Practical Work & How Science Works Flashcards
Covers required practicals 7 - 12, which can appear on paper 2 and paper 3. Also contains questions relating to other experiments and typical 'how science works' questions.
RP7 Chromatography
Explain why the student marked the origin using a pencil rather than using ink.
Ink and (leaf) pigments would mix
OR
(With ink) origin/line in different position
OR
(With pencil) origin/line in same position
OR
(With pencil) origin/line still visible;
RP7 Chromatography
Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin (2 marks).
- Level of solvent below origin/line;
- Remove/stop before (solvent) reaches top/end;
RP7 Chromatography
The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.
(Absorb) different/more wavelengths (of light) for photosynthesis;
Accept light-dependent reaction /photophosphorylation /photoionisation for photosynthesis.
RP7 Chromatography
What two key factors determine the distance travelled by the photosynthetic pigments on the chromatography paper?
Solubility in the running solvent
Size of the pigment
Smaller mass + increased solubility = closer to solvent front
RP7 Chromatography
Describe how to separate the photosynthetic pigments by chromatography?
1. Draw line/origin on (chromatography) paper
(using ruler and pencil);
2. (Use pipette/tubing/dropper to) add
chlorophyll/solution to origin/line;
3. Add solvent below line/origin;
4. Remove/stop (from glassware) before solvent
reaches end (of chromatography paper)
OR
Mark (position) where solvent reaches/front;
RP7 Chromatography
TRUE or FALSE:
The Rf value is specific to a photosynthetic pigment
TRUE
RP7 Chromatography
TRUE or FALSE:
Changing the running solvent will NOT affect the calculated Rf value
FALSE
Rf values depend on the running solvent used
RP7 Chromatography
Why calculate the Rf value?
Allows comparisons ;
Determines which pigments are present in a photosynthesising organism;
RP7 Chromatography
Why is the Rf value always between 0-1?
Rf = distance moved by pigment / distance moved by solvent front ;
As solvent front distance is always larger than the pigment distance, Rf value must be below 1.
RP7 Chromatography
Pigment E has a low …………
Solubility
(in the running solvent used)
RP7 Chromatography
Pigment E has a large …………
Mass / size
(therefore does not move far from the origin)
How science works
Large range/difference/increase in numbers;
RP8 Dehydrogenase
The solution that the student used to produce the chloroplast suspension had the same water potential as the chloroplasts.
Explain why it was important that these water potentials were the same (2 marks).
- Osmosis does not occur;
- Chloroplast does not burst / lyse / shrivel / shrink;
RP8 Dehydrogenase
DCPIP solution is blue when oxidised and colourless when ___________ .
reduced
DCPIP acts as an artificial electron acceptor
RP8 Dehydrogenase
Tube 1 contained 1 cm^3 of solution without chloroplasts and 9 cm^3 of DCPIP solution in light.
Why was this tube set up?
- To show light does not affect DCPIP;
- To show chloroplasts are required (are the source of electrons to reduce DCPIP);
RP8 Dehydrogenase
Tube 3 contained 1 cm^3 of chloroplast suspension and 9 cm3 of DCPIP solution in light.
After 30 minutes DCPIP turned from blue to colourless.
Explain why (2 marks).
- Reduction of DCPIP by electrons;
- (From) chlorophyll / light dependent reaction;
RP8 Dehydrogenase
Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds (3 marks).
- Less / no ATP produced;
- Less / no reduced NADP produced;
- Less / no GP reduced to TP;
RP9 Respiration in Yeast
Concentration/mass of yeast
Concentration/mass of glucose/sugar (solution/s) Concentration of oxygen (in solution)
Volume of yeast
Volume of glucose/sugar (solution/s) pH (of glucose/sugar solution/s)
Species/type of yeast
Size/diameter/volume of test tubes
RP9 Respiration in Yeast
(So the) oxygen is used/absorbed/respired;
RP9 Respiration in Yeast
Figure 2 shows a typical population growth curve for yeast under laboratory conditions.
Many yeast cells die during the death phase.
Suggest one reason why.
Decrease/no glucose/substrate
OR
Increase in ethanol/carbon dioxide/acidity;
How Science Works
Correlation does not mean _____________
causation
How Science Works
Draw out a linear relationship
Look for a straight line / constant gradient
How Science Works
Linear or non-linear:
Non linear
No straight line and the gradient changes
How Science Works
Linear or non-linear:
There is a proportional Y increase as X increases
Linear
How Science Works
When to use a t test?
When comparing the differences between two means (e.g. control vs. treatment group)
How Science Works
Name of statistical test used to assess the strength of relationship between two continuous variables.
Correlation coefficient
How Science Works
When to use the chi squared test?
