How I teach valid and accurate

I’ve been trying the following approach for around a year now, prompted by the vexed question of the dreaded ‘practical questions.’ I was never satisfied with some earlier strategies, such as teaching accuracy and precision using dartboard graphics (this seems to be an extra, unnecessary layer of thinking), and the more definitional approaches adopted by some exam boards struck me as not easily accessible, particularly to younger students who would benefit from getting these ideas in their heads during KS3.

Validity

I noticed that many questions about validity, at least from the biology perspective, expected an answers related to variables. There’s an easy link: V for Valid, V for Variable. Of course, variables are an area that can also cause problems, but when I say down and thought it through there were actually a limited number of variables that are ever in play. I came up with the following list:

C – Concentration

L – Light intensity/wavelength

A – area/length

p- pH

S – species

T – Time/rate

T – temp

V – volume/mass

That’s it, just these eight. Sure, there may be other potential variables, and I only added species in later when I started teaching more of the ecology topics and realised it could be a useful variable to include. Essentially, most experiments in biology has its variables, independent, dependent and controlled, within this list. My GCSE and A level students now know that on a question about validity, to think first in terms of what the variables are in the experiment and then work out which ones haven’t been controlled. That is invariably (ho-ho) the way to answer the question.

Here are the AQA trilogy RPAs, and how the variable list fits in. Variables are not necessarily relevant to all of them. IV = Independent variable, DV = Dependent variable, CV = Controlled variable

	IV	DV	CV
Microscopy
Antibiotic growth	Conc	Area	pH, Time, Temp, Volume
Osmosis	Conc	Mass or length	Time, Temp, Volume
Food tests			Volume/mass
Enzymes	pH	Time/rate, Volume	Conc, Temp, Volume
Photosynthesis	Light intensity or wavelength, length (distance), Species	Time/rate or Volume	Conc, Area (of leaves), pH, Species, Time, Temp, Volume
Reaction time	*hands, Conc e.g. caffiene	Time or length	*Same person, *ruler position
Germination	Light, *gravity	Length	Conc, Area (of dish) pH, Species, Time, Temp, Mass (number of seeds)
Quadrats	Light intensity, pH, species (e.g. grazer presence)	Species (frequency)	Area, pH, Time (seasonal)
Decay	Temperature	pH	Conc, Time, Volume

Apart from the ruler drop experiment, most of the experiments can be viewed through a limited number of variables. Yes, there are a few details to be clarify, but from the point of view of giving a starting point for validity questions, having an easily recallable structure is a good starting point for students. They can recall the mnemonic CLAPSTTV fairly easily, and then they have a better shot at identifying the variables that have not been adequately controlled.

Accuracy and repeatability

I find the best place to start here is with the word accurate. I describe an accurate result as the true, or real result. Even in Year 7 students can work out that experiments to measure things are prone to getting wrong measurements, so the idea that an accurate experiment gives the ‘true’ result is a useful starting point. No need for dartboards and archery.

After that, time to go to everyone’s pal, Excel. If an experiment would usually result in a proportional relationship, I would gather a set of class results, usually putting up a blank spreadsheet and getting the students to put their results in. There are normally going to be some anomalous results in there. For example, I recently got this from a yeast respiration experiment:

Temperature oC	Bubble rate per minute
38	7
45	22
47	33
47	30
47	3
36	2
40	14
39	9
44	10

Firstly, we organised the results into ascending order, then made a scatter graph on Excel (this is important!). The graph was placed next to the table and adjusted so it was clear to see. Next, students could identify where a rough line of best fit would be. I then used Excel to fit a line, and it became even more obvious where the anomalous results appeared. Knowing that anomalous results should be identified and removed, we deleted them from the table. Each time you do this, the graph updates, shifting your line of best fit to a better (more ACCURATE) position. Students can see in real time the effect of this, and the reason why anomalous results are removed.

