6.3.1 Theory of evolution (biology only)
6.3.2 Speciation (biology only)
Speciation
- Populations become extremely varied & no interbreed anymore
- Formation of new species (a group of organisms able to interbreed & produce fertile offspring)
Charles Darwin – see 6.2.2 Evolution
Alfred Russel Wallace
- Published joint writings with Darwin in 1858
- Best known for his work on warning colouration in animals & his theory of speciation
Describe the steps which give rise to new species
- Genetic variation – each population has wide range of alleles that control characteristics
- Natural selection
- Speciation
- Isolation
- 2 population of a species become geographically separated
- Different mutations take place in isolated groups
- Overtime species evolve to be different to each other – cannot interbreed
6.3.3 The understanding of genetics (biology only)
Gregor Mendel
- Carried out breeding experiments on pea plants
- Inheritnace of each characteristic is determined by ‘units’ (genes) that are passed onto descendants unchanged
Describe the development of our understanding of genetics including the work of Mendel
- Mid-19th century – Gregor Mendal carried out breeding experiments on plants
- Late 19 – behaviour of chromosomes during cell division was observed
- Early 20th century – chromosomes and Mendel’s ‘units’ behaved in similar ways – led to the idea that the ‘units’, now called genes, were located on chromosomes.
- Mid-20th century – structure of DNA was determined & the mechanism of gene function worked out
Why using large no of offspring plants can improve the investigation (2)
- Large no so more reliable
- Anomalies can be identified
Why importance of Mendel’s discovery wasn’t recognised at that time? (2)
- DNA not discovered
- Mendel wasn’t considered as a scientist / wasn’t part of academic establishment
6.3.4 Evidence for evolution
See 6.3.5 Fossils, 6.3.6 Extinction & 6.3.7 Resistant bacteria
6.3.5 Fossils
Fossils – the ‘remains’ of organisms from millions of years ago, which are found in rocks
Where are fossils formed? (3)
- Parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
- When parts of the organism are replaced by minerals as they decay
- As preserved traces of organisms, such as footprints, burrows and rootlet traces
How fossils are formed?
- Animal / plant dies & body covered in sediment
- Soft parts decay
- Hard parts (bones) don’t decay and are replaced by minerals
- Lack of O2 and moisture prevent microorganisms to decay
- Preserved traces of organisms eg footprints, burrows & rootlet traces
- Soft parts decay, bones / shells don’t decay
Suggest how insects came to be preserved in the amber (2)
- Trapped and engulfed by amber
- Prevented decay (due to lack of O2 and moisture)
How can fossils give evidence for evolution? (1)
- Show how organisms changed as life developed on Earth
Why scientists are uncertain about how life began on Earth? (1)
- Insufficient evidence
Suggest 2 reasons why there are gaps in the fossil record (2)
- Fossils not found yet
- Fossils are destroyed by geographical activities eg volcanoes
- Conditions not right for fossilisation
6.3.6 Extinction
Extinction – occur when there are no remaining individuals of a species still alive
Why a species may become extinct? (3)
- Environmental changes – species can’t adapt fast enough
- Natural disaster eg flooding, drought
- New predator / disease eg no resistant alleles
- Human activities eg hunting, deforestation
- Competition for food / mates
- Catastrophic event wipe out species eg asteroid killed dinosaurs
6.3.5 Resistant bacteria
Bacteria can evolve rapidly because they reproduce at a fast rate
How pathogens produce new strains via mutation (6)
- Mutations of bacterial pathogens produce new strain
- Some strains might be resistance to antibiotics and so are not killed
- Some survive and reproduce by binary fission
- Gene for resistance passed on to offspring so pathogen being immune
- Population of resistant strain rises
- Resistant strain then spread coz ppl not immune to it & has no effective treatment
Methicillin-resistant Staphylococcus aureus (MRSA)
- Bacterium that has evolved to be resistant to lots of antibiotics (superbugs bacteria)
How to reduce rate of development of antibiotic resistant strains? (3)
- Doctors reduce use of antibiotics for non-serious / viral infections
- Patients complete course of antibiotics to kill all bacteria so none survive to mutate & form resistant strains
- Restrict agricultural use of antibiotics
Development of new antibiotics
- Costly
- Slow
- Unlikely to keep up with the emergence of new resistant strains