Biology November: B14 B15 B16


B14.2 Evolution by natural selection

Natural Selection = The process by which evolution takes place. 

Organisms produce more offspring than the environment can support. Only those that are most suited to their environment will survive to breed and pass on their useful characteristics to their offspring. 

The theory of evolution states that all species of living things have evolved from simple life forms that first developed over 3 billion years ago. 

The key stages in natural selection:

Mutation of gene → Advantage to survival → Breed → Pass on genes

Mutation = A change in the genetic material of an organism

If two populations of a species become so different they can no longer interbreed to form fertile offspring, they have formed two new species.

1 of 7

B15.5 Evidence for evolution

Fossils = The remains of organisms from millions of years ago that can be found in rocks, ice, and other places.

How are fossils formed?:

  • When an animal or plant does not decay after it has died.

  • Many fossils are formed when harder parts of the animal or plant are replaced by minerals as they decay and become part of the rock.

  • Some of the fossils found are not of actual animals or plants, but are preserved traces they have left behind.

The fossil record is not complete for many reasons:

  • Many of the earliest forms of life were soft-bodied organisms. This means they have left little fossil trace.

  • Fossils could also have been destroyed by geological activity.

  • Most organisms that died did not become fossilised, as it is hard to have the right conditions for fossilisation.

  • Many fossils have not been found yet.

2 of 7

B15.6 Fossils and Extinction

Extinction is the permanent loss of all the members of a species.

Living organisms can cause extinction and change in an environment in many different ways:

  • New predators can wipe out unsuspecting prey animals very quickly if the prey animals do not have adaptations to avoid them.

  • New diseases can bring a species to the point of extinction.

  • One species can cause another to become extinct by successful competition.

3 of 7

B15.8 Antibiotic resistant bacteria

Bacteria can evolve rapidly because they reproduce at a fast rate. Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics so are not killed. They survive and reproduce, so the population of the resistant strain increases by natural selection. The resistant strain will then spread because people are not immune to it and there is no effective treatment.

MRSA is a methicillin-resistant bacterium, called staphylococcus aureus, it is an antibiotic resistant bacteria that is spread easily. It is spread as doctors and nurses move from patient to patient.

Deaths were reduced by:

  • Only using antibiotics when really needed

  • Medical staff washing their hands and wearing disposable clothing when necessary

  • Hospitals having a high standard of hygiene

  • Patients that are infected with antibiotic resistant bacteria being isolated

  • Visitors of hospitals washing their hands as they come and go

The development of new antibiotics is costly and slow and is unlikely to keep up with the emergence of new resistant strains.

4 of 7

B15.9 Classification - The modern classification s

  • Developed by Carolus Linnaeus

    • Consists of 7 levels, known as the taxonomic hierarchy

      • Kingdom, Phylum, Class, Order, Family, Genus, Species.

  • Kingdoms

Traditionally all living things have been grouped into 5 kingdoms.

  • Prokaryotes - very simple

  • Protista -very simple w/ organelles, plasmodium

  • Fungi - mushrooms, very small threads

  • Plants

  • Animals

As evidence of the internal structures of organisms became more developed due to improvements in microscopes, and the understanding of biochemical processes progressed, new models of classification were proposed.

5 of 7

Binomial Nomenclature

  • Developed by Carolus Linnaeus

  • First name = organism’s genus

  • Second name = organism’s species


  1. The first letter of the genus is always capitalised

  2. The first letter of the species is never capitalised

  3. Should be underlined or in italics

6 of 7

Modern Classification - The 3 domains system

New evidence, for example DNA analysis, suggests that the 5 kingdom system classification is not accurate.

Instead the 3 domain system is better.

The 3 domain system:

  • Archaea

    • These are primitive forms of bacteria that include the extremophiles that can live in extreme conditions

      • 1 kingdom, the Archaea

  • Bacteria

    • True bacteria and bacteria that can photosynthesise

      • 1 kingdom, the Eubacteria

  • Eukaryota

    • All organisms with a nucleus in their cells

      • 4 kingdoms, Protista, fungi, plants, animals

7 of 7


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Variation and reproduction resources »