. 2/2

     (ii) Proteins made in the RER are transported to the convex face ü of the Golgi apparatus in vesicles. The vesicles fuse ü with the Golgi and the proteins inside are modified ü by adding sugars to make glycoproteins .ü  They are packaged inside membranes ü  and sent to the cell membrane.

* All correct. 3/3

(b) If it was a prokaryotic celi it wouldn't have a nucleus ü and it would have a cell wall. ü

* Correct. 2/2 .

In this section is a practice examination paper, similar to the Cambridge International AS Level Biology paper 2. All of the questions are based on the topic areas described in the previous sections.












Youhave 1 hour and 15minutes to do the paper. There are 60 marks on the paper, so you can spend just over one minute per mark. If you find you are spending too long on one question, then move on to another that you can answer more quickly. If you have time at the end, then come back to the difficult one.

Some of the questions require you to recall information that you have learned. Be guided by the number of marks awarded to suggest how much detail you should give in your answer. The more marks there are, the more information you need to give.

Some of the questions require you to use your knowledge and understanding in new situations. Don't be surprised to find something completely new in a question - something you have not seen before. Just think carefully about it, and find something that you do know that will help you to answer it.

Do think carefully before you begin to write. The best answers are short and relevant - if you target your answer well, you can get a lot of marks for a very small amount of writing. Don't say the same thing several times over, or wander off into answers that have nothing to do with the question. As a general rule, there will be twice as many answer lines as marks. So you should try to answer a 3 mark question in no more than 6 lines of writing. If you are writing much more than that, you almost
certainly haven't focused your answer tightly enough.

Look carefully at exactiy what each question wants you to do. For example, if it asks you to 'Explain', then you need to say how or why something happens, not just describe what happens. Many students lose large numbers of marks by not reading the question carefully.

Following each question in the practice paper overleaf, there is an answer that might get a C or D grade, followed by an examiner's comments. Then there is an answer that might get an A or B grade, again followed by an examiner's comments. You might like to try answering the questions yourself first, before looking at these.

Notice that there are sometimes more ticks on the students' answers than the number of marks awarded. This could be because you need two correct responses for one mark (e.g.QI (a) (I))or because there are more potential mark points than the total number of marks available (e.g. QI (a) (U)). Even if you get four or five ticks for a three-mark question, you can't get more than the maximum three marks.

1 In an experiment investigating the effect of one variable on another, the independent variable is the one that you change and the dependent variable is the one that you measure. All other variables should be controlled (kept constant).








 2 The range of the independent variable is the spread from lowest to highest value. The interval is the distance between each value in the range.

 3 Temperature can be kept constant or varied using a water bath. pH can be kept constant or varied using buffer solutions.

 4 The accuracy of a measurement is how true it is. For example, an accurate measuring cylinder reads exactly 50 cm3  when it contains 50 cm³ of liquid.c

 5 The precision of a measuring instrument is how consistent it is in giving exactly the same reading for the same value.

 6 The reliability of a set of measurements is the degree of trust that you can have in them. A reliable set of measurements are likely to be very similar if you are able to do the same experiment again. If you are concerned about reliability, then do at least three repeat measurements for each value of your
independent variable, and calculate a mean.

 7 In general, the error in any measurement is half the value of the smallest division on the scale. For
example, on a measuring cylinder marked in 2 cm³ divisions, the error in any reading will be ± 1cm³. If you are taking two readings and calculating the diff erence between them, then the error is ± 1 cm³ for each reading, making a total error of ± 2 cm³.

8 Results tables should be constructed with the independent variable in the first column and the
readings for the dependent variable(s) in the next column(s). Units go in the headings, not in the body
of the table. Each value should be recorded to the same number of decimal places. This is also the case for any calculated values.

 9 In a line graph, the independent variable goes on the x-axis and the dependent variable on the y-axis. Headings must include units. Scales must go up in even and sensible steps. Points should be plotted as small crosses or as encircled dots. Lines should be best fit or ruled between successive points. Do not extrapolate.

10 Bar charts are drawn when there is a discontinuous variable on the x-axis. Bars do not touch.

11 Frequency diagrams or histograms are drawn when there is a continuous variable on the x-axis. Bars touch.

12 Conclusions should be short and to the point. They should use the results to answer the question posed by the investigation. They should not go beyond what is shown by the results. Do not confuse
conclusion with discussion.

13 When describing data displayed on a graph, begin by stating the general trend and then describe any points at which the gradient of the curve changes. Quote figures from the x-axis and y-axis coordinates for these points. Do not use language suggesting time (e.g. ‘faster’) if time is not shown on the x-axis or y-axis.

