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

How Science Works

Correlation does not mean _____________

Answer 18

causation

Question 19

How Science Works

Draw out a linear relationship

Answer 19

Look for a straight line / constant gradient

Question 20

How Science Works

Linear or non-linear:

Answer 20

Non linear

No straight line and the gradient changes

Question 21

How Science Works

Linear or non-linear:

There is a proportional Y increase as X increases

Answer 21

Linear

Question 22

How Science Works

When to use a t test?

Answer 22

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

Question 23

How Science Works

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

Answer 23

Correlation coefficient

Question 24

How Science Works

When to use the chi squared test?

Answer 24

Categorical data;

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

Question 25

How Science Works

A t-test produced a p value of 0.03.

What can you conclude?

Answer 25

Significant difference between means;

LESS than 5% probability the DIFFERENCE is due to chance

OR 3% probability the DIFFERENCE is due to chance

Question 26

How Science Works

A t-test produced a p value > 0.11

What can you conclude?

Answer 26

NO Significant difference between means;

MORE than 5% probability the DIFFERENCE is due to chance

Question 27

How Science Works

A t-test produced a p value = 0.001.

What can you conclude?

Answer 27

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 28

How Science Works

A correlation coefficient produced a p value > 0.2.

What can you conclude?

Answer 28

NO Significant correlation

MORE than 5% probability the CORRELATION is due to chance

Question 29

How Science Works

A correlation coefficient produced a p value < 0.045.

What can you conclude?

Answer 29

Significant correlation

LESS than 5% probability the CORRELATION is due to chance

Question 30

How Science Works

A correlation coefficient produced a p value < 0.001.

What can you conclude?

Answer 30

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 31

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 31

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 32

RP10 Choice Chamber

Answer 32

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 33

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 33

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 34

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 34

(No)

Equal numbers / 50% turn each way;

Would expect this by chance / at random;

Question 35

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 35

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 36

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 36

Mean and standard deviation

Question 37

How Science Works

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

Answer 37

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 38

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 38

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;