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level: 9.4 Types of selection

Questions and Answers List

level questions: 9.4 Types of selection

QuestionAnswer
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