Practical Work & How Science Works

Question 1

RP7 Chromatography

Explain why the student marked the origin using a pencil rather than using ink.

Answer 1

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;

Question 2

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).

Answer 2

1. Level of solvent below origin/line;
2. Remove/stop before (solvent) reaches top/end;

Question 3

RP7 Chromatography

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.

Answer 3

(Absorb) different/more wavelengths (of light) for photosynthesis;

Accept light-dependent reaction /photophosphorylation /photoionisation for photosynthesis.

Question 4

RP7 Chromatography

What two key factors determine the distance travelled by the photosynthetic pigments on the chromatography paper?

Answer 4

Solubility in the running solvent

Size of the pigment

Smaller mass + increased solubility = closer to solvent front

Question 5

RP7 Chromatography

Describe how to separate the photosynthetic pigments by chromatography?

Answer 5

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;

Question 6

RP7 Chromatography

TRUE or FALSE:

The Rf value is specific to a photosynthetic pigment

Answer 6

TRUE

Question 7

RP7 Chromatography

TRUE or FALSE:

Changing the running solvent will NOT affect the calculated Rf value

Answer 7

FALSE

Rf values depend on the running solvent used

Question 8

RP7 Chromatography

Why calculate the Rf value?

Answer 8

Allows comparisons ;

Determines which pigments are present in a photosynthesising organism;

Question 9

RP7 Chromatography

Why is the Rf value always between 0-1?

Answer 9

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.

Question 10

RP7 Chromatography

Pigment E has a low …………

Answer 10

Solubility
(in the running solvent used)

Question 11

RP7 Chromatography

Pigment E has a large …………

Answer 11

Mass / size

(therefore does not move far from the origin)

Question 12

How science works

Answer 12

Large range/difference/increase in numbers;

Question 13

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).

Answer 13

1. Osmosis does not occur;
2. Chloroplast does not burst / lyse / shrivel / shrink;

Question 14

RP8 Dehydrogenase

DCPIP solution is blue when oxidised and colourless when ___________ .

Answer 14

reduced

DCPIP acts as an artificial electron acceptor

Question 15

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?

Answer 15

1. To show light does not affect DCPIP;
2. To show chloroplasts are required (are the source of electrons to reduce DCPIP);

Question 16

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).

Answer 16

1. Reduction of DCPIP by electrons;
2. (From) chlorophyll / light dependent reaction;

Question 17

RP8 Dehydrogenase

Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds (3 marks).

Answer 17

1. Less / no ATP produced;
2. Less / no reduced NADP produced;
3. Less / no GP reduced to TP;

Question 18

RP9 Respiration in Yeast

Answer 18

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

Question 19

RP9 Respiration in Yeast

Answer 19

(So the) oxygen is used/absorbed/respired;

Question 20

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.

Answer 20

Decrease/no glucose/substrate

OR

Increase in ethanol/carbon dioxide/acidity;

Question 21

How Science Works

Correlation does not mean _____________

Answer 21

causation

Question 22

How Science Works

Draw out a linear relationship

Answer 22

Look for a straight line / constant gradient

Question 23

How Science Works

Linear or non-linear:

Answer 23

Non linear

No straight line and the gradient changes

Question 24

How Science Works

Linear or non-linear:

There is a proportional Y increase as X increases

Answer 24

Linear

Question 25

How Science Works

When to use a t test?

Answer 25

When comparing the differences between two means (e.g. control vs. treatment group)

Question 26

How Science Works

Name of statistical test used to assess the strength of relationship between two continuous variables.

Answer 26

Correlation coefficient

Question 27

How Science Works

When to use the chi squared test?

Answer 27

Categorical data;

e.g. comparing observed vs. expected offspring in genetic crosses

Question 28

How Science Works

A t-test produced a p value of 0.03.

What can you conclude?

Answer 28

Significant difference between means;

LESS than 5% probability the DIFFERENCE is due to chance

OR 3% probability the DIFFERENCE is due to chance

Question 29

How Science Works

A t-test produced a p value > 0.11

What can you conclude?

Answer 29

NO Significant difference between means;

MORE than 5% probability the DIFFERENCE is due to chance

Question 30

How Science Works

A t-test produced a p value = 0.001.

What can you conclude?

