Transport in Animals (OCR A Level Biology): Flashcards

The bulk movement of materials in a directed manner, driven by some kind of force.

Diffusion still occurs, but only at specific exchange sites at the start and end of the route travelled by the substances (e.g. the lungs are the exchange site of the gas exchange system).

• Bring substances quickly from one exchange site to another

• Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings

• Ensure effective cell activity by keeping the fluid environment of cells within a suitable metabolic range

The circulatory system.

The one-way flow of blood within the blood vessels carries essential nutrients and gases to all the cells of the body, with the lungs and capillaries acting as sites of exchange.

False — the surface area : volume ratio decreases, because volume increases much more rapidly than surface area.

True

In large organisms the diffusion distances are too great, so materials such as oxygen and glucose would take far too long to diffuse to every cell.

Single-celled organisms can gain these reactants directly across their surface membranes, and short diffusion distances allow molecules to reach all parts of the cell quickly.

A system that connects specialised exchange surfaces to the rest of the body and transports fluids containing oxygen, nutrients and waste, overcoming the problem of large diffusion distances.

• In a single circulatory system, the blood passes through the heart once during one complete circuit of the body.

• In a double circulatory system, the blood passes through the heart twice during one complete circuit of the body.

Fish have a single circulatory system, while mammals have a double circulatory system.

• Deoxygenated blood is pumped to the gills from the heart.

• At the gills (the exchange site) oxygen and carbon dioxide are exchanged between the water and the blood.

• Oxygenated blood then flows from the gills to the rest of the body, delivering oxygen and nutrients through the capillaries.

• The blood then returns to the heart.

The fish heart has just one atrium and one ventricle.

• Blood in the right side of the heart (deoxygenated) leaves and travels to the lungs.

• The blood returns to the left side of the heart.

• Oxygenated blood is then pumped from the left side around the rest of the body.

• After passing through the organs and tissues, the blood returns to the right side of the heart.

The septum keeps oxygenated and deoxygenated blood separate:

• The left side contains oxygenated blood (pumped to the body).

• The right side contains deoxygenated blood (pumped to the lungs).

When blood passes through a capillary network, its pressure and speed drop significantly.

• In a single system, blood passes through two capillary networks before returning to the heart.

• In a double system, blood passes through only one capillary network before returning to the heart.

So double circulation maintains a higher blood pressure and speed of flow, keeping a steeper concentration gradient for efficient exchange of nutrients and waste with the tissues.

• In a closed circulatory system, blood is always contained within a network of blood vessels (found in all vertebrates and many invertebrates).

• In an open circulatory system, blood is not contained within vessels but is pumped directly into body cavities (found in arthropods and molluscs).

• Pulmonary circulation: the right side of the heart pumps deoxygenated blood to the lungs for gas exchange.

• Systemic circulation: blood returns to the left side of the heart, which pumps oxygenated blood at high pressure around the rest of the body.

The name given to the blood of an insect. It is pumped by the tubular heart into the dorsal vessel and released into the haemocoel (body cavity), where it surrounds the organs but is not directed towards specific ones.

• The tubular heart in the abdomen pumps haemolymph into the main blood vessel, the dorsal vessel.

• The dorsal vessel delivers haemolymph into the haemocoel (body cavity), where it surrounds the organs.

• Haemolymph eventually re-enters the heart through one-way valves called ostia.

Because oxygen is not transported by the haemolymph. Instead, oxygen is delivered directly to the tissues via the tracheae (a system of tubes) that connect directly to the outside air.

True

False — oxygen is delivered directly to the tissues via the tracheae, not by the haemolymph.

A blood vessel that transports blood away from the heart, usually at high pressure, to the tissues.

A blood vessel that transports blood to the heart, usually at low pressure.

• Tunica intima (innermost)

• Tunica media (middle)

• Tunica adventitia/externa (outermost)

It is a thick layer made of smooth muscle cells and elastic tissue.

It is one cell thick and very smooth, which reduces friction and allows free blood flow.

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

The narrow lumen helps to maintain a high blood pressure as blood is transported away from the heart.

Arterioles have a muscular layer with many muscle cells and few elastic fibres.

These muscle cells contract to close the lumen, partially cutting off and regulating blood flow to specific organs (e.g. reducing flow to the stomach during exercise so more blood reaches the muscles).

