The Blood Vessels (GCSE Biology, OCR and AQA A-level biology)

(When you learn these topics depends on what course you’re doing. Check your specification. Sorry, but there are too many GCSE specifications now to write separate articles for all of them!)

Blood vessels entering and leaving the heart 

Here’s a table of the biggest blood vessels in your body. This is written in order as blood goes from the body to the heart and back out again: Blood Vessels So four key blood vessels to learn: the vena cava, pulmonary artery, pulmonary vein, aorta. On many courses, you’re meant to know which atriums (atria) and ventricles they go to and from.

Other key blood vessels 

On Edexcel iGCSE biology and AQA AS-level biology, you’re meant to know a few more. Here’s a table of them: Blood Vessels 2That makes the renal artery and vein, hepatic artery and vein and the hepatic portal vein.

On AQA AS-level and OCR A2 biology, you’re also meant to know about the coronary arteries. These loop round from the aorta to the heart muscle itself, giving it oxygen and food to beat with.

What’s the hepatic portal vein for? Simple. Blood coming from the small intestine is carrying a real mixture of stuff absorbed from food in the gut. Lots of useful chemicals, some not-so-useful ones, even some toxic ones. The liver takes them and reprocesses them into new, more useful chemicals before they’re allowed to go to the rest of the body.

But if the hepatic portal vein is taking blood into the liver, what’s the hepatic artery for? That’s simple too.  The liver uses lots of energy to do its jobs, but the hepatic portal vein carries deoxygenated blood. That’s no good for aerobic respiration! To give the liver some energy, the hepatic artery carries oxygenated blood to it. So the liver gets everything it needs to do its job: food from the small intestine, oxygen from the heart.

Extension:

This isn’t on the syllabus, but if you’re planning to do medicine you might want to know that there are actually two renal arteries and two renal veins (each kidney has its own renal artery and renal vein). There are also two venae cavae (Stupid Latin plurals! Why can’t it be vena cavas or venus cava or something?): one from the body above the heart and one from below the heart, and there are several separate hepatic veins from different parts of the liver.

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How to answer respiration questions (GCSE Biology)

To this day, I can remember the smile on my biology teacher’s face as he explained to us how we’d had it wrong all these years.

In the real world, you’re told that respiration is breathing. In, out, your chest pumping up, down.

In the real world, maybe that’s what it means. But not in science.

In science, respiration means one simple thing: getting energy out of food. And it explains a lot of things about how your body works:

  • Every place in your body needs to do respiration separately, so everywhere in your body needs food sent to it. That’s why your heart beats: pumping it round.
  • Doing respiration takes oxygen, so your blood needs to carry it round: that’s why your blood is red. The red is haemoglobin, a chemical that lets your red blood cells carry oxygen.
  • Every cell in your body has to do it by itself. Your chest can’t do respiration for your lungs. Your brain can’t do respiration for your eyes. So every bit of your body needs oxygen and food.

Getting energy out of food

The word equation for respiration should look familiar from chemistry. It’s the same word equation as for burning petrol (except with glucose replacing petrol, obviously).
Respiration 1So you breathe in oxygen and breathe out carbon dioxide. Blood carries food and oxygen to every part of your body, and carries water and carbon dioxide away.

Another kind of respiration

In an emergency, you need to run fast. So fast that your muscles run out of oxygen.

At this point, they start to do another kind of respiration, called anaerobic respiration (that means literally without air). That means normal respiration is called aerobic respiration. Continue reading

The Artery Wall: OCR AS-level Biology

4450859134_e9660e92d4_oOCR want you to know how to describe what does what in the artery wall. Here’s what to learn.

Blood is squeezed out of the ventricle in lumps. The artery keeps them moving forward and at high pressure by squeezing down on the blood, keeping it in tight lumps so it stays moving forward under high pressure. That means the artery needs to be strong.

The artery wall is complicated. Let’s run through what does what:

  • First, there’s collagen. Collagen is strong and stops the wall from bursting.
  • Next, there’s elastic fibres. These act like rubber bands wrapped round the artery: they pull it tight and snap down on the blood, stopping it from expanding. That keeps the blood at a high pressure.
  • Finally, there’s smooth muscle. This, again, pulls tightly in on the artery

The other way the artery can cope with high pressure is that the endothelium, the inner lining of the artery, is folded or corrugated: it can stretch out easily to let blood pass through.

