How to Experimental Design Questions in Written Papers About Practicals

Design Questions – IGCSE – June 2005 P6 Q2d(i)  Here is an example of a design question from IGCSE: 1.It has been suggested that petal colour is important to attract insects to collect nectar and to pollinate the flowers. (i) Outline how you would carry out an investigation to find out which petal colour would attract most insects.

Design Questions – IGCSE – How to Answer  How should a student set about answering such questions?  Before writing anything there are four things they should try to work out in rough: 1. What is the Independent Variable (IV) in this study? How can we operationalise (change) it? 2. What is the Dependent Variable (DV) in this study? How can we operationalise (measure) it? 3. What confounding variables must be controlled? How can we control them? 4. What apparatus would we use to carry out an investigation of this type?  So answer these 4 questions! Try to think of at least 5 confounding variables which we need to control.

Design Questions – IGCSE – The Answers  IV – Petal colour  DV – Number of insects landing on the flower  Confounding variables – 1. Petal size 2. Petal shape 3. Light intensity 4. Wing Speed 5. Temperature 6. Time  Apparatus – Sticky Trap (or something else which would work)

Design Questions – IGCSE – What to write  IV – Quite simple in this case, take five cans of paint of different colours and paint five wooden boards. Try to always use a range of at least 5.  DV – Cover with clear glue and count the number of insects that stick to them.  Controls – In each case an answer “use the same size board” is not good enough. Details must be specified, e.g. A wooden square 0.2 X 0.2m is left for 12 hours.

Design Questions – IGCSE – CIE Mark Scheme  Here is the CIE Mark scheme answer:  [answer should be written as ‘doing’ something]  using different coloured flowers (A) shades (A) petals/ use some coloured shape to represent flower;  same, species/shape/size;  same insect species;  counting insect visits (A) ‘how many’ detail;  keep named condition/variable constant;  other condition/variable;  repeat (whole investigation);  AVP;;(e.g. way of getting insects and flowers in proximity, use a  range of insects) Any viable procedure?  [max 4]

Design Questions – IGCSE – June 2004 P6 Q2b  Now try this one: 2.In the human alimentary canal, starch is broken down by amylase. The pH of the alimentary canal varies between pH 2 and pH 8.5. alimentary canal varies between pH 2 and pH 8.5. Suggest how you could investigate the effect of pH on the activity of amylase. [5]

Design Questions – IGCSE – CIE Mark Scheme  2(b) 1 same amount / volume / concentration of amylase;  2 same amount / volume / concentration of starch;  3 same temperature;  4 vary pH, at least 3 for a range ;  5 reasonable suggested detail to obtain a different pH, ideally use of buffer;  6 regular timing for testing;  7 repetition;  8 3 named items of apparatus selected; [ to include reference to timer / white tile/ test tubes / beakers / water bath / stirrer etc] [ to include reference to timer / white tile/ test tubes / beakers / water bath / stirrer etc] [MAX 5]

A Level Design Questions – November 2003 P5 Q3  Here is an example of an A level design question. 1.Rennin is an enzyme that coagulates milk protein and is found in the stomach of young mammals. You are required to plan but not carry out an investigation into the effect of temperature on the activity of the enzyme. You may use the following equipment:  a solution of rennin  milk  a water-bath  a thermometer  test-tubes  a graduated pipette  a stopwatch. Explain your procedure.

A Level Design Questions – How to Approach Them  Fundamentally the process of designing the experiment is the same. Beginning with a rough analysis of IV, DV, Controls and Apparatus.  The main difference is the amount of detail they expect. The quantities and concentrations should be detailed; no marks will be awarded for vague references to controls or range for the IV. Students must be familiar with all the experiments detailed in the syllabus.

CIE Mark Scheme  1 Correct use of equipment;  2 Range of at least three suitable temperatures;  3 Mix / add milk and renin;  4 Same vols of milk and renin for each temp;  5 Leave for same time / time measured;  6 Repeat;  7 Average determined;  8 Indication of positive result;  9 Method of recording data;  10 Scientific knowledge ie kinetic energy of molecules;  11 Would it work?

What to Warn Against in Student Answers  The most common problem is lack of detail: 1. Detail of the values for IV 2. Details of the process by which the DV is measured 3. Details of exactly how the confounding variables are controlled and at what value.  Also, students frequently fail to think clearly about the practicability of such a method. In most cases the question says ‘which you could do’. This must be made clear.  Finally, some students often need a complete review of the scientific method in its entirety.