1. AS Biology UNIT F212 Module 3 – Biodiversity and Evolution Evolution
Sona Arya
E – mail:

2. Aims To provide an overview of Evolution
All tasks/activities are on the worksheet given last lesson – also on Moodle under “Revision Activities”
OCR Biology 1 Chapter on Moodle on Evolution

3. Exam Objective Define the term variation
The presence of differences between individuals

4. Variation between individuals may be due to……
Mutations in the genes or chromosomes.
Meiosis, which produces non- identical gametes.
Random fertilisation of the eggs.

5. Random fertilisation

6. So each gamete produced by an individual is unique and can lead to variation

7. Exam Objectives
Discuss the fact that variation occurs within a species as well as between species

8. Which is Which? Intraspecific or Interspecific? Within species?
E.g. Weight, colour of beak of same birds
Between species?
Interspecific
E.g. Weight, colour of beak of different types of birds

9. Continuous and Discontinuous
Variation in which there is a full range of intermediate values between two extremes
Continuous
Variation in which there are discrete groups with no intermediate values
Discontinuous

10. Discontinuous variation

11. Exam Objectives
Describe the differences between continuous and discontinuous variation using examples found in a range of characteristics found in
plants
animals
microorganisms

13. On your white boards ....
Continuous or Discontinuous? Sex Discontinuous Antibiotic resistance Length of leaves of plants Continuous Colour

14. On your white boards ....
Continuous or Discontinuous? Blood Group Discontinuous Presence of flagella Number of leaves Continuous Height

15. Variation Differences between individuals can be produced by
Genetic and /or Environmental influences
What does this mean?

16. Exam Objectives
Explain both genetic and environmental causes of variation

17. Genetic Variation
Involves different versions of the same genes (alleles)
Genes and alleles make up an organisms genotype and phenotype (displayed characteristics)
Inherit genes from parents
Variation is inherited
E.g: Blood group (humans)
Antibiotic Resistance in bacteria

18. Environmental Variation
Involves differences in the environment e.g. Climate, diet, lifestyle
Characteristics can change over an organism’s life
E.g: accents
Pierced ears

19. Both
Genetic factors determine what characteristics an organism is born with, but environmental factors can influence how some characteristics develop
E.g. Height
Flagellum

20. Adaptations
Behavioural Adaptations

21. Physiological Adaptations

22. Anatomical Adaptations

23. Examples of the adaptations of xerophytes

24. Exam Objectives
Outline the behavioural, physiological and anatomical (structural) adaptations of organisms to their environment
Do as Table using Revision Guide / Textbook

25. Examples of adaptations which help organisms survive p3
Behavioural
Earthworm burrows when touched to avoid predators and drying out
Hedgehog rolls into a ball to avoid predators
Fennec fox in desert remains in burrow in day and emerges at night
Venus flytrap plant leaves close around insect when sensitive hairs touched
Stomata of xerophyte may open at night and close in day
Physiological
Humans produce more haemoglobin at high altitudes
Humans with sickle cell allele can survive malaria
Plants near the sea have cytoplasm with low water potential so water is still absorbed by osmosis
Venus flytrap plant leaves secrete extracellular enzymes which digest insects
Yeast fungus can respire aerobically or anaerobically
Some bacteria species have alleles for antibiotic resistance
Anatomical
Mammals e.g. cats have hair for heat insulation
Mammal predators e.g. lions have large canine teeth to kill
Fennec fox in desert has large ears to lose heat effectively and give good direction of sound
Xerophytic plants have long roots, thick waxy cuticle, leaves with small surface area, rolled leaves, stem stores water, fewer stomata, protected stomata
Bacteria may have a flagellum for locomotion

26. Exam Question Hedgehogs are commonly found in gardens
throughout the UK.
They are brown with small ears, feet with claws
and long, spiky fur.
They hibernate over winter and can roll into a ball
when alarmed.
Question
Describe one behavioural, one physiological and two anatomical adaptations of hedgehogs.
Suggest how each helps hedgehogs to survive.

27. EVOLUTION
Explain the links.

28. They were all part of Charles Darwin’s voyage of discovery.

29. Evolution - Definition
Evolution is the cumulative change in the heritable characteristics of a population.
What do we mean by cumulative, heritable and population?

