Category: IGCSE Biology posts

IGCSE Biology 2017 paper 2 predictions

This post starts with a massive proviso of course.  Making predictions as to which topics might appear in a future exam is a very risky business.  The paper 2 you will all sit after half term can test material from the entire specification (including all the specification points in bold) and there is absolutely no guarantee that topics tested in paper 1 may not reappear in some form in paper 2.

So the proviso is this:  the only way to be fully prepared for paper 2 is to revise the entire specification so that you are prepared for whatever the examiners might throw at you.

But having said that, it seems sensible to focus your revision for paper 2 onto topic areas that were not examined in paper 1.  If I were in your position, these are the topic areas for which I would be doing most of my revision in the coming weeks:

  • Respiration 2.33 – 2.37
  • Gas exchange in Plants 2.38-2.43
  • Transport in Plants 2.49 – 2.56
  • Transport in Humans 2.57 – 2.66
  • Kidney 2.68 – 2.76
  • Reproduction 3.1 – 3.12
  • Food Chains and Energy Flow 4.4 – 4.7
  • Nitrogen and Water Cycles 4.8, 4.10
  • Human Influences on Environment 4.11 – 4.17
  • Food Production (including fish farming) 5.1 – 5.9
  • Selective Breeding and Genetic Modification 5.10 – 5.16

The bad news is that this list above still forms a large proportion of the extensive EdExcel IGCSE Biology specification but the good news is that there are PMGBiology blog posts on all the above.  So please use the search function on my homepage to find material to help you revise.

Practice papers and mark schemes are available online (and for my students on the school Firefly page)

Keep working hard – you are almost there and the summer to come will be long and restful….

Three days to go…..

For those students following the EdExcel IGCSE Biology course there are now just three days to go until the paper 1.  This is the two hour exam covering all the specification (with the exception of the handful of content points in bold).  If you started revision early enough, you should know be feeling confident that you have the knowledge and understanding needed for whatever challenge the examiner might throw at you.  So how best to use your time in the final few days…?  It is a tricky question as the answer will vary for different people – you must always do what you think is best for you and your chances.

But if it were me, I would be trying to do the following:

  1. Have a go at as many past paper questions as possible over the weekend.  Answer the questions under exam conditions, then mark them yourselves using the mark schemes available online.  Pay particular attention to marks lost due to poor reading/interpretation of the question or poor-exam technique.
  2. Prepare yourself for the questions that you “know” will come up on Tuesday.  It is almost certain that there will be a genetics question to make sure you remember how to set out genetic crosses correctly.  There is always a graph to plot and questions asking you to describe the pattern in a set of results.  How can you ensure you always get full marks on these questions which require no biological understanding to answer?
  3. Look at the experimental design questions and continue to practise them.  Check over all the required practicals mentioned in the specification and ensure you understand how they work.

Finally on Monday night, please get an early night so you are refreshed and ready for a 2 hour paper.  There is no point doing hours and hours of last minute cramming as it simply doesn’t work.  If the Biology exam were like a Spanish vocab test then I would encourage you to spend four hours before the paper going over and over the material….. But your exam is going to require you to interpret data, to make suggestions and come up with explanations for things you haven’t seen before.    You cannot think clearly or concentrate fully on reading the question when you are exhausted.  So if you decide to cram, the chances are that many more marks will be lost through tiredness than will be gained by any short-term memory gains.

Please go to bed at a normal time on Monday night and wake up at a normal time on Tuesday morning.

And the very best of luck to you all!

Banned Words in IGCSE Biology answers

There are one or two words which you should never use in your answers to IGCSE Biology papers.

  •  The boys I teach know that amount is a banned word.  If you find yourself writing amount, please cross it out immediately and think which of the following terms is actually the word you should be using:  concentration, volume, mass, number .

[Amount has a specific meaning in science:  it means the number of moles of a substance and seeing as you don’t need to know about the dreaded mole for Biology, it should never be used.]

Mole (this is a good photo of the dreaded mole)

  • Be wary of using the word nutrient without giving an example of what molecule you mean.  A nutrient is food molecule like glucose, amino acid or lipid.  When you are describing the things in soil that are absorbed into the roots and are transported in xylem, it is better to refer to them as minerals.

