Practicals Flashcards
3 marks
A student did an investigation. He did not have a colorimeter.
Describe a method this student could use to prepare colour standards and use them to give data for the total pigment extracted.
- Use known concentration of pigment
- Prepare dilution series
- Compare results with colour standards to give concentration
5 marks
An environmental scientist investigated a possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees.
- Use a random sample of seeds from each population
- Use large enough sample to be representative of whole population
- Indication of what size was measured e.g. mass
- Calculate and mean and SD for each population
- Use the students t-test
- Analyse whether there is a significant difference between the means of the 2 populations
5 marks
The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The sundew can trap and digest insects.
Describe how you could estimate the size of a population of sundews in a small marsh.
- Use a grid
- Use random number generator to obtain random coordinates
- Count number/ frequency in each quadrat
- Large sample (repeat 30 times) and calculate mean
- (Mean number of plants per qudrat/ area of marsh) x number of quadrats in the marsh
3 marks
Describe how the scientists could use aseptic techniques to transfer 0.3 cm3 of C. difficile in liquid culture from a bottle onto an agar plate
- Wash hands with soap/ Disinfect surfaces
- Use sterile pipette to transfer bacteria
- Remove bottle lid and flame neck of bottle
- Lift lid of agar plate at an angle
- Work close to upward air movement
- Use sterile spreader
- Place pipette into disinfectant immediately after use
3 marks
Describe the aseptic techniques that would be used when flooding the agar plate with bacteria.
- Sterilisation of equipment
- Use of pipette to transfer culture suspension to plate
- Use of spreader
2 marks
One way of testing the effectiveness of antibiotics is to use discs of paper soaked in antibiotic. These are placed in the centre of an agar plate covered by bacteria. A clear zone forms around the disc if the antibiotic is effective. Give two reasons why it would be important to use sterile techniques during this investigation.
- To prevent contamination of apparatus with other microorganisms / bacteria
- To prevent personal contact with bacteria
- To prevent release of bacteria into air
1 mark
The antibiotic reached the bacteria by diffusion. Suggest why an effective antibiotic may produce only a small clear zone.
Diffuses slowly
2 marks
Give two factors, other than cost, that should be considered when selecting an antibiotic to treat a bacterial disease
- Side effects / allergic reactions
- Interaction with other drugs
- Should only act on the problem bacteria
- How much resistance the bacteria have built up
2 marks
The minimum inhibitory concentration (MIC) is the lowest concentration of a substance that prevents the growth of a microorganism. When antibiotics are prescribed for treating patients, higher doses than the MIC are recommended. Suggest two reasons why
- May not all be absorbed
- May be broken down quickly
- To kill the microorganisms / bacteria
- Reference to antibiotic resistance
3 marks
A bacterial infection that cannot be treated with one sort of penicillin can be treated with a
different sort. Use your knowledge of enzyme action to explain why the different sort of penicillin is effective in treating the infection.
- Different penicillin has different tertiary structure / active site has specific tertiary structure
- No longer binds to active site / not complementary to active site / does not form E-S complex
- Different) penicillin not broken down
2 marks
Farmers often keep large numbers of cattle together. Farmers used to give cattle food which had antibiotics added to it. Suggest how adding antibiotics to the food of the cattle increased profit for the farmers.
- Kills pathogenic / harmful bacteria
- Disease less likely / improves health / animals healthier
- Faster growth / more productive animals / more food converted to meat/ increased yield
2 marks
Adding antibiotics to the food of cattle is now banned in many countries. Use your knowledge of selection to explain why adding antibiotics was banned.
- Adding antibiotics selects in favour of antibiotic resistance / resistant bacteria more likely to survive
- Increase in numbers / higher proportion of resistant bacteria
