variation

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why do biologists take many measurements of the same thing?
because they are usually measuring some aspects of living organisms and all living organisms are different.
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how can measurements be reliable?
if the individuals are representative of the population as a whole
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why might sampling not be reliable?
sampling could be bias, or by chance they may not be representative.
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how can you prevents sampling being bias?
eliminate any human involvement in choosing the samples
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what are some ways of eliminating bias?
random sampling, using a large sample size, analysis of the data collection
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describe a random sampling method:
divide the study area into a grid of number lines, use random numbers from a table/ generated by a computer to give a series of coordinates, take samples at intersection of a pair of coordinates
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how does a large sample size eliminate bias?
more individuals=smaller the probability that chance will influence the results
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how does analysing the data collection avoid sampling being bias?
accepting that chance will play a part, the data collected can be analysed using statistical tests to determine the extent which chance may influence the data. see whether variation is due to chance or have a cause
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what is variation a result of?
genetic differences and environmental influences. in most cases a combination of both
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how are genetic differences caused?
different genes that each individual organism possesses
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what results in genetic variation arising?
mutations, meiosis, fusion of gametes
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how does mutations causes genetic variation?
sudden changes to genes and chromosomes may be passed onto the next generation
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how does meiosis lead to genetic variation
forms gametes which mixes up the genetic material before it is passed into the gametes
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how does the fusion of gametes cause genetic variation?
offspring inherit the characteristics of each parent therefore are different from both of them, the fusion of gametes during fertilisation is random adding to the variety.
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how can variety in asexual reproducing organisms be increased?
mutations
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how can variety in sexual reproducing organisms be increased?
meiosis mutations and fusion of gametes
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how does the environment cause variation?
effects the way an organisms genes are expressed
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how does the environment effect the way an organisms genes are expressed?
genes have set limits, the environment determines where within those limits and organism lies
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why is it difficult to draw conclusions about the cause of variation?
it is hard to distinguish between the effects of the many genetic and environmental influences that combine to produces difference between individuals
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how can variation due to genetic factors be represented and why?
on a bar char or pie graph. because where variation is the result of genetic factors organisms fit into a few distinct forms and there are no intermediate types
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give an example of a genetic factor which could be represented on a bar graph:
ABO blood group, because there are four distinct groups and a character displaying this type of variation is usually controlled by a single gene.
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how can variation due to environmental influences be presented and why?
line graph where all points are joined. this is because characteristics grade into one another forming a continuum
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give an example of variation which causes a continuum in a graph?
in humans, height and mass. the characteristics are displayed by polygenes and environment, the environment plays a major role in determining where on the continuum an organism lies. i.e. an organism grows to different heights rather than the same height.
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what is a bell shaped curve known as ?
a normal distribution curve.
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what does a normal distribution curve always have?
the same basic shape
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how does a distribution curve vary?
in its maximum height and width.
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what does the curve represent?
the mean and the standard deviation (how far the values deviate from the mean)
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what is the mean?
measurement of the actual height of the curve, provides an average value and is useful information when comparing one sample with another.
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whats a disadvantage of using the mean?
it does not give any information about the range of values within the sample
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What is the standard deviation
a measure of the width of the curve, it gives an indication of the range of values either side of the mea, where the curve changes from being convex or concave,
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What does the standard deviation show?
68% of all measurements lie within +- 1.0 standard deviation of the mean. if the width is almost to +-2.0 the standard deviation is 95%
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Card 2

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how can measurements be reliable?

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if the individuals are representative of the population as a whole

Card 3

Front

why might sampling not be reliable?

Back

Preview of the front of card 3

Card 4

Front

how can you prevents sampling being bias?

Back

Preview of the front of card 4

Card 5

Front

what are some ways of eliminating bias?

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