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AQA GCSE

(9–1) Biology

Required Practicals Lab Book

Emily Quinn


Contents

How to use this book

iv

Biology practicals 4.1.1.5

Microscopy

1

4.1.1.6

Microbiology

5

4.1.3.2

Osmosis

9

4.2.2.1

Enzymes

13

4.2.2.2

Food tests

16

4.4.1.2

Photosynthesis

19

4.5.2.1

Reaction time

23

4.5.4.1

Plant responses

28

4.7.2.1

Field investigations

32

4.7.2.3

Decay

37

Answers

41


4.1.1.6

Microbiology

For hospitals, choosing the right antiseptics or antibiotics to achieve the appropriate hygiene levels is essential. The correct dilution is also important: a concentration high enough to work, but not so high as to be wasteful. You will investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition. The most effective antiseptic or antibiotic will prevent the growth of bacterial. Learning outcomes

Maths skills required

Formulae

 Investigate the effects of antiseptics.

 Measure diameters accurately.

 Calculate cross-sectional areas of colonies or clear areas around colonies using

 Calculate the area of your zone of inhibition.

area = πr ² where r = half of the mean diameter.

 Suggest improvements to methods to reduce the growth of bacteria. Apparatus list  one agar plate of bacterial cultures, readymade and NOT incubated (Bacillus subtilis, Escherichia coli, or Micrococcus luteus)

 chromatography paper discs cut with a hole punch  beaker of disinfectant  five different antiseptic solutions

 five pairs of sterile forceps

 eye protection

 adhesive tape Safety notes

 After you have incubated your plates, make sure they have extra sticky tape around the edge. You do not want any of these bacteria escaping!  If you are using ethanol to sterilise to equipment, make sure it is kept well away from any naked flames. Ethanol is very flammable and will catch fire.  DISINFECTION: You are dealing with bacteria. Disinfection is VERY important!  All equipment and materials and work surfaces must be disinfected using excess 1% Virkon for at least 10 minutes.  Always wear eye protection when using Virkon solution.  Wash your hands both before and after this practical. Common mistakes  Be careful not to rush your work. While it is important to work quickly in order to minimise contamination, you need to be methodical and careful in your work.  Make sure you don’t put tape all the way around your closed agar plate. Condensation in the plate needs to be able to escape and oxygen needs to get in.  Clear zones might not be perfectly circular. To get an accurate diameter, measure the diameter twice (at 90° to each other) and calculate a mean diameter for each clear zone.

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Methods Read these instructions carefully before you start work. Activity 1 – Preparation of sample 1.

Wash your hands or wear gloves.

2.

On the underside of the agar plate, use a marker pen to divide the plate into five equal sections.

3.

Using sterile forceps, dip one paper disc into each of the antiseptic solutions and allow excess antiseptic to drain off. (Use a separate pair of forceps for each paper disc.) Place the disc carefully onto the respective section on the unsealed agar plate containing the bacteria, as shown in Figure 1.

4.

Place the used forceps into the beaker of disinfectant.

5.

Seal the plate with tape, ensuring there is a gap so that oxygen can enter and condensation can escape.

6.

Place the plate upside down and incubate for three or four days below 25 °C.

7.

Place any used equipment in the beaker of disinfectant.

Figure 1

Activity 2 – Analysis of sample 1.

Remove your agar plate from where it has been incubating and seal around the edge with extra adhesive tape.

2.

Measure the diameter of the clear zone around each disc by placing the ruler across the centre of the disc. Record the measurement in the Measurement 1 column of Table 1.

3.

Measure again at 90° to the first measurement and record the measurement in the Measurement 2 column of Table 1.

4.

Calculate the mean diameter. Record this in the final column of Table 1.

Record your results Table 1 – Diameter of clear zones Diameter of clear zone (mm)

Type of antiseptic Measurement 1

AQA GCSE (9–1) Biology Required Practicals Lab Book

Measurement 2

6

Mean

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Check your understanding 1. Observe your agar plate. a. Which of your samples inhibited the growth of bacterial colonies the most, and which inhibited the growth of bacterial colonies the least?

[2 marks]

Sample that inhibited growth the most: ........................................................................................ Sample that inhibited growth the least: ........................................................................................ b. Which of these samples would be most effective as an antiseptic?

[1 mark]

........................................................................................................................................................... 2. Calculate the cross-sectional area of your clear areas around colonies. Use

area = πr²

[1 mark]

where r = half of the mean diameter

Give your answer in mm2. ...........................................................................................................................................................

Exam-style questions 1. Four antiseptics were compared for their effectiveness in inhibiting antibacterial growth. The results are shown in Figure 2. Figure 2

a. Identify the independent and dependent variables in this experiment.

[2 marks]

Independent variable: .................................................................................................................. Dependent variable: ....................................................................................................................

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b. One variable that needs to be controlled during this experiment is the temperature. State the temperature at which agar plates in schools should be incubated.

[1 mark]

........................................................................................................................................................... c. Suggest another variable that should be controlled during this experiment.

[1 mark]

........................................................................................................................................................... d. Compare the effectiveness of these different antiseptics.

[3 marks]

........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ...........................................................................................................................................................

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