Transport in Humans and Animals
Large animals need a transport system to carry oxygen, nutrients and wastes. This chapter covers the human circulatory system, the heart and its beat, blood clotting, blood groups, and the lymphatic system.
It is a diagram-heavy chapter, so labelling the heart and blood vessels accurately matters.
Content standard 10.2 expects detail on what blood itself is made of, not only where it flows. Plasma, a pale yellow liquid, carries dissolved food, wastes, hormones and carbon dioxide; red blood cells carry oxygen bound to haemoglobin; white blood cells defend the body against pathogens; and platelets trigger clotting at a wound.
The cardiac cycle then describes how the heart's chambers contract in sequence, atria first and ventricles a moment later, with valves snapping shut between beats to stop blood flowing backwards, producing the two-part heart sound heard through a stethoscope.
The lymphatic system and its health issues, standards 10.7 and 10.8, are often the least revised part of this chapter yet appear regularly in Paper 2. Lymph vessels drain excess tissue fluid that has leaked from capillaries, filter it through lymph nodes packed with white blood cells, and return it to the bloodstream, so the system supports both fluid balance and defence.
Filariasis, spread by mosquitoes, can block these vessels and cause severe swelling called lymphoedema, while atherosclerosis and hypertension are the circulatory-system health issues most often asked about together with their causes and prevention.
One-hour paid trial · Same-day reply
Content standards in this chapter
- 10.1 Types of Circulatory System
- 10.2 The Circulatory System of Humans
- 10.3 Mechanism of the Heart Beat
- 10.4 Mechanism of Blood Clotting
- 10.5 Blood Grouping in Humans
- 10.6 Health Issues Related to the Human Circulatory System
- 10.7 Lymphatic System of Humans
- 10.8 Health Issues Related to the Human Lymphatic System
Key concepts
- Types of circulatory system
- Humans have a closed, double circulatory system: blood passes through the heart twice per full circuit.
- The heart
- Four chambers (two atria, two ventricles) with valves that keep blood flowing one way.
- Mechanism of heartbeat
- The heart muscle contracts (systole) and relaxes (diastole), controlled by the SA node.
- Blood vessels
- Arteries carry blood away from the heart at high pressure; veins return it; capillaries allow exchange.
- Blood clotting
- Platelets and clotting factors turn fibrinogen into fibrin, forming a clot that seals a wound.
- Blood groups & lymphatic system
- ABO and Rhesus groups determine safe transfusions; the lymphatic system returns tissue fluid and helps defence.
- Pulmonary and systemic circuits
- In pulmonary circulation, the right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs, where it picks up oxygen and returns through the pulmonary vein to the left atrium. In systemic circulation, the left ventricle pumps oxygenated blood through the aorta to the rest of the body, and deoxygenated blood returns through the vena cava to the right atrium.
- Stages of the cardiac cycle
- During atrial systole the atria contract and push blood into the ventricles; during ventricular systole the ventricles contract, closing the atrioventricular valves and forcing blood into the arteries; during diastole all chambers relax and fill with blood. The valve closures produce the familiar 'lub-dub' heart sound heard through a stethoscope.
- Capillary structure and exchange
- A capillary wall is only one cell thick, giving a short diffusion distance between blood and body cells. This thin wall, together with a narrow lumen that slows blood flow, allows oxygen, nutrients and carbon dioxide to diffuse efficiently between the blood and the surrounding tissue fluid.
- Composition of blood
- Blood is made of a pale yellow liquid called plasma, which carries dissolved nutrients, wastes and hormones, together with red blood cells that transport oxygen using haemoglobin, white blood cells that defend against pathogens, and platelets that trigger clotting at a wound.
- ABO blood group compatibility
- Red blood cells carry A and/or B antigens, or neither in group O, while plasma carries antibodies against the antigens a person lacks. Transfusing incompatible blood causes the antibodies to make the donor's red blood cells clump together, or agglutinate, which can block vessels, so blood group must always be matched before a transfusion.
- Rhesus factor
- The Rhesus (Rh) system is a second blood group system based on the presence, Rh-positive, or absence, Rh-negative, of the Rhesus antigen on red blood cells. An Rh-negative person can develop anti-Rh antibodies after exposure to Rh-positive blood, so Rh status, alongside ABO group, must be checked before a safe transfusion.
- Structure of the lymphatic system
- The lymphatic system is a network of lymph vessels, lymph nodes and organs such as the spleen. Lymph vessels collect excess tissue fluid that leaks from capillaries, filter it through lymph nodes containing white blood cells that trap pathogens, and return the cleaned fluid, now called lymph, to the bloodstream near the heart.