You need to divide these things into two groups: the ones that let the artery withstand the pressure, and the ones that maintain it-keep it high.

Past paper question:

Withstand and maintain It’s a tough one: big and lots of marks. 8% of the paper, so full marks on this could easily push you up a whole grade.

Here’s what the mark scheme says you need to say. Here’s a diagram, then we’ll talk through it:

Withstand and maintain 2

To withstand the pressure, the artery has:

  • A thick wall
  • Made out of collagen
  • With a folded endothelium

Then explain that:

  • All mean that the artery wall isn’t damaged when it stretches. (Simple, no?)

Then, to maintain the pressure, the artery has:

  • Elastic tissue, aka elastin
  • And a thick layer of smooth muscle

And what they do is:

  • Keep the artery narrow
  • And make it go back to the original width (recoil) once blood’s gone past

What points they’ll accept:

You can’t just answer one side of these questions, so make sure your revision plan is comprehensive!

To get full marks, you need four points, no more than three from describing and no more than three from explaining; no more than three on withstand and no more than three on maintain.  The fifth mark is a quality of written communication (QWC) mark: it’s for how good your spelling is.

For people whose mum is a doctor tutoring them advanced material or whose tutor doesn’t know the syllabus or something, they say they will accept any other valid point in the explain, but not the description, sections.

Image credit:

The header image for this post was created by Pierre Bédat, and comes from here. It’s released under this licence.

Going to Extremes in GCSE Chemistry

Potassium chlorate & sulphuric acid Deradrian CCASA2Here’s a classic exam technique mistake people make: not specifically answering exactly what a question is asking for. Often, people have basic, works-in-any-situation answers memorised, but they’re not specific enough for the problem. But it’s easy to fix: you can quickly change what you’re doing and get higher marks and grades. Let’s look at how.

Bad Answer:

Going to extremes 1 That answer looks good! Francium’s outermost electron is easy to remove. Nothing about that answer is scientifically incorrect. Why didn’t we get any marks? (There’s a discussion of the science of what this question means below.)

Simple: it’s a stock answer, and it’s not detailed enough.

Francium isn’t just a reactive group 1 element, it’s the most reactive group 1 element. We need an extreme answer that emphasises that.

Going to extremes 4Maybe not like that.

We also need a bit more detail. What exactly makes it easy to pull the outermost electron off of francium?

Perfect Answer:

Here’s a perfect answer, emphasising the ways it’s tailored to give exactly what they want. Not many more facts, but it’s clear about the question it’s answering.

Going to extremes 2

Hint: Think if your answer has enough points in it to get all the marks on the mark scheme. Three marks means three points.

Of course, that’s a perfect answer. You might not be able to say all that much, or have time. Let’s strip that down to a minimal perfect answer: the shortest thing we can write that gets all the marks on this (AQA) paper. You don’t need anything inside the brackets.

Going to extremes 3 Continue reading

GCSE Biology: How do you measure the rate of photosynthesis?

PondweedThis post is primarily intended for people taking the Edexcel iGCSE, on which this is particularly large topic. But it might be useful for anyone taking any board, since they all ask about experimental design. 

Scientists who want to understand how plants grow and photosynthesis happens have tried to research this by growing plants at different conditions and testing them. (They’re also keen to know what will happen to world food supplies if climate change continues.) You’re meant to know a simple example of this.

Recap: what is photosynthesis?

Photosynthesis is a chemical reaction: it’s how plants make food using light energy from the sun, carbon dioxide and water.

Waterweed in a beaker

This is a simple way of measuring photosynthesis. As photosynthesis happens, the plant makes bubbles of oxygen. You can count the bubbles, or (more accurately) use a measuring cylinder to measure how fast the plant is producing oxygen.

Why is measuring with a measuring cylinder more accurate? It’s a common question. The answer is that the bubbles might not all be the same size.