Categorical data;
e.g. comparing observed vs. expected offspring in genetic crosses
How Science Works
A t-test produced a p value of 0.03.
What can you conclude?
Significant difference between means;
LESS than 5% probability the DIFFERENCE is due to chance
OR 3% probability the DIFFERENCE is due to chance
How Science Works
A t-test produced a p value > 0.11
What can you conclude?
NO Significant difference between means;
MORE than 5% probability the DIFFERENCE is due to chance
How Science Works
A t-test produced a p value = 0.001.
What can you conclude?
HIGHLY Significant difference between means;
LESS than 5% probability the DIFFERENCE is due to chance
OR 0.01% probability the DIFFERENCE is due to chance
How Science Works
A correlation coefficient produced a p value > 0.2.
What can you conclude?
NO Significant correlation
MORE than 5% probability the CORRELATION is due to chance
How Science Works
A correlation coefficient produced a p value < 0.045.
What can you conclude?
Significant correlation
LESS than 5% probability the CORRELATION is due to chance
How Science Works
A correlation coefficient produced a p value < 0.001.
What can you conclude?
Highly significant correlation
LESS than 5% probability the CORRELATION is due to chance
OR LESS than 0.1% probability the CORRELATION is due to chance
How Science Works
The scientists’ hypothesis at the start of the investigation was that crop plants genetically engineered to produce the protein GB would become more resistant to high environmental temperatures.
The scientists developed this hypothesis on the basis of previous research on crops that are grown in hot climates.
Suggest how the scientists arrived at their hypothesis.
1. Looked for information / journals / research, on crop plants that grow at high temperatures;
2. Crop plants cited in this research contain / make GB;
3. So assumed making plants produce GB makes them resistant to high temperatures;
RP10 Choice Chamber
There is no (significant) difference in behaviour of COTS with constant or flashing light
OR
The type of light has no effect on the behaviour of COTS
RP10 Choice Chamber
The crown-of-thorns starfish (COTS) is one of the main causes of the decline of the world’s coral reefs.
Marine biologists used a choice chamber to investigate the effects of flashing and constant light on the behaviour of COTS.
The natural habitat of COTS is coral reefs of tropical oceans.
Suggest two factors that should be kept constant in the choice chambers so that COTS display normal behaviour.
Salinity / salt concentration of the water
Temperature (of the water)
Concentration / distribution of food
pH (of the water)
Oxygen / carbon dioxide concentration
Intensity / wavelength of (constant and flashing) light
RP10 Choice Chamber
Can you conclude from the below information that woodlice show turn alternation behaviour when the distance between the forced turn and the second turn was 10 cm? Explain your answer (2 marks).
(No)
Equal numbers / 50% turn each way;
Would expect this by chance / at random;
RP10 Choice Chamber
Use the below information to give two reasons why the woodlice were left for 15 minutes before their movement was recorded.
1. Time to establish humidity to that required / time for substance to absorb water;
2. So that behaviour typical of humidity;
3. Woodlice no longer affected by handling;
OR allow acclimatisation idea
How Science Works
The student could determine the median, mode and range from his measurement of shell heights in two populations of snails.
Give two other statistical values the student could calculate from his measurement of shell heights in these populations.
Mean and standard deviation
How Science Works
Suggest how the scientist measured the rate of water flow in a river.
Movement of (floating) object over known distance and over given time
OR Time to fill container of known volume
OR Use of data logging device;
How Science Works
It was important that the sampling procedure was standardised when collecting the Slate Drake mayflies from the two sites.
Give one way in which the sampling procedure could be standardised.
Same size of area (sampled)
OR Same size net/mesh
OR Same sampling time
OR Samples taken at same time of day/on same day;
How Science Works
When the patients recorded the intensity of pain, suggest two reasons why it was important to use a statistically valid scale.
1. Pain is subjective
OR Pain sensitivity/threshold/tolerance varies;
2. To ensure that differences were significant
OR For (valid) comparison;
RP11 Calibration Curve
Creatinine is produced in muscle tissues. Creatinine diffuses into the blood. The kidneys then excrete creatinine.
A calibration curve can be used to determine the concentration of creatinine in urine. One method of producing a calibration curve needs:
- creatinine solution of known concentration
- distilled water
- creatinine-detecting solution
- a colorimeter.
Creatinine-detecting solution reacts with creatinine to produce an orange colour.
Use the information provided to describe how you could produce a calibration curve for creatinine (4 marks).
