Tag Archives: biology

CIE Biology: How to Ace Paper 3

This post is specifically for the CIE Biology International A level qualification. What follows are my attempts to help guide students to do the best they can in the advanced practical skills exam, Paper 3. However, the information below is no substitute for proper revision and the dedicated practise of actually carrying out a variety of biology experiments. Additionally, I would strongly recommend you use the past papers section of CIE’s website to sit as many “mock” practical exams as possible.

Command words in a question

Describe:

  • Say what is going on, e.g. the trend or pattern of results.
  • When describing data, always use units if appropriate (e.g. °C or cm3).

Explain:

  • Say why a trend or pattern is occurring.
  • When explaining data, always link it to A level Biology.

Although describe and explain are the most common command words, you might find yourself answering questions with any of the following:

  • Calculate: use mathematics to find an answer. E.g. mean, percentage, percentage change, rate, ratio, etc.
  • Measure: use a suitable measuring instrument to take a reading, being sure to include units after the numerical answer.
  • Suggest: there is no one correct answer; you should look through the information you have been given for some clues.

Even more rarely you might find one of the below command words in a question:

  • State: give a brief answer – maybe one word or a phrase.
  • Define: give a definition – these should be concise.
  • Determine: explain how you could take measurements and calculate an answer from these measurements (e.g. in an experiment).

How many answers should I give?

  • If a question states “identify two” then only the first two responses will be marked.
  • If a question states “record observable differences” then all responses will be marked.

How great is the risk?

If a question asks you to “state the hazard with the greatest level of risk” for your practical, do not choose one you deem to be low risk. E.g. warm water in a thermostatically-controlled waterbath set at 30°C, is a hazard that is low risk and so would not gain a mark. A better answer would identify a risk that was either medium or high, e.g. hydrogen peroxide is harmful to the skin. The key is to identify a hazard with “the greatest level of risk”.

Deciding independent variable values

Give five values at roughly even intervals (e.g. every 5°C or 10 cm3) when deciding what values to use for your independent variable. Always use units if appropriate (e.g. °C or cm3).

Recording numbers and drawing tables

Do not go past one decimal place when recording the results from your experiment, usually whole numbers are fine. And always use units if appropriate (e.g. °C or cm3).

Table Headings:

  • Put the independent variable (IV) on the left and dependent (DV) on the right.
  • Draw a line between the top row and the body of the table, e.g. underline the IV and DV.
  • Use the full name of the IV and DV (e.g. temperature of hydrogen peroxide and time taken to rise).
  • Only use units  in the headings, not the body of the table (e.g. temperature of hydrogen peroxide / °C and time taken to rise / s).

table

Results

  • Record results for at least five values of the IV.
  • Results should show the pattern or trend theoretically expected of the practical.
  • Use whole numbers.
  • Record results for two trials and calculate a mean average.
  • The mean average should be recorded to no more than one decimal place.

Identifying sources of error

Think carefully about your experiment, where might there have been an error? E.g. if you are looking at colour changes this is subjective and will be a source of error. Ensure you state the error and the reason it occurred.

Describe how an element of a practical can be investigated.

  • Use five values.
  • State how these five values will be made, e.g. if the IV is concentration of enzyme, “use simple or serial dilution” or if it is temperature “use a thermostatically-controlled waterbath at 20°C, 30°C, 40°C, 50°C and 60°C”.

Constructing graphs

  • You will normally use data that is given to you in the paper.
  • Put the IV on the x axis, DV on the y axis.
  • Use the full title from the table to label each axis, e.g. “initial rate of catalase activity / s-1“.
  • Always use units if appropriate (e.g. s or seconds but not sec).
  • Look at the values and use a logical scale. E.g. a scale of 0.06 or 0.04 for every large square of graph paper is not logical. However, a scale of 0.05 is logical.
  • Each plot will be checked to see whether it is accurate to within half a small square of the graph paper. It is recommended you use an x mark to do this.
  • There should be no labelling within the area of the graph.
  • Lines will be judged for their quality*.

Bar graphs

  • Ensure lines are not too thick, as the quality of each one will be judged*.
  • Bars can be touching. However, if you chose to leave gaps the gaps must be evenly spaced.
  • The horizontal lines at the top must be perfectly straight, parallel to the x axis.