30. Exam Objectives
Explain the consequences of the four observations made by Darwin in proposing his theory of natural selection

31. Use pages 222 and 223……or RG pg 103/purple OCR 214
To answer the questions on page 4 of the booklet about Darwin’s four observations.

32. Charles Darwin and the theory of evolution by natural selection p4
Observations
Organisms produce many offspring
Members of a species vary
Some variations are inherited
Population size remains fairly constant
Conclusions
There is competition for survival
Individuals which are better adapted to the environment are more likely to survive and reproduce so their genes / alleles are passed on
Over time organisms may change and develop into new species
(changes in genes to make new alleles are due to random mutation)

33. Examples of Selection Pressures
Availability of suitable food
Predators
Diseases
Physical and Chemical factors i.e. Hot and cold places

34. Natural selection and selection pressures
Ability of xerophytic plants to survive in areas with little water
2) Camouflage and predators
e.g. peppered moth and banded snails
3) Ability of grasses to grow roots in soil
containing copper ions
4) Survival of bacteria with allele for antibiotic resistance in the presence of that antibiotic
5) Survival of humans with allele for sickle cell anaemia when infected with malaria parasite

35. Peppered moths – evolution in action http://www. techapps
Which moths survive? Why are the moths
Why? different colours in different areas?

36. Banded snails Caepea nemoralis and camouflage

37. Genetic diversity Which antibiotics could be used to kill these bacteria? How does this demonstrate adaptation and natural selection?

38. Genetic diversity in humans Normal and sickle cell haemoglobin – adaptation and natural selection

39. Natural Selection Read page 223.
Now in pairs, write it out as a flow chart
but including the terms:
competition / mutation / variation / allele / phenotype / selection pressure / survival / reproduce / pass on allele / allele frequency / increases
When you are happy with your chart, make a note of it.
Sort the cut and stick on last page.

40. Natural Selection Survival of those with new allele
Competition Reproduce, so pass
allele to offspring.
Changed characteristic
Mutation/Variation
(phenotype)
Selection Pressure Allele frequency rises
Survival of those with new allele

41. Exam Practice
Some plants living where there is little soil water have short roots but most have an extensive root system.
Can you explain this using ideas from natural selection?
Answer
Intra specific variation in root length
Caused by a random mutation in a gene  new alleles  new phenotypes e.g. short or long roots
Competition for water = selection pressure
Plants with longer roots are better adapted and are more likely to survive and reproduce
Allele for long roots passed to offspring and its frequency in the gene pool increases

44. Evolution can lead to Speciation – the formation of a new species p5
A species is a group of organisms with similar anatomical, behavioural and biochemical features which can reproduce to produce fertile offspring
To produce a new species a population must become separated so it cannot reproduce / breed with the original group. It is reproductively isolated.
Then the separate populations will continue to adapt to their environment so that eventually the individuals cannot produce fertile young with members of the original group.
A new species has evolved.
Find out the similarities and differences between the 2 ways of forming a new species = allopatric speciation and sympatric speciation (p228 text + workbook p6)

45. Exam Objectives
Define the term speciation

46. Speciation - forming a new species over time.
Allopatric speciation needs a geographical barrier separating populations.
Sympatric speciation occurs when genetic differences appear between populations.

47. Speciation – pages 5 and 6
Populations must be reproductively isolated – alleles / genes cannot mix
Allopatric – geographical isolation
e.g. sea, river, mountain
Sympatric – isolation is behavioural, biochemical, time of reproduction (spring/summer) etc
Then individuals in the population adapt through random mutation to the environmental selection pressures

48. Sympatric or Allopatric ?

49. Finches on the Galapagos Islands p5
Common ancestor
Geographical isolation on islands
Random mutations  better adapted to environment e.g. beak shape and size for different foods = selection pressure
Different changes on different islands
Populations are eventually so different that they cannot reproduce to produce fertile offspring
Allopatric speciation has occurred

50. Allopatric Speciation – Key Points for Exam Answers
Physical barrier (isolating mechanism) separates members of a population.
Selection Pressures different in 2 regions.
Different alleles selected for in each region.
Random Mutations.
Chromosome numbers change over time,
so individuals from 2 populations can no longer interbreed successfully
So new species formed

51. 3 Jackal species live in the same regions of East Africa but do not interbreed. Why not? Speciation Type?
Side-striped Jackal
Golden Jackal Black-backed Jackal

52. Sympatric Speciation – Key Points
Isolating mechanism is a genetic difference between individuals.
E.g. a mutation produces the wrong number of chromosomes, so offspring are infertile.
A mutation produces different markings so individuals do not recognise each other as the same species.

