Questions

Q1.
 
Cell division can be affected by various chemicals. The effects of these chemicals can be studied by observing tissues.
The photograph shows onion root cells undergoing mitosis.

(i)  Draw a line labelled M to one cell at metaphase and a line labelled A to one cell at anaphase.
(2)
(ii)  The rate at which cells are dividing can be determined by calculating the mitotic index.
The mitotic index is the percentage of cells in a sample undergoing mitosis.
The table shows the number of cells at different stages of the cell cycle in one sample.

Calculate the mitotic index for the sample of cells shown in the table.
(2)

Answer ........................................................... %
 
(Total for question = 4 marks)

Q2.
 
The image shows a cross section of part of a plant stem examined using a light microscope.

(i)  Label a sclerenchyma fibre with the letter S.
(1)
(ii)  Calculate the magnification of this image.
(3)

Answer ........................................................... 

(Total for question = 4 marks)

Examiner's Report

Q1.
 
(i)
The vast majority of candidates gained both marks for this question.

Results Plus: Examiner Comments
This response gets both marks for correctly identifying the cells in each stage.

Results Plus: Examiner Tip
Labelling onto a diagram can be unclear. Make sure you follow the guidance in the question.

Results Plus: Examiner Comments
The candidate has made a clear indication of the correct cells and is awarded 2 marks.

(ii)
Most candidates correctly identified the stages of mitosis and therefore were able to gain full marks. The difficulties were often in rounding up too far or incorrectly, although some candidates neglected to multiply by 100.

Results Plus: Examiner Comments
This candidate rounded up their answer to 13 and lost the final mark. Thankfully they gained one mark as they showed how they arrived at the answer.

Results Plus: Examiner Tip
Always show your working, questions like this gain marks for each stage in the answer.

Results Plus: Examiner Comments
A good response, this candidate has also shown that they have given their answer to 3 significant figures. Both marks were awarded.

 

Q2.
 
(i)
A simple question that had a large number of blank responses. Candidates could make any indication: an S in the diagram or the preferred option of a labelled line.
(ii)
This question produced a large number of incorrect responses. Many chose to measure an unspecified section of the image rather than measure the scale bar. There was an apparent difficulty in converting to μm.

Results Plus: Examiner Comments
Writing out the equation in this way clearly demonstrates where each mark can be awarded.

Results Plus: Examiner Tip
Numbers alone can be unclear − remember to include units in your answers.

Results Plus: Examiner Comments
This is a good example of the importance of showing the process of getting to your final answer. There is an error, due to the conversion to μm, that makes this incorrect by a factor of ten. 

The correct steps shown allow two marks to be awarded.

 

Mark Scheme

Q1.

 

Q2.