Category: IGCSE Biology posts

Evidence for Climate Change: Grade 9 understanding for IGCSE Biology (part 2) 4.13 4.14 4.15

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?


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.


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…..


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.


Air pollution and climate change: Grade 9 understanding for IGCSE Biology (part 1) 4.13 4.14 4.15

Climate change remains one of the more controversial topics in the IGCSE Biology specification.  Just in the past few weeks, the USA (one of the finest nations on the planet) has elected as their President someone who has stated on record that he believes in some giant conspiracy theory about climate science centred around the Chinese….


The overwhelming majority of climate scientists do not support this interpretation of the facts.  They are able to provide evidence of rapid climate change over the past few decades and link this to human-induced changes in the composition of the atmosphere due to pollution.  When these facts are linked by a sensible scientific theory that proposes how and why certain gases might lead to an increased warming effect in the atmosphere (the so-called greenhouse effect) the evidence in support of human-induced climate change becomes compelling.  Keeping US manufacturing competitive is important of course, but not at the expense of the enormous environmental and financial costs of allowing our pollution of the atmosphere to continue unchecked.  I am not sure I will be able to convince President-Elect Trump (he probably doesn’t read my blog in any case) but perhaps I can show you the kind of understanding needed to generate A* answers in GCSE questions on this topic…?


I am going to organise this work into several sections and will post on each topic in the coming week….

  1. What is the evidence for climate change?
  2. What is the greenhouse effect?
  3. How are human activities altering the make up of the atmosphere?
  4. What are the predicted consequences of climate change in the coming years?

Bacteria and Yoghurt: Grade 9 understanding for IGCSE Biology 5.7

Biology is a great subject to teach:  you get to introduce young minds to the wonders of the natural world, to show them how evolution has been able to take an ancient planet with a few self-replicating molecules in some deep sea vent and end up today with perhaps 100 million different species all occupying unique niches in an ever changing ecosystem.  You can take students onto a journey into the cell so that they understand and appreciate the complexities of DNA as a coding molecule and how proteins have evolved to carry out the myriad processes of cellular biology.

And you also get to teach the role of bacteria in yoghurt making.  This will be a short post.

This is yoghurt.  It is made from milk.


Milk contains a sugar, lactose.  Yoghurt is made when a culture of Lactobacillus bacteria is added to the milk.  The two most important bacterial species involved in yoghurt making are called Lactobacillus bulgaricus and Streptococcus thermophilus (although only the former is mentioned in the specification).  Perhaps they didn’t want the excitement levels to get too high….?


Lactobacillus use the lactose in the milk as a respiratory substrate producing lactic acid as a waste product.  This lactic acid gives the yoghurt its bitter taste as well as lowering the pH so that the yoghurt takes on its gel like appearance.

Respiration in Lactobacillus:

Lactose ——> Lactic Acid

That’s the limit of my knowledge and interest in this topic:  hope it helps…….

Yeast and Brewing: Grade 9 Understanding for IGCSE Biology 5.5

Humans first discovered how to make beer around 7000 years ago and brewing has been an integral part of human civilisations ever since.  Yeasts are a family of single celled fungi that can use the sugars in fruits and seeds as a source of energy for respiration.  Yeast can respire both aerobically and anaerobically and you should know the equations for these two processes.

Aerobic respiration

Glucose + Oxygen ——-> Carbon Dioxide + Water

Anaerobic respiration (aka Fermentation)

Glucose ——> Ethanol + Carbon Dioxide


So when yeasts respire anaerobically they produce ethanol and carbon dioxide as the waste products.  Ethanol is also known as alcohol and humans learned a long time ago that alcohol is a drug that changes the way you think or feel, often in a pleasurable way in moderate doses.  Making drinks that were alcoholic also helped to kill potentially harmful bacteria and other pathogens in pre-industrial times when drinking water was not readily available.

If you add yeast to a source of sugar in anaerobic conditions, the yeast cells will ferment the sugars into alcohol and carbon dioxide.  In order to make beer, the source of sugar comes from germinating barley seeds.  Hops (dried flowers of a hedgerow plant) are added later to give the bitter flavour beer drinkers seem to like…..


The flow diagram above shows the stages in making beer.  I can’t imagine you would be expected to know the details.  Any question on this topic would presumably focus on the anaerobic respiration of the yeast rather than the details of the brewing process.

In case anyone is interested, I am not a huge fan of beer although I can occasionally be forced by peer pressure into consuming one or two.  My preferred fermentation reactions happen not in the copper tuns of English breweries but in the beautiful Northern Rhone valley in France, where skilled wine-makers can take Syrah grapes grown under the influence of the cooling mistral wind and turn them into beautiful Cote Rotie or Hermitage.  Now there’s a happy thought for a cold November evening……..


Fertilisers: Grade 9 understanding for IGCSE Biology 5.3

Fertilisers is the term used for “chemicals or natural substances added to soil to promote the growth of plants”.