53. Checking your learning What do these words mean?
Species
Speciation

54. And what do these words mean?
Reproductive isolation
Allopatric speciation
Sympatric speciation

55. Why are these so important to biologists?

56. Evolution of the horse

57. Human evolution Increased brain size + becoming bipedal

58. Exam Objectives
Discuss the evidence supporting the theory of evolution, with reference to fossil, DNA and molecular evidence
Do as a table using Revision Guide/OCR book

59. Using DNA bases as evidence which 2 animals are most closely related
Using DNA bases as evidence which 2 animals are most closely related? And which are most distantly related?
Animals
% difference in bases C, G, A and T in coding DNA
human / chimpanzee
0.87
human / gorilla
1.04
human / orang-utan
2.18
chimpanzee / gorilla
0.99
chimpanzee / orang-utan
2.14
gorilla / orang-utan
2.25

60. Video – short circuit – the theory of evolution – 20 mins
Evidence for evolution – page whale evolution animal evolution + music
1) Fossils
horses  increased size and the development of hooves
Archeopteryx – reptile / bird (missing link)
humans – increased brain size and become bipedal
2) DNA base sequence
similarities suggest a common ancestor;
the lower the differences the more recent the
separation of the species
3) Amino acid sequence
DNA codes for order of amino acids in proteins;
similarities in amino acid sequences suggest evolution from a common ancestor
Video – short circuit – the theory of evolution – 20 mins

61. Variations + Adaptations + natural selection
An adaptation is a character that increases the chances of the survival and reproduction of that organism
Variations between organisms in different species and between members of the same species mean that some organisms are better adapted to survive in an environment than others; this is natural selection

62. Exam Objectives
Outline how variation, adaptation and natural selection are major components of evolution

63. Natural selection Variation in characteristics
Selection pressure – environmental factor
Some organisms more likely to reproduce than others and pass their alleles to the next generation
Allele frequency in population will change if new selection pressure occurs

64. Some key words to use to discuss your answer:
Variation
Overpopulation
Competition
Selection pressure
Adaptation
Inheritance
Allele frequency

65. Is evolution still happening?
Use textbook pages 225 – 227 and revision book pages 104 – 105 to complete page 8 in workbook
Try SAQs 5, 6 and 7

66. Is evolution still happening? P224-6

67. Antibiotic Resistance in Bacteria
Use natural
selection to
explain the
resistance
shown by these
bacteria.
Make a note of it
as a flow chart.

68. Exam Objectives
Discuss why the evolution of pesticide resistance in insects and drug resistance in microorganisms has implications for humans

69. Is evolution still happening? page 8
Resistance to antibiotics in bacteria
(selection pressure = antibiotic in environment)
random mutation = change in DNA bases during semi- conservative replication (making copies of DNA)
some bacteria species are now not killed by many antibiotics
e.g. MRSA = methicillin resistant Staphylococcus aureus;
e.g. antibiotic resistant TB
therefore scientists need to develop new antibiotics

70. Is evolution still happening? page 8
2) Resistance to pesticides in insects
(selection pressure = pesticide in environment)
a) random mutation – change in DNA bases
b) more difficult to control spread of malaria if Anopheles species are resistant;
for other insects, crops may fail
c) chemicals can pass along food chain;
use biological control – natural predators;
insects not killed by pesticide pass allele for resistance to offspring;
then time and money needed to develop new pesticides

71. Stretch and challenge
Why does evolution seem to happen more quickly in microorganisms and insects than in mammals?
Suggested reasons:-
length of life cycle
frequency of mutations
variety of selection pressures

72. Is evolution still happening?

79. Finally.... http://www.becominghuman.org/
Use the website to find out what you want to know about evidence, anatomy and culture of our ancestors.

80. Exam Practice End of Chapter OCR1 Book on Moodle
Exam Qs on Moodle under “Evolution”
Past Papers F212