Transport Systems in Mammals, Grade 10: The Blood Vessel Unit That Is One Sentence Long

Unit 5 of this topic is blood vessels. Its entire revision summary is one sentence.

"Arteries carry blood away from the heart; capillaries join arteries to veins; veins carry blood towards the heart."

That is direction and nothing else. No wall thickness, no valves, no lumen, no one-cell-thick capillary. And the standard question on blood vessels is not which way the blood goes. It is relate the structure of each vessel to its function, which cannot be answered from that sentence at all.

This page gives all eight units, five places where the printed account is wrong or incomplete, and the vessel table the summary should have had.

Where this fits in the curriculum

Subject Life Sciences
Grade 10
Term 3
Topic Topic 7, Transport systems in mammals
Units Eight. Circulation systems, the heart, direction of blood flow, controlling the cardiac cycle, blood vessels, blood, the lymphatic system, diseases of the heart
Formal assessment None
Marks Our worksheet is 88

Finding 1: a whole unit reduced to a direction

Here is what the one-sentence summary leaves out, and every row of it is examinable.

Artery Capillary Vein
Direction Away from the heart Between the two Towards the heart
Wall Thick, muscular and elastic One cell thick Thin, much less muscle
Lumen Narrow Just wide enough for one red blood cell Wide
Valves None None Yes, along their length
Pressure of the blood High, and it pulses Falling Low and steady
Why it is built that way It has to survive the surge each time the heart contracts, and the elastic recoil keeps the blood moving between beats Thin enough for substances to diffuse through Low pressure means the blood needs help, so valves stop it running backwards and the skeletal muscles squeeze it along

The last row is where the marks are. "Arteries have thick walls" scores one. "Arteries have thick elastic walls because blood leaves the heart in high pressure surges, and the recoil keeps it flowing between beats" scores the question.

Finding 2: the heart beats on its own, and the summary never says so

"The sinoatrial (SA) node is the natural pacemaker of the heart. The SA node, together with the atrioventricular (AV) node, regulates the heart beat. The sympathetic nerve speeds up the heart beat and the parasympathetic nerve slows down the heart beat."

Read that as a learner. Nerves regulate the heartbeat. So the nerves cause the heartbeat. That is the obvious reading and it is wrong.

The idea that is missing Why it matters
The heartbeat is myogenic. It starts in the heart muscle itself, in the SA node, with no signal from the brain at all It is the reason a transplanted heart beats, and the reason a heart kept in solution keeps beating after it has been removed
The nerves only adjust the rate. They speed it up or slow it down. They do not start it This is the actual examinable distinction, and it is the difference between controlling something and causing it

The summary also ends on a sentence that does not work: "They attach the SA node to the brain." Nerves connect rather than attach, and the part of the brain is never named. It is the cardiac centre in the medulla oblongata, which is the same structure that controls breathing.

Finding 3: the parts of blood, and separately the jobs of blood

Unit 6 gives two lists and never joins them.

The components, as listed The functions, as listed
Plasma Carries substances around the body
Red blood cells Important in fighting infection
White blood cells Regulates body temperature
Platelets

Nothing says which component does which job. A learner reading only this could not tell you that red blood cells carry oxygen, and the word haemoglobin does not appear at all.

Component What it does
Plasma The straw-coloured liquid. Carries dissolved food, carbon dioxide, hormones, waste and heat
Red blood cells Carry oxygen, bound to haemoglobin. Biconcave, and they have no nucleus, which leaves more room for haemoglobin
White blood cells Fight infection. Some engulf bacteria, some make antibodies
Platelets Clot the blood at a wound

Haemoglobin is the single most important word in this unit and the summary does not contain it. Without it there is no answer to why red blood cells are red, why they have no nucleus, or how oxygen gets anywhere.

Finding 4: low blood pressure listed as a cardiovascular disease

"Cardiovascular diseases are high blood pressure (hypertension), low blood pressure, heart attacks and strokes."

Low blood pressure does not belong in that list. It sits between hypertension and heart attack as though the three were comparable, and they are not.

What it is Is it a cardiovascular disease
Hypertension Sustained high pressure that damages the artery walls over years Yes, and it is the one that causes the others
Heart attack A coronary artery blocks and part of the heart muscle dies Yes
Stroke A vessel in the brain blocks or bursts Yes
Low blood pressure Often harmless, and when it is not it is usually a symptom of something else, such as blood loss, dehydration or infection Not in the same sense at all

Finding 5: four valves and not one of them is named

"The atrioventricular valves between the atria and ventricles as well as semi-lunar valves at the beginning of the aorta and the pulmonary artery prevent the backflow of blood through the heart."

