| Date | November 2010 | Marks available | 2 | Reference code | 10N.2.SL.TZ0.2 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 2 | Adapted from | N/A |
Question
The following sequence of pictures, made using an electronic imaging technique, shows a cell undergoing division.
State the stage of mitosis typified by image II.
List two processes that involve mitosis.
State the process that results in tumour (cancer) formation or development.
Explain, using one example, how non-disjunction in meiosis can lead to changes in chromosome number.
Markscheme
anaphase
a. growth (through increasing cell number);
b. embryonic development;
c. tissue production/repair;
d. (asexual) reproduction;
uncontrolled mitosis/cell division
a. pair of homologous chromosomes moves in same direction/does not separate during anaphase I / chromatids move in same direction/do not separate during anaphase II;
b. leaving a cell with an (some) extra chromosome(s)/missing chromosome(s);
c. an example; (e.g. Down syndrome where there is an extra chromosome number 21);
Examiners report
Anaphase was usually given, perhaps Image II had not been studied in relation to Images I and III.
Some candidates understood the question to mean phases of mitosis. Others wrote ambiguous answers such as “repair” instead of “tissue repair”.
Mainly correct. It was essential to include the term “uncontrolled”. A few candidates were unclear about tumour formation and answered “mutation”.
There were very few descriptions of how non-disjunction in meiosis can produce a change in the chromosome number. However, the example of Down syndrome where there is an extra chromosome 21 was almost always given.
