National 5 Biology Lab Skills for SQA Assessment

Uncorrected Sample Pages

National 5

Biology Lab Skills for SQA assessment

Billy Dickson & Graham Moffat

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Contents

How to use this book

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Biology practicals 1 Estimating plant cell size – Calculating the average length of an onion epidermal cell

1

2 Osmosis – Measuring the concentration of cell sap in potato tissue

4

3 Measuring enzyme activity 1 – Comparing catalase activity in different tissues

8

4 Measuring enzyme activity 2 – Effect of temperature on the activity of diastase

13

5 Using a respirometer – Measuring the effect of temperature on the rate of respiration in germinating pea seeds

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6

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Reaction time – Effect of practice on reaction time

7 Potometer – Effect of surface area on transpiration rate from geranium leaves

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8 Using a transect line – Measuring changes in the abiotic factors light intensity and soil moisture in a habitat

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9 Sampling with quadrats and pitfall traps – Measuring the distribution of daisy plants and invertebrates along a transect line

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10 Measuring the rate of photosynthesis – Effect of light intensity on the rate of photosynthesis in Cabomba 37 Appendices Appendix 1

Table of reaction times

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Appendix 2

Paired statement key

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Appendix 3

Notes for teachers

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Appendix 4

Assignment planning grid

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Answers

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Check your understanding and Exam-style questions For each experiment, there are questions designed to check your understanding of the work you’ve just completed. There is also an exam-style question to help you prepare for exam questions based on experimental and scientific inquiry skills. Skills questions in your exam are worth about 30% of the overall mark.

Assignment support Your assignment is worth 20% of your grade for National 5 Biology. For your assignment you will have to carry out an experiment and collect your own results data. You could consider using a technique from one of the experiments in this book. You will also need to find related data by research. It is worth considering if any of the data published here in the exam-style questions might be usable. Your teacher will be able to help you make decisions about assignment topics and methods. Make sure your teacher is happy with what you decide to do.

The table below shows a checklist of sections in an assignment report, with descriptions of how marks might be gained. There is a grid in Appendix 4 which could be used to plan an assignment based on this checklist.

Section

Description

Marks

Title

The report has an informative title.

1

Aim

A description of the purpose of your investigation.

1

A description of the biology relevant to your aim, which shows your understanding.

Underlying biology

You need a minimum of three biology points along with their descriptions or explanations at National 5 level.

3

You must use your own words as much as possible.

A brief description of your experimental/fieldwork method.

Data collection and handling

Graphical presentation

You must show that you can summarise your experimental/fieldwork method and must not give a full description.

1

Sufficient data from your experiment/fieldwork.

1

Data from your experiment/fieldwork presented in a table with headings and units.

1

Values correctly calculated from your experimental/fieldwork data.

1

Data/information from an internet/literature source that you can compare with the data from your experiment/fieldwork.

1

A reference for the internet/literature source.

1

Appropriate type of graph used to present your experimental/fieldwork data.

1

Suitable scales.

1

Suitable labels and units on axes.

1

All data plotted accurately.

Have points which are joined with a line (line graph) or clear bar tops (bar chart).

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Section

Description

Marks

Analysis

Experimental/fieldwork data compared to data/information from internet/literature source.

1

Conclusion

A conclusion relating to your aim, based on data/information in your report.

1

Identification of a factor affecting the reliability, accuracy or precision of your experiment/fieldwork and a related explanation. You must then explain either: Evaluation

• w hat you did or could have done to minimise the effect of this factor; or

2

• how you know this factor had a significant effect.

Structure

A report which can be easily followed.

1

Total

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1 Estimating plant cell size – Calculating the average length of an onion epidermal cell Underlying biology Plant cells have cell walls, which helps make them easily visible using simple microscopes. Coloured stains can be used to improve the visibility of plant cell structures even more. The epidermal tissue from onion is a great source of thin layers of plant cells.

Cell measurements are usually given in micrometres (µm). There are 1000 micrometres (µm) in a millimetre (mm) and 1000 millimetres (mm) in a metre (m).

Learning outcomes • Know and understand that plant cells have a cell wall visible by microscope.

• Process information by converting measurements between millimetres and micrometres.

• Process information by calculating averages.

• Process information by calculating ratios.

• Present information as a line drawing.

Aim To determine the average cell length in onion epidermis.

Apparatus list • dropper and bottle of iodine solution* (1)

• light microscope (1)

• glass microscope slide (1)

• paper towel (1)

• cover slip (1)

• paper tissue (supply)

• forceps or mounted needle (1)

• safety glasses (pair each)

• thin sample of fresh onion epidermis cut for you (1)

Safety notes • Iodine is harmful to the skin and eyes – use carefully and wear eye protection. Wash any spills with plenty of water.

Precautions • Try to have your onion epidermis flat against the slide – folds make observation more difficult.

• Try to lower the coverslip carefully to avoid air bubbles – forceps or a mounted needle should help.

Method 1. Set up your microscope according to your teacher’s instructions.

2. Adjust the magnification to low power – ×40.

3. Have the objective lens as far from the stage as possible.

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4. Place a clear plastic ruler onto the stage and focus on the scale.

5. Increase the magnification to ×100 and estimate the diameter of the field of view in millimetres using the ruler. Multiply your answer by 1000 to convert your estimate into micrometres. Record you result in the section below.

