3.1.6 Living Organisms Vary Flashcards
What is variation?
Differences that exists between individuals
What is intraspecific variation?
Variation between members of a species
What is interspecific variation?
Variation between species
Name 2 causes of variation
- Genetic factors
- Environment
Differences in environment cause variation _____ species
within
Describe how genetic factors cause variation between species
Different species have different genes = variation between species
Describe how genetic factors cause variation within species
- Individuals of same species have same genes but different alleles
- Polygenes - lots of genes can control one feature
What is most variation within species caused by?
A combination of genetic and environmental factors
Give an example of how both genetic and environmental factors can cause variation
e.g. genes determine how tall organism can grow but nutrient availability affects how tall organism actually grows
Samples are used as ____ for a whole population
models
Why does a sample has to be random?
∵ it’s used to draw conclusions about a whole population ∴ has to accurately represent the whole population
How do you make sure a sample isn’t biased?
By making sure it’s random
Describe how you would carry out random sampling
e.g.
- Divide field into grid and use random number generator to select coordinates
- Take samples at the intersection of each pair of coordinates
Name 2 ways to minimise the variation observed in a sample occuring due to chance
- Analysing data statistically
- Using a large sample size
How will analysing data statistically minimise the variation observed in sample occuring due to chance?
Allows us to decide whether variation observed is due to chance or some other cause
How will using a large sample size minimise the variation observed in sample occuring due to chance?
More individuals selected = smaller the probability that chance will influence the result
What can the mean used be for when measuring variation?
Can be used to look for variation between samples
What type of graph do most samples (of continuous variation) result in and why?
Bell-shaped graph, AKA normal distribution, ∵ most samples will include values either side of mean
Sketch a normal distribution curve & label where the mean would be
Measuring Variation
What does the standard deviation tell you?
Tells you about variation within a sample i.e. how much values in a single sample vary
What is standard deviation?
Measure of the spread of values about the mean
What does a large standard deviation mean?
Values in sample vary a lot
What does a small standard deviation mean?
Most of sample is around mean value = varies little
In normal distribution curve, how is the standard deviation represent?
By the width of the curve
What is meant by 9 ± 3?
Means that mean = 9 & that the standard deviation = 3 so most of the vaules are spread between 6-12
Standard deviations can be plotted on a graph/chart of mean values using ____ _____
error bars
Error bars extend one…
standard deviation above and one standard deviation below the mean
The longer the error bar…
the larger the standard deviation & more spread sample data is from mean
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)
So that anomalies of either very short or very long don’t skew the results
What is discontinuous variation caused by?
Due to genetic factors (& organisms fit into few distinct groups)
How is discontinuous variation represented?
Represented by bar/pie chart
What is continuous variation caused by?
Due to many genes and environmental factors
What is continuous variation represented by?
Normal distribution curve
Describe how discontinuous variation differs from continuous variation in terms of genetic control
Few genes versus many / polygenic
Describe how discontinuous variation differs from continuous variation in terms of the effect of the environment
Limited / none versus significant
Describe how discontinuous variation differs from continuous variation in terms of the range of phenotypes
Limited / few versus wide / many
Why should you use a large sample? (1)
- Makes sure sample is representative
- Produces more reliable mean
- Reduces effect of extreme values
Explain how standard deviations of mean values help to interpret data (2)
- 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
Describe how you would use chromatography to separate chlorophyll and other pigments from 2 different leaves
- Add of solvent to a boiling tube & place a bung on it
- Put them into a rack
- Draw pencil line near the bottom of chromatography paper (origin)
- Cut disc from 1st leaf
- (Avoid veins and midrib)
- Place disc onto middle of origin
- Crush each leaf with glass rod so it leaves a stain
- Pin the chromatography paper to bung and put it into the tube
- Make sure it the paper doesn’t come into contact with the sides
- Make sure end of paper is in solvent but solvent doesn’t come above origin
- Let solvent run up until almost reaches the top
- Remove paper and draw pencil line to show how far the solvent moved up the paper
- Repeat same steps but with 2nd leaf
- Then calculate Rf values
When using chromatography to investigate pigments present in leaves, what safety procedures should you take?
Wear eye protection and work in well-ventilated room or fume cupboard
When using chromatography to investigate pigments present in leaves, why should you work in well-ventilated room or fume cupboard?
∵ chemicals used are volatile and the vapours are hazardous
How do you calculate a Rf value?
Why should the origin line be drawn in pencil and not ink?
Ink (pigments) would dissolve in solvent/would be carried up paper by solvent
Why should the level of the solvent be below the origin?
Otherwise the pigments (e.g. sugars) wouldn’t be carried up the paper by solvent
Why should a small volume of substance be added to origin?
To give better separation
When the chromatography paper is removed from the tank, why should the position of the solvent front be marked immediately?
Solvent evaporates so front vanishes
