WJEC Biology for AS Level Student Book: 2nd Edition

Answering examination questions Unit 1 Before you even pick up your pen, read the question very carefully, several times if necessary. Be sure you know what is being asked. Resist the temptation to write all you know on a topic, just having spotted a particular word in the question. A question will contain a command word. This is the word that tells you what to do. Make sure you understand command words and that you do what they say. Many questions increase in complexity as you go through: ▪ A question may start by asking you to name a structure, make a statement or give the meaning of a term. Such questions require you to have learned your notes by heart. ▪ Next you may be asked to apply your knowledge e.g. in a calculation, labelling a diagram, interpreting photographic images or reading from a graph. ▪ You may then be asked to evaluate evidence, suggest an explanation for experimental findings or design a method of testing a hypothesis. The example below shows this increase in complexity in a question covering Unit 1 topics. The command words are in purple . (a) Muscle cells can be been stained with dye which causes the DNA to be visible. State , specifically, where in the cell most of the dye will occur. [1] You should recall that most of a cell’s DNA is in the nucleus. But as the questions asks for the specific location, ‘chromosomes’ is the appropriate answer. (b) Explain why a small amount of stain would be seen in parts of the cell other than the nucleus. [2] As the question is worth two marks, you should give an answer with at least two relevant points. You should apply your knowledge that a small amount of DNA is also found mitochondria. DNA also occurs in chloroplasts, but as this question is about animal cells, you would receive no marks for mentioning that in your answer. (c) In 2019, the first instance of encephalitis caused by ticks was seen in the UK. This inflammation of the brain is potentially fatal and so understanding the biology of the ticks that cause it is important. The table below shows the percentage of cells in the leg muscles of younger and older deer ticks, with either 3.3 au or 6.6 au of DNA in their nucleus. Percentage of cells Mass of DNA in nucleus / au Younger deer tick Older deer tick 6.6 20 5 3.3 80 95 Use the data to draw a conclusion relating to the frequency of mitosis in these ticks. [3] In this question you are being asked to look at the data provided and draw conclusions. It is important to understand that during part of mitosis, the DNA content is doubled. So with a higher proportion of cells undergoing mitosis, there is a higher proportion of cells with double the mass of the DNA. Remember to write about both younger and older ticks, as the question refers to both. Link Command words are explained on p10. WJEC Biology for AS Level 132