Circulatory Systems, Heart & Blood Vessels (Cambridge (CIE) IGCSE Biology)

False.

Deoxygenated blood enters the right side of the heart from the body, via the vena cava.

The pulmonary vein is the only vein to carry oxygenated blood, returning blood to the heart after gas exchange has taken place.

True.

Arteries carry blood away from the heart while veins carry blood into the heart.

The activity of the heart can be monitored as follows:

• ECG

• measuring pulse rate, e.g. at the wrist

• listening to the valves close, i.e. listening to the heart beat

True.

During physical activity the heart rate increases.

The effect of exercise on heart rate can be investigated by:

1. measuring heart rate at rest, e.g. by recording pulse rate in beats per minute

2. taking part in exercise for a specified time period

3. repeating the heart rate measurement

This can be repeated several times at the same level of exercise, and could be extended by taking part in exercise at different intensity levels.

In an investigation into the effect of exercise on heart rate, the dependent variable is heart rate, e.g. in beats per minute

Variables that would need to be controlled when investigating the effect of exercise intensity on heart rate include:

• the person whose heart rate is measured

• the type of exercise

• the time period for which exercise is carried out

• the method of measuring heart rate

• the rest period between repeats

Coronary heart disease (CHD) occurs when the coronary arteries narrow due to build-up of fatty deposits; this reduces the flow of blood through the coronary arteries of the heart.

Risk factors for CHD include:

• diet

• inactivity

• stress

• smoking

• age

• biological sex

A good diet can reduce blood cholesterol, reduce blood pressure and aid weight loss; these can all reduce the risk of CHD.

True.

Exercise can reduce the risk of CHD because it lowers blood pressure and reduces stress.

The valves labelled X and Y are:

• X = semilunar valve

• Y = atrioventricular valve

The left ventricle has a thicker muscle wall so that it can pump oxygenated blood at high pressure throughout the body, while the right ventricle pumps deoxygenated blood at lower pressure to the lungs.

False.

The atria have thinner walls than the ventricles. This is because they only need to pump blood the short distance to the ventricles, so they do not need to generate high pressures.

The septum separates the left and right sides of the heart, preventing oxygenated and deoxygenated blood from mixing.

True.

The muscular contractions of the atrial walls force blood downwards into the ventricles.

The heart valves enable forward flow of blood while preventing backflow as follows:

• high blood pressure in front of a valve forces the valve open, enabling forward flow of blood

• high blood pressure behind a valve forces it closed, preventing blood from flowing backwards

During exercise the heart rate increases because:

• increased blood flow increases the supply of oxygen and glucose to the muscles

• muscle cells can respire faster and release more energy for muscle contraction

• waste products of respiration (e.g. carbon dioxide) can be removed from the cells faster

Arteries carry blood away from the heart.

The blood vessel in the diagram is an artery because:

• the wall is thick

• the lumen is narrow

• no valves are present

Veins carry blood at low pressure towards the heart.

The blood vessel is a vein because:

• the wall is thin

• the lumen is wide

The key feature of veins that is not visible in the diagram is the presence of valves.

The function of capillaries is to transport oxygenated blood from the arteries to the cells, and deoxygenated blood from the cells to the veins.

In doing so they supply the cells with oxygen and nutrients, and remove waste products from the cells.

The blood vessels are:

• A = pulmonary artery

• B = vena cava

• C = aorta

• D = pulmonary vein

The blood vessel that carries deoxygenated blood to the lungs from the heart is the pulmonary artery.

False.

The pulmonary vein carries oxygenated blood to the heart from the lungs.

False.

The renal vein carries deoxygenated blood away from the kidneys.

Arteries are adapted for their function as follows:

• thick, muscular walls can withstand high pressure

• elastic fibres in the walls allow them to stretch

• a narrow lumen maintains high blood pressure

Veins are adapted to their function as follows:

• a wide lumen increases the volume of blood that flows at any one time

• the wide lumen reduces friction between blood and the blood vessel walls

• valves prevent the backflow of blood

Capillary adaptations shown include:

• walls that are one cell thick, and that are made of flattened cells to reduce diffusion distance

• a narrow lumen to increase contact between blood and the capillary walls, increasing diffusion

Note that while capillaries also have gaps between the cells in their walls to increase permeability, this feature cannot be seen in this image.

Blood vessels A-C are:

• A = hepatic vein

• B = hepatic artery

• C = hepatic portal vein

The main components of blood are:

• red blood cells

• white blood cells

• platelets

• plasma

Structures X and Y are:

• X = red blood cell

• Y = white blood cell

The function of red blood cells is to transport oxygen (via haemoglobin) to tissues and organs.

White blood cells are involved in the immune response; they carry out:

• phagocytosis

• antibody production

False.

Platelets are involved in the blood clotting process. Red blood cells transport oxygen.

Substances transported in the plasma include:

• blood cells

• ions

• nutrients

• urea

• hormones

• carbon dioxide

Blood clotting is important because it:

• prevents significant blood loss from wounds

• seals wounds with a scab, preventing entry of microorganisms that could cause infection

Blood cell types A-C are:

• A = lymphocyte

• B = phagocyte

• C = red blood cell

False.

Lymphocytes produce antibodies. Phagocytes engulf and destroy pathogens.

The function of phagocytes is to engulf and destroy pathogens during phagocytosis.

False.

Soluble fibrinogen proteins are converted to insoluble fibrin proteins during the blood clotting process.

Fibrin forms an insoluble mesh across the wound, trapping red blood cells to form a clot, which eventually dries to become a scab.