Classification and evolution
What is classification?: The organisation of living things into groups according to their similarities.
What is a species?: Members of the same species are very similar. It is a group of organisms which can breed together and produce fertile offspring.
What do evolutionary trees tell us?: Evolutionary trees tell us how species have evolved, why some animals have certain adaptations and how different species link together as they have evolved. It shows the common ancestors between species.
Evidence for evolution: Fossils show us that there have been other species on Earth than the ones we see today, and that they have changed over time. We can also see from breeding species that characteristics can change over time. This is evidence to support the THEORY OF EVOLUTION.
Charles Darwin had a theory about evolution, he realised:
1) Organisms produce more offspring than the amount that are able to survive
2) There is variation in the characteristics shown by an organism within a population
3) There is a struggle for survival (Selection pressure)
4) Those who survive and reproduce will pass on their advantageous genes to the next generation.
These observations helped to form how we know evolution occurs:
1) Variation exists due to genetic mutation
2) Survival of the fittest because there is a selection pressure
3) Fittest reproduce to pass on genes to offspring- repeated over generations
How does antibiotic resistance occur?: Antibiotic resistant bacteria evolve like any other organism:
1) Naturally resistant bacteria already exist in a population of non resistant bacteria, due to genetic mutation
2) Antibiotics kill off the competition for survival from the non resistant bacteria, this means the resistant survive and can reproduce more
3) The antibiotic resistant gene is passed on to their offspring and this is repeated over generations until you have an entire population of antibiotic resistant bacteria.
This is why there has to be a limit on the use of antibiotics- because antibiotic resistant bacteria have more of a chance if antibiotics are used often.
Darwin wasn't the only scientist who had a theory about evolution. Darwin's ideas weren't accepted for a long time because his theory conflicted with the religion and he had no solid evidence because no-one knew about genetics.
Another scientist called Lamarck also thought that species changed over time, but unlike Darwin he thought it was because of environmental changes in the animal's lifetime which were passed onto offspring. E.g. If a mouse had its tail cut off so would it's offspring.
Natural selection: There is always variation but natural selection chooses the fittest in their environment to be able to survive and pass on their genes.