International A and A2 Biology Paper 3 Guide

…………………………………….CAL BIOLOGY PRACTICAL REVISION…………………………….

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. 1 You are required to investigate how much glucose diffuses from a plant tissue extract through a partially permeable wall of Visking (dialysis) tubing. Fig. 1.1 shows the apparatus you will set up for this investigation.

Proceed as follows: 1. Tie a knot in the Visking tubing as close as possible to one end so that it seals the end. 2. To open the other end, wet the Visking tubing and rub the tubing gently between your fingers. 3. Without mixing P, put some of P into the Visking tubing to the level shown in Fig. 1.1. 4. Rinse the outside of the Visking tubing by dipping it into the water in the container labelled V. 5. Put the Visking tubing into the large test-tube. (a) (i) State the volume of W needed to reach the water level as shown in Fig. 1.1.

volume of W

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cm [1]

6. Put the volume of W, as decided in (a)(i), into the large test-tube. 7. Put the large test-tube with the Visking tubing into a test-tube rack and leave for 20 minutes. 9

…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. During the 20 minutes: • set up a boiling water-bath ready for step 11 • make a serial dilution of 1% solution G which reduces the concentration of G by half between each successive dilution. 3

You will need to make up 20 cm of each concentration of solution G. (ii) Complete Fig. 1.2 to show how you will make four further concentrations of G, starting with the 1% solution, G.

Note: How many times dilution Total volume? Decide on volume if dH2O and stock solutions units • • •

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. 8. Prepare the concentrations of G as decided in (a)(ii) in the containers provided. 9. After 20 minutes, which started at step 7, remove the Visking tubing and put it into the container labelled ‘for waste’.

10. Pour the water from the large test-tube into a container and label it S. 11. Carry out the Benedict’s test on all 6 solutions (five of G and one of S). 3

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You will need to use 2 cm of each of the solutions of G and S with 2 cm of Benedict’s solution. Test each solution separately and record the time taken for the first appearance of any colour change. If there is no colour change after 120 seconds record ‘more than 120’. (iii) Prepare the space below and record your results.

Note: Proper table format Headings with unit No units in body Time recorded as whole number and appropriate unit Correct trend Follow instructions [If there is no colour change • • • •

• •

after 120 seconds record ‘more than 120’]

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. (iv) Complete Fig. 1.3 below to show

• the positions of each of the percentage concentrations of solution G • the letter S to show where the sample fits in the series of concentrations.

(v) A colorimeter could not have been used in this investigation.

Describe three other modifications to this investigation which would improve the confidence in your results.

Note: Area to improve: 1.Independent variable 2.Control variable 3.Dependent variable

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. In a similar investigation, a student investigated how changing the concentration of glucose solution (independent variable) in the Visking tubing affected the quantity of glucose diffusing through the wall into the surrounding solution. After 20 minutes a dye was added to the surrounding solution. This produced different intensities of colour depending on the glucose concentration in the surrounding solution. A colorimeter was used to measure the absorbance of light by the coloured solution. Other variables were considered and kept to a standard. The student’s results are shown in Table 1.1.

(b) (i) Plot a graph of the data shown in Table 1.1.

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. (ii) Explain the difference in the results for the glucose concentration at 10 arbitrary units and at 15 arbitrary units.

(iii) Explain the difference in the gradients of the line between the glucose concentrations of 10 arbitrary units and 25 arbitrary units and between 25 arbitrary units and 30 arbitrary units.

(iv) The student used a measuring cylinder t o measure the volumes of glucose solution. 3 The smallest division on the measuring cylin der scale was 0.2 cm . 3 State the actual error in measuring a volume of 5 cm using this measuring cylinder.

Note: Uncertainty / error = ½ smallest division

5 cm3 ± ......................................... cm3 [1]

[Total: 20]

By Ms.Lena (adapted from ON12/31)

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. Advice on drawing from the mi croscope Here is some advice on drawing low power plan diagrams and high power drawings of cells. Plan Diagram A plan diagram shows the distribution of tissues in a section. It also shows the proportions of the different tissues. Although called a low power plan diagram you may use high power to identify the different tissues and to be sure you are putting the boundaries of those tissues in the right place. You do not draw any cells in a lower power plan diagram. When you make a plan diagram, follow these simple rules: •

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make the drawing fill most of the space provided; leave space around the drawing for labels and annotations (if required by the question) use a sharp HB pencil (never use a pen) use thin, single, unbroken lines (often called ‘clear and continuous lines’) show the outlines of the tissues make the proportions of tissues in the diagram the same as in t he section do not include drawings of cells do not use any shading or colouring

Add labels and annotations (notes) to your drawing only if you are asked for these in the question. Use a pencil and a ruler to draw straight lines from the drawing to your labels and notes . Write labels and notes in pencil in case you make a mistake and need to change them. You may leave your labels and notes in pencil – do not write over them in ink. High Power Drawings High power drawings should show a small number of cells and they should be drawn a reasonable size so you can show any detail inside them. When you make a high power drawing, follow these simple rules: •

