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About a year ago, one of my International Baccalaureate (similar to A Level) students sent me a list of topics that he was not happy with. To him, they looked like a great big pile of completely unrelated ideas. Yes, they were all to do with living things but they were all in their own little boxes. Learn one. Learn another. Learn one more and the first one falls out of your brain.
So we connected them into a sensible "story". Each topic then supports and explains the other ones, making understanding them a lot more straightforward. We used these three rules:
- Use technical words, because you can put a big idea into one word without having to explain everything about it, every time.
- Say a little about each idea, just a sentence or two. But you must say what a process or a feature is actually for.
- When you find a part where you really can't say what it is for, and you can't find a way to incorporate it into the story, then you have struck gold! That's the topic you really do not understand, the one where you need to concentrate your efforts on. Sort it out, understand it, and it no longer has any power over you. You literally own it.
Here's our pile, in no particular order: respiration, photosynthesis, plant transport, plant reproduction, animal nervous, hormonal and immune systems, allergies, DNA, RNA, cell division, proteins, protein synthesis, enzymes.
And here's the story we wrote together, with the IB specification references still in place.
"All living organisms have a store of instructions for building proteins. These instructions are in the form of the sequence of bases on their DNA molecules (3.1 and 7.1). Every cell possesses the full sequence – in fact when a cell divides, a full copy is made of the entire DNA, so each daughter cell gets a complete, identical copy. (3.4 and 7.2)
The DNA is just too valuable to be let out into the chemical factory of the cytoplasm. So when part of the information (a gene) needs to be used, a temporary copy of the gene is made from RNA (3.5 and 7.4). The RNA is “read” by a ribosome, and used to assemble a protein (3.5 and 7.4)
The information in the gene is now having real effects on how the organism works, because the proteins (7.5) made are doing jobs like transport in and out of cells, carrying oxygen, acting as structural support, and – this is the big one – catalysing chemical reactions (7.6), persuading them to go forwards at a low, low activation energy.
The enzyme trick brings the amount of energy living organisms need down to an achievable level. Down to the amounts of energy you could get from breaking down organic compounds like glucose, say. Each cell can release the energy from glucose a little bit at a time by respiration (8.1).
Where did this glucose originally come from? Well, here we have to go up a few levels of organisation and look at the architecture of a highly evolved organism, a plant (9.1). Plants build up glucose and many other chemicals from smaller, simpler molecules. The plants use light energy from the sun to do this (3.8 and 8.2), and the energy ends up embodied in the glucose.
The cells doing photosynthesis are supported by an elegant transport system (9.2) which brings water and carbon dioxide to them and takes away the sugars they manufacture to wherever in the plant they are needed.
One target location would be the plant organs involved in reproduction (9.3), as they will be actively growing. In reproduction, the successful plant will be passing on its useful genes to the next generation.
Our particular family of plants, the angiosperms, do this by distributing genes in the form of pollen either carried by insects, or released into the wind.
And possibly inhaled by another complex organism, a mammal. We mammals have a much more frantic pace of metabolism. We are warm, nutrient-rich, and a great place for microorganisms to feed and multiply in. We have a fast-response immune system to keep them from killing us. (6.3, 11.1) Sometimes, the system mounts an unfortunate, inappropriate response such as treating a harmless inhaled pollen grain as a deadly invader and giving us a bout of hay fever.
Such a fast paced organism needs multiple control systems just to keep our temperature under control, or to make sure we don’t suffer from huge swings in blood sugar levels between meals. (6.5) Faster still, we need a system to respond immediately to changes in our environment (stimuli), and help us carry out complex survival behaviours such as hunting. For this, we have frighteningly complicated networks of nerve cells with tiny decision-making junctions called synapses between them. (6.5 and Option E)."
I won't pretend that this is an easy exercise. But one of the wonderful things about taking your study to a higher level is that it actually does make your mind a bit more agile, better at making these kinds of connections. And I won't say "don't be afraid", because just a little bit of "afraid" is a good thing, making you sharper.
So enlist the help of a chum, and have a go at an exercise like this yourself. And remember, the bit you don't understand is gold.