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AQA A Level Biology > Practical Skills > Flashcards

Practical Skills Flashcards

1
Q

What is a prediction/hypothesis?

A

Specific testable statement about what will happen in experiment

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2
Q

Define precise results

A

Results that don’t vary much from mean

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3
Q

Define Valid

A

Free of error

(Valid results answer original question)

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4
Q

How do you obtain valid results?

A

By controlling all variables to make sure you’re testing thing you want

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5
Q

Define accurate results

A

Results that really come close to the true value

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6
Q

What can decrease accuracy of results?

A

Human interpretation of measurement (e.g. determining colour change)

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7
Q

How can precision be reduced?

A

Reduced by random errors

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8
Q

Define Reproducible

A

If someone different does experiment, using slightly different method or piece of equipment, results will be the same

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9
Q

Define Repeatable

A

If same person repeats experiment using same methods and equipment = get same results

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10
Q

Define Calibration

A

Marking a scale on a measuring instrument

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11
Q

Define Resolution

A

Smallest change a measuring instrument can detect

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12
Q

Define a zero error

A

Systematic error caused by using equipment that isn’t zeroed properly

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13
Q

Define a random error

A

Unpredictable way in which all measurements wary

(e.g. human errors in measuring)

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14
Q

How can you reduce the effect of random errors

A

By repeat readings & finding the mean

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15
Q

Define a systematic error

A

Measurement wrong by same amount every time

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16
Q

Define a measurement error

A

Difference between measured value and true value

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17
Q

Define uncertainty

A

Amount of error your measurements might have

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18
Q

How can you calculate a percentage error of your measurements?

A
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19
Q

Name 2 ways you can reduce uncertainty

A
  1. Using most sensitive equipment available
  2. Measure a greater amount of something
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20
Q

Define categoric variables

A

Values that are labels e.g. names of plants

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21
Q

Define nominal variables

A

Type of categoric variable where there is no ordering of categories

e.g. red flowers, pink flowers, blue flowers

22
Q

When is it suitable to use a scatter graph?

A

When you’re looking at relationship between 2 discrete/independent variables

23
Q

Name 2 reasons why have a control group with a placebo makes your results more reliable

A
  • Removes researcher biasis
  • Control group can’t show psychologial effects
24
Q

Data is often given as percentages of people dying from each cause.

Explain the advantage of giving these data as percentages. (2)

A
  • Easier to compare if sample size effectively the same
  • Different no. of people in each group
25
Q

If experimental group are given the treatment via injections, suggest how the control group should be treated (2)

A
  • Given only saline
  • Otherwise treated exactly the same way
26
Q

What does standard deviation tell you?

A

Spread from the mean

27
Q

Comment on the effectiveness of taxol when used separately and as a combined treatment (related to SD)

A

SD overlap for OGF with taxol and taxol on its own so not conclusive/could be chance/both treatments effective

28
Q

Why should you repeat experiments?

A
  • To increase the reliability of your results
  • Anomalies can be identified
29
Q

What does an overlap in standard deviation mean?

A

Unlikely that any difference (in results) is significant

30
Q

An investigation was carried out into the effect of carbon dioxide concentration and light intensity on the rate of photosynthesis in a species of plant. The temperature was kept constant during the investigation. Explain why. (2)

A
  • Temperature affects the rate of photosynthesis
  • ∴ any change in photosynthesis rate is the result of CO2/light intensity
31
Q

Explain how the results from tube D help to confirm that the explanations for the other tubes are valid. (1)

A

Shows that indicator alone doesn’t change colour in light

32
Q

Explain the advantages of collecting a large number of results (2)

A
  • Easier to spot anomalies/increases reliability of results
  • Allows use of statistical test
33
Q

Explain why both indentical and non-identical twins are used in investigations (2)

A
  • Identical twins show genetic influence/differences
  • Non-identical twins also show an environmental/non-genetic influence
34
Q

Explain why it is an advantage to apply the treatment (i.e. 250 seeds per m2) to each row and each column (2)

A
  • Different envrionment or different variables in field
  • Minimises the effect of variables
35
Q

An investigation to determine whether pH affects the rate of an enzyme controlled reaction. Write a null hypothesis.

A

There is no significant difference between the rate at which the enzyme works at different pHs

36
Q

Name 3 statistical tests

A
  • Standard error and 95% confidence limits
  • Chi-squared test
  • Spearman rank correlation
37
Q

When should you use standard error and 95% confidence limits?

A
  • When testing for a difference between 2 sets of data
  • The data is continuous and means can be calculated
    • “looking for significant differences (between mean values)”
38
Q

When should you use chi-squared test?

A
  • When testing for a difference between 2 sets of data
  • The data is in discrete categories
39
Q

When should you use spearman’s rank correlation test?

A

When testing for a correlation between 2 sets of data

40
Q

For correlation coefficient:

Calculated value is _____ than the critcal value so ___ null hypothesis

A

Calculated value is greater than the critcal value so reject null hypothesis

Calculated value is less than the critcal value so accept null hypothesis

41
Q

For correlation coefficient:

Why do we reject the null hypothesis when the calculated value is greater than the critical value?

A

A probability of less than 0.05 or 5% that the correlation in results is due to chance

42
Q

For correlation coefficient:

Why do we accept the null hypothesis when the calculated value is less than the critical value?

A

A probability of more than 0.05 or 5% that the correlation in results occurred due to chance

43
Q

Chi-squared Test:

When do we reject our null hypothesis?

A

When our calculated value of Chi-squared is greater than the critical value of Chi-squared

44
Q

Chi-squared Test:

When do we accept our null hypothesis?

A

When our calculated value of Chi-squared is less than the critical value of Chi-squared

45
Q

Why do we reject our null hypothesis when our calculated value of Chi-squared is greater than the critical value of Chi-squared?

A

∵ there’s less than 5% probability that the differences between the observed and expected data are due to chance

46
Q

Why do we accept our null hypothesis when our calculated value of Chi-squared is less than the critical value of Chi-squared?

A

∵ there’s more than 5% probability that the differences between the observed and expected data are due to chance

47
Q

Give the reason why logarithmic scales have been used on the y-axes in the graph

A

large range of values/numbers

48
Q

Scientists found a postive correlation between the inhibition of germination and the concentration of the extract. Describe how they could find out whether this correlation was significant. (3)

A
  • Produce null hypothesis
  • Carry out Spearman Rank correlation test / find correlation coefficient
  • Use values to show P < critical value / find probability of results being due to chance
49
Q

What does the histogram indicate about the inheritance of this feature? Explain your answer. (2)

A
  • polygenic inheritance / several genes
  • many categories / continuous range / single or multiple allele inheritance would produce discrete categories
50
Q

The standard error of the mean was calculated. What information would this give about the mean height of 17-year-old males? (2)

A
  • (SE gives idea of) variability of mean
  • time / population mean would lie within these limits in 68% / 70% / 2 / 3 of samples
51
Q

Explain why the means and standard deviations are more useful than the ranges for detecting any differences between two samples (3)

A
  • Range = just extreme values / outliers
    • OR not typical / not representative / could be anomalies
  • Mean and SD uses all the values or less affected by anomalies
  • Mean and SD can be used in a statistical test
    • OR can be used to see if two results differ significantly

AQA A Level Biology (41 decks)

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