IB Biology SL - Evolution

5.4 Evolution

5.4.1 Define evolution

·      The cumulative change in the heritable characteristics of a population.

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.

5.4.3 State that populations tend to produce more offspring than the environment can support.

·      Populations tend to produce more offspring than the environment can support.

5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.

more offspring may be produced than the environment can hold;

struggle for existence can occur;

offspring whose traits best adapt them to environment will survive/survival of fittest;

change in environment will lead to survivors with new/different traits;

correct use of term natural selection/selective pressure;

variation is heritable / over time more offspring born with new trait;

change in gene pool;

when entire population (of a species) exhibits new trait, evolution has occurred;

5.4.5 state that the members of a species show variation

·      members of a species show variation

5.4.6 Explain how sexual variation promotes variation in a species

offspring vary in traits;

variation results from sexual reproduction;

independent assortment of alleles (during meiosis of spermatogenesis/ oogenesis) contributes to variation;

meiosis is the cellular process that produces gametes;

crossing over (during meiosis) increases variation;

fertilization (combination of different genomes) contributes to variation;

5.4.7 Explain how natural selection leads to evolution.

Darwin’s theory

populations produce more offspring than can survive;

individuals show variation;

limited resources;

create a struggle for survival/competition;

survival of the fittest / some are better suited to the environment and survive; variation/characteristic must be heritable;

 best fitted individuals survive to reproduce;

advantageous variation/characteristic/allele passed on;

over time advantageous variation/characteristic/allele increases in the population;

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

Example 1
Antibiotic resistance in bacteria (for example Gonorrhea)
Environmental change: exposure to the antibiotic;

Response 1: antibiotic-sensitive bacteria die/ antibiotic-resistant ones survive;
Response 2: pass on antibiotic-resistance gene/inheried trait;

Drug-resistance gene transferred to other bacteria (by plasmids);

Over time resistance in the population is increased

Example 2
Galapagos finches, some with strong big beaks and some with small beaks

Environmental change: wet years with abundant small seed chang e to drought years with only large seeds (as prevalent food source);

Response 1: small beaked finches die leaving primarily finches with strong/large beaks/ vice cersa
response 2: finches with large beaks survive to pass gene/ inherited trait to offspring;

Over time large beaks predominate