The image shows a transverse section of an intestinal wall at 100 x magnification.

Identify the tissues labelled I and II on the image.

I:  .....................................................................
II:  .....................................................................
 

All motor neurons use acetylcholine to activate skeletal muscle. Explain the effect of neonicotinoid pesticides in insect synapses in the central nervous system.

Resistance to neonicotinoid pesticides has been observed in some insects. Describe briefly how this resistance could have arisen in populations of insects.

I and II are both muscle
circular and longitudinal

Neonicotinoid pesticides are similar to nicotine «chemically»

Bind to nicotinic/acetylcholine receptors

Not broken down by «acetyl» cholinesterase
OR
binding is irreversible

Prevents/blocks acetylcholine binding

Blocks transmission from CNS  Reject slows transmission.
OR
blocks signals going to muscle
OR
muscle contraction blocked
OR
causes paralysis

Mutations «for resistance in some insects»  Do not award mark if the answer implies directed mutations or that the pesticide causes the mutation.

«Mutation causes» breakdown of pesticide/detoxification of pesticide/changes to receptor site

Natural selection for resistance Do not accept natural selection if not in context.
OR
resistant insects survive and reproduce
OR
non-resistant killed leaving only resistant insects

Do not accept answers that use the term immunity instead of resistance.

This was possibly the least successfully answered question on the paper. Very few candidates were able to name the two tissue layers. In retrospect it was probably unreasonable to use two marks for a small and perhaps insignificant aspect of the programme. Candidates were expected to see that layer II was circular muscle because of the orientation of the muscles cells in this transverse section. In practice almost no candidates did this. A few knew that I and II were circular and longitudinal muscle. No penalty was made for getting these layers the wrong way round but even so very few marks were awarded. Many candidates were clearly guessing and in some cases the answers showed a misunderstanding of the organs being a group of tissues. These candidates suggested a wide range of answers in including types of cells or parts of cells.

This application was not well known by the majority but even without specific knowledge of neonicotinoid pesticides it was possible to score some marks by sensible use of the information provided in the question and wider biological understanding. This type of pesticide is under intense research at the moment because of its effect on bees so it is a topical example of the nature of science.

Many candidates included the idea of a mutation in their answer and also that insects with genes for resistance would survive, breed and pass on these genes to their offspring. The only common mistake was to confuse resistance and immunity.