Commentary on Zondle GCSE Biology Revision challenge 1 questions

I hope that those of you who played the GCSE Biology revision challenge this afternoon enjoyed the process.  I would welcome comments on this blog post along the lines of www (what went well) and ebi (even better if)….

The questions were grouped into several topic areas.

Questions 1 to 4 were on thermoregulation.  Understanding vasoconstriction, vasodilation and sweating are the key things here and if you haven’e done already, I would read my blog post on this topic.

https://pmgbiology.wordpress.com/2014/05/29/skin-a-understanding-for-igcse-biology/

Questions 5 – 9 were on plant transport and these were well answered by almost all players.  Remember that phloem sieve tubes move sucrose and amino acids around the plant.  Water and minerals are transported in xylem vessels of course, but the other distractor answers included various polymers (starch and proteins) that are made in photosynthesis in the leaves but which are too large and insoluble molecules to be transported in phloem.

Questions 10-15 were all on the bacteria in the Nitrogen cycle.  This is a tricky topic but one that rewards patient work by candidates to master it. In reality the Nitrogen cycle is not difficult to understand but it is easy to muddle the names and roles of the four types of bacteria involved.  Again there are a couple of blog posts on Nitrogen cycle that I would encourage you to read….

https://pmgbiology.wordpress.com/2014/04/12/bacteria-of-the-nitrogen-cycle-a-understanding-for-gcse-biology/

https://pmgbiology.wordpress.com/2014/04/12/nitrogen-cycle-for-igcse-biology/

Questions 16-23 were on digestive systems.  These were generally well answered although many players didn’t appreciate that peristalsis doesn’t just happen in the oesophagus: it is the process that moves the food along the entire length of the gut tube from top of oesophagus to the end of the rectum.  The role of the lacteal in transporting fatty acids and glycerol away from the villi in the small intestine is also one of the trickier topics here.  Amino acids and sugars diffuse into the blood capillaries in the villus but fatty acids and glycerol (the products of digestion of lipids) don’t go into the capillaries but instead into a separate vessel called a lacteal. This forms part of the lymphatic system and the liquid formed ends up back in the blood but effectively bypasses the liver, preventing the cells in the liver being overloaded with fatty acids following a fatty meal.

Questions 24-29 were on the heart and circulation.  There were quite a few incorrect answers here but perhaps this was because enthusiasm levels were dropping….  The flow of blood through the heart is an important topic to appreciate – into RA through vena cava, then into RV through right AV valve, then into PA through semilunar valve, then to lungs, back from lungs in pulmonary veins, into LA, through Left AV valve into LV, then into aorta through the aortic semilunar valve…..

The heart strings in the heart (chordae tendinae) are commonly misunderstood.  They play no role at all in opening or closing the AV valves (this is done simply by the balance of blood pressures in atrium and ventricle) but do provide tension to stop the valve “blowing back” and thus opening when the ventricle contracts.  Have a look at pictures of a real heart dissection to see that these tendons attach to the valve flaps and ensure they cannot blow open when the pressure in the ventricles rise during ventricular contraction.  Ask me for more detail if this doesn’t make sense.

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