Correct, and a labelled heart diagram needs names.

Valve Where Also called
Tricuspid Right atrium to right ventricle Right atrioventricular valve
Bicuspid Left atrium to left ventricle Mitral valve, or left atrioventricular valve
Pulmonary semi-lunar Right ventricle into the pulmonary artery
Aortic semi-lunar Left ventricle into the aorta

Tricuspid has three flaps and sits on the right. Bicuspid has two and sits on the left. Three comes before two and right comes before left, which is the wrong way round and is exactly why people remember it.

One thing to add in class

The summary says cardiovascular disease "can be the result of congenital conditions and poor lifestyle choices".

Poor lifestyle choices is doing far too much work in that sentence. It names no actual risk factor, and it quietly puts the whole thing down to the person.

Things a person can change Things a person cannot
Smoking, diet high in salt and saturated fat, inactivity, excess alcohol, untreated diabetes Age, family history, sex, and whether you can afford fresh food or a safe place to walk

Name the factors and the sentence becomes useful. Leave them as "choices" and a learner cannot answer a question about risk factors, which is what gets asked.

What the eight units cover

Unit What is in it
1. Blood circulation systems Closed systems, and the mammalian double circulation: pulmonary to the lungs, systemic to the body
2. The heart External and internal structure, the coronary vessels, the four chambers, the valves, and the cardiac cycle
3. Direction of blood flow Both circuits traced all the way round
4. Controlling the cardiac cycle The SA and AV nodes, the sympathetic and parasympathetic nerves, and exercise
5. Blood vessels Arteries, capillaries, veins. See finding 1
6. Blood The four components and what blood carries
7. The lymphatic system Tissue fluid and lymph, lymph vessels and nodes, and fat absorption
8. Diseases Cardiovascular disease and its treatments

The two circuits, which are four marks every year

Deoxygenated Oxygenated
Body Lungs
Venae cavae, superior and inferior Pulmonary vein
Right atrium Left atrium
Right ventricle Left ventricle
Pulmonary artery Aorta
Lungs Body

The pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood. They are the only two vessels in the body that break the usual rule, and they are the two that get asked about.

Why the left ventricle wall is thicker, which is the other standard question

Both ventricles pump the same volume. The right one pushes blood to the lungs, which are next door. The left one pushes blood to the whole body, including up to the brain and down to the feet. More distance and more resistance means more pressure, which means more muscle.

What this topic costs

There is one item here that answers finding 1 directly and it costs R29,00.

Item Price In stock For
Artery, vein and nerve slide, transverse section R29,00 82 An artery and a vein side by side on one slide. The thick wall and the narrow lumen stop being words and become something you can see
Enlarged heart model, 2 parts R750,00 3 Opens to show the four chambers and the valves
Life-size heart model, 7 parts R1 150,00 1 The detailed one, if the budget runs to it
Circulatory system model R850,00 3 Both circuits in one piece, which is Unit 3
Educational stethoscope R81,42 11 Hear the two sounds the valves make. Lub is the AV valves closing, dub is the semi-lunars
The heart wall chart R85,00 1 Unit 2 on the wall
Blood and circulation wall chart R85,00 1 Units 5 and 6

What we cannot supply, and it is the one Unit 6 needs

The blood smear slide is out of stock. It is the slide that would show red cells, white cells and platelets, which is exactly what finding 3 is about, and we have none.

Four heart models are also at zero: the extra large on a base, the 2x four part, the heart with lungs and larynx, and the 3 part. We are not linking you to any of them. Both wall charts are down to one each.

If you buy one thing for this topic, buy the artery and vein slide. R29,00, 82 on the shelf, and it turns the single weakest unit in the topic into the one a learner can actually see.

Microscopes at microscopes, charts at educational wall charts.

What you should be able to do by the end

  • Explain what a double circulation is and why a mammal needs one
  • Label a heart, chambers, vessels and all four valves by name
  • Trace both circuits and know which two vessels break the artery and vein rule
  • Explain why the left ventricle wall is thicker
  • Give the three stages of the cardiac cycle
  • Explain that the heartbeat is myogenic, and what the nerves actually do
  • Relate the structure of artery, capillary and vein to function, not just direction
  • Name the four components of blood and what each one does, haemoglobin included
  • Explain what the lymphatic system returns, and why it has valves
  • Name real risk factors for cardiovascular disease, both the changeable and the fixed

Free worksheet and marking memo

Both free, no sign up, straight to the PDF.

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