14 Show every small step whenever you are asked to do a calculation.

15 Do not confuse mistakes with experimental errors. Mistakes should not happen. Experimental
errors are often unavoidable, unless you have the opportunity to use a better technique or better
apparatus. Systematic errors are those which have the same magnitude and direction throughout the
experiment, and are usually caused by limitations in the measuring instruments. Random errors are
those which vary in magnitude and direction during the experiment, and may be caused by difficulty
in controlling variables or in making judgements. When asked to suggest improvements in an experiment, concentrate on the main sources of error and suggest ways of reducing them.

16 When making drawings from a microscope, a low-power plan should show only the outlines of
tissues and no individual cells. Be prepared to go up to high power to get more information about where one tissue ends and another begins. High-power drawings should show as much detail as possible, including details of individual cells.


An investigation   is carried   out  into  the  effect  of substrate   concentration    on  the  activity   of catalase.  What   could  be the dependent    variable?
A   the  concentration    of catalase
B   the  pH  of the  enzyme   solution
C   the  rate  of production     of oxygen
D   the  temperature     of the  substrate
     iii no. of squares of graph paper covered by lignifi ed tissue in root counted; [1]
 
     iv no. of squares of graph paper covered by whole root section counted; [1]

     v % squares occupied by lignifi ed tissue in root calculated correctly from student’s
answers to iii and iv; (answer should be around 1%) [1]

   vi no. of squares covered by lignifi ed tissue in stem counted;
        no. of squares covered by whole stem counted;
         % squares occupied by lignifi ed tissue in stem calculated correctly; (answer should
be around 1%) [3]

   vii stem needs more support than root;
         because upright in air and needs support to prevent it falling over / collapsing; AW [2]

   viii roots subjected to tugging/pulling pressure from parts above ground;
        roots spread out, so like a series of guy ropes;
        stem a single column;
        greater strength from a ring of rods than from one central rod;
       ring of rods provides greater resistance to compression from above than a single central rod;
       accept any reasonable suggestion(s) which are based on diff erent stresses to which roots and
      stems are subjected. [max.2]

5 a i ‘Temperature / °C’ on x-axis and ‘Enzyme activity / mean number of carbon dioxide
bubbles released per minute’ on y-axis;
      suitable scales on both axes – range from 10 or 15 to 40 on x-axis and 0 or 5 to 20 on
y-axis, in intervals of 2 or 5;
      all points plotted accurately, using crosses or encircled dots;
      thin, clear, best-fi t line drawn or points joined with ruled lines – no extrapolation; [4]

       ii correct reading from graph, including unit (mean number of bubbles per minute); [1]

      iii accuracy: use water bath to change independent variable;
          control of signifi cant named variable plus method of control (e.g. use same type of yeast);
          use named apparatus (e.g. gas syringe) to collect gas (for measurement of dependent
variable);
        reliability: increase number/range of temperatures;
        repeat each temperature three times and calculate mean; [max. 3]

b hypothesis is supported;
   quote figures for change in mean number of bubbles between any two temperatures between
15 °C and 40 °C;
    reference to no data below 15 °C or above 40 °C;
    so cannot tell if hypothesis is also supported outside this range; [max. 2]

6 a x-axis is ‘Time / minutes’, y-axis is ‘Number of individuals’;
       scales on both axes with suitable range and interval;
       all bars plotted accurately or points plotted accurately (using a cross or an encircled dot);
       all lines neat and thin, plus key; [4]
 b on both days, minimum time taken is 35 min and maximum time taken is 55 min;
     on both days, number of individuals is greatest near the centre of the range;
     on day 1, greatest number of individuals take 45 minutes to digest starch, but on day 2 greatest number of individuals take 10 minutes to digest starch;
      mean time is greater on day 1 than on day 2; [max. 3]

c temperature may have been higher on day 2;
   animals on day 2 may have eaten recently and so had more saliva/amylase in their mouths; [max. 1]

d use individuals of same age/mass/body weight;
   ensure pre-treatment is the same (e.g. food given, environment);
   use same volume of saliva;
    use same volume and concentration of starch;
     keep temperature the same by using a water bath; [max. 3]

One of the questions in the exam is likely to involve drawing a specimen on a slide, using a microscope, or drawing from a photomicrograph (a photograph taking through a microscope).