A vein has a much thinner tunica media because it carries blood at low pressure, so it does not need a thick muscular layer.

They prevent the backflow of blood, helping to return blood to the heart against low pressure.

Venules connect the capillaries to the veins and have few or no elastic fibres and a large lumen.

A pulse is present in arteries and absent in veins.

A network of capillaries that branches between cells and acts as an important exchange surface within the circulatory system.

• Walls one endothelial cell thick – short diffusion distance for oxygen and carbon dioxide.

• Very small lumen – forces blood to travel slowly, giving more time for diffusion.

• Large numbers branching between cells – short diffusion distance to tissues.

• Pores in the walls – allow blood plasma to leak out and form tissue fluid.

They squeeze through the intercellular junctions (gaps) in the capillary walls to reach the affected tissues.

The smooth muscle allows the artery to withstand high pressure and to contract to narrow the lumen, reducing blood flow.

The elastic tissue stretches and recoils to maintain blood pressure and even out fluctuations in pressure.

A vein has a much larger lumen, which ensures blood returns to the heart at an adequate speed and reduces friction with the endothelium.

False — arteries transport blood away from the heart.

True

The fluid that surrounds the cells of the body, formed when some plasma leaks out through gaps in the walls of capillaries. It bathes almost all cells outside the circulatory system and is the medium through which substances are exchanged between cells and the blood.

As blood passes through capillaries, some plasma leaks out through gaps in the capillary walls to surround the cells of the body, forming tissue fluid.

Tissue fluid has a very similar composition to plasma but contains far fewer proteins.

The pressure exerted by a fluid. In a capillary this is the blood pressure, generated by the contraction of the heart muscle, which tends to force fluid out of the capillary.

The osmotic pressure exerted by plasma proteins within a blood vessel. The plasma proteins lower the water potential inside the vessel, causing water to move into the blood vessel by osmosis.

At the arterial end the hydrostatic pressure is greater than the oncotic (osmotic) pressure.

The hydrostatic pressure is high enough to force fluid out of the capillary, so the net movement of water is out of the capillary into the tissue fluid.

• The hydrostatic pressure inside the capillary has fallen (due to increased distance from the heart and slowing of blood flow)

• The water potential (osmotic) gradient remains the same as at the arterial end

• The osmotic pressure is now greater than the hydrostatic pressure, so water flows back into the capillary from the tissue fluid

The hydrostatic pressure falls from the arterial end to the venous end.

The water potential gradient (osmotic pressure) stays the same at both ends.

Roughly 90% of the fluid lost at the arterial end of a capillary is reabsorbed at the venous end. The remaining 10% is collected by lymph vessels and returned to the circulatory system.

The accumulation of fluid around the tissues. It occurs when blood pressure is high (hypertension), as the increased hydrostatic pressure at the arterial end pushes more fluid out of the capillary than can be reabsorbed.

Larger molecules that cannot pass back through the capillary wall enter the closed-ended lymph vessels (which have large pores) through small valves.

If plasma proteins were not removed from the tissue fluid, they could lower the water potential of the tissue fluid and prevent the reabsorption of water back into the blood at the capillaries.

After digestion, lipids are transported from the intestines to the bloodstream by the lymphatic system.

Plasma proteins are too large to fit through the gaps in the capillary walls, so they remain in the blood.

The lymph moves along the larger vessels by compression caused by body movement, with valves preventing any backflow.

True

False — plasma proteins are too large to fit through the gaps, so they remain in the blood.

• The two atria (top chambers)

• The two ventricles (bottom chambers)

A wall of muscular tissue that separates the left and right sides of the heart, ensuring oxygenated and deoxygenated blood do not mix.

• The interatrial septum separates the left and right atria

• The interventricular septum separates the left and right ventricles

A tough, fibrous sac that surrounds and protects the heart within the chest cavity.

They open when the pressure of blood behind them is greater than the pressure in front of them.

• They keep blood flowing forward in the correct direction and stop it flowing backwards

• They help maintain the correct pressure in the chambers of the heart

The atrioventricular valve, also known as the tricuspid valve.

The mitral valve, also known as the bicuspid valve.

The right ventricle and the pulmonary artery are separated by the pulmonary valve, while the left ventricle and aorta are separated by the aortic valve.

• Vena cava

• Pulmonary vein

The arteries on the surface of the heart that supply the heart muscle with oxygenated blood for aerobic respiration.

