Transport in organisms for O-Level Biology (SEAB 6093): blood and its components, the heart and blood vessels, the double circulatory system, and transport in plants by xylem and phloem

What this module covers

Transport in organisms explains how materials are moved around large bodies, in both animals and plants. In O-Level Biology (SEAB 6093) you need to know the components of blood and their functions, the structure of the heart and how arteries, veins and capillaries are adapted, why humans have a double circulation, and how plants move water and food through xylem and phloem. The same exchange and adaptation ideas from earlier modules return here at the level of whole organs.

This overview links every dot point in the module; work through them, then test yourself at the end. See the full set at /sg-o-level/biology/syllabus.

Blood: the transport medium

Start with what is being moved. The page on blood and its functions describes the four components (red cells, white cells, platelets and plasma), how red cells are adapted to carry oxygen, and how blood transports, defends and clots. Learn each component with its job so you can answer "state the function" questions cleanly.

The heart and the blood vessels

Next, the pump and the pipes. The page on the heart and blood vessels describes the chambers and valves of the heart, why the left ventricle wall is thicker, and how arteries, veins and capillaries are each adapted. The vessels are a classic structure-and-function comparison the examiner returns to often.

The double circulatory system

Now the layout. The page on the human circulatory system describes the double circulation, the pulmonary and systemic circuits, the path of blood, and the advantage of passing through the heart twice. Be ready to trace a drop of blood from the lungs, through the heart, to the body and back.

Transport in plants

Finally, the plant side. The page on transport in plants describes the roles of xylem and phloem, the transpiration stream that pulls water up, and the factors that affect the rate of transpiration. Keep the two tissues clearly distinct: xylem carries water up, phloem carries food in any direction.

How this module is examined

• Component with function. Blood questions reward naming a component and giving its job; the most missed point is that white cells include both phagocytes and antibody-producing cells.
• Structure matches pressure. Heart and vessel questions reward linking wall thickness and the lumen to the pressure the vessel must handle.
• Trace the path. Circulation questions reward a correct, ordered route through the named vessels and chambers.
• Xylem versus phloem. State the substance carried, the direction, and whether the cells are living, for each tissue.

Check your knowledge

A mix of recall, comparison and application questions. Attempt them, then check against the solutions.

1. State the function of red blood cells and one way they are adapted to it. (2 marks)
2. Explain why the wall of the left ventricle is thicker than the right ventricle. (2 marks)
3. Give one structural difference between an artery and a vein, and explain it. (2 marks)
4. State two differences between xylem and phloem. (2 marks)