Transport in Humans and Animals, practice questions

D, Blood always remains inside vessels (closed) and passes through the heart twice per full circuit (double).

B, The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs; arteries are defined by direction (away from the heart), not oxygen content.

B, The sinoatrial (SA) node, in the wall of the right atrium, is the heart's natural pacemaker.

C, Platelets are fragments of larger cells that gather at a wound and trigger the clotting cascade.

B, Group O plasma contains anti-A antibodies, which bind to the A antigen on the transfused red blood cells and cause them to clump together.

B, Atherosclerosis is the gradual build-up of fatty deposits inside the walls of arteries, narrowing the lumen.

B, Tissue fluid forms first when plasma is forced out of capillaries; the excess of it later drains into lymph vessels and is then called lymph.

B, The lymphatic system has no central pump; lymph is moved mainly by the squeezing action of nearby skeletal muscles together with one-way valves.

B, Thread-like worms settle in lymph vessels and physically block lymph flow, causing lymphoedema.

C, A capillary wall is one cell thick, which shortens the diffusion distance for exchange between blood and tissue fluid.

• 'Lub' is produced by the closing of the atrioventricular valves at the start of ventricular systole
• 'Dub' is produced by the closing of the semilunar valves at the start of diastole
• The atrioventricular valves must close to stop blood flowing back into the atria when the ventricles contract
• The semilunar valves must close to stop blood flowing back into the ventricles from the arteries once the ventricles relax

• Group O red blood cells carry neither the A nor the B antigen
• So the recipient's own anti-A and/or anti-B antibodies have no matching antigen on the donor cells to bind to, avoiding agglutination of the transfused red blood cells
• The Rhesus (Rh) system must also be checked
• An Rh-negative recipient given Rh-positive blood can still develop anti-Rh antibodies and react against future Rh-positive transfusions

• The disease suggested is filariasis (leading to lymphoedema)
• Thread-like parasitic worms are transmitted through mosquito bites and settle inside the lymph vessels
• The worms block the affected lymph vessels, preventing lymph and excess tissue fluid from draining away properly
• Fluid then builds up in the surrounding tissue of the limb, causing severe swelling (lymphoedema)

Humans have a closed, double circulatory system: blood passes through the heart twice per full circuit.

Four chambers (two atria, two ventricles) with valves that keep blood flowing one way.

The heart muscle contracts (systole) and relaxes (diastole), controlled by the SA node.

Arteries carry blood away from the heart at high pressure; veins return it; capillaries allow exchange.

Platelets and clotting factors turn fibrinogen into fibrin, forming a clot that seals a wound.

ABO and Rhesus groups determine safe transfusions; the lymphatic system returns tissue fluid and helps defence.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.