Drawing diagrams

  • Quality of lines will be judged*.
  • No ruler straight lines for your diagram: nature is not straight!
  • No labels or writing within the drawing.
  • Label only what is asked of in the question.
  • Do not draw in anything that you do not see. E.g. smaller organelles.

Plan diagrams

  • The diagram should be at least 60 mm wide at its greatest width.
  • There should be no shading.
  • There should be no cells in  plan diagram. Do not be tempted to draw them in!
  • Use the correct section of the slide. This will be in the instructions of the questions, but make sure you actually draw what it wants you to!

Diagrams of cells

  • Cells should be at least 50 mm at their greatest width.
  • Draw exactly the number of cells stated in the question.
  • Do not include half cells. The questions always state “whole cells”.
  • Cells should not overlap but may be abutting (e.g. touching each other or sharing an outermost line).

Calculations

  • Always show your working and the steps you take to come to your answer.
  • Always show units, but do not mix units. E.g. not 1 mm and 50 µm.
  • When converting units, show the conversion. E.g. 1 mm to µm: 1 x 1,000 = 1,000 µm.
  • Try not to go beyond one decimal place, or the same level of precision as is given in the question.
  • Give ratios to the lowest common denominator. E.g. 168:58 should be 84:29.

Comparing observable differences using a table

  • Organise the table as three columns; one for the differences and two for the samples. E.g

table-2

  • Underline the headings and divide the columns as per the table above.
  • If asked for differences, do not give similarities!
  • Differences would ideally be “X is thick” and “Y is thin”.

*Quality of lines

Each line you draw for a graph or drawing could be judged for its quality. E.g. whether it has been drawn by a sharp pencil as a thin and continuous line. This is really important as you don’t want to lose silly marks for not sharpening your pencil!

wooden_pencil_sharpener

Image by Asim18, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=3129973

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Five books all Biology A level students should read

This is part one of a series of posts listing, in no particular order, essential reading for A level Biology students.

  1. The Red Queen: Sex and the Evolution of Human Nature by Matt Ridley

This is truly essential reading for anyone interested in biology. As the title suggests it is a compendium of ideas and thoughts pertaining to evolution and in particular how they might impact on being human. After reading it in the first year of university it immediately had a profound and significant effect on my understanding of the subject. Its many themes have stuck with me throughout and since starting teaching I have come back to it time and again as a source of inspiration for both teaching and improving my understanding of key topics within biology. Each chapter is written in an accessible style and abounds with humour. Whether pondering the absence of male bdelloid rotifers to discussing the Inca sun-king’s “house of virgins” Ridley writes with authority and clarity. Forgive my hyperbole but The Red Queen is among my absolute favourite books; even if you do not study biology put this on the top of your reading list!

  1. The Immortal Life of Henrietta Lacks by Rebecca Skloot

A book with a significant and poignant historical perspective, it looks beyond the science of the immortal HeLa strain of cells to explore the civil rights movement in 1950s America. Consequently this is a perfect recommendation for any student studying History and Biology at A level. Additionally the ethically dubious actions described would also promote great discussion beyond these two subjects. As a journalistic exposé and investigation into an appalling miscarriage of ethical justice it is superb. Furthermore it also highlights the incredible advancements that were made as a result of this malpractice and poses the question; do the ends justify the means in medical research? Beyond being a great book about biology this is also, as the Times reported, “as gripping and rich as any work of fiction you will read”. I am incredibly thankful to my former colleague who gave this to me as a leaving present and whole heartedly recommend it.

  1. Life Ascending: The Ten Greatest Inventions of Evolution by Nick Lane

As a Biology teacher I was amazed when I first read Life Ascending; it is almost a perfect accompaniment to A level Biology. Not only does the chapter-structure mean that you can dip in and out, reading sections that pique the interest at will, but at least six of the chapters are directly relevant to the subject specification. For example it is easy to see how DNA, Photosynthesis, Movement and Sight are connected to A level, but even The Origin of Life (respiration – see Nick Lane’s other cheekily titled Power, Sex, Suicide: Mitochondria and the Meaning of Life) and The Complex Cell (eukaryotic v prokaryotic cells) are germane to Sixth Form study of biology. I would, of course, argue that every chapter was relevant and incredibly useful in building up and linking together the big ideas in biology to create a schema for the subject. Perhaps the best epithet is from the aforementioned Matt Ridley “If Charles Darwin sprang from his grave, I would give him this fine book to bring him up to speed.”

