| Types of selection | - Directional selection
- Stabilising selection |
| Directional selection | - When individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other
- Could be response to environmental change
- Changes the characteristic of the population
e.g. bacteria antibiotic resistance |
| Stabilising selection | - Selection may favour average individuals
- Preserves the characteristics of an individual
- Occurs when environment isn't changing
- Reduces range of possible characteristics
e.g. human birth weight |
| Directional selection (antibiotic resistance) | - Some individuals in pop. have alleles that give them resistance to an antibiotic
- Pop. is exposed to antibiotic, killing bacteria without resistant allele
- Resistant bacteria survive + reproduce without competition, passing resistant allele to offspring
- After some time, most organisms in pop. will carry the
antibiotic resistant allele |
| Stabilising selection (human birth weights) | - Humans have a range of birth weights
- Very small babies are less likely to survive, find it hard to maintain body temperature
- Giving birth to large babies can be difficult, so large babies less likely to survive
- Conditions most favourable to medium-sized babies, tends to shift towards middle range |
| Different types of adaptations | - Behavioural
- Physiological
- Anatomical |
| Behavioural adaptations | - Ways an organism acts that increase its chance of survival + reproduction
e.g. playing dead |
| Physiological adaptations | - Process inside an organism's body that increase its chance of survival
e.g. hibernating during winter, lowers rate of metabolism, conserving energy |
| Anatomical adaptations | - Structural features of an organisms body that increase survival
e.g. thick fur |
| Two ways for testing the effects of antibiotics | - Agar plates |
| What is an agar plate | - Petri dish with agar jelly |
| Testing the effects of antibiotics using agar plates | - Bacteria grown in liquid broth
- Use sterile pipette to transfer bacteria to agar plate
- Spread bacteria over the plate
- Place paper discs soaked with different antibiotics spaced apart
- Add negative control disc soaked only in sterile water
- Tape lid on, incubate plate at 25c for 48 h
- Allows bacteria to grow, can see inhibition zones |
| Inhibition zones meaning | - Anywhere the bacteria cant grow appears as clear patch in the lawn of bacteria
- Size of inhibition zone tells us how well an antibiotic works
- The larger it is, the more the bacteria were inhibited from growing |
| Antiseptics and disinfectants | - Prevents contamination of cultures by unwanted microorganisms
- Important as contamination can affect growth of the microorganism that you're working with
- Can also making you ill |