Key point:  in spite of what it says on this packet of fertiliser, fertilisers are not food for plants. (Just adding this photo to the post makes me feel slightly sick inside:  how could MiracleGro be so happy to confuse generations of people who visit garden centres…..?)


Plants are autotrophic: they make their own food molecules in the amazing process of photosynthesis.  Plants use carbon dioxide from the air plus water from their roots to produce a whole range of organic molecules powered by the energy from sunlight.

But remember that in order to make amino acids, proteins and DNA plants will also need a source of nitrogen atoms.  Carbon dioxide and water do not contain any nitrogen atoms and yet nitrogen is needed for building amino acids, proteins and DNA.

Where do plants get this nitrogen from?

Well the key idea is that they do not take it from the air.  Nitrogen gas in the air is very un-reactive and cannot be fixed in the plant.  But the soil contains nitrate ions and plants can absorb these by active transport in their root hair cells.  Nitrate ions are transported up the plant in the xylem and can be used to make amino acids etc. in the leaf cells.

Nitrates are not the only mineral ions taken up by plants in their roots.  Plants absorb phosphate (for making DNA), magnesium (for making chlorophyll), potassium (for a wider variety of cellular processes) amongst many others.

So fertilisers are a way of replenishing the concentration of these essential minerals in the soil.  More fertiliser, more minerals, faster plant growth as more proteins/DNA etc. can be made in the leaves…. Simples!


The commonest type of inorganic (chemical) fertiliser are called NPK fertilisers.  (Nitrogen, Phosphate, Potassium).  These can be bought in handy 50kg sacks (see picture above), stored and then spread easily over fields.

Farmers can also use manure which is an organic fertiliser.  Here are some advantages/disadvantages of organic fertilisers in case you are interested…. It is smelly, bulky and difficult to store.



Glasshouses and Polythene tunnels: Grade 9 understanding for IGCSE Biology 5.1 5.2

Growing crop plants is basically a section about maximising rates of photosynthesis.  If a plant is photosynthesising at the fastest rate, it will be growing fast thus increasing the rate of food production.

One of the simplest ways of maximising photosynthetic rates is to grow crops in a greenhouse (laughably called a glasshouse in the syllabus to avoid confusing you) or a polytunnel.  Greenhouses are made of glass; polytunnels are much cheaper to build as they are made of transparent plastic.


What are the advantages of growing crops in a greenhouse or polytunnel?

Temperatures are increased due to the insulating effects of the glass or plastic.

Watering can be controlled.  Artificial lighting can be used to optimise the light intensity for a maximum photosynthetic rate.

Carbon dioxide concentrations in the air can be artificially increased if the doors to the greenhouse are kept closed.  Often carbon dioxide is released into the greenhouse – this is good for the environment as it reduces emission of greenhouse gases and good for the farmer as crop yields increase.

These points above link into the work you will have done on rates of photosynthesis.  (For more information on this, please refer to my posts on section 2.19)

Fertilisers can be added to the soil (see posts on section 2.21 and 5.3).

Pests can easily be kept out or removed (see posts on section 5.4)

How to answer multiple choice questions: a quick guide

Many of the students I teach are facing end-of-term exams next week.  And for my Y9 and Y10 students these are multiple choice papers which pose a different challenge to the more usual structured answer format.  So here is a quick PMG guide to help you score the highest mark you can on this kind of paper.  Good luck!

1) Don’t underestimate the opposition!

The biggest mistake students make with these exams is to be over-confident.  The reason GCSE exams no longer contain any multiple choice questions is because it was felt that this type of question is too difficult.  The examiner, by selecting four incorrect responses to every question, is trying to catch you out and the more plausible the incorrect responses, the better the question!  So your understanding needs to be really good to not be tricky by these underhand tactics…. Get revising!

2) Read the question carefully.

This skill is tested even more fully in a multiple choice exam. You spend less time writing answers (obviously), so this allows more time for reading and thinking.  Even with a “mark a minute” time frame, there is time for thinking and planning before deciding on a correct answer.  Write on the question paper, use it for rough work and planning.  And RTQ carefully – with many similar but incorrect answers on the page, it is so easy to decide too quickly what the correct response is and so miss out on marks you could obtain with a little more care.

3) Try to eliminate the obviously incorrect answers:  this will mean you are only focussing your thinking on the possibles.  It also means if you have to guess, you are maximising your odds of being lucky!  But be careful….. This strategy has an obvious flaw so be careful in what you eliminate.

4) Your best chance of getting a question right is the first time you answer it. So I suggest you leave blank any answers you are unsure of on your first go through the paper.  Don’t spend more than a minute on any question on this first pass through the paper.  You can come back to look at the harder questions at the end of the exam.  It is much harder in an exam to spot an error in a question you have already answered, so I would leave answers blank unless I am sure I am right….

5) Keep an eye on the time.  After 20 minutes of the exam, check that you are ahead of the time.  Most multiple choice exams are a “mark a minute” but I know that in our internal exams this isn’t always the case, so check.

