The Circulatory System (Edexcel A Level Biology (A) SNAB): Flashcards

It continually removes substances that have diffused across the surface and brings fresh substances to it.

This maintains a steep concentration gradient, so diffusion continues rapidly.

A dipole is a separation of charge within a molecule, caused by the electrons in its covalent bonds being shared unevenly.

The oxygen atom attracts the shared electrons more strongly than the hydrogen atoms do.

This leaves a slightly negative region on the oxygen and slightly positive regions on the hydrogens.

Covalent bonds, in which electrons are shared between the atoms.

Weak hydrogen bonds form between the slightly positive and slightly negative regions of neighbouring water molecules.

False.

Covalent bonds join the atoms within a water molecule; separate water molecules are held to each other by hydrogen bonds.

The positive regions of water are attracted to the negative ions and the negative regions to the positive ions.

Water molecules surround the charged particles.

The surrounded particles break apart into separate ions, which are now dissolved.

Metabolites can be carried around the body efficiently in a dissolved state.

Dissolved solutes are also free to move, so they are more chemically reactive and can take part in metabolic reactions.

Because the oxygen atom carries a slight negative charge, water can surround and dissolve positively charged ions.

Cohesion is the attraction of water molecules to one another, caused by hydrogen bonding between them.

Adhesion is the attraction of water molecules to other molecules, such as those in the wall of a vessel.

Water molecules pull one another along, so water flows easily as a continuous column rather than breaking apart.

True.

Glucose is a polar molecule, so water molecules are attracted to it and surround it, allowing it to dissolve and be transported in the blood.

The right atrium and left atrium (upper chambers).

The right ventricle and left ventricle (lower chambers).

The septum is the wall of muscular tissue separating the left and right sides of the heart, which stops oxygenated and deoxygenated blood from mixing.

The left ventricle pumps blood at high pressure all the way around the body.

The right ventricle only pumps blood the short distance to the lungs, so needs less muscle.

The right atrium and right ventricle are separated by the tricuspid valve.

The bicuspid valve, an atrioventricular (AV) valve.

The pulmonary artery carries deoxygenated blood to the lungs.

The aorta carries oxygenated blood to the body.

The vena cava brings deoxygenated blood from the body.

The pulmonary vein brings oxygenated blood from the lungs.

The coronary arteries are the vessels that branch from the aorta and run across the surface of the heart to supply the heart muscle itself with oxygenated blood.

False.

The right side carries deoxygenated blood, which it pumps to the lungs for gas exchange.

They attach the atrioventricular valves to the heart walls, preventing the valves from flipping inside out under high pressure.

The semilunar valve between the left ventricle and the aorta is called the aortic valve.

When the pressure of the blood behind the valve is greater than the pressure in front of it.

To transport blood away from the heart to the tissues, usually at high pressure.

To transport blood towards the heart, usually at low pressure.

The endothelium, a smooth lining one cell thick.

A layer of smooth muscle and elastic tissue.

An outer wall containing collagen.

The elastic tissue stretches as blood surges through and then recoils.

This evens out fluctuations in pressure and helps maintain blood pressure between heartbeats.

A narrow lumen helps to maintain the high blood pressure needed to carry blood away from the heart to the tissues.

The wall is a single layer of endothelial cells, only one cell thick.

This gives a short diffusion distance for oxygen and carbon dioxide between the blood and the tissues.

Red blood cells must pass through in single file, which forces the blood to travel slowly.

This allows more time for diffusion to occur.

A capillary bed is a network of capillaries branching between cells, forming an important exchange surface within the circulatory system.

Veins contain valves which prevent the backflow of blood.

False.

A pulse is absent in veins because they are far from the heart and the blood within them is at low pressure.

A wide lumen reduces friction between the blood and the endothelium.

This helps blood return to the heart at an adequate speed despite the low pressure.

Collagen is a strong structural protein that protects the vessel from damage by over-stretching.

They allow blood plasma to leak out and form tissue fluid.

They also let white blood cells squeeze through to fight infection in the surrounding tissues.

The cardiac cycle is the series of events that take place in one heart beat, including the contraction and relaxation of the heart muscle.

Systole is the contraction of the heart muscle.

Diastole is the relaxation of the heart muscle.

The volume of the chamber decreases.

The pressure inside it therefore increases.

The walls of the atria contract, so atrial volume decreases and atrial pressure rises.

Pressure in the atria rises above that in the ventricles, forcing the atrioventricular valves open.

Blood is forced into the ventricles, which are relaxed at this point.

The walls of the ventricles contract, so ventricular pressure rises.

Pressure rises above that in the atria, forcing the atrioventricular valves shut.

Pressure then rises above that in the aorta and pulmonary artery, forcing the semilunar valves open so blood leaves the heart.

The atria and ventricles are both relaxed.

Ventricular pressure drops below that in the aorta and pulmonary artery, so the semilunar valves close.

The atria fill with blood, pressure rises above that in the ventricles, the atrioventricular valves open and blood flows passively into the ventricles.

When the pressure of the blood in front of the valve is greater than the pressure behind it.

