Module 4 : Section 3 - Variation

Question 1

Define variation

Answer 1

The differences that exist between individuals

Question 2

Variation can occur ….

Answer 2

• within species
• between species

Question 3

What is meant by variation within species

Answer 3

• Variation within a species is called intraspecific variation
• e.g. European robins weigh between 16g to 22g and show some variation in many other characteristics including length, wingspan, colour and beak size

Question 4

What is meant by variation between species

Answer 4

• the variation between different species is called interspecific variation
• e.g. the lightest species of bird is the bee hummingbird, which weighs around 1.6 on average. The heaviest species of bird is the ostrich which can weigh up to 160kg

Question 5

Varaition can be….

Answer 5

• continuous
• discontinuous

Question 6

What is continuous variation

Answer 6

• When the individuals in a population vary within a range
• there are no distinct categories
• e.g. humans can be any height within a range (139cm, 175cm, 185.9cm, etc), not just tall or short

Question 7

Give examples of continuous variation in animals

Answer 7

• Milk yield, e.g. cows can be produce any volume of milk within a range
• Mass, e.g. humans can be any mass within a range

Question 8

Give examples of continuous variation in plants

Answer 8

• Number of leaves, e.g, a tree can have any number of leaves within a range
• Mass, e.g. the mass of the seeds from a flower head varies within a range

Question 9

Give examples of continuous variation in microorganisms

Answer 9

• Width - e.g. the width of E. coli bacteria varies within a range
• Length - e.g. the length of the flagellum can vary within a range

Question 10

What is discontinuous variation

Answer 10

• discontinuous variation is when there are two or more distinct categories
• each individual falls into only one of these categories, there are no intermediates

Question 11

Give examples of discontinuous variation in animals

Answer 11

• Blood group, A, B, AB or O

Question 12

Give examples of discontinuous variation in plants

Answer 12

• colour, e.g. courgettes are either yellow, dark green or light green
• seed shape, e.g. some pea plants have smooth seeds and some have wrinkled seeds

Question 13

Give examples of discontinuous variation in microorganism

Answer 13

• Antibiotic resistance, e.g. bacteria are either resistant or not
• pigment production, e.g. some types of bacteria can produce a coloured pigment, some can’t

Question 14

What can variation be caused by

Answer 14

• Genes
• the environment
• or both

Question 15

What does genetic factors in causing variation referring to

Answer 15

• Different species have different genes
• individuals of the same species have the same genes but different versions of them (alleles)
• the genes and alleles an organism has make up its genotype
• the differences in genotype result in variation in phenotype
• examples of variation caused by only genetic factors include blood group and antibiotic resistance in bacteria
• you inherit your genes from your parents. This means variation caused by genetic factors is inherited

Question 16

What is phenotype

Answer 16

The characteristic displayed by an organisation

Question 17

What does environmental factors in causing variation refer to

Answer 17

• variation can also be caused by differences in the environment e.g. climate, food, lifestyle
• characteristics controlled by environmental factors can change over an organisms life
• examples of variation caused only by environmental factors include accents and whether people have pierced ears

Question 18

What does genetic factors and environmental factors causing variation refer to

Answer 18

Genetic factors determine the characteristics an organism’s born with, but environmental factors can influence how some characteristics develop for example:
- height, genes determine how tall an organism can grow. But diet and nutrient availability affect how tall an organism actually grow
- flagellum, genes determine if a microorganism can grow a flagellum, but some will only start to grow them in certain environments e.g. if metal ions are present

Question 19

How do you investigate variation

Answer 19

• usually you take samples of a population
• the mean is an average of the values collected in a sample
• it can be used to tell if there is variation between samples

Question 20

Give an example that can be used to tell if there is variation between samples

Answer 20

The mean height of a species of tree in:
Woodland A = 26m
Woodland B = 32m
Woodland C = 35m
So the mean height varies

Question 21

What is normal distribution

Answer 21

A normal distribution is symmetrical about the mean. Most samples will include values either side of the mean so you end up with a bell-shaped graph

Question 22

What do you use to tell you about variation within a sample

Answer 22

Standard deviation

Question 23

What is standard deviation

Answer 23

The standard deviation tells you how much the values in a single sample vary. It’s a measure of the spread of values about the mean

Question 24

Sometimes you’ll see the mean written as e.g. 9_+_3. What does this mean

Answer 24

This means that the mean is 9 and the standard deviation is 3, so the most of the values are spread between 6 and 12

Question 25

What does a large standard deviation mean

Answer 25

It means the values in the sample vary a lot

Question 26

What does a small standard deviation mean

Answer 26

It tells that most of the sample data is around the mean value, so varies a little