Interspecific Variation: when one species
differ from another.
Intraspecific Variation: when members of
the same species differ from each other
Sampling
samples should be representative of the
population as a whole
sampling bias: selection process may be biased due to
unrepresentative choices from the samplers. for example, samples
may only be taken from dry, not muddy areas of a field.
chance: by pure chance, chosen samples may not be representative.
minimise the effects of chance by: 1. having a bigger sample size. 2.
analysing data collected, for example spotting anomalies
Random sampling helps to eliminate bias. One method is to: 1. divide study area into grid
of numbered lines. 2. using a random number generator obtain coordinates. 3. take
samples at intersections of pairs of coordinates.
Causes of Variation
Genetic differences
due to different genes that each organism posesses
mutations - sudden changes to genes may be
passed on to the next generation
meiosis - the type of nuclear division that forms the gametes. this mixes
up genetic material before it is passed into the gametes
fusion of gametes - in sexual reproduction, offspring inherit
some characteristics of each parent and are therefore
different from both of them
Environmental influences
e.g in plants: pH, food avaliability and
climatic conditions can affect plant's
growth etc.
Types of Variation
due to genetic factors
represented on bar charts or pie charts as
characteristics like eye colour are not continuous
due to environmental influences
characteristics such as height and mass - controlled by
polygenes and environmental factors.
portrayed on normal distribution curves
Mean and Standard
Deviation
Mean - a measurement at the maximum height of the
curve, provides an average value and useful for comparison
Standard deviation - a measure of the width of the curve. it gives an
indication of the range of values either side of the mean