 

  • Level does not mean the same as concentration.  Don’t write about the level of oxygen when you mean concentration.

 

CORMS is dead: Long live DORIC

In Ancient Greece, the Doric order was one of their favoured architectural styles and offered the simplest way of decorating columns.. As you can see from the featured image, Doric columns have an undecorated square capital at their top.

I am sure you won’t get questions on ancient architectural styles in your GCSE Biology, but Doric (now DORIC) is perhaps a simpler way of remembering the key points to include in the experimental design questions in the exam.  I have written about CORMS before and there is nothing new in this post, simply a new acronym.

D stands for Dependent Variable.   This is what you will measure in your experiment.  The mark is often for how you plan to measure the dependent variable, how frequently you will take measurements etc.

O stands for Organisms.  What are the key variables relating to the organisms involved?  If using a living organism in your experiment (other than humans) often this involves using organisms of the same species, the same age and sometimes the same mass.  If you are using humans, you often need to standardise your groups for gender, health, age etc.

R stands for Repeats.  If you do more than one replicate of each set of conditions, it allows you to see how reliable your method is and also allows an average result to be calculated.  Think about how many repeats you think you would do: it depends on the experiment of course.  In a laboratory experiment, three might be sensible, if you are growing seeds to investigate germination, you might grow 200 identical seeds in a tray…..

I stands for Independent Variable.  This is the thing you are going to alter in the experiment.  So how do you intend to alter it and over what range?

C stands for Control Variables:  what are the variables that need keeping the same in every experiment in order to make the investigation a fair test?  Think what other factors might affect the dependent variable other than the one you are investigating.  And then think how you would keep them constant in an experiment.  I would suggest you need to identify at least two or three of the most obvious control variables to ensure you get full marks.

Simple!  DORIC is the new CORMS….

IGCSE Biology Revision resources on Quizlet

https://quizlet.com/join/TABNg5Jmp

I have created a group for IGCSE Biology students on Quizlet and you are welcome to join using the link above.  There are some topics already there in this group and I hope to add more material over the coming weeks.  Please join and I hope you find it useful.

Most of the sets are modified from other users but I have been through and edited them, to make them ideal for A* learning.

Enjoy!

How to revise in the holidays: some PMGBiology tips for 2017….

 

Screen Shot 2017-03-28 at 11.40.24Sometimes the hardest thing with revision is getting started…..  This post is meant to help you think about how best to make the most difficult first steps towards securing your A* grade.  I went through this with my Y11 classes before the end of term so this is just a re-cap.  There are very few original thoughts here (story of my life….) but perhaps I can inspire you to get started early in the holidays with your Biology revision….?

Most important – have a plan for the Easter holidays

Work out how many days you have available to revise over the holidays.  This will not be the same as the total number of days of holiday as you should have rest days where you do no work at all.  Ask your parents what family commitments you have coming up, think about your social life and subtract the days when it will be impossible for you to work.  This gives you a number of “working days”.

What do you do on a “working day”?

I suggest that you never try to do more than 4-5 hours of work in any one day.  Revision is not measured in hours, it is measured in progress and learning.  2 hours of effective work might be better than 10 hours inefficient time at your desk.  The aim here is to maximise the benefit you gain from your revision, not simply clocking up the hours.

Here is how I would organise things if it were me…..  Divide the working day into three sessions:

  • Morning:  9.30am – 12pm
  • Afternoon:  2pm – 4.30pm
  • Evening:  7pm – 9.30pm

The plan is this.  On a working day you always work in the morning session, every day, no excuses…. Ask your parents to be ruthless in waking you up and don’t allow yourself ever to sleep later than 8.30am or so.  There will be plenty of time for lie-ins and getting up at lunchtime in the summer holidays.  By midday, you will always have done half the work of the day.  How happy will that make you feel? Then choose either the afternoon or evening session (but never both) depending on how you feel and what other plans you have for the day.