In other words, this is how I approach the accuracy/reliability question:

They are about METHOD. If you were writing out an experiment, one of your numbered points would hopefully to be to repeat so you can identify anomalous results and calculate a mean. How do you make an experiment more accurate? Look to the method, there will usually be a step missing about the repeats.

Fine, but students usually write ‘repeats’ as a guess anyway on these type of questions, so have we really improved the situation? I think so, since it has modelled WHY removing anomalous results improves accuracy, and that repeats (you can model this too on Excel by having repeated results and again, identify and remove anomalies from the table to get a real time update on the graph).

There is one trap here though, and it usually appears on the Osmosis and Enzyme RPAs. Here, the accurate result is not a relationship but a specific value, optimum pH or isotonic point. In this case, stress repeats should be done oat smaller intervals around the accurate value. This would of course be another method instruction, since intervals measured should be mentioned within a method.

So now students should be looking for answers involving repeat to identify anomalous results BETWEEN a range of points. This approach will answer most of the questions that they come across asking about accuracy. Sure, there will be exceptions and caveat, but when answering this type of question I feel having a framework is useful for many students.

Ecology games

An approach I’ve used when teaching sustainability concepts is to borrow from the field of psychology and introduce some simple games. In particular I use a version of the Prisoner’s dilemma and The tragedy of the commons, in both cases just using pen and paper, though more complex versions are no doubt available. I’ve used this for year 11 as well, since I’ve found it an interesting way to help students understand the underlying problems of sustainability.

The Prisoner’s dilemma.

This classic psychology thought experiment works by giving two people the chance to act either cooperatively or against each other. In my version I usually start by getting two volunteers to demonstrate the game mechanics and then allow students to play each other.

Rules and outline

1. Select two students as ‘prisoners’. Explain there has been some kind of crime (I usually say bank robbery). The police are not sure who did it, but have arrested two known criminals who they strongly suspect (the two volunteers), called for example Alan and Barbara. The aim of the game is to get away with the least possible years.
2. As known criminals, the police have enough evidence to put each of the suspects in jail for 3 years. The suspects initially COOPERATE with each other and do not say anything to the police.
3. Make each student an offer: if they agree to DEFECT and give evidence on the other suspect, they get 0 years and the other person gets 7 years. If both DEFECT they both get the full 7 years. Neither suspect can communicate when making their choice.
4. There are four possible outcomes:
   1. Alan cooperates – 3 years, Barbara cooperates – 3 years
   2. Alan defects – 0 years, Barbara cooperates – 7 years
   3. Alan cooperates – 7 years, Barbara defects – 7 years
   4. Alan defects – 7 years, Barabra defects – 7 years
5. I would then play maybe three rounds, with the volunteers facing away from each other and holding up a mini white board with their decision on (C or D) that they can hold up, keeping score on the board. Some other students will already be working out a strategy at this point.
6. Allow students to play against each other, for 5 or 10 rounds. You can then get them to play against other students too.
7. Points to note: the game models sustainability concerns by showing that some people will often act to maximise a benefit to themselves (defectors), whereas others are more cooperative, even if it means that they are less likely themselves to ‘win’. There will be students who prefer a strategy of always defecting first simply to ensure they don’t ‘lose’, since once you are behind the opponent can always defect and cannot be caught. This mirrors the overuse of resources and links to the next game, tragedy of the commons. I’ve used this game to link to all sorts of things like pollution, littering, burning fossil fuels, car use, climate change and so on. It can be done with an actual prize but doesn’t have to be.

I usually then show some YouTube clips from ‘Goldenballs’, the game show that uses Prisoner’s dilemma as its basis. The best two are the controversial steal and the unusual psychological tactic used by one contestant.

The tragedy of the commons

Another game that can be modelled with pen and paper to demonstrate one of the problems with sustainability. It may work best with the offer of some kind of prize, but you don’t need to have one.

The game models the problems that can happen when a shared resource, like a fishery or common land, is exploited.

