Outline the process of gas exchange necessary for aerobic respiration in a unicellular eukaryotic organism.

Explain how the process of evolution occurs.

Oxygen must be taken up AND carbon dioxide must be released (Both needed)

Gases pass through a cell membrane by simple diffusion

Require a concentration gradient
OR
pass from high concentration to low concentration

Without requiring energy
OR
passive process

Large SA: vol ratio

Evolution is «cumulative» change in population/species over time
OR
change in allele frequency

A population has variations amongst the individuals

Due to meiosis
OR
sexual reproduction

Due to mutations

Certain variations give an advantage to some organisms over others in certain environments

Populations/species produce more offspring than the environment can support

Individuals of the species compete for the same resources

The better-adapted organisms tend to survive and reproduce
OR
less adapted organisms tend to die or reproduce fewer offspring

Individuals «that reproduce» pass on their «heritable» characteristics/alleles/genes to their offspring (“Traits” is an acceptable alternative to “characteristic”)

Natural selection increases the frequency of «heritable» characteristics/alleles/genes of the better-adapted organisms (Accept “genes”)

Specific example described (Example must be “described” to award marks)

Award [7 max] if no reference to heritable characteristics or alleles.

Gas exchange and simple diffusion – Most candidates knew what aerobic respiration was, but could not apply it to the question. Perhaps under the pressure of the examination, candidates many did not progress to the second line and therefore missed the expression ‘unicellular eukaryotic organism’. Detailed knowledge of the alveoli and the Krebs cycle did not gain marks.

Evolution – Several G2 comments were made which questioned whether the candidates should be answering a question on evolution. It is a topic that has appeared on the examination many times and well prepared candidates had no trouble answering it. The number of ‘Lamarckian’ answers where individuals instead of populations or species were evolving showed the continued decrease shown over the last few years.