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Flashcards in 8.2 Deck (16):

When large numbers of offspring are produced within a population, what type of competition occurs?

Intraspecific competition


phenotypic variation within a population will mean that some offspring will die or will not reproduce as:

they are more susceptible to disease
less able to escape predators
less able to find a mate or unable to obtain sufficient food


The offspring best suited to their environment are most likely to survive, reproduce and pass on their alleles to the next generation - this is the basis of:

natural selection and the survivors are said to have a selective advantage


Natural selection is:

Process by which the best adapted organisms in a population survive, reproduce and pass on their alleles to their offspring


Selective advantage is:

a variation that gives an organism advantage over another, therefore it is most likely to survive and reproduce


As microorganisms (e.g. bacteria) reproduce very rapidly, changes in allele frequency within a population can be:

observed taking place over a relatively short time


Bacteria vary in their susceptibility to a particular:



The bacteria most susceptible will...

die first when the population is exposed to the antibiotic


Gradually the proportion of most resistant bacteria in the population ...



The bacteria that can survive exposure to the antibiotic are able to reproduce and...

pass on their genes for resistance to their offspring


The antibiotic is exerting a ...

selection pressure on the bacterial population and the frequency of the gene for the resistance to it is increasing within the population


Selection pressure is:

the environmental force altering the frequency of alleles in a population


If a person completes their course of prescribed antibiotics, the chance of any bacteria surviving is small. Their immune system can...

destroy the remaining bacterial cells


However, if a person stops the treatment early - a high proportion of the surviving bacteria will be resistant. Therefore would need stronger doses of...

that antibiotic or another type of antibiotic to combat the infection


If incomplete antibiotic treatment is repeated often enough, then after many generations, all of the bacteria in the population will have...

evolved complete antibiotic resistance


In the absence of antibiotics, the proportion of resistance genes in the population tends to decrease to a low level this is because within the population, the resistant bacteria tend to be

at a disadvantage relative to those that are not resistant to antibiotics