AQA AS Biology: 2.7 Variation

Georgia Knight
Mind Map by Georgia Knight, updated more than 1 year ago
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A Levels A Levels (Biology) Mind Map on AQA AS Biology: 2.7 Variation, created by Georgia Knight on 02/25/2015.
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AQA AS Biology: 2.7 Variation
1 Interspecific Variation: when one species differ from another.
2 Intraspecific Variation: when members of the same species differ from each other
3 Sampling
3.1 samples should be representative of the population as a whole
3.1.1 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.
3.1.2 chance: by pure chance, chosen samples may not be representative.
3.1.2.1 minimise the effects of chance by: 1. having a bigger sample size. 2. analysing data collected, for example spotting anomalies
3.2 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.
4 Causes of Variation
4.1 Genetic differences
4.1.1 due to different genes that each organism posesses
4.1.1.1 mutations - sudden changes to genes may be passed on to the next generation
4.1.1.2 meiosis - the type of nuclear division that forms the gametes. this mixes up genetic material before it is passed into the gametes
4.1.1.3 fusion of gametes - in sexual reproduction, offspring inherit some characteristics of each parent and are therefore different from both of them
4.2 Environmental influences
4.2.1 e.g in plants: pH, food avaliability and climatic conditions can affect plant's growth etc.
5 Types of Variation
5.1 due to genetic factors
5.1.1 represented on bar charts or pie charts as characteristics like eye colour are not continuous
5.2 due to environmental influences
5.2.1 characteristics such as height and mass - controlled by polygenes and environmental factors.
5.2.2 portrayed on normal distribution curves
6 Mean and Standard Deviation
6.1 Mean - a measurement at the maximum height of the curve, provides an average value and useful for comparison
6.2 Standard deviation - a measure of the width of the curve. it gives an indication of the range of values either side of the mean
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