Making decisions about what to draw

You might have to decide which part of a micrograph to draw. For example, there might be a micrograph of a leaf epidermis, and you are asked to draw two guard cells and four epidermal cells. It is really important that you do exactly as you are asked and choose an appropriate part of the micrograph.

Producing a good drawing

It is very important that you draw what you can see, not what you think you ought to see. Forexample, during your AS course you may have drawn a TS of a stem where the vascular bundles were arranged in a particular way, or were a particular shape. In the exam, you could be asked to draw a completely different type of vascular bundle that you have never seen before. Look very carefully and draw what you can see.

Your drawing should:

• be large and drawn using a sharp pencil (preferably HB, which can be easily erased if necessary) with no shading, using single, clear lines;
• show the structure or structures in the correct proportions. The examiners will check that the overall shape and proportions of your drawing match those of the specimen. Don't worry - you don't need to be a wonderful artist - a simple, clear drawing is all that is required;
• show only the outlines of tissues if you are asked to draw a low power plan (LPP). A LPP should not show any individual cells.


However, if you are using a microscope, you may need to go up to high power to check exactly where the edges of the tissues are.


You may be asked to label your drawing. In that case:
• use a pencil to draw label lines to the appropriate structure using a ruler, ensuring that the end of the label line actually touches the structure you are labelling;
• make sure that none of your label lines cross each other;
• write the actual labels horizontally;
• write the actual labels outside the drawing itself.

Tips

During your course:

• Make sure you are familiar with the appearance of all of the structures listed in the syllabus that you could be asked about on the practical paper. You need to know the names and distribution of the tissues. Look in particular at the learning outcomes marked with [PA] at the beginning.
• Practise drawing specimens from micrographs, getting used to using your own eyes to see what is really there, rather than what you think ought to be there;
• Practise using an eyepiece graticule to help you work out the relative proportions of different pares that you are drawing.
• Take every opportunity to practise drawing specimens from micrographs or microscope slides, and either mark them yourself using a ClE-style mark scheme, or get your teacher to mark them for you. Find out what you need to do to improve, and keep working at it until you feel really confident.

In the exam:

• Take one or two sharp HB pencils, a pencil sharpener, a clean ruler that measures in mm and a good eraser.
• Settle down and take time to get your drawing of the specimen right.
• Use your eyes first, then your memory.

Calculating magnification or size 

The use of a stage micrometer and eyepiece graticule is described on the post #3.
You might be asked to do this on Paper 3.
You could also be given the magnification of an image, and asked to calculate the real size of something in the image. Below is an example of the kind of thing you might be asked to do.
This micrograph shows some cells from a moss. Notice that the magnification is given.


Let us say you are asked to find the mean width of a cell from the tissue in the micrograph. There are several steps you need to work through here.

First, decide how many cells you are going to measure. It is generally sensible to measure a randomly selected sample of 5 to 10cells.

Next, decide which ones you will measure. Choose cells where you can see the edges as clearly as possible, and where you can see the whole cell. If cells are evenly distributed, it is best to measure the total width of five cells in a row. That means you have to make fewer measurements, do fewer calculations and - better still - it reduces the size of the uncertainty in your measurements. However, if cells are irregularly shaped or distributed, you should measure each one individually.

Once you have decided which five cells to measure, mark this clearly on the micrograph. It doesn't matter exactly how you do this - perhaps you could carefully use a ruler to draw a line across the five cells, beginning and ending exactly at the first edge of the first cell, and the last edge of the fifth cell.

Now measure the length of the line in mm and write it down.

Next, calculate the mean length of one cell. Show clearly how you did this.

Next, convert this length in mm to a length in 11m. (Alternatively, you could do this right at the end of the calculation.)

Next, use the magnification you have been given to convert this mean length of the image to a mean real length.

Here is what your answer might look like:


Making comparisons

You may be asked to compare the appearance of two biological specimens or structures. You could be observing these using the naked eye or a lens, or using a microscope, or you could be looking at two micrographs.

The best way to set out a comparison is to use a table. It will generally have three columns, one for the feature to be compared, and then one for each of the specimens.

For example, you might be asked to observe two leaves and record the differences between them. Your table and the first three differences might look like this:


Notice:

• The table has been drawn with ruled lines separating the columns and rows.
• The descriptions of a particular feature for each specimen are opposite one another (that is, they are in the same row) .
• Each description says something positive. For example, in the first row, it would not be good to write 'not toothed' for Leaf A, as that does not tell us anything positive about the leaf margin.

Note that the practical examination is likely to ask you to describe or compare observable features, not functions. Do not waste time describing functions when this is not asked for.