IP Biology Notes: Transport in Humans (Upper Sec 05)

Study guide26 Nov 2025, 00:00 Z

Free IP Biology notes on the circulatory system, blood components, the heart cycle, and CHD for Sec 3 to Sec 4.

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Use this as a free IP Biology notes chapter on transport in humans for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.

Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

The core idea is simple: Human transport is about moving materials fast and in one direction.

Use it as a working check: Learn the double circulation route, the structure of arteries, veins, and capillaries, and how blood components match their functions.

Then go one layer deeper: Example: arteries are named by direction away from the heart, not oxygen content. The pulmonary artery carries deoxygenated blood to the lungs.

Double circulation route map

When a pathway question appears, trace the blood in order and state both the vessel name and the oxygenation change.

Circuit stage	Route	Oxygenation change
Body back to heart	Body tissues → vena cavae → right atrium	Blood is deoxygenated after delivering $\ce{O2}$

Reviewed by

Ezekiel Tan·Academic Advisor (Biology)

Sources

SEAB GCE O-Level Biology (6093) syllabus (examinations from 2026)

Vessel	Main job	Structure to mention	Why it helps	Common trap
Artery	Carry blood away from the heart at high pressure	Thick muscular and elastic wall, small lumen	Wall withstands and smooths pressure changes	Defining artery by oxygen content.
Vein	Return blood to the heart at lower pressure	Wider lumen, thinner wall, valves	Valves prevent backflow when pressure is low	Saying veins need thick walls like arteries.
Capillary	Exchange substances with tissues	One-cell-thick wall, narrow lumen, many branches	Short diffusion distance and slower flow improve exchange	Saying capillaries mainly carry blood quickly.

Stage	What is happening	Direction of movement	Common trap
Tissue fluid forms	Some plasma is forced out of capillaries into spaces around cells.	Blood capillary to tissue spaces.	Saying red blood cells leave the capillary with the plasma.
Exchange with cells	Oxygen and glucose move to cells; carbon dioxide and other wastes move away from cells.	Between tissue fluid and cells.	Writing only "diffusion happens" without naming what moves where.
Fluid returns to blood	Most tissue fluid re-enters nearby capillaries.	Tissue spaces back to blood capillaries.	Treating tissue fluid as a separate dead-end liquid.
Excess enters lymph vessels	Remaining tissue fluid enters lymph vessels and becomes lymph.	Tissue spaces to lymph vessels, then back toward the bloodstream.	Forgetting that lymph vessels have valves for one-way flow.

Stage	Pressure comparison	Valve action	What to say
Ventricles filling	Atrial pressure is higher than ventricular pressure.	Atrioventricular valves open.	Blood moves from atria into ventricles.
Ventricular systole begins	Ventricular pressure rises above atrial pressure.	Atrioventricular valves close.	Backflow into atria is prevented.
Ventricular pressure exceeds artery pressure	Ventricular pressure is higher than aorta or pulmonary artery pressure.	Semilunar valves open.	Blood is forced into the arteries.
Ventricles relax	Artery pressure becomes higher than ventricular pressure.	Semilunar valves close.	Backflow from arteries into ventricles is prevented.

Question cue	Cause-effect link to write	Common trap
Fatty deposits or atheroma	The lumen of a coronary artery narrows, so less blood flows to heart muscle.	Saying the heart receives less blood without naming the coronary artery.
Angina or chest pain	Heart muscle receives less oxygen during demand, so aerobic respiration falls and less energy is released.	Jumping straight from "fat" to "heart attack" without the oxygen step.
Complete blockage	Part of the heart muscle is starved of oxygen and may die, causing a heart attack.	Saying all blood flow in the body stops.
Prevention or treatment	Reduce risk factors or restore blood flow so the heart muscle receives enough oxygen.	Listing lifestyle changes without linking them to blood flow or oxygen supply.

Recipient blood group	Antibodies in recipient plasma	Red blood cell donors that avoid agglutination	Why
O	anti-A and anti-B	O only	A or B antigens from donor cells would be attacked.
A	anti-B	A or O	Donor B antigens would be attacked.
B	anti-A	B or O	Donor A antigens would be attacked.
AB	none against A or B	A, B, AB, or O	No anti-A or anti-B antibodies are present to attack donor cells.

IP Biology Notes: Transport in Humans (Upper Sec 05)

Double circulation route map

Sources

What you must know

Vessel structure checkpoint

Detailed notes

Tissue fluid and lymph checkpoint

Cardiac cycle pressure checkpoint

Coronary heart disease cause-effect checkpoint

ABO compatibility checkpoint

ABO donor-recipient checkpoint

Worked walkthroughs

Pitfalls and fixes

Practice drills

Quick applications

Exam cues

Next steps

Related Posts

Step	Question to ask	What it prevents
1	What antigens are on the donor red blood cells?	Mixing up donor blood group with recipient blood group.
2	What antibodies are in the recipient's plasma?	Forgetting that the recipient's antibodies cause the agglutination risk.
3	Will any recipient antibody match a donor antigen?	Calling an incompatible transfusion safe just because the donor has fewer antibodies.
4	If there is a match, what happens?	Missing the explanation: antibodies bind donor cells and cause agglutination.