6) Finally, make sure you answer every question.  There is only positive marking in these exams so you should always guess (see point 3 above).  The only way you can guarantee you won’t get a mark is if you leave the question blank!

Take a pencil and a rubber to these exams – both will be useful!  And good luck……..

Comments and Suggestions welcome…..

Dear Readers,

Please feel free to send me any comments/suggestions/improvements so I can make this blog better and more useful to the GCSE students who read it…..  I will be writing some new posts in the Christmas holidays to complete the current IGCSE specification, and perhaps then to address the new material included for examination in 2019….?

But please tell me if there are particular topics you would like me to expand on…. If you don’t understand it fully, then lots of other readers won’t either!

And keep working hard – no short cuts in Biology GCSE…..

Please click the “Leave a Comment” link below this post to pass on any feedback.

Fish Farming: Grade 9 Understanding for IGCSE Biology 5.9B

5.9 explain the methods which are used to farm large numbers of fish to provide a source of protein, including maintenance of water quality, control of intraspecific and interspecific predation, control of disease, removal of waste products, quality and frequency of feeding and the use of selective breeding.

fish-farm-l-eribollBefore we start it is worth me being completely clear – I hate the topic of fish farming.  I am not saying it isn’t important, just that when you read the specification point above, it hardly lifts your spirits does it?  Perhaps this is why I have waited until the evening before the 2016 paper 2 exam before writing about it on the blog.

Background understanding needed:

Humans have overfished all the world’s oceans over the past 20-30 years.  This means that fishermen have become so successful at collecting fish from the oceans due to advances in trawling technology and echolocation, that fish populations have crashed.  It is a truly sobering thought that almost every studied fish species in the ocean has only 10% of the numbers that we know were present 50 years ago.  90% of all fish have been removed by fishing.

Fish provide the  major source of dietary protein for a large proportion of the world’s population.  When you combine this with the fact that fish are becoming so scarce in the ocean, it is getting harder and harder to catch them, it is clear we have a potential problem on our hands.  Farming fish rather than catching wild fish might (stress might) provide a possible solution…..

Fish Farming

Farming fish is really as dull as it sounds.  Large floating cages are anchored often in estuary waters and small fish are added.  They are fed regularly (with fish food made from other less tasty fish that humans are extracting from the ocean), predators are kept out by the clever use of nets and fine mesh cage, antibiotics and other chemicals added to control lice and bacterial pathogens and after a few months, the fish can be harvested.


Maintenance of Water Quality

If the fish farm is in a tidal part of an estuary, then the tide will twice a day replace the water in the cage with fresh seawater containing high concentrations of oxygen for respiration in the fish.

Control of Intraspecific and Interspecific Predation

Intraspecific predation means predation within a species.  This means the fish will eat each other…. This is prevented by only having fish of the same age in any particular cage.  There won’t be any bigger fish to eat the smaller ones.  Interspecific predation means other species eating your precious fish.  This is prevented by keeping predators out of the cage using a mesh size that doesn’t let predatory fish and seals in plus covering your cage with netting to deter sea birds.

Control of Disease

The density of fish living in the cage will be much higher than would ever occur in the wild.  This means the conditions are perfect for fish parasites such as lice to spread.  This is controlled by adding toxic chemicals to the water.  Bacterial pathogens too can be a problem in which case antibiotics would be added to the fish food.

Removal of Waste Products

(See tidal solution above)

Quality and frequency of feeding

The farmed fish need to be fed a diet that is rich in protein for growth.  Obviously the frequency of feeding is important:  too often and food will not all be eaten and will leak out into surrounding waters, too rarely and the fish will grow too slowly.

Use of Selective Breeding

The characteristics a fish farmer wants in his fish are very different from those that might be selected for in a wild population.  For this reason, selective breeding might have to be used to produce fish that have the desired characteristics.  These might include an ability to grow rapidly when fed on a cheap diet of fish pellets and to produce tasty and attractive meat, a resistance to lice and other parasites, a willingness to grow even when swimming opportunities are rather limited, a friendly disposition so thousands can live happily crammed into a single cage etc.

I have written this post in a bit of a rush the night before the exam.  So there may be things I have left out, but at least I have given you something to read to help you sleep the night before the exam!  Good luck.


Last minute panic

Clearly there is a lot of last minute cramming going on before IGCSE Biology paper 2 tomorrow….

Screen Shot 2016-06-09 at 21.40.19

That is absolutely fine but please remember you also need a good night’s sleep so your head is clear.  Knowledge is only a part of the skills required tomorrow in the exam and at least as big a part will be played by your ability to read the question, to think clearly, to recall good answers and to show your understanding clearly on the page.  All of these will benefit if you get a good night’s sleep tonight!

Take your time to read the question carefully and before you start writing any response, take a moment to think “what are the key scientific terms I need to use to show my understanding?”  So many marks are lost by waffling on without actually stating the key idea!