Variation & Natural Selection Flashcards
Antibiotics
2 marks
Substance that controls the spread of bacteria in the body by killing them or stopping them reproducing.
Gene
2 marks
A short length of DNA that codes for a particular characteristic.
Histogram
(1 mark)
A graphical representation of the distribution of numerical data.
Mutation
(3 marks)
Random + spontaneous change in the structure of a gene, chromosome or number of chromosomes.
Species
3 marks
Type of organism that is the basic unit of classification.
Individuals of different species are not able to interbreed successfully.
Continuous variation
3 marks
This is a gradual change in a characteristic across a population, e.g human height, mass + shoe size.
- it is represented as a histogram.
Histogram should show
2 marks
Normal distribution, with most individuals around the average value + a few at the extremes.
Discontinuous variation
4 marks
Individuals will fit into a group – there are no intermediates.
e. g ability to roll your tongue, blood group + hand dominance
- it is represented as a bar chart.
How is Discontinuous Variation represented?
1 mark
Bar chart
Main Blood Groups
4 marks
A, B, AB, O
All Blood Groups
8 marks
A-, A+, B-, B+, O-, O+, AB-, AB+
Causes of Genetic Variations
7 marks
Changes to chromosomes or genes (DNA);
- Mutations are random changes in the number of chromosomes or the structure of a gene.
- Independent assortment during meiosis increases variation because it results in genetically different gametes.
- The random nature of sexual reproduction also gives rise to variation.
Mutations are random changes in
4 marks
The number of chromosomes (e.g. Down syndrome)
or the structure of a gene (e.g. cystic fibrosis).
The random nature of sexual reproduction also gives rise to
1 mark
Genetic variation
Independent assortment during meiosis increases variation because
(1 mark)
It results in genetically different gametes.
Example of environmental variation
2 marks
Human height is genetically controlled but actual height reached will depend on the nutrition available.
Causes of Variation
2 marks
Genetic + Environmental factors
How is Continuous variation represented?
1 mark
As a histogram.
Natural selection
1 mark
Living organisms are adapted to their environments in order to survive.
Thorny devil
4 marks
- Lizard native to the Australian Outback.
- In between its scales; microscopic channels that catch + carry water.
- Drink through their scales (like sipping through straws); by opening/ closing mouth
Fennec fox
4 marks
- Has huge, bat-like ears to pinpoint their prey, even when buried under the shifting sands.
- Ears also lined with blood vessels; help regulate + cool body temp.
Cuttlefish
3 marks
- Can change colour + texture of their skin; disguise themselves as clumps of floating seaweed - as they stalk their prey or hide from predators.
Atlantic Bluefin tuna
3 marks
- Has an internal heating sytem; special blood vessel structure allows them to maintain a body temp higher than the cold surrounding water.
Competition makes adaptations for survival
1 mark
Very important - only the best adapted will survive.
The theory of natural selection – Charles Darwin
4 marks
There is variation among the phenotypes of individuals in a population.
- Competition (food etc) causes a struggle for existence.
Differential survival
2 marks
The best-adapted individuals survive
+ the less well-adapted individuals do not survive.
The Surviving Phenotype
2 marks
(The fittest) is able to reproduce;
- passes it’s beneficial gene to the next generation.
Natural selection: antibiotic resistance
2 marks
There is variation within bacterial phenotypes.
Some are resistant to antibiotics and some are not.
Resistant individuals survive + non-resistant individuals do not survive
(1 mark)
Differential survival.
The Resistant Bacteria
3 marks
Increase in number - able to reproduce; pass on the resistance gene to the next generation.
Resistant individuals
1 mark
Survive
Non-resistant individuals
1 mark
Do not survive.
Gene for antibiotic resistance
2 marks
Usually caused by a beneficial mutation in the bacterial cells.
Bacterial phenotypes
2 marks
Some are resistant to antibiotics + some are not.
Treating Bacteria with Antibiotics
1 mark
Provides competition.
Evolution
3 marks
A continuing process of natural selection - leads to the gradual change of an organism over time.
- May result in the formation of a new species.
Darwin used the theory of natural selection to
1 mark
Explain the process of evolution.
Fossils
2 marks
Remains of living organisms that have been preserved in rock for millions of years.
Fossils provide
4 marks
Evidence for evolution by showing how an organism looked millions of years ago + how it has changed over time.
- They have provided us with info on some extinct species.
Extinction
1 mark
Species are extinct if there are no living examples left.
Cause of Extinction
2 marks
Species fails to adapt to changes in its environment.
Examples of Extinct Species
2 marks
Dinosaurs + dodos.
Cause of the Extinction of Dinosaurs
1 mark
Meteor strike.
Cause of the Extinction of Dodos
1 mark
Hunted by humans.
Endangered species
1 mark
Species that are at risk of becoming extinct.
Cause of the Extinction of a Species
8 marks
- Climate change.
- Natural disaster.
- Hunted by humans.
- Hunted by non-native animals (introduced by humans).
- Disease.
- Loss of habitat (e.g. deforestation).
Extinction can be avoided by:
8 marks
- Legislation; preventing hunting
- International agreements; limit climate change.
- Special programmes; Nature reserves.
- Education; encourages people to do their part.
How can Legislation help prevent the extinction of a Species
(1 mark)
Preventing the hunting of endangered species.
How International agreements can help prevent the Extinction of a Species
(1 mark)
Agreements that plan to limit climate change.
What Special programmes can help prevent the Extinction of a Species?
(2 marks)
Nature reserves to protect habitats.
How can Education help prevent the Extinction of a Species?
1 mark
Encouraging people to do their part in protecting the environment.
Selective Breeding/Artificial Selection
4 marks
Manipulating natural selection by selecting desirable characteristics in crop plants/domesticated animals that are of use to humans.
Selective Breeding/Artificial Selection Process
4 marks
Humans select individual plants/animals with desirable characteristics (e.g increased crop yield, disease resistance + longer shelf life).
- Are then bred to produce offspring.
Repeated Selection + Breeding Over Many Generations
1 mark
Results in all offspring containing the desirable characteristic.
Wheat has been bred over many years to produce these characteristics:
(5 marks)
- Shorter stalk length less likely to suffer wind damage;
- Uniform size that’s easier to harvest;
- Larger yield.
Benefits of Shorter Stalk Length in Wheat
(1 marks
Less likely to suffer wind damage.
Benefit of Uniform Size Wheat
1 mark
Easier to harvest.
