5. Investigating Variation

Question 1

Variation

Answer 1

Differences that exist between individuals

Variations within and between species

Question 2

What can variations in the population be due to ?

Answer 2

Genetics - different species have different genes.
And alleles (Within species)

Environment - climate / food / lifestyle.

Most variation due to combination of both - genes determine how tall an organism is but nutrient availability affects how tall they will acc grow.

Question 3

Why can you not look at the whole population and only a sample .

Answer 3

Time consuming

Impossible to catch all individuals in group

Samples used as representative models.

Question 4

What is variation BETWEEN species called ?

Answer 4

Interspecific variation

Question 5

What is variation called within a species ?

Answer 5

Intraspecific variation

Question 6

What must the sample data be ?

Answer 6

Accurate - to represent whole population.

Any patterns observed are tested to make sure they’re not due to chance.

Question 7

What kind of sampling reduces bias?

Answer 7

Random

Question 8

How could you do random sampling ?

Answer 8

If you were looking at plant species in a field you could pick a random sample sites by dividing the field into a grid and using a random number generator to select coordinates.

Using random number generator

Question 9

When will a sample be considered biased?

Answer 9

If it doesn’t represent the population as whole.

Eg looking at average height of students in school but only measured the heights of people from one particular class - biased

Question 10

How do we ensure any variation in the sample isn’t due to chance ?

Answer 10

Analyse results statistically

Allows more confidence

True reflection of what is happening in whole population

Question 11

What things can you use to measure how much variation there is in a sample ?

Answer 11

Mean and standard deviation

Question 12

Mean

Answer 12

Average number of values collected in a sample.

Obtained by adding all the values together and dividing by the total number of values in sample

Used to see if there’s variation between samples

Question 13

How do we know if the mean varies ? Thank

Answer 13

If the results vary them selves

Not similar

Question 14

Normal distribution curve

Answer 14

Bell shapes curve symmetrical about the mean

Values either side of the mean

Question 15

Standard deviation

Answer 15

A measure of the spread of values about the mean

Question 16

How do you often see the mean written as ?

Answer 16

9 + 3
-

9 is the mean
3 standard deviation

So values spread between 6 and 12 as it’s 9-3 and 9+3

Question 17

Describe a narrower normal distribution

Answer 17

Values are similar
Close to mean

Data varies little

Graph is steep

SD is small

Question 18

Describe a wider normal distribution curve

Answer 18

Values vary a lot
Not that close to mean

Data varies a lot

Graph wider

SD larger

Question 19

So the smaller the SD…

Answer 19

The values closer to mean
Little variation

More accurate

Question 20

What is another way of calculating dispersion of data ?

Answer 20

Range

Difference between highest and lowest

Question 21

Why Is SD better than range?

Answer 21

Takes into account all values in data

Range only takes into account 2 values.

Range more affected by anonymous results

Question 22

What do error bars do ?

Answer 22

Extend one SD above mean.

Extends one SD below mean.

Total length of error car is twice length of SD

Question 23

The longer the error bar …

Answer 23

The larger the SD and more spread out the sample data from mean.