Double circulation: follow a red cell sim
Drag a red bead (one red blood cell) round a classroom double-circulation board through the lungs, heart, liver, gut, kidney or legs, predict each next vessel, read its oxygen saturation and the two pressure gauges, and record and graph the readings.
Transport in humans · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model: one red cell's trip from the right atrium round the body and back, by one of five trips. Its haemoglobin saturation is set by model.mjs: about 98 % after the lungs, and on return about 70 % from the head, neck and arms, 67 % from the liver, 90 % from the kidney and 72 % from the legs; on the first trip it starts at 75 %. Mean pressures from about 3 to 93 mmHg; gauges 120/80 and 25/10 mmHg. All values illustrative, for a healthy adult at rest, from memory. Front view: the patient's left is on the right of the page. Not to scale; one kidney and one lung block shown. Nothing moves on its own.
- The red bead: one red blood cell; bright red when its haemoglobin is full of oxygen, darker as it gives oxygen up
- Clear tubes: bright red = oxygenated blood, dark red = deoxygenated blood (never blue)
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
More biology sims
- Blood glucose control: insulin, glucagon and diabetes simDrag a plate to the mouth, a shoe onto the track or an insulin pen to the arm. Watch the islet's beta and alpha cells release insulin and glucagon, the liver's glycogen store fill and empty, and blood glucose return to normal on a live graph. Switch to type 1 or type 2 diabetes and compare peaks and recovery times in a results table.
- The digestive journey simDrag a meal from the mouth to the rectum. Each region shows its enzymes, its pH and how much starch, protein and fat is left, with live bars, a graph and a results table.
- Enzymes and pH: amylase and starch simPour a pH buffer into a tube of amylase, drag it into a 37 °C water bath, add warm starch and start the stopwatch. Drag the dropping pipette to the spotting tile every 10 s: the iodine stays blue-black until the starch is gone, then stays orange-brown. Fill a results table with pH, time to the end point and rate = 1/t, and plot your own graph of rate against pH.
- The heart and the cardiac cycle simDrag through one heartbeat on a front view of the heart in section. The chambers contract, the four valves open and shut as the pressures cross, and a linked graph shows atrium, ventricle and aorta pressure, with a results table to fill.
- The kidney and the nephron simDrag a drop of filtrate through one nephron, zoomed from the kidney. See what ultrafiltration lets through, what selective reabsorption takes back, and how water, glucose, urea and salts change, with a live concentration graph and a plasma, filtrate and urine table to fill.
- Breathing: the mechanism and a spirometer trace simThe student contracts the diaphragm and intercostal muscles on a model chest to make air flow in and out, then reads tidal volume, vital capacity and breathing rate from a spirometer trace at rest and in exercise.