OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.1.6 Living Organisms Vary Exam Questions
Free OxfordAQA International A Level Biology revision for 3.1.6 Living Organisms Vary: what you need to know, common mistakes and exam-style questions with answers. Covers intraspecific and interspecific variation, random sampling, normal distribution, standard deviation and causes of variation.
Practise 3.1.6 Living Organisms Vary with past papers
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About OxfordAQA International A Level Biology 3.1.6 Living Organisms Vary
Living organisms vary is a short but data-heavy Unit 1 topic. You need to distinguish variation within a species from variation between species, explain why samples must be random and large enough to reduce the effect of chance, and interpret normal distributions using the mean and standard deviation. The specification states that you will not be asked to calculate standard deviation in the written papers, but you must understand what it shows. You also need to explain how both genetic and environmental factors cause variation. This topic supports later work on meiosis, genetic diversity, selection and statistics in Unit 3, and it is a common source of data analysis questions.
What you need to know
- Types of variation Intraspecific variation is variation between members of the same species. Interspecific variation is variation between different species.
- Sampling Samples should be random to avoid bias, for example using random number tables or coordinates. A large sample size reduces the effect of chance, so the sample is more likely to be representative of the population.
- Normal distribution Continuous characteristics such as height often give a bell-shaped curve with the mean at the centre. The mean, mode and median are the same in a perfect normal distribution.
- Standard deviation Standard deviation measures the spread of data around the mean. About 68% of values lie within one standard deviation of the mean and about 95% within two. Overlapping error bars or standard deviations suggest a difference may be due to chance.
- Causes of variation Genetic variation arises from mutation, meiosis and random fertilisation. Environmental factors such as diet, light or temperature also affect phenotype, and many characteristics are influenced by both.
Common mistakes in 3.1.6 Living Organisms Vary
- Saying a larger sample makes results more accurate. A larger sample reduces the effect of chance and makes the sample more representative; say this rather than 'accurate'.
- Concluding a difference is real when standard deviations overlap a lot. Large overlap suggests the difference could be due to chance.
- Thinking standard deviation shows the size of the mean. It shows the spread of the data around the mean.
- Describing all variation as genetic. Many characteristics are influenced by environment as well, so they show continuous variation.
Try three 3.1.6 Living Organisms Vary exam-style questions
1. Explain why it is important to collect a random sample. (2 marks)
Show the mark scheme answer
To avoid bias / selecting particular individuals; so the sample is representative of the population.
2. Two populations of snails have mean shell lengths of 18 mm and 22 mm, each with a standard deviation of 4 mm. Suggest what this shows about the difference between them. (2 marks)
Show the mark scheme answer
Standard deviations overlap a lot (14 to 22 mm and 18 to 26 mm); so the difference in means may be due to chance / may not be significant.
3. Distinguish between intraspecific and interspecific variation. (2 marks)
Show the mark scheme answer
Intraspecific variation is variation between members of the same species; interspecific variation is variation between members of different species.
3.1.6 Living Organisms Vary FAQs
What does OxfordAQA International A Level Biology 3.1.6 Living Organisms Vary cover?
It covers intraspecific and interspecific variation, random sampling, normal distribution, standard deviation and causes of variation.
Which unit is 3.1.6 Living Organisms Vary examined in?
It is part of Unit 1, The diversity of living organisms, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
Do I need to calculate standard deviation?
The specification says you will not be asked to calculate standard deviation in the written papers. You must be able to interpret it, for example deciding whether overlapping standard deviations mean a difference could be due to chance.