The atrioventricular valves close during ventricular systole to prevent the backflow of blood into the atria.

True.

While the atria contract to push blood into the ventricles, the ventricles are relaxed and filling.

False.

One cardiac cycle is followed immediately by the next in a continuous process.

Read off the time taken for one complete cycle in seconds.

Divide 60 by that time.

For example, a cycle lasting 0.7 s gives 60 ÷ 0.7 = 85.7 beats per minute.

Any four of:

• Caffeine, alcohol or other drugs

• Temperature

• Sex, weight or height

• Diet or dehydration

Daphnia have transparent bodies.

This means their internal organs, including the beating heart, can be observed directly using a light microscope.

On the dorsal side, just above the gut and in front of the brood pouch.

Transfer a Daphnia to a cavity slide using a pipette and observe it under low power.

Use a stopwatch to time 20 seconds and record each beat as a dot on paper, since the heart beats too fast to count directly.

Count the dots and multiply by three to give beats per minute.

Distilled water, containing no caffeine.

A range of caffeine concentrations can be prepared accurately using the serial dilution technique.

Plot mean heart rate on the y axis against caffeine concentration on the x axis.

The graph should show a positive correlation: as caffeine concentration increases, heart rate increases.

It allows a mean to be calculated, which reduces the effect of natural variation between individuals and makes the results more reliable.

False.

Daphnia still deserve respect: they cannot give consent to be studied and cannot express pain.

Invertebrates have less sophisticated nervous systems, so they may not feel pain in the same way that vertebrates do.

Precautions include:

• Handling the animals gently

• Keeping examination periods as short as possible and returning them promptly to the holding tank

• Avoiding extreme ranges of the variable being tested, such as very strong caffeine solutions

So that any change in heart rate can be attributed to the independent variable being tested, rather than to another factor.

Atherosclerosis is the progressive hardening and narrowing of the arteries, caused by damage to the endothelium followed by an inflammatory response and the build-up of plaque.

An atheroma is the plaque that forms beneath the endothelium of an artery, made up of cholesterol, lipids, macrophages and platelets.

The endothelium of the artery is damaged, for example by high blood pressure.

An inflammatory response occurs and white blood cells such as macrophages accumulate at the site.

Lipids and cholesterol clump with the macrophages beneath the endothelium, forming fatty streaks.

Platelets add to the deposit and a plaque (atheroma) builds up, narrowing the lumen and raising blood pressure.

To reduce friction between the blood and the inside of the artery, allowing free blood flow.

Any four of:

• High levels of certain types of cholesterol

• Smoking

• Diabetes

• Obesity or old age

The clumping of lipids, cholesterol and macrophages beneath the endothelium forms fatty streaks, one of the first signs of atherosclerosis.

The plaque narrows the lumen of the artery.

This restricts blood flow, so the same volume of blood must pass through a smaller space, raising the pressure.

Raised blood pressure causes further damage to the endothelium, which triggers more plaque formation in a positive feedback cycle.

It can calcify and harden.

This reduces the elasticity of the artery wall, further increasing blood pressure.

False.

The plaque builds up beneath the endothelium, although it can later rupture through it.

Macrophages.

Atherosclerosis is described as a progressive disease, meaning that it worsens over time.

Thrombosis is the process of blood clotting, brought about by a cascade of chemical reactions involving several plasma proteins.

The damaged blood vessel releases thromboplastin.

Thromboplastin, together with calcium ions, converts soluble prothrombin into the enzyme thrombin.

Thrombin catalyses the conversion of soluble fibrinogen into insoluble fibrin.

Fibrin fibres mesh together, trapping platelets and red blood cells to form a clot.

Thromboplastin.

Thrombin is an enzyme that catalyses the conversion of soluble fibrinogen into insoluble fibrin.

Soluble prothrombin is converted into thrombin by thromboplastin and calcium ions from the plasma.

A blood clot:

• Prevents excessive blood loss

• Prevents the entry of pathogens

• Forms a barrier, or scab, under which wound healing can occur

False.

It is the other way round: fibrinogen is soluble and is converted into insoluble fibrin, which forms the mesh of the clot.

The plaque can rupture through the endothelium, damaging it and leaving a rough surface.

This damage triggers the process of thrombosis.

The clot restricts blood flow, reducing the delivery of oxygen to the surrounding cells.

This reduces respiration, so the cells cannot produce enough ATP to function and may die.

A stroke is a sudden loss of brain function in a localised area, caused by disruption of the blood flow to the brain. One caused by a blood clot is an ischaemic stroke.

Blood flow to part of the heart muscle is restricted, so less oxygen is delivered and respiration falls.

The cells cannot produce enough ATP to contract, reducing the force of the heartbeat.

If the cells die, permanent damage results — a myocardial infarction.

Deep vein thrombosis (DVT) is the formation of a blood clot in a vein deep inside the body, most commonly in the legs. Causes include prolonged inactivity and old age.

It can travel to other blood vessels in the body.

If it reaches the brain it can block an artery there and cause a stroke.