  1. The Epigenetics Revolution by Nessa Carey

This is the book which smashes open the fascinating world of epigenetics. So you think DNA is a stable template that does not change? Think again. Carey describes plenty of inherently interesting examples, even if you weren’t interested in the underlying biology her writing would cause you to be absorbed in these well-written illustrations. One in particular is drawn from the Dutch Hunger Winter and suggests that malnourishment in early pregnancy increases the risk of obesity in not only the children of the malnourished mother, but her grandchildren too. Why? Obviously I would recommend you read Carey’s lucid and accessible narration to find out, but it is the seemingly magical interactions with the nucleotide bases that make up DNA itself that is epigenetics. To me the topic is the future of the subject and if students want to be part of this “revolution” this book is a must-read.

  1. Darwin’s Island by Steve Jones

Admit it, you’re thinking “Ah! The Galapagos Islands”. But no the title actually refers to Britain and is an outstanding account of the experiments Charles Darwin investigated in and around his home county of Kent. Jones writes with wit and enthusiasm, this craftsmanship is best illustrated by the fact that my favourite chapter is the final one entitled The Worm Crawls In which centres on soil.  In some hands thirty-two pages on this topic might drag, but once finished I was inspired to present an assembly on the humble earthworm. More than anything this book allows readers to see past the rightfully headline grabbing HMS Beagle voyage to cast an eye over the incredibly rich and detailed research that does not necessarily receive the credit it is due. As Jones points out Darwin’s visit to the Galapagos Islands only lasted five weeks, compared to the forty years working in Britain.

Part tow in this series of recommended reads is Another book all Biology A level students should read.

Biology A Level: International Rescue?

This blog has been at least a year in the making. In fact ever since 2013 when we decided to change our A level exam board to an International A level, I have tried to keep a check of our rationale for doing so. After giving a talk at a Cambridge International Examinations seminar at the end of November I had written down a long list of reasons and originally planned to post these during the Christmas holiday, but life events rather overtook me. What follows below is a précis of the reasons for leaving AQA and the other domestic exam boards for the exotic climes of an international qualification. As such it focuses on the perceived benefits of the change; I aim to redress this balance, should I need to, in the future with information about limitations. Although it was originally me, as HoD, that initiated and steered a course towards International A levels, my department were very much behind the decision from the off. In fact due to the huge uncertainty of what exactly the new Science A level specifications were going to include and how the practical work would be assessed we “jumped ship” early – officially deciding back in September 2013. Students at Sixth From are now studying the “International” A level from Cambridge International Examinations.

International rescue?

International rescue? (Image taken from Wikimedia Commons)

The decision making process was made easier by our disenchantment with EMPA and ISA “practical examinations”. Students constantly performed well below their attainment in theory papers. In fact with a little (very lightweight, unreliable, insignificant, etc) statistical analysis I demonstrated that on average our Biology A level students were performing one and a half grades below their theory paper attainment; and this is from pupils who carried out practical work almost every week and were scoring close to full UMS in the theory papers. The International A level offers a “proper” practical examination, one beyond any suspicions of “interference” so that students are awarded marks that correspond to their performance in theory papers. I could probably write a whole post on my total disillusionment with the proposed changes to domestic Science A level practicals… I will leave that for another time, suffice to say I am disappointed by the approach of the domestic exam boards and dismayed that practical assessment will not form part of the overall A level grade. More reasons are shared below and are taken from notes I used when discussing International A levels at a CIE seminar held at Somerset House in November. It is a fairly comprehensive list of the motivations behind why I think the award would suit pupils at our school:

  • Natural progression following on from the principles of IGCSE, which we teach at Key Stage 4.
  • Syllabus is more thorough; the content manages to balance a broad range of topics and goes into an appropriate depth of knowledge. In particular it favours breadth of knowledge over “sound bites”.
  • Assessment is not modular, encouraging students to think about the “big ideas in Biology”. This links directly to the syllabus; it is not divided into topics that are then examined in separate papers.
  • Encourages more exhaustive learning and rewards those who work hard and understand the topics.
  • The emphasis is on students carrying out and planning practical work. Experiments are present throughout the two year course…
  • …even more importantly these experiments are formally assessed, thus rewarding students who have grasped basic practical skills. This maintains the significance of actually having to do practicals properly in the classroom whilst learning the course and removes any suspicions of interference. Pupils therefore are awarded marks that match their ability and correspond to attainment in theory papers.
  • Grades are criterion-referenced.
  • Better preparation for university, particularly if students plan to study a biology-related degree.