1. Use distilled water and creatinine solution of known concentration to produce dilutions series;
2. Add constant volume of creatinine detecting solution (to each solution);
3. To constant volume of each concentration in the dilution series;
4. Record absorbance/transmission of solution/s using a colorimeter;
5. Plot dilution/concentration of (creatinine) solution on x-axis against absorbance/transmission on y-axis;
RP11 Calibration Curve
Describe how you would determine the concentration of creatinine in a urine sample using your calibration curve (2 marks).
1. Use same volumes of solutions as used in producing (calibration curve)
2. Read off (creatinine) concentration against absorbance/transmission (value) obtained;
RP12 Sampling
Describe how you would determine the mean percentage cover for beach grass on a sand dune (3 marks).
1. Method of randomly determining position (of quadrats) e.g. random numbers generator;
2. Large number of quadrats (20 or more);
3. Divide total percentage by number of quadrats;
RP12 Sampling
The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes.
Describe how you could estimate the size of a population of sundews in a small marsh (5 marks).
1. Use a grid
2. Method of obtaining random coordinates/numbers e.g. random numbers generator;
3. Count number/frequency in a quadrat;
4. Large sample (20 or more) and calculate mean number (per quadrat/section);
5. Valid method of calculating total number of sundews, e.g. mean number of plants per m2 multiplied by number of m2 in marsh;
RP12 Sampling
Lettuce is classified in the same family as dandelions. Dandelions commonly grow on roadside verges and may accidentally be sprayed with salt when salt is added to the road in winter.
Describe how you could use a transect to investigate whether the distribution of dandelions changed with increased distance from the road (4 marks).
- Lay tape / rope at right angle / perpendicular to road;
- Take samples at regular / stated intervals;
- Using a quadrat;
- Count numbers / percentage cover of dandelions;
- Use several transects;
How Science Works
Explain why a log scale is used to record the number of cells.
Large range/difference/increase in numbers;
How Science Works (Maths)
How Science Works (AO3)
Why should a sample be large?
To ensure it is representative;
To calculate a mean so results are more reliable;
Identify anomolus results;
How Science Works (AO3)
Why should sampling be random?
To reduce bias
This also make the results / experiment more reliable
How science works (AO3)
The scientist used the reduction in total leaf area of the experimental plants as an indicator of plant growth.
Outline a method by which you could find the area of a plant leaf.
Draw around leaf on graph paper and count squares;
How science works (AO3)
Suggest why the scientist made repeat measurements.
Increases reliability (of results)
OR
Anomalous results can be identified;
How science works (AO3)
Median
Reason
Presence of outliers / anomalies e.g. 80, 70
OR small sample size/8 (measurements);
How science works (AO3)
The scientists estimated the mean mass of fibre eaten per day using a food frequency questionnaire (FFQ).
The FFQ asks each person how often they have eaten many types of food over the past year.
An alternative method to calculate fibre eaten is for a nurse to ask each person detailed questions about what they have eaten in the last 24 hours.
Suggest one advantage of using the FFQ method and one disadvantage of using the FFQ method compared with the alternative method.
Advantage
Over longer period so more representative;
OR Diet may vary during the year/from day to day;
OR More cost effective because fewer people/nurses required;
Disadvantage
Relies on (long term) memory so may not be accurate
OR Recall of 24 hr diet likely to be more accurate
How science works (AO3)
Give two reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue.
1. Distribution may not be uniform
OR So it is a representative sample;
2. To obtain a (reliable) mean;
How science works (AO3)
Suggest appropriate units the student should use to compare the distribution of stomata on leaves.
Stomata per mm^2 or cm^2
How science works (AO3)
Correlation does not mean _____________
causation
How science works (AO3)
Researchers carried a correlation coefficient to assess the relationship between the concentration of carbon monoxide and the number of asthma attacks.
They found R = 0.50, with P <0.0001
Explain the meaning of the result of their calculations.
1. Positive correlation (R = 0.50) - as carbon monoxide increases, the number of asthma attacks increases;
2. P value of <0.0001 shows a highly significant correlation;
3. Less than a 5% probability this correlation is due to chance;
How science works (AO3)
Write out a null hypothesis for an experiment that requires a correlation coefficient.
e.g. There is no correlation between exercise per day (mins) and the % of people with lung cancer
Always use context of the question
How science works (AO3)
Write out an alternative hypothesis for an experiment that requires a t test.
e.g., there is a (significant) difference between the mean glucose concentration between the control group (+placebo) and the treatment group (+new diabetes drug)
Always use context of the question
How science works (AO3)
Write out a null hypothesis for an experiment that requires a t test.
e.g. there is a NO (significant) difference between the mean glucose concentration between the control group (+placebo) and the treatment group (+new diabetes drug).
Always use context of the question
How science works (AO3)
Write out a null hypothesis for an experiment that requires a chi squared test
There is no significant difference between the categories (e.g. observed vs. expected)
