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AQA A Level Biology > 3.1.6 Living Organisms Vary > Flashcards

3.1.6 Living Organisms Vary Flashcards

1
Q

What is variation?

A

Differences that exists between individuals

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2
Q

What is intraspecific variation?

A

Variation between members of a species

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3
Q

What is interspecific variation?

A

Variation between species

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4
Q

Name 2 causes of variation

A
  1. Genetic factors
  2. Environment
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5
Q

Differences in environment cause variation _____ species

A

within

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6
Q

Describe how genetic factors cause variation between species

A

Different species have different genes = variation between species

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7
Q

Describe how genetic factors cause variation within species

A
  • Individuals of same species have same genes but different alleles
  • Polygenes - lots of genes can control one feature
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8
Q

What is most variation within species caused by?

A

A combination of genetic and environmental factors

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9
Q

Give an example of how both genetic and environmental factors can cause variation

A

e.g. genes determine how tall organism can grow but nutrient availability affects how tall organism actually grows

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10
Q

Samples are used as ____ for a whole population

A

models

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11
Q

Why does a sample has to be random?

A

∵ it’s used to draw conclusions about a whole population ∴ has to accurately represent the whole population

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12
Q

How do you make sure a sample isn’t biased?

A

By making sure it’s random

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13
Q

Describe how you would carry out random sampling

A

e.g.

  1. Divide field into grid and use random number generator to select coordinates
  2. Take samples at the intersection of each pair of coordinates
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14
Q

Name 2 ways to minimise the variation observed in a sample occuring due to chance

A
  • Analysing data statistically
  • Using a large sample size
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15
Q

How will analysing data statistically minimise the variation observed in sample occuring due to chance?

A

Allows us to decide whether variation observed is due to chance or some other cause

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16
Q

How will using a large sample size minimise the variation observed in sample occuring due to chance?

A

More individuals selected = smaller the probability that chance will influence the result

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17
Q

What can the mean used be for when measuring variation?

A

Can be used to look for variation between samples

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18
Q

What type of graph do most samples (of continuous variation) result in and why?

A

Bell-shaped graph, AKA normal distribution, ∵ most samples will include values either side of mean

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19
Q

Sketch a normal distribution curve & label where the mean would be

A
20
Q

Measuring Variation

What does the standard deviation tell you?

A

Tells you about variation within a sample i.e. how much values in a single sample vary

21
Q

What is standard deviation?

A

Measure of the spread of values about the mean

22
Q

What does a large standard deviation mean?

A

Values in sample vary a lot

23
Q

What does a small standard deviation mean?

A

Most of sample is around mean value = varies little

24
Q

In normal distribution curve, how is the standard deviation represent?

A

By the width of the curve

25
Q

What is meant by 9 ± 3?

A

Means that mean = 9 & that the standard deviation = 3 so most of the vaules are spread between 6-12

26
Q

Standard deviations can be plotted on a graph/chart of mean values using ____ _____

A

error bars

27
Q

Error bars extend one…

A

standard deviation above and one standard deviation below the mean

28
Q

The longer the error bar…

A

the larger the standard deviation & more spread sample data is from mean

29
Q

When comparing variation in size between 2 groups of organisms, it is often considered more useful to compare standard deviations rather than ranges. Explain why. (2)

A

So that anomalies of either very short or very long don’t skew the results

30
Q

What is discontinuous variation caused by?

A

Due to genetic factors (& organisms fit into few distinct groups)

31
Q

How is discontinuous variation represented?

A

Represented by bar/pie chart

32
Q

What is continuous variation caused by?

A

Due to many genes and environmental factors

33
Q

What is continuous variation represented by?

A

Normal distribution curve

34
Q

Describe how discontinuous variation differs from continuous variation in terms of genetic control

A

Few genes versus many / polygenic

35
Q

Describe how discontinuous variation differs from continuous variation in terms of the effect of the environment

A

Limited / none versus significant

36
Q

Describe how discontinuous variation differs from continuous variation in terms of the range of phenotypes

A

Limited / few versus wide / many

37
Q

Why should you use a large sample? (1)

A
  • Makes sure sample is representative
  • Produces more reliable mean
  • Reduces effect of extreme values
38
Q

Explain how standard deviations of mean values help to interpret data (2)

A
  • SD gives a measure of variation/spread
  • More SDs overlap = the more likely differences caused by chance / less likely it is that differences are real
39
Q

Describe how you would use chromatography to separate chlorophyll and other pigments from 2 different leaves

A
  1. Add of solvent to a boiling tube & place a bung on it
    1. Put them into a rack
  2. Draw pencil line near the bottom of chromatography paper (origin)
  3. Cut disc from 1st leaf
    1. (Avoid veins and midrib)
  4. Place disc onto middle of origin
    1. Crush each leaf with glass rod so it leaves a stain
  5. Pin the chromatography paper to bung and put it into the tube
    1. Make sure it the paper doesn’t come into contact with the sides
    2. Make sure end of paper is in solvent but solvent doesn’t come above origin
  6. Let solvent run up until almost reaches the top
    1. Remove paper and draw pencil line to show how far the solvent moved up the paper
  7. Repeat same steps but with 2nd leaf
  8. Then calculate Rf values
40
Q

When using chromatography to investigate pigments present in leaves, what safety procedures should you take?

A

Wear eye protection and work in well-ventilated room or fume cupboard

41
Q

When using chromatography to investigate pigments present in leaves, why should you work in well-ventilated room or fume cupboard?

A

∵ chemicals used are volatile and the vapours are hazardous

42
Q

How do you calculate a Rf value?

A
44
Q

Why should the origin line be drawn in pencil and not ink?

A

Ink (pigments) would dissolve in solvent/would be carried up paper by solvent

45
Q

Why should the level of the solvent be below the origin?

A

Otherwise the pigments (e.g. sugars) wouldn’t be carried up the paper by solvent

46
Q

Why should a small volume of substance be added to origin?

A

To give better separation

47
Q

When the chromatography paper is removed from the tank, why should the position of the solvent front be marked immediately?

A

Solvent evaporates so front vanishes

AQA A Level Biology (41 decks)

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