As stated in my introduction I will be revisiting this list and possibly adding more to it. I also want to share our experiences of actually teaching the qualification as well as any problems we encounter. Perhaps it will prove to be our International Rescue, but for now I am pleased to type: “FIVE, FOUR, THREE, TWO, ONE. THUNDERBIRDS ARE GO!”.

Header image taken from Flickr.

The Biology of Superpowers: Part I

Disclaimer 1: My knowledge of comic book and film Superheroes is very limited. I am by no means an expert and my only real familiarity comes from watching a few film adaptations. A cursory internet search here or there helped supplement my limited understanding for the purpose of this post.

Disclaimer 2: This post has nothing to do with explaining the biological processes behind a country projecting dominating power and influence over the world (a joke for the historians).

On Monday I took an assembly and decided to try to engage in some biological discussion over Superheroes and their superpowers. By presenting The Biology of Superpowers: Part I I hoped the students would find the subject matter interesting and also allow us to tackle some quite in-depth biology. Although the former was true, the latter did not necessarily occur as accurately as hoped. What follows is my pretty poor effort to try to summarise our explorations of biological explanations for the Avengers’ superpowers. Why the Avengers? Perhaps because there was too good a pun to be had with Avengers Assembly? Or maybe it was because there was lots of material available and some movie trailers to watch in case I needed any “filler”? To be honest I probably should have focused on the X-Men and macroevolution, but this is only Part I

Dr Bruce Banner / The Incredible Hulk

Firstly I must mention Banner’s “genius level intellect”, but what is more interesting is the Jekyll and Hyde nature of his power. During the assembly I mentioned that quite a few teachers are prone to an anger-induced tendency to “hulk-up”, often triggered by dodgy excuses for not completing homework.

HULK SMASH FOR NOT HANDING YOUR HOMEWORK IN ON TIME (Image taken from Wikipedia)

HULK SMASH FOR NOT HANDING YOUR HOMEWORK IN ON TIME
(Image taken from Wikipedia)

However, where we can get into the biology is the physical manifestation of Hulk’s powers due to absorbing “massive amounts” of gamma radiation. As I am sure most people know, our DNA codes for our phenotype and therefore changes to the DNA could cause changes to the phenotype. In addition gamma rays are a form of ionizing radiation that can cause major problems to living organisms in that they damage DNA. Therefore if Bruce Banner’s DNA was altered by the gamma radiation it could, potentially, cause observable changes to his phenotype. Although the idea of mutations causing changes to DNA, which cause changes to genes, which cause changes to phenotype is a very observable phenomenon it is unlikely it would ever lead to the Hulk coming into being. In fact it is more likely the “massive amounts” of gamma radiation would in fact cause radiation sickness, cellular death and increased incidence of cancer. I guess that wouldn’t make such a great story though…

Steve Rogers / Captain America

The story of Rogers’ heroic perseverance despite his scrawny and frail body is inspiration to us all; many a student could learn from this dedication when applying the same concept to work ethic and ability. We focused on two ideas from after Rogers had transformed into the mighty Captain America:

  1. The ability of Rogers’ body to replenish the “Super-Serum” that transformed his speed, endurance, agility, reflexes, durability and healing to the “zenith of human capabilities”. We decided this was very unlikely, e.g. a type 1 diabetic does not regenerate beta cells in the Islets of Langerhans following regular injections of insulin. However, it could have been a very early trial of gene therapy which just might be possible in today’s world; perhaps the “Super-Serum” was in fact a crude way of administering a plasmid vector to supplement the DNA in Captain America’s cells… There does appear to be a modicum of biological theory that mightsupport this and gene modification is an area with a lot of interest. Although how to do so to result in Cap’s powers is another thing.
  2. Being frozen for “decades” in suspended animation. Well there certainly is a precedent in nature through rotifers, tardigrades and even humble sea monkeys.
    A tardigrade, aka a waterbear (Image taken from Wikipedia)

