Practicals Flashcards
Mitotic Index =
Number of cells in mitosis ÷ Total number of cells in field of view
1 mark
Why did he put the plant root in HCl?
To hydrolyse the cell wall
2 marks
State 2 precautions required when working with hydrochloric acid
- Wear goggles
- Wear gloves
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
2 marks
Describe two precautions the student should take when clearing away after the dissection.
- Carrysharp instruments by pointing away from body
- Disinfect instruments/surfaces
- Wash hands with soap and water
- Put organ/gloves/paper towels in a separate bin bag to dispose
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
3 marks
The scientists used the following null hypothesis.
‘The proportion of plants that produce 2n gametes will not change from one breeding
cycle to the next.’
The scientists tested their null hypothesis using the chi-squared statistical test. After 1 cycle their calculated chi-squared value was 350. The critical value at P=0.05 is 3.841. What does this result suggest about the difference between the observed and expected results and what can the scientists therefore conclude?
- There is a less than 0.05/5% probability that the differences occurred by chance
- Calculated value is greater than critical value so the null hypothesis can be rejected
- The proportion of plants that produce 2n gametes does change from one breeding cycle to the next
4 marks
A student used chromatography to separate the different photosynthetic pigments in a chlorophyll solution. She had the following materials.
Chromatography paper
A ruler and pencil
Suitable glassware
A solvent (solvent A)
2 cm3 of the chlorophyll solution
Describe how she could use these materials to separate the photosynthetic pigments by chromatography.
- Draw line on chromatography paper using ruler and pencil
- Use pipette to add chlorophyll/solution to origin line
- Add solvent below line
- Remove from glassware before solvent reaches end of chromatography paper
Using solvent A, the student separated five pigments. She then repeated her method using a different solvent, B. Using solvent B, she separated six pigments.
Explain the difference between these results.
one pigment is only soluble in solvent B
1 mark
Explain why a log scale is used to record the number of cells.
Large range
1 mark
Explain why the student marked the origin using a pencil rather than using ink.
Ink and pigment would mix
2 marks
Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin.
- Level of solvent below origin line
- Remove before solvent reached top
1 mark
The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.
Absorb different wavelengths for photosynthesis
2 marks
Apart from temperature and pH, give two variables the scientist would have controlled when preparing the liquid medium cultures.
- Volume of stock bacteria culture
- Concentration of stock bacteria culture
- Concentration of glucose
- Volume of ammonium chloride
- Time bacteria/culture left to divide
- Concentration/volume of oxygen
- Concentration/volume of nitrogen
5 marks
Explain what limits the size of populations in a climax community.
1.nutrient availability such as nitrogen, phosphorus
2.numbers ofproducers (plants, algae)providingenergyfor a food chain /lightintensity affecting the rate ofphotosynthesis
3.diseasekillingweaker members of species
4.space for nest building / niches
5.competition for a named limited resource- food, space, water, or mates
4 marks
The shore crab has recently spread to, and has established large populations in, the coastal waters of the USA, where it is not a native species. Explain how the shore crab has been able to establish large populations and why this is causing concern to ecologists in the USA
- Shore crab rapidly colonises (rapid growth)
- Ability to live different environments
- Shore crab better comptitor/more aggressive
- Decreased population of prey species
- Ecosystem less stable
2 marks
With some samples, the scientists decided they needed to carry out a series of dilutions of the sample before counting the bacteria. Explain why dilutions were necessary for some samples but not for others.
log scale graph
- Log scale on graph shows big range in number of bacteria
- Some samples too many to count (so dilute) but some countable (so don’t dilute)
3 marks
Outline a method the ecologists could have used to determine the plant species richness at one site.
- Use a grid and random number generator to generate coordinates
- Use of quadrat
- Identify plant species in each quadrat/ Count number of different plant species in each quadrat
4 marks
Plantations of trees are often created to remove carbon dioxide from the atmosphere, to help to balance the carbon dioxide released by burning fossil fuels.
For different species of tree, information is available for:
* the relationship between diameter of trunk and freshly cut biomass
* the percentage of water in fresh-cut wood
* the mean dried density of wood.
Suggest how the mass of carbon in the wood of a plantation of trees of a particular species could be estimated.
Start with measuring the diameter of a large number of trees.
Assume that the dry biomass of a tree consists of biological molecules that contain carbon.
- Calculate a mean diameter
- Use this to determine the mean fresh biomass of trees
- Use the percentage water content to find the dried biomass
- Use the dried density to calculate the mass of trees
- Count the number of trees in plantation and multiply by mean carbon content to find total carbon
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 random sample of seeds from each population
- Use large sample to be representative of whole population
- Indication of what size was measured e.g. mass
- Calculate a mean and standard deviation (for each population)
- Use the Student’s t-test
- Analyse whether there is a significant difference between the means of the two populations
2 marks
The values for the biomass of the barley plants are different in each quadrat.
Suggest an explanation for this difference.
1 Quadrats from different parts of field
2 Biotic & abiotic factors different
1 mar
The researchers measured the dry biomass of the barley plants and the barley grain.
What is the advantage of using dry biomass for these measurements?
Water content varies
2 marks
A farmer uses a herbicide which reduced biomass of weeds in field. Explain why would this herbicide give a higher crop yield.
1 Fewer weeds left
2 Fewer weeds to produce seeds
3 Less contamination of crop by weeds
4 Fewer weeds to separate from crop
5 Less competition between crop and weeds