1. Group students, four or five is ideal

2) Each student keeps track of their own score on paper. It helps to have a whiteboard to act as a common resource. I use the example of a fishery.

3) The game works by each student catching a fish from the shared pool, one turn at a time. A student must always take at least one fish to represent the need to stay alive.

4) Start with a pool of 10 or 12 fish. Students take it in turns (e.g. clockwise from a random starting student) have a choice to take anywhere between 1 and 3 fish on their go. Each declares how many they want to take on their catch, and at the end of the round take away the fish caught from the total. For example, starting with 12 fish if four students took out the following A2 B1 C1 D3 that would be a total of 7 fish so 5 would remain at the end of the round.

5) When everyone has fished, double the amount of fish left in the pool to represent breeding and repeat the same steps for the next round. You can rotate the starting player or keep the same order for additional resentment. After a certain number of rounds (say four or five), the winner has the most fish at the end.

Some of the students will quickly collapse their fisheries as they grab as many resources as they can, hence the ‘tragedy’. Others will cooperate to work out sustainable levels. You can change up during the game by introducing random events like bad weather for one round, or the ability to have a bigger boat which means you can now catch more fish.

Greek and Latin literacy

I’ve organised and tidied up some of the prefixes I’ve posted before. They could be used as starters (there are around 30 of them) at A level or for higher achieving GCSE, homework or compiled into larger sections. Where I’ve used them so far I’ve encouraged students to find example words containing the prefixes to make more sense of them.

Please note, some of the terms are clearly not common even in biology and are included more for a ‘huh’ factor. They aren’t easily guessed either.

Etymology Colours and physiologyDownload

Etymology Counting and chemicalsDownload

Etymology LifeDownload

Etymology locationsDownload

Separate Biology GCSE AQA 6 questions

6 QUESTIONS AND ANSWERS TRIPLE

For your eyes only, a version of the 6 questions per spread of the AQA Biology GCSE textbook. There may be a few odd spelling errors etc, but what do you want for free? Anyway, knock yourselves out.

Argument planning

Huh, just realised I’d not put this on the site despite posting about it here. Nothing fancy, a single slide to help students form balanced arguments. They generally find this difficult, but I like to think that it is at least getting them to consider building arguments more effectively. The categories I chose can be changed of course, and if you don’t like the $$$ for ‘economic’ arguments feel free to change it.

I use it primarily with GCSE students with pollution/waste type topics, also some aspects of health like stem cells and vaccinations. Printed versions may be more appropriate for some students.

Argument planner

Reading about science

Inspired by a @DrWilkinsonSci post, (see also on his blog) I cobbled together some reading for science ideas. There are ten here, mainly to do with people involved in scientific discoveries in some way but also some parts on organs just to see what they play like. The idea is to get students reading about science and encountering unfamiliar words to develop vocabulary, use annotation skills and also expand extra-curricular knowledge. They are split into paragraphs so they can be read out loud easily (ish) by students in class. I would pitch this around Year 9.

I’ve left them in .doc format so people can edit themselves as they see fit.

LIT small intestineLIT Semmelweiss and AgparLIT new medicinesLIT MicroorganismsLIT Mary MontaguLIT KidneysLIT HeartLIT evidence in medicineLIT Charles DarwinLIT Anatomy

AQA Trilogy Biology 6 questions per spread PowerPoint resources

These are taken from the 6 Question and Answers I wrote (you can find that here), but has been done as a separate slide for each of the units. These can be used at the start of lessons as recap or recall later on. Nothing new in here, just a change to make things more accessible for those who want them. As usual, feel free to let me know if you find any glaring errors.