    A tardigrade, aka a waterbear
    (Image taken from Wikipedia)

    Cryptobiosis is most definitely a survival strategy, although generally based on almost total dehydration similar to how seeds can remain dormant for many years. However, once again although there is a glimmer of possibility it is unlikely that the frozen in ice concept (as per the storylines) would work nor even the anhydrobiotic mechanism on a complicated multicellular organism.

Tony Stark / Iron Man

My favourite depiction of Tony Stark the man is from The Avengers:

Steve Rogers: Big man in a suit of armour. Take that off, what are you?

Tony Stark: Genius, billionaire, playboy, philanthropist.

In terms of superpower Stark relies on his suit, powered by the electromagnet in his chest. This magnet saved his life by preventing shrapnel from entering his heart and killing him. In a twist of fate that comic books so love, the shrapnel cannot be removed either. Therefore Iron Man / Stark is dependent on the electromagnet, which turns out to also be a convenient energy source for his superpowered suit giving him abilities such as flight and super strength. So what about the biology? It is perfectly possible for shrapnel to be lodged in the body and for the person to survive. What is unlikely is that it would *still* be moving inwards and therefore continuously require the magnet to prevent it entering the pericardium. In addition it is more than probable that having an electromagnet in one’s chest would lead to serious infection… Therefore our verdict was, although it was possible to have shrapnel in one’s body that is being prevented from going in any further, it is unlikely that Iron Man / Stark would be healthy enough to actually be a superhero.

Natasha Romanoff / Black Widow

My favourite Avenger (this caused much mirth from the male teenage audience, I can’t imagine why). However, I admire Black Widow because she is not a superhero and does not have any superpowers. Indeed she is world class athlete, master tactician and expert in martial arts and in spite of her lack of powers. She is a polymath rumoured to have agility greater than “an Olympic gold medallist” and is also an accomplished ballerina. I would suggest that this is well within the realms of the biological world and would point to Malcolm Gladwell’s Outliers or Matthew Syed’s Bounce. Both books argue that 10,000 hours of ever increasingly difficult practice will make someone an expert or world class in a sport. As a product of the former Soviet Union it is easy to imagine that a young Natasha Romanoff could have been whisked away to put in the desired volume of training in the quest to produce a super spy.  Black Widow’s superpower is easily the best because it is something that is replicable, time allowing.

Thor

Thor is a deity with superhuman durability, longevity, speed and strength. His hammer, Mjolnir, allows him to transport between dimensions, manipulate electricity and the weather. Being based on a Norse god we decided to home in on the idea that he could control weather. As god of thunder Thor is well known beyond the Superhero universe and is a mainstay of early Scandinavian mythology. You might imagine that looking up at lightning, humans tried to rationalise this unknown as an angry god hurling thunderbolts. As such if people are happy to believe in gods they may well attribute forbidding and unfathomable events to those supernatural beings. Perhaps it is in the human psyche that such gods exist? Therefore there is perhaps a biological basis for Thor, Asgardian god of thunder, to exist in the mind as action potentials and firings of synapses. Or at the very least it would be very difficult to argue with someone who uses faith and belief to come to the opinion that Thor is controlling the weather.

As a final summary I will admit that I purposefully left out Hawkeye from the ensemble / assembly. As great editors might say, it was a question of pace and timing (and also perhaps that he is not a particularly interesting character, or at least IMHO having watched the film at least once). In addition I would once again invite any criticism, both canonical or biological, to put me right. However, I will end with the proviso that this was all just to elicit biological discussion rather than to mess with any comic book pedantry. I will also be exploring the issue further in my Sixth Form extension classes as a stimulus to talk about the big ideas in biology. The final word falls to a student who, having watched my assembly last year on “Dinosaurs in the Movies” discussing the biological limitations that mean Jurassic Park will not happen anytime soon, commented “what childhood memory are you going to destroy next time, Sir?”

Header image taken from Wikimedia Commons.