| Date | November 2015 | Marks available | 1 | Reference code | 15N.2.HL.TZ0.2 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Calculate | Question number | 2 | Adapted from | N/A |
Question
The micrograph shows a cell from the root of an onion (Allium cepa) during mitosis.
Calculate the magnification of the image.
Deduce the stage of mitosis shown in the micrograph.
The onion (Allium cepa) is an angiospermophyte. The honey bee (Apis mellifera) is an arthropod. State three structural differences between the cells of an onion and a honey bee.
State what is indicated by the presence of polysomes in a cell.
Markscheme
136 (accept answers in the range of 132 to 140)
anaphase
Award [1] for two correct, [2] for three correct answers.
To award the mark both parts of a comparison must be stated explicitly or unambiguously implied.
much protein of one type needed/produced by polysomes;
mRNA is being repeatedly translated;
Examiners report
About half of candidates calculated the magnification of the image correctly. Those that did not were usually one more orders of magnitude away from the answer. A common problem was the use of centimetres rather than millimetres to measure the size of the scale bar image. This very often leads to an error of one order of magnitude.
This was well answered with more than 90% of candidate recognising that the cell was in anaphase.
This was also well answered by many candidates with each of the three statements in the answer referring both to honey bee cells and to onion cells. A few only mentioned one organism or the other so failed to score any marks. It is not enough to imply a difference in questions such as this – the difference should be stated explicitly.
This was very poorly answered with fewer than 25% of candidates knowing that polysomes are groups of ribosomes that are translating the same mRNA, which indicates that the cell needs multiple copies of one particular polypeptide.