6. Place your microscope slide onto a paper towel and add a drop of iodine onto the middle of the slide.

7. Use forceps to add a small piece of onion epidermis to the stain and try to flatten it out.

8. Use the forceps to gently lower a cover slip.

9. Use a tissue to soak up any excess stain.

10. Observe your slide at ×100.

11. Swivel the slide on the stage so that the cells are lined up across the field of view, as shown in the diagram in the exam-style question below.

Record your results 1. Add the field of view details to the boxes below.

2. Draw some of the cells you can see in the field of view.

3. Count the number of cells which can be seen across the diameter of the field of view.

4. Calculate the average width of one cell in the spaces below.

Figure 1.1 Field of view = ....... µm at a magnification of × .......

Diameter of the field of view at ×100

=

Number of cells across the field of view at ×100

=

Average width of one onion cell

= ………………… micrometres

Check your understanding 1. Explain why it’s important to make a flat preparation of onion epidermis.

[1]

………………………………………………………………………………………………………………

2. Explain why it’s useful to stain onion epidermis before viewing under a microscope.

[1]

………………………………………………………………………………………………………………

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3. Express the following sizes in micrometres.

[3]

a. 5 mm ………………… µm b. 0·5 mm ………………… µm c. 0·05 mm ………………… µm

Exam-style question a. The diagram below shows the field of view of a microscope with some stained onion epidermal cells.

Field of view = 1·2 mm at ×100 magnification = 12 µm Figure 1.2

i. Calculate the average estimated length and height in μm of one onion epidermal cell.

Length: ………………… µm

Height: ………………… µm ii. Calculate the ratio of average cell length to average cell height in this example.

[2]

[1]

………………… length : ………………… height

b. The diameter of a human red blood cell was estimated at 0·008 millimetres.

Convert this value from millimetres into micrometres.

………………… μm

[1]

c. Describe how a student could estimate the diameter of a human cheek cell.

[4]

…………………………………………………………………………………………………………. .

…………………………………………………………………………………………………………. .

…………………………………………………………………………………………………………. .

…………………………………………………………………………………………………………. .

Assignment support You could use this technique to generate data for your assignment.

You could investigate if the size of an onion epidermal cell depends on the variety, size or age of the onion. The oldest epidermal cells of an onion are in the outermost layers of epidermis.

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Answers 1 Estimating plant cell size

Exam-style question

Check your understanding 1. So that cells don’t cover each other and are easier to observe [1] 2. To make the cells more easily visible/easier to count [1] 3. a. 5000 µm [1] b. 500 µm [1] c. 50 µm [1] Exam-style question a. i. Length = 300 µm Height = 120 µm ii. 5 : 2 b. 8·0 µm c. Measure the field of view (in micrometres) at ×100 Make a stained cheek cell slide Estimate how many cells can be seen across the field of view at ×100 Divide the field diameter by the number of cells

[1] [1] [1] [1] [1] [1]

a. Scales and labels with units [1] Accurate plots connected by straight lines [1] b. As the temperature increased up to 40°C the rate of reaction increased [1] But as the temperature increased above 40°C the rate of reaction decreased [1] c. Same set up but change pH in each tube (using buffers/ acid and alkali) [1] Keep temperature constant [1]

4 Measuring enzyme activity 2 Check your understanding

2 Osmosis

1. As temperature increases the activity of diastase increases then deceases [1] 2. Number of grains added to each dish Concentration of starch in agar Mass of agar in each dish Time left [any 3, 1 mark each] 3. Extent to which grains are pushed into the agar [1] Make a mash of grains and add to a well in the agar [1]

Check your understanding

Exam-style question

1. The lower the water concentration, the more the tissue loses weight/water by osmosis [1] 2. Shape of potato tissue Volume of solution used Temperature Time in solutions [any 3, 1 each] 3. Repeat the experiment (and find average of weight changes) [1]

a. Scale and labels including units [1] Accurate plots joined by straight lines [1] b. As the pH increases from 5 to 7 the activity of diastase increases [1] But as pH rises further to pH 10 the activity of diastase decreases [1] c. Repeat the experimental procedure (and take average of the diameters) [1]

Exam-style question

5 Using a respirometer

a.

b. c.

Check your understanding

[1] [1]

−0·21 [1] −10% [1] Starting masses of tissue not the same [1] A solution which gave no change in mass would be equal in concentration to the tissue; 5% gives an increase and 10% gives a decrease so somewhere in between is equal.

[2]

3 Measuring enzyme activity 1 Check your understanding 1. Different plant tissues have different concentrations/ amounts of catalase [1] 2. Temperature Mass of tissue Time for reaction Volume/concentration of hydrogen peroxide [any 3, 1 each] 3. Masses of tissue slices could be different [1] Weigh to determine mass [1] OR Bubbles of oxygen foam might burst [1] Collect gas in a separate tube/use detergent to make the foam bubbles stronger [1]

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1. As temperature increases, the rate of oxygen uptake increases [1] 2. Mass/number of seeds Width of the respirometer arm Age of germinating peas as extra options Volume of air in tube at start Time for respiration [any 3, 1 each] 3. Temperature of the respirometer may physically affect the volume of gases within [1] Ensure enough time is allowed for gases to come to temperature before stopper is added [1] Exam-style question a. 1·3 mm per minute b. Increasing temperature increases the rate of respiration in pea seeds OR Dead peas do not respire c. High temperature denatures enzymes Respiration is an enzyme-controlled process d. Control allows comparison with experiment To show that it is the peas which use up the oxygen in the respirometer

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[1]

[1] [1] [1] [1] [1]

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