Making it a fair test

A common question is asking how you can make the test fair. That’s important because what a scientist doing this would want to do is compare how plants grow under different conditions.

Here are some things you’d definitely want to keep the same:

iGCSE Biology measuring rates of photosynthesis 3And then you’d want to vary one of these between the plants but keep all the others the same:

iGCSE Biology measuring rates of photosynthesis 4Common trick questions

Of course, that’s not the only way they can ask this. They could give you a wrong answer and explain why it’s wrong. So:

iGCSE Biology measuring rates of photosynthesis 1It’s carbon dioxide, but why? Simple. Oxygen is a product. It’s not needed to make photosynthesis happen.

iGCSE Biology measuring rates of photosynthesis 2

A real measurement of photosynthesis. The entire tree is being covered in a bag to seal it off from the air.
A real measurement of photosynthesis. The entire tree is being covered in a bag to seal it off from the air.

Well, the plant is actually in water: it’s not going to run out of it! But the amount of nutrients might be important to it growing. Mineral concentration matters more.

Obvious next steps

This is just one topic, and it would probably be connected to others. Obvious other things to connect it to are:

- What minerals do: you need to know that plants need magnesium to make chlorophyll and nitrates to make amino acids, proteins, and ultimately enzymes - Limiting factors: these are things that, if increased, could let the plant do photosynthesis faster. If something isn’t a limiting factor, then it’s not a bottle neck right now: the plant has all it needs to to photosynthesis at the moment - High temperatures and why they stop plants from doing photosynthesis: the enzymes that make photosynthesis happen can be denatured (have their shape changed) so they no longer have the right shape (and especially active site shape) to do the reaction. Varying the question

Examiners know you read through past papers, and expect that you’ll be familiar with them. (You aren’t? Might want to think about changing that.) So they often vary questions a little bit to make the question more difficult: common variations have been to ask questions about measuring the rate of respiration, or transpiration.

Image credit:

The picture of measuring a tree’s rate of photosynthesis comes from the US Department of Agriculture. It’s available here, released under the terms of this licence.

Why don’t science words mean anything in English?

Blame pretentious scientists.

In the 18th and 19th century, scientists tended to coin names based on Latin and Ancient Greek. Of course, the Romans and Ancient Greeks didn’t know about enzymes, or cell nuclei, or ozone or oxygen. So many of the terms used in science are pretty much meaningless: they’re based on Latin and Greek, but the best-educated person from 1AD wouldn’t have a clue what they mean.

Here are some examples of that, with rough translations:

Name Means
Ozone Smell in Greek. (It does!)
Plastic From Greek to shape: it used to mean something squidgy like clay.
Enzyme Comes from risen bread-bread that’s risen and has bubbles in it.
Nucleus The inside of a nut in Latin (kernel in English).
Ammonia Greek attempt to pronounce the name of an Egyptian god, a temple to whom was next to a well-known fertiliser works in Greek-ruled Egypt.
Cytoplasm From Greek for container and the same root as plastic.
Oleum From Latin for oil. (It’s not: it doesn’t contain carbon at all.)
Antenna Latin for ship’s yard (part of the mast), maybe from Greek to set up.
Aluminium From Latin for tanned leather: an aluminium ore is used to make it and took the name. (The metal wasn’t discovered until the 1820s.)
Chlorine From Latin for green, like chlorophyll and chloroplast.
Copper A real ancient Latin word for once! Comes from metal from Cyprus.

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No such word as exdothermic: when bad handwriting loses you marks

In general, examiners work hard to be fair to candidates with bad handwriting. (Honestly. I did OK and my handwriting when I was your age was… embarrassing.)

Those are a 1 vs. 2., 1 vs. 7 and a 9 vs. a 4.
Those are a 1 vs. 2., 1 vs. 7 and a 9 vs. a 4.

But sometimes it’s possible to slip up. Especially since you know what you mean, and your teacher probably does too. Have a look at these, based on real examples of bad handwriting I’ve seen. Does yours look like that when you’re in a hurry? 

If your handwriting looks like this, probably the best ways to deal with it are to be careful putting in the corners of the numbers, and, at the end of the exam, to check through your answers to make sure they’re all really clear. 
Continue reading