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make the drawing fill most of the space provided; leave space around the drawing for labels and annotations (if required by the question) use a sharp HB pencil (never use a pen) use clear, continuous lines (see above) draw only what is asked in the question, e.g. three cell types or one named cell and all cells adjoining it show the outlines of the cells the proportions of cells in t he drawing must be the same as in the section you are drawing plant cell walls should be shown as double lines with a middle lamella between the cells; the proportions of cell walls should be drawn c arefully. show any details of the contents of cells – draw what you see not what you know should be present do not use any shading or colouring

By Ms.Ko Soo San

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. It is important when making a biological drawing that the following points are carefully noted: (i) Make sure that the relationships and proportions of the parts are correct. You may have to enlarge what is being observed, for example when drawing from a microscope, or reduce the size if the specimen is very large. (ii) In all cases get into the habit of drawing large diagrams. The actual size will of course depend on the size of the page and how much room has to be left for labels and notes around the diagram. (iii) Always use a sharp HB pencil, which produces clear lines which are easy to erase if mistakes are made. Draw firm continuous lines, not scratchy lines. (iv) A method which helps to ensure that the proportions are correct is to draw a box of a suitable size and divide it into equal squares, four if the specimen is radially symmetrical, or six squares if it is elongated. (v) Take each square in turn and draw light marks as guides to accurate shapes and proportions. Then draw in the outlines and finally complete the details. STEPS for a biological drawing Step 1: Draw light marks to give an idea of inner and outer boundaries Step 2: Draw proper lines for inner and outer boundaries. Step 3: Draw the epidermis and cambium Step 4: Complete by filling in the remaining structures.

Step 2

Step 1

Step 3

Step 4

LABELLING Labelling a biological drawing ensures that you are able to recognise specific structures and helps you to remember what they look like. • •

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The labels should be connected to the drawing by leader lines. These lines should be parallel wherever possible to the top edge of the page and should not cross one another so that there is no confusion regarding what structure the label refers to. The point to which the label refers should NOT have an arrowhead or a large dot at the end of the leader line

By Ms.Ko Soo San

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XYLEM

EPIDERMIS

CAMBIUM

PHLOEM

PITH

PITH CAVITY

ANNOTATION Annotating means that you include short explanatory notes in brackets below the labels on the biological drawing. In an examination, these should only be included when requested to do so. Otherwise you should always annotate whenever you draw and label. Annotating helps you to highlight the biological significance of the structures, especially regarding their functions.

Xylem (Large lumen; Stained in red, Thick wall)

Sclerenchyma (Stained in red, small cells with thick wall)

Cambium Phloem (green cells)

Pith

Pith cavity By Ms.Ko Soo San

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Practical drawing skills: PLAN DRAWINGS tutorials Clean single lines Proportions to scale Layers of tissue identified Shape appropriate

Make a low power, plan drawing

By Mr. Balachandran

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By Mr. Balachandran

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Practical drawing skills: DETAILED DRAWINGS tutorials Clean single lines No shading Select appropriate cells No more than 3 cells necessary (READ & REFER to actual exam Q) Proportions to scale Based on the micrographs given, prepare a detailed labelled diagram of the cells. ONION CELL

X400 magnification Elodea

LEAF CELL

POTATO CELLS

X400

By Mr. Vilas

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. MAMMALIAN CHEEK CELLS

X400 CILIATED EPITHELIAL CELLS

X400 BLOOD CELLS

X400

By Mr. Vilas

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Practical drawing skills: COMPARE & CONTRAST tutorial Similarities and Differences Suitable table of comparison Check: Shape, Size, numbers, structures

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. SAMPLE QUESTIONs

2 J1 is a slide of a transverse section through a plant. (a) (i) Describe one observable feature on J1 which identifies this specimen as a root.

(ii) Draw a large plan diagram of the whole specimen on J1.

On your diagram, use a label line and label to show the cortex.

Fig 2.1: Specimen on J1

http://flickrhivemind.net/Tags/bio185/Interesting

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. (iii) Make a large drawing of one group of four complete touching xylem vessels as observed on the specimen on J1. On your drawing, use a label line and label to show one lumen. Annotate your drawing with one observable feature.

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. Fig. 2.1 shows a diagram of a stage micrometer scale that is being used to calibrate an eyepiece graticule. One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines. The length of one division on this stage micrometer is 0.1 mm.

(b) (i) Using this stage micrometer, where one division is 0.1 mm, calculate the actual length of one eyepiece graticule unit using Fig. 2.1 by completing Fig. 2.2.

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. Fig. 2.3 is a photomicrograph showing part of an organ from a plant of a different species.

Use the calibration of the eyepiece graticule unit from (b)(i) and Fig. 2.3 to calculate the actual length of the plant tissue from X to Y. You will lose marks if you do not show all the steps in your calculation and do not use the appropriate units.

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…………………………………….CAL BIOLOGY PRACTICAL REVISION……………………………. (c) Prepare the space below so that it is suitable for you to record observable differences between the specimen on slide J1 and in Fig. 2.3, to include: • the vascular tissue • at least two other tissues.

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International A and A2 Biology Paper 3 Guide

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