| Date | May 2013 | Marks available | 3 | Reference code | 13M.2.SL.TZ1.4 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | State | Question number | 4 | Adapted from | N/A |
Question
State three processes occurring in a cell during interphase of the cell cycle but not in mitosis.
1. ....................................................................
2. ....................................................................
3. ....................................................................
Explain how sexual reproduction can allow evolution to occur.
Markscheme
a. growth (of cells);
b. transcription/protein synthesis/translation;
c. DNA replication / genetic material copied;
d. production of organelles/mitochondria/chloroplasts;
e. named normal activity of cell (eg active transport, movement, secretion);
NB Do not accept G1, S, G2 unless linked to correct process.
a. sexual reproduction promotes variation in species;
b. independent assortment of genes / random orientation of chromosomes in metaphase/meiosis;
c. crossing-over provides new combinations of alleles;
d. production of great variety of gametes (by meiosis) / different combinations of chromosomes in gametes;
e. (random) combination of gametes from both parents (in fertilization);
f. (genetic) variation allows natural selection which leads to evolution;
Examiners report
Various cellular processes occur during interphase. Any three of the following were accepted: growth (of cells), protein synthesis/translation, DNA replication, production of organelles or named normal activity (e.g. active transport, movement, secretion etc.). It was not necessary to name the sub phases such as G1, S or G2. If that was done the sub phase had to be linked to a correct process to achieve a mark. It should be noted that cells grow in all three phases by producing proteins and organelles. DNA replication, however, only occurs in the S phase.
Explaining how sexual reproduction can lead to variation and then evolution challenged many candidates. Some candidates began with the premise that sexual reproduction produces variation, but did not explain how the variation occurs.This was the heart of the question. Others tried to answer what evolution is, instead of explaining how sexual reproduction allows it to occur. Too many answers just stated the terms independent assortment, crossing over, random fertilization and natural selection without further developing them, i.e. their effect on genes, allele combination or gametes. Sometimes mutation was mixed into the answer gaining no credit.