How to organise a “revision session”

00957a1-800x800_4       838338.1106

You need a kitchen timer like the one shown above (not to scale as the textbook is quite large and the timer is quite small…..).  I bet if you ask nicely your mum or dad will let you borrow the one in the kitchen.  For Biology work, you also need your textbook and revision notes.   This is how I suggest you work.  Set the timer to 25 minutes, switch off your phone and start work.  Work at a topic until the buzzer sounds – no distractions allowed…. If your phone beeps, ignore it.  Snapchat can wait!    After 25 minutes stop and have 5 minutes off.  Make a cup of tea, check your phone and repeat.

I suggest that you revise 5 different subjects in one session.  (5 x 25 minutes)  You must try to make your revision interesting so you don’t get bored.  Bored people do not learn anything……

Different people learn best in different ways so do what works for you.  What works for no-one is just reading….  Make notes, revision cards, write out definitions of key facts, use IT if that rocks your boat, whatever you like just do not sit and read your textbook.  The key thing is to go over ideas as many times as possible, test yourself on your recall of facts and then try to practise some past paper questions.  Most importantly, try to have fun!  If you are enjoying it, you will be learning and that is the idea I guess.

Finally, the main benefit of having a plan is this….. When you are not supposed to be working (according to your beautifully crafted plan), you can switch off properly without feeling even a teeny bit guilty.  You can combine revising with getting on with enjoying your life.  The two things are not mutually exclusive!!  And with luck you will avoid feeling like Stewie in the picture below. If only he had a proper revision plan…..

IMG_3499

Human Influences on Greenhouse Effect: A* understanding for IGCSE Biology 4.12 4.13 4.14

I established in a previous post that the Greenhouse Effect is a good thing for life on the planet.  So what is the problem?  Well the simple idea is that human activities and the massive growth in human populations seen over the past two hundred years have changed the composition of the atmosphere.  The concentration of greenhouse gases has risen and this enhanced greenhouse effect is causing climate change.

The principal gases in the atmosphere responsible for the greenhouse effect are carbon dioxide, methane and water vapour.  Have a look at these two tables taken from the following website from the Center for Climate and Energy solutions:

http://www.c2es.org/facts-figures/main-ghgs

The first image shows the main gases in the atmosphere that contribute to the Greenhouse Effect.

number-1

Anthropogenic means “caused by mankind” and so you can see what humans are doing to generate an enhanced greenhouse effect.  The GWP figure stands for Global Warming Potential and gives a relative value for how each gas might contribute to climate change.  One molecule of CFC-12 is as powerful as a greenhouse agent as 10,900 molecules of carbon dioxide.

number-2

This second table shown above demonstrates how the composition of the atmosphere has changed from pre-indutrial to modern times.   I am going to focus on the two greenhouse gases at the top of the list:  carbon dioxide and methane.

Carbon Dioxide concentrations in the atmosphere

Scientists at the Maunua Loa Observatory in Hawaii have been measuring atmospheric carbon dioxide concentrations since the 1950s.  Here is a graph of their results.

keelingcurve-large

What do you notice about this graph?

  1. There is a gradual upward trend such that the average concentration has risen steadily over the 50 year period.
  2. Within each year, there is an annual peak and an annual trough in the carbon dioxide concentration.  The “peak” corresponds to northern hemisphere winters when there is less photosynthesis by plants and more fossil fuels are burned.  The “trough” is northern hemispere summer when photosynthesis rates are high and so carbon dioxide is removed from the atmosphere

If you want data going back further into the past, you need to look at ice core data.  Tiny volumes of the atmospheric gases are trapped within ice as it forms in Antartica and by drilling out a core and analysing the gases it contains, one can determine the concentration of the atmosphere when the ice was formed.  The deeper parts of the core formed longer ago so a journey through an ice core is like travelling back in time…..

co2_10000_years

What human activities might be responsible for these changes in carbon dioxide?

