Diversity

Question 1

Describe the key stages in the process of natural selection

Answer 1

Random mutation can result in new alleles of a gene
•Many mutations are harmful but, in certain environments, the new allele of a gene might be advantageous
•Organisms with the advantages allele survive and reproduce (more than other individuals)
•So the advantageous allele is passed on to the next generation
•(As a result, over many generations) the new allele increases in frequency in the population.

Question 2

Explain how competition can play a part in the evolution of a particular characteristic*

Answer 2

variation in the specific characteristic (due to previous mutations)
•Individuals with the specific characteristic (state which type of the characteristic is advantageous, e.g. the darkest/longest/biggest) outcompete / have a selective advantage
•These individuals survive and reproduce
•Pass on the advantageous allele for …specific characteristic to offspring;
•Frequency of this allele increases in the population

Question 3

A difference in the molecular structure of a protein may arise in a small population. Explain how the difference may arise and how it may spread in the population.

Answer 3

mutation causes variation;
•genes (coding) for protein with different structures;
EITHER

•individuals with a modified protein have a selective advantage
•are more likely to survive and reproduce
•allele frequency increases over generations / time;

OR
•changed structure does not affect protein function;
•these structural differences accumulate over time;

Question 4

Explain what is meant by stabilising selection and describe the circumstances under which it takes place. [4]

Answer 4

Occurs in an unchanging environment;

2. Selection against extremes / selection for the mean / mean / median / mode unaltered
3. Range / S.D is reduced
4. Increasing proportion of populations becomes well adapted to environment;

Question 5

Frequent treatment with certain antibiotics can result in resistant strains of bacteria. Explain how. [3]

Answer 5

Mutation present / occurs;
Ignore antibiotic causes mutation.
2. Resistance gene / allele;
Reference to immunity disqualifies first credited marking point.
3. Resistant bacteria (survive and) reproduce (by binary fission);

Question 6

Describe how selection has increased the difficulty of treating bacterial infections with antibiotics [4]

Answer 6

Antibiotic) resistant gene/allele;
2. Vertical (gene) transmission;
3. Resistant bacteria (survive and) reproduce / population of
resistant bacteria increases;
4. Increase in frequency of (resistant) allele/gene (in future generations);

Question 7

Explain how bacteria evolve resistance to an antibiotic.

Answer 7

mutation;
•resistant individuals survive/susceptible ones killed by antibiotic/
mutants have selective advantage;
•survivors breed, so the proportion of resistant alleles in population increases;
•overuse of antibiotic gives resistant bacteria a selective advantage

Question 8

Penicillin has been the antibiotic of choice for the treatment of bacterial meningitis. Since the year 2000, strains of Neisseria meningitidis that are resistant to penicillin, sulfonamides and rifampin have been discovered in the UK. Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics. [4]

Answer 8

A random mutation occurs in one bacterium causing it to be resistant to penicillin

2. This bacterium is more likely to survive and divide by binary fission, passing on the allele for resistance to penicillin to its offspring
3. The frequency of the penicillin resistance allele increases in the population of bacteria
4. Another random mutation occurs in one of these bacteria which gives it resistance

Question 9

Describe aseptic techniques which should be used when transferring a sample of broth culture on to an agar plate. Explain why each is important [6]

Answer 9

Keep lid on Petri dish OR Open lid of Petri dish as little as possible;

2. To prevent unwanted bacteria contaminating the dish
3. Wear gloves / Wash hands;
4. To prevent contamination from bacteria on hands/mouth AND to prevent spread of bacteria outside the lab;
5. Use sterile pipette OR Flame the inoculating loop OR Flame the neck of the container of the culture;
6. To maintain a pure culture of bacteria;

Question 10

Suggest and explain the advantages of asexual and sexual reproduction

Answer 10

Asexual
Fewer stages so quicker;
Only one parent involved so can colonise new environment;
Produces clone so successful (geno/pheno)type maintained;

Sexual
increases genetic diversity so greater chance of survival/success;