Answer 30

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

Question 31

How Science Works

A correlation coefficient produced a p value > 0.2.

What can you conclude?

Answer 31

NO Significant correlation

MORE than 5% probability the CORRELATION is due to chance

Question 32

How Science Works

A correlation coefficient produced a p value < 0.045.

What can you conclude?

Answer 32

Significant correlation

LESS than 5% probability the CORRELATION is due to chance

Question 33

How Science Works

A correlation coefficient produced a p value < 0.001.

What can you conclude?

Answer 33

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

Question 34

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.

Answer 34

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;

Question 35

RP10 Choice Chamber

Answer 35

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

Question 36

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.

Answer 36

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

Question 37

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).

Answer 37

(No)

Equal numbers / 50% turn each way;

Would expect this by chance / at random;

Question 38

RP10 Choice Chamber

Use the below information to give two reasons why the woodlice were left for 15 minutes before their movement was recorded.

Answer 38

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

Question 39

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.

Answer 39

Mean and standard deviation

Question 40

How Science Works

Suggest how the scientist measured the rate of water flow in a river.

Answer 40

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;

Question 41

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.

Answer 41

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;

Question 42

How Science Works

When the patients recorded the intensity of pain, suggest two reasons why it was important to use a statistically valid scale.

Answer 42

1. Pain is subjective

OR Pain sensitivity/threshold/tolerance varies;

2. To ensure that differences were significant

OR For (valid) comparison;

Question 43

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).

Answer 43

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;

Question 44

RP11 Calibration Curve

Describe how you would determine the concentration of creatinine in a urine sample using your calibration curve (2 marks).

Answer 44

1. Use same volumes of solutions as used in producing (calibration curve)

2. Read off (creatinine) concentration against absorbance/transmission (value) obtained;

Question 45

RP12 Sampling

Describe how you would determine the mean percentage cover for beach grass on a sand dune (3 marks).

Answer 45

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;

Question 46

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).

Answer 46

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;

Question 47

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).

Answer 47

1. Lay tape / rope at right angle / perpendicular to road;
2. Take samples at regular / stated intervals;
3. Using a quadrat;
4. Count numbers / percentage cover of dandelions;
5. Use several transects;

Question 48

How Science Works

Explain why a log scale is used to record the number of cells.

Answer 48

Large range/difference/increase in numbers;

Question 49

How Science Works (Maths)

Answer 49

Hint: C1 x V1 = C2 x V2

Question 50

How Science Works (AO3)

Why should a sample be large?

Answer 50

To ensure it is representative;

To calculate a mean so results are more reliable;

Identify anomolus results;

Question 51

How Science Works (AO3)

Why should sampling be random?

Answer 51

To reduce bias

This also make the results / experiment more reliable

Question 52

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.

Answer 52

Draw around leaf on graph paper and count squares;

Question 53

How science works (AO3)

Suggest why the scientist made repeat measurements.

Answer 53

Increases reliability (of results)

OR

Anomalous results can be identified;

Question 54

How science works (AO3)

Answer 54

Median

Reason
Presence of outliers / anomalies e.g. 80, 70

OR small sample size/8 (measurements);

Question 55

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.

Answer 55

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

Question 56

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.

Answer 56

1. Distribution may not be uniform

OR So it is a representative sample;

2. To obtain a (reliable) mean;

Question 57

How science works (AO3)

Suggest appropriate units the student should use to compare the distribution of stomata on leaves.

Answer 57

Stomata per mm^2 or cm^2

Question 58

How science works (AO3)

Correlation does not mean _____________

Answer 58

causation

Question 59

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.

Answer 59

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;

Question 60

How science works (AO3)

Write out a null hypothesis for an experiment that requires a correlation coefficient.

Answer 60

e.g. There is no correlation between exercise per day (mins) and the % of people with lung cancer

Always use context of the question

Question 61

How science works (AO3)

Write out an alternative hypothesis for an experiment that requires a t test.

Answer 61

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

Question 62

How science works (AO3)

Write out a null hypothesis for an experiment that requires a t test.

Answer 62

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

Question 63

How science works (AO3)

Write out a null hypothesis for an experiment that requires a chi squared test

Answer 63

There is no significant difference between the categories (e.g. observed vs. expected)