  1. Deforestation (see my post on this topic)
  2. Combustion of Fossil Fuels (coal, oil, gas)
  3. Cement production

 Methane concentrations in the atmosphere

world_cattle_inventory_vs_human_population_country_1_635794680294204000

Methane is also a potent greenhouse gas. It is produced as waste product of the bacterial reactions that happen inside the rumen and intestines of cattle.  (The rumen is the large first chamber of their stomach in which bacteria digest cellulose in the cow’s food)  I was once told that each cow produces 65 litres of methane a day but I have never measured it myself…….  Seeing as the world population of cattle is estimated at 1.4 billion, that is a lot of methane each day being released into the atmosphere.

Methane is also produced by bacteria that break down our domestic waste in land fill sites and by anaerobic bacteria that live in paddy fields in which rice is grown.    More humans means more cattle, more rice and more landfill and all of these are responsible for the rise in methane concentrations seen in the atmosphere in recent times.

Greenhouse Effect: A* understanding for IGCSE Biology 4.12 4.13 4.14

The Greenhouse Effect is the name given to the way in which the earth’s atmosphere acts to warm up the planet.  The earth and the moon gain almost exactly the same incident radiation from the sun and yet average temperature on the earth is stable at around 14 degrees Celsius.  On the moon the temperature fluctuates wildly from 1oo degrees Celsius during the day to minus 153 degrees Celsius at night.   Life would be impossible in such extreme and variable conditions and so the greenhouse effect is definitely a “good thing” for life on our planet.

How does the greenhouse effect work?

Well the main idea here is that there are certain gases in the atmosphere that can trap the infrared radiation that the earth emits and prevent it escaping the atmosphere.  These greenhouse gases are warmed as they absorb the infrared and so the atmosphere heats up.

greenhouseeffectdiagram

Remember that because the sun is so hot, it emits radiation at a much higher frequency.  This is mostly in the “visible light” part of the spectrum together with some ultraviolet.  The gases in the atmosphere cannot trap visible light (air is transparent as you have probably noticed) and so most of the solar radiation passes through the atmosphere and hits the earth.

greenhouseeffect

Which gases can act as greenhouse gases?

The two most prevalent gases in the atmosphere are nitrogen (N2) and oxygen (O2) and neither is able to trap infrared so cannot act as a greenhouse gas.  The principle greenhouse gases in the atmosphere are

greenhouse-gases-most-common

  • carbon dioxide
  • water vapour
  • methane
  • ozone
  • nitrous oxide

So what’s the problem?

Well of course the problem is that human activities over the past century or so have altered the composition of the atmosphere so that the concentration of greenhouse gases has risen.  This has meant more heat is trapped and climate systems are altered in consequence.  This enhanced-greenhouse effect is the problem and I will look at this in the next post…..

total-heat-content

Evidence for Climate Change: A* understanding for IGCSE Biology (part 2) 4.12 4.13 4.14

Before you can look at the science of climate change and how human activities are causing it, you first need to accept that we are currently undergoing a period in which our climate is changing at an unprecedented and rapid rate.

What would you expect to see in a warming world?

ten-indicators-of-global-warming

Well the first and most obvious point is that you would expect to see measurable changes in land and sea temperatures.

All three of these graphs represent in different ways the changes in temperature over the past century or so.  It is true of course that there have been times in the past when global temperatures were much warmer than they are now but the rate of change seen since the Industrial revolution is totally unique in the 4.6 billion year history of our planet.

The top ten hottest years on record have all happened since 1998.

2016globalnumbers_toptenyearsupdate

There is excellent evidence from all over the planet of glaciers shrinking; polar ice caps are shrinking and it may be that the North Pole is free of summer sea ice for the first time in 100,000 years some time in the coming decades.  (This is controversial as it is a prediction based on computer models of future climate: different models make different predictions and with a system as chaotic and interwoven as global climate, it can be very difficult to predict)

As the oceans have warmed, this has impacted on extreme weather systems.  This graph shows the incidence of North Atlantic Tropical Storms over the past century or so.  It has continued to rise since 2007…..

nats_frequency

When you look at all this evidence, it is hard to believe that our climate has been stable over the past century.  In fact very few people try to dispute the fact of climate change.  The dispute is whether human activities are causing this climate change and indeed whether it matters…..  I hope in later posts I can convince you the answers to these two questions are yes and yes.