General Bio Knowledge & Science Skills for Exams

Question 1

e.g. if coloured juice leaks out of a frozen fruit, what word would you use to describe the colour?

Answer 1

pigment

Question 2

blank solution

Answer 2

a solution containing no substance being measured, usually used to calibrate instruments e.g. a colorimeter

Question 3

Explain one reason why it’s important for plant cells to be turgid.

Answer 3

To prevent wilting / loss of rigidity
If a cell is flaccid, photosynthesis/respiration may be impacted, or the opening and closing of stomato is disrupted

Question 4

A student is investigating the effect of alcohol on the permeability of plant cell membranes.
They place samples of onion epidermis into different concentrations of ethanol. After five minutes they add a few drops of Evans Blue to the sample, which stains the cells’ nuclei. After a further five minutes, the samples are viewed under a light microscope. They observe 20 cells and record the number of which that contain a nucleus.

Identify one limitation of the method the student followed.

Answer 4

• Volume of ethanol not stated.
• Size of onion epidermis not stated.
• Same onion / position onion epidermis removed from not stated.

Question 5

By changing the temperature, a student concludes that yeast cells are killed between 50°C and 70°C. Suggest one way that the student can improve the accuracy of the experiment.

Answer 5

Repeat experiment with smaller temperature intervals between 50°C and 70°C.

Question 6

By changing the temperature, a student concludes that yeast cells are killed between 50°C and 70°C. Suggest one way that the student can improve the reliability of the experiment.

Answer 6

• Repeat the experiment four more times at each temperature.
• Ignore any anomalous results.

Reliablility = repeats

Question 7

Explain why repeats are important.

Answer 7

Anomalies can be ignored so the mean is more reliable.

Question 8

You have drawn a graph of the absorption of red light (from 0.25 a.u. to 1 a.u.) against the percentage of glucose concentration. An unknown solution has an absorption of 0.19 a.u. of red light. How can you estimate the glucose concentration of the unknown solution?

Answer 8

You can’t as you can’t extrapolate data.

Question 9

You measured the glucose concentration at 0.06%, 0.13%, 0.25% and 0.50%. Where does your line of best fit end?

Answer 9

Ends at your first data point to the last one - you can’t extrapolate your line of best fit. This means it never reaches the y-axis (never goes beyond 0.06% glucose concentration).

Question 10

What lines do you need to draw for a table?

Answer 10

Pencil lines between the columns and rows & box it - you must draw a box around the whole table.

Question 11

unit M = ?

Answer 11

mol/dm³ or
moldm^-3

Question 12

unit mol/dm³ or
moldm^-3 = ?

Answer 12

M

Question 13

negative control

Answer 13

A control test that isn’t expected to have any effect on the experiment, used to check that only the independent variable is affecting the dependent variable (and not any other external factors). They do not have the reagents/treatments that is expected to have an effect

Question 14

negative control example

Answer 14

• Not giving a group of people the treatment (e.g. antibiotic) that might have an effect
• Not adding an enzyme when investigating enzyme activity

Question 15

positive control

Answer 15

A control which shows what positive results look like, to check that it is possible with the current setup

Question 16

positive control example

Answer 16

Known treatment/reagent/material that works

Question 17

difference between a reading and a measurement

Answer 17

Reading = judgement of 1 value
Measurement = judgement of 2 values, difference of these values is recorded

Question 18

uncertainty and margin of error for a 10cm³ syringe with increments of 1cm³

Answer 18

Uncertainty = +- half of resolution = =- 0.5cm³
Margin of error = resolution or twice the uncertainty = 1cm³

Question 19

How can you minimise the uncertainty in data?

Answer 19

• Use equipment with a greater resolution
• Use a larger sample size
• Measure a greater quantity (the uncertainty of the measuring equipment stays the same but the reading increases, decreasing the percentage uncertainty)

Question 20

greater/higher resolution

Answer 20

apparatus with a greater resolution have smaller increments (e.g. 0.01g rather than 0.1g) so can measure a quantity more finely

Question 21

valid data

Answer 21

Data that can answer the original question (it’s precise & accurate). All other variables must have been controlled

Question 22

reliable

Answer 22

A measure of how repeatable an experiment is, so that it gets the same results. Reliability encompasses accuracy and precision

Question 23

What causes a lack of precision?

Answer 23

Random error

Question 24

What causes a lack of accuracy?

Answer 24

Random and systematic errors

Question 25

How can you increase precision?

Answer 25

Reducing the effect of random errors e.g.
* Use equipment with a greater resolution
* Allow things to acclimatise (e.g. letting something sit in a water bath for a constant but long enough time)

Question 26

How can you increase accuracy ? (2)

Answer 26

• Use quantitative data rather than qualitative data (more accurate methods)
• Repeat the experiment with smaller intervals between values for the independent variable around a point of interest

Question 27

How can you increase validity?

Answer 27

• Keep control variables constant throughout the experiment
• Repeat the measurements at least three times (minimum) to identify/ignore anomalies and calculate the mean
• Use more intermediate values so the trend can be identified more clearly

Question 28

How can you increase reliability?

Answer 28

• Keep control variables constant throughout the experiment
• Repeat the measurements at least three times (minimum) to identify/ignore anomalies and calculate the mean

Question 29

How does repeating an experiment at least twice improve the investigation? [2 marks but 3 points]

Answer 29

improves reliability (accuracy not credited)
assess the variability / spread of results (or calculate the standard deviation)
allows calculation of (more accurate) mean

Question 30

Explain why repeats are important.

Answer 30

Anomalies can be identified and ignored.
This makes the mean more reliable (reduces the effect of anomalies on the mean).

Question 31

impervious

Answer 31

not allowing fluid to pass through

Question 32

structural diagram

Answer 32

The diagram showing the elements and bonds between them in a molecule

structural formula

Question 33

inorganic - in terms of cofactors

Answer 33

Carbon isn’t bound to hydrogen

Question 34

You have the radius of a field of view of cells. How do you calculate the cell density of this area?

Answer 34

Calculate the area using A = π r²
Count the number of cells that are over 50% in the image
Cell density = number of cells / area (think density = mass / volume i.e. size)

Question 35

What can you say about “a few drops”?

Answer 35

The volume used isn’t controlled, so an improvement could be to measure a set volume with a syringe.

Question 36

When observing a colour change, what does holding a white spotting tile behind the solution do?

Answer 36

Increases the contrast

Question 37

Lauren is measuring the time taken for a lipid solution with lipase and phenolpthalein to turn colourless. She repeated the experiment five times and then repeated the whole investigation with different temperatures.
How could Lauren modify her experiment to obtain a more accurate value for the optimum temperature for lipase activity? [2]

Answer 37

Reduce human error (1?) by using a colorimeter / pH meter (1) which can give numerical values for each temperature and repeat - these can then be compared / a mean calculated (1?)