1.6 - Populations, epidemics and natural selection

Question 1

What were the parameters used to characterise the covid pandemic? (P/R) (2)

Answer 1

1. P: prevalence - proportion of infected individuals
2. R: reproductive rate - no. of people infected by each person with covid

Question 2

what are the 2 models for disease spread? (2)

Answer 2

1. SIR = Susceptible - infected - recovered
2. SIS = Susceptible - infected - susceptible

Question 3

Describe the SIR model for disease spread

Answer 3

Susceptible - infected - recovered:
- Prolonged immunity exhausts supply of susceptible individuals, epidemic extinguishes itself

Question 4

Describe the SIS model for disease spread

Answer 4

Susceptible - infected - susceptible:
- No immunity, susceptible individuals replenished by previously infected individuals, epidemic moves to equilibrium

Question 5

Whats the process of researching a population dynamic? (3)

Answer 5

1. Observation, measured pop. densities
2. model
3. experiment to test model

Question 6

What was the observation made in the study of Lynx and Hare population dynamics?

Answer 6

Snowshoe Hare and lynx pop. densities fluctuate periodically and are linked

Question 7

What are the 3 possible explanations for why Hare populations oscillate? (3)

Answer 7

1. Bottom up - food supplies paramount
2. Top down - predation and disease dominates
3. Social behaviour model - social interactions (territoriality or infanticide)

Question 8

What research did Charles Krebs perform?

Answer 8

Tested models of Hare population dynamics over a 10 year cycle

Question 9

What 2 independant variables did Charles Krebs test relating to Hare populations? (2)

Answer 9

1. Adding food
2. Excluding predators

Question 10

What was the effect of adding food in Charles Krebs Hare population research? (1)

Answer 10

Food supplementation had no effect

Question 11

What were the effects of Excluding predators in Charles Krebs Hare population research? (2)

Answer 11

1. Abolished cycle (no decrease in population)
2. Increased reproduction rate

Question 12

What increases chronic stress in Hare populations? (2)

Answer 12

1. abundance of predators
2. when population is low

Question 13

What does chronic stress effect in Hare populations?

Answer 13

Reproduction rate (decreases reproduction)

Question 14

What do the Lotka-Volterra equations assume? (5)

Answer 14

1. Prey pop. has ample food
2. Predator food supply depends on size of prey pop.
3. Rate of change of pop. proportional to its size
4. Fixed environment
5. Predators have limitless appetite

Question 15

How can changes occur (natural selection) (2)

Answer 15

1. mutation
2. recombination

Question 16

what are the 4 components of natural selection? (4)

Answer 16

1. Variation - individuals of species differ
2. Inheritance - some variation inheritable
3. Competition - populations remain constant size
4. Mutation - new variants can appear

Question 17

What is a phenotype, genotype and trait? (3)

Answer 17

1. Phenotype - observable characteristics of individual
2. Genotype - individuals genetic composition
3. Trait - phenotypic character (e.g. colour or height)

Question 18

What causes cancer?

Answer 18

Somatic mutations cause dysregulation of cell division and tissue growth

Question 19

What can lead to mutations that confer resistance in cancer cells?

Answer 19

Selection on tumour cells by natural defences and chemo

Question 20

What shows that different parts of the tumour cell can evolve cancer driver mutations independantly?

Answer 20

Genomic sequencing

Question 21

What process is important to understand for cancer therapy?

Answer 21

Mechanisms of resistance and mutation selection processes in cancer cells