 

B1 6 Q and AnswersB2 6 Q and AnswersB3 6 Q and AnswersB4 6 Q and AnswersB5 6 Q and AnswersB6 6 Q and AnswersB7 6 Q and AnswersB8 6 Q and AnswersB9 6 Q and AnswersB10 6 Q and AnswersB11 6 Q and AnswersB13 6 Q and AnswersB14 6 Q and AnswersB15 6 Q and AnswersB16 6 Q and AnswersB17 6 Q and AnswersB18 6 Q and Answers

Language on the 2018 exam papers

In a passing Twitter comment a few months back @ejsearle mentioned that there was a rumour that there were “more words on the bio gcse paper this year than English lit.” I thought this was an interesting idea, since I’d also noticed from some exam board meetings that I thought the biology material supplied seemed overly wordy in comparison to similar questions from the chemistry and physics side, both in the combined (trilogy) and separate sciences. So here is my quick and rather fuzzy analysis of the language used on some of the papers this year.

As a starting point, I used the idea of ‘Tiers’ to describe language, something I came

Infinite science equation generator

Formula practice

Formula practise

Something I was fiddling around with at the end of last term – basically a random number generator tied to common equations used in science. You could use this at the start of a lesson or at any point as a quick recap to keep things ticking over. There are 25 equations on here, covering things like percentages, volumes, energy, speed, pressure etc. which can be set to have random values each time so no need to think work out numbers yourself (answers are on the slide after in each case). If you want to have students remember parts of the equation instead then paste a box over whichever parts of the equation you don’t want them to do.

In most cases there are 4 questions per slide, along with a copy of the relevant equation. You may want to adjust wording for personal taste. The equations will either be a straightforward plug in the numbers, require rearrangement, have different units or require different decimal places (check answer slides again for clarity).

I’ve used mainly biology to GCSE and physics to GCSE as a guide, but its by no means complete. If people particularly want me to add others I can, or maybe do another version. If you spot any mistakes please leave a message and I’ll rectify if possible. The xls file by the way doesn’t particularly follow any logical pattern because reasons, but what are you going to do?

 

***PLEASE PAY ATTENTION TO (2) REGARDING SAVING THESE FILES***

How to use:

1. Download both files I’ve attached: one pptx and one xls (the reason they have different spellings is because I wanted to be inclusive and give the UK and US spellings of ‘practise’, and not because I made a mistake, no siree. You could change them both to the ‘s’ spelling but I wouldn’t recommend it, since the pptx file will look for the file named ‘practice’ so you’ll have to redo all the links which will be a royal pain).
2. Save both the files, making sure they are saved with the original names and not as ‘Copy of formula practice’ etc. This is because the pptx file will be looking for the original file name. *EDIT – as pointed out by @Mr_S_dA on twitter, when you save the files it might change the name to ‘Formula_practice’. Resave it as ‘Formula practice’ – this is the name the pptx will be looking for and if it is not the same the whole thing will not work.
3. OPEN THE XLS FILE FIRST. It must be open for the pptx to work.
4. Open the ppt file, and when asked to update links do so.
5. The list of the 25 equations is on the first slide. Any time you go to the xls file and press ‘F9’ while on a blank cell the numbers will be reselected and will automatically change on the pptx.

 

 

Random prefix and suffix generator

Prefixes and suffixes

Prefixes and suffixes

 

258 prefixes and suffixes of words. A variety of Greek, Latin and all sorts of others. Can be used at start of lesson or as a kind of ‘word of the day’ or to shove in your lesson when someone asks about literacy. You know the deal.

Instructions for use:

1. Download and save the two attached files, an Excel and a PowerPoint.
2. Save to somewhere, making sure that the Excel is saved as ‘Prefixes and suffixes’ and not as ‘Copy of Prefixes…’ or the PowerPoint won’t know where to look.
3. Open both files.
4. On the Excel first tab, press F9 to refresh the random number. A random prefix or suffix will appear on the PowerPoint.
5. I think I’ve caught any mistakes, but there may be one or two lurking. For example, ‘neur’ was spelt ‘meur’.
6. Look up what ‘genu’ means as a prefix. Who knew?