- Health issues of the circulatory system
- Atherosclerosis is the build-up of fatty deposits inside artery walls, narrowing them and restricting blood flow; if this blocks a coronary artery it can cause a heart attack. Hypertension, or persistently high blood pressure, strains the heart and blood vessels and is linked to diet, inactivity and smoking.
- Health issues of the lymphatic system
- Filariasis, caused by thread-like parasitic worms spread by mosquito bites, can block lymph vessels and cause lymphoedema, a painful swelling of the limbs sometimes called elephantiasis. Avoiding mosquito bites and controlling mosquito breeding sites are the main preventive measures against this disease.
- Heart rate regulation
- The heart is myogenic, meaning it can initiate its own beat without an external nerve signal, though the nervous system and hormones such as adrenaline can speed it up or slow it down. Exercise, emotion, body temperature and fitness level are among the factors that change heart rate to meet the body's changing demand for oxygen.
How this chapter is examined
SPM Biology is assessed over three papers. Paper 1 has 40 objective questions (40 marks) in 1 hour 15 minutes; Paper 2 carries 100 marks across Sections A, B and C in 2 hours 30 minutes; Paper 3 is the practical, testing science process skills. Content from this chapter can appear in any of them, so lessons drill recall for Paper 1 and structured answers for Paper 2.
Common exam angles
- Labelling the heart and tracing the path of blood.
- Comparing arteries, veins and capillaries in a table.
- Explaining blood clotting or blood group compatibility.
- Tracing the path of blood through the pulmonary and systemic circuits, naming each chamber and vessel in order.
- Explaining why a blood transfusion between incompatible ABO or Rhesus groups is dangerous.
- Describing the structure and role of the lymphatic system in returning tissue fluid and defending the body.
Common mistakes
What students write: Saying all arteries carry oxygenated blood.
What earns the mark: The pulmonary artery carries deoxygenated blood to the lungs; arteries are defined by carrying blood away from the heart.
What students write: Writing that veins carry blood at high pressure.
What earns the mark: Veins carry blood at low pressure and have valves to prevent backflow; arteries carry it at high pressure.
What students write: Confusing the left and right sides of the heart.
What earns the mark: The left ventricle pumps oxygenated blood to the body; the right pumps deoxygenated blood to the lungs.
What students write: Calling fibrinogen the clot.
What earns the mark: Soluble fibrinogen is converted to insoluble fibrin, which forms the mesh of the clot.
What students write: Saying the atria and ventricles contract at the same time.
What earns the mark: The atria contract first (atrial systole) to fill the ventricles, then the ventricles contract (ventricular systole) slightly later to pump blood out.
What students write: Describing a capillary as having a thick wall like an artery.
What earns the mark: A capillary wall is only one cell thick, which shortens the diffusion distance and allows efficient exchange between blood and tissue fluid.
What students write: Thinking plasma is mainly red blood cells.
What earns the mark: Plasma is the pale yellow liquid part of blood; red blood cells, white blood cells and platelets are suspended within it.
What students write: Saying a person with blood group O can never donate blood.
What earns the mark: Group O red blood cells carry neither A nor B antigen, so group O is often called the universal donor for red cell transfusions, though plasma compatibility still matters.
What students write: Confusing the Rhesus system with the ABO system.
What earns the mark: ABO grouping is based on A and B antigens; the Rhesus system is a separate classification based on the presence or absence of the Rh antigen.
What students write: Saying lymph vessels carry blood.
What earns the mark: Lymph vessels carry lymph, a fluid derived from tissue fluid, not blood; only blood vessels carry blood.
What students write: Treating atherosclerosis and hypertension as the same condition.
What earns the mark: Atherosclerosis is the narrowing of arteries by fatty deposits; hypertension is persistently high blood pressure, though each can worsen the other.
What students write: Saying filariasis is caused by a virus.
What earns the mark: Filariasis is caused by parasitic worms spread through mosquito bites, not by a virus, and it can block lymph vessels and cause lymphoedema.
What students write: Assuming the lymphatic system pumps lymph the way the heart pumps blood.
What earns the mark: The lymphatic system has no central pump; lymph is moved mainly by the squeezing action of surrounding skeletal muscles and one-way valves in the lymph vessels.
What students write: Saying the heart needs a nerve impulse from the brain to start beating.
What earns the mark: The heart muscle is myogenic and can contract rhythmically on its own; nerves and hormones only adjust the rate, they do not initiate each heartbeat.
Study this chapter
Processes in this chapter
Structures in this chapter
Frequently asked questions
Why is the human circulatory system called a double circulation?
What is the difference between arteries and veins?
How does blood clot at a wound?
What are the four components of blood and their functions?
Why must blood groups be matched before a transfusion?
What does the lymphatic system do?
What is filariasis and how does it affect the lymphatic system?
Source:SRC-DSKP-EN, SRC-FORMAT
Related
One-hour paid trial · Same-day reply