Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 310–325 of the course textbook. Image credits are on slide 22.
At the arteriole end, high blood pressure forces plasma out through gaps in the capillary wall (pressure filtration), leaving proteins and cells behind. At the venule end, blood pressure is lower than the osmotic pull of the plasma proteins, so most of the fluid drains back in.
Tissue fluid is plasma without large proteins or red blood cells. Cells take oxygen, glucose, amino acids and ions from it and release carbon dioxide, urea and other wastes into it, by diffusion and membrane transport.
Excess tissue fluid enters lymph capillaries, which have thin walls with gaps. Valves keep lymph flowing one way, and it returns to the blood in veins near the heart. Without drainage, tissues swell (oedema).
In bony fish, blood goes heart → gills → body → heart, passing through the heart once, and reaches the body at low pressure. Mammals have a pulmonary and a systemic circuit, so blood passes through the heart twice and is re-pumped to the body at high pressure.
Branched, myogenic cardiac muscle contracts rhythmically; the SA node sets the pace. Thin-walled atria fill the thick-walled ventricles (left thickest). AV and semilunar valves stop backflow, the septum separates the two sides and coronary vessels supply the muscle.
The SA node fires, the atria contract, the AV node delays the impulse, then the ventricles contract. Valves open and close with pressure differences: AV valves shut as ventricular pressure rises; semilunar valves open when it exceeds arterial pressure and shut when the ventricles relax. Blood pressure is written systolic/diastolic, for example 120/80 mmHg.
Root cells pump mineral ions into the xylem by active transport. Water follows by osmosis, creating positive pressure that pushes sap up when transpiration is too low, for example in humid air or in spring before leaves open.
Sieve tube elements have sieve plates, little cytoplasm and no nucleus, so sap flows easily. Companion cells have many mitochondria and are joined to them by plasmodesmata, supplying ATP for loading sucrose at sources. Sap flows from sources to sinks.
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Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all eight statements, from quick recall to data questions and a longer answer. It has 40 marks and takes about 40 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Heart from a butcher, dissection tools, tray, disposable gloves. If dissection is not suitable, use a heart model or images
Safety: Follow your school's dissection policy, and offer an alternative. Take care with blades. Gloves, then disinfect surfaces and wash hands.
Carry this out with your teacher's supervision and follow your school's lab rules.
In the early 1900s, Einthoven's string galvanometer recorded the heart's electrical activity, leading to the modern ECG.
An ECG trace is meaningless without training. Consider what makes expert interpretation reliable, and when experts might disagree.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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