Blockages reduce the heart muscle's oxygen supply, which could lead to angina or a heart attack (myocardial infarction).

They close when the pressure of blood in front of them is greater than the pressure behind them.

• Pulmonary artery

• Aorta

False — the two upper chambers are the atria; the ventricles are the lower chambers.

True

They allow the internal structures of organs to be examined, so that theories can be made about how the organs function.

• Concern about how the animals are raised and killed

• It goes against the religious beliefs of some individuals

• The specimen should come from a reputable source and be disposed of in the correct manner

They should be taken from individual organisms of the same species and roughly the same age.

This makes any comparisons between specimens valid and reliable.

• Scissors

• Scalpel

• Tweezers / forceps

• Dissection board

• Paper towels

• Biological specimen

• Pins

• Gloves

• Goggles

To avoid contamination with biological material, which could otherwise cause an allergic reaction.

• Scissors are used for cutting large sections of tissue, where cuts do not need to be precise

• A scalpel enables finer, more precise cutting and needs to be sharp to ensure this

• Cut away from your body

• Keep your fingers far from the blade to reduce the chance of cutting yourself

To move other sections of the specimen aside, leaving the desired structure exposed.

• It can be hard to see some of the smaller, finer structures within organs

• The specimens do not reflect how the tissue would look in a living organism

• If only a single specimen is dissected, anomalies within it may be ignored or glossed over

The left ventricle is much larger (with a thicker wall) than the right ventricle.

Note that, just as in diagrams, the right ventricle appears on the left side of the heart when viewed.

In the heart, the right ventricle connects to the right atrium via the tricuspid valve.

You must name the specific tools that should be used (e.g. scissors and forceps), rather than referring to tools in general terms.

True

False — the right ventricle appears on the left side of the heart when viewed, just as it does in diagrams.

The valve between the right atrium and right ventricle that prevents the backflow of blood.

The cutting open of a biological specimen to examine its internal structures.

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

The contraction of the heart muscle.

The relaxation of the heart muscle.

• When volume decreases, pressure increases

• When volume increases, pressure decreases

Contraction of the heart muscle decreases the volume of the chamber, and relaxation increases it again.

• The walls of the atria contract, so atrial volume decreases and atrial pressure increases

• Atrial pressure rises above ventricular pressure, forcing the atrioventricular (AV) valves open

• Blood is forced into the ventricles

• The ventricles are relaxed (ventricular diastole coincides with atrial systole)

• The walls of the ventricles contract, so ventricular volume decreases and ventricular pressure increases

• Ventricular pressure rises above atrial pressure, forcing the AV valves closed (preventing backflow)

• Ventricular pressure rises above that in the aorta and pulmonary artery, forcing the semilunar (SL) valves open

• Blood is forced into the arteries and out of the heart; the atria are relaxing (atrial diastole)

• The ventricles and atria are both relaxed

• Ventricular pressure drops below that in the aorta and pulmonary artery, forcing the SL valves closed

• Blood returns to the heart via the vena cava and pulmonary vein, and the atria fill with blood

• Atrial pressure rises above ventricular pressure, forcing the AV valves open, so blood flows passively into the ventricles

A valve opens when the pressure of blood behind it is greater than the pressure in front of it.

• Atrial systole: AV valves open, SL valves closed

• Ventricular systole: AV valves closed, SL valves open

• Diastole: AV valves open, SL valves closed

One cardiac cycle is followed by another in a continuous process – there is no gap between cycles where blood stops flowing.

On a cardiac cycle pressure graph, the AV valve shuts when the pressure in the ventricle exceeds the pressure in the atrium.

As the ventricle continues to contract, the pressure in the left ventricle exceeds that in the aorta. This forces the aortic valve open and blood is forced into the aorta.

Step 1: Read off the time for one complete cardiac cycle (one heart beat) from the graph

Step 2: Calculate beats per second by dividing 1 by the cycle length in seconds

Step 3: Multiply the beats per second by 60 to give beats per minute

A valve closes when the pressure of blood in front of it is greater than the pressure behind it.

False — the AV valves are closed during ventricular systole to prevent backflow of blood into the atria.

True

The volume of blood pumped by the heart per unit of time (usually expressed in dm³ or litres per minute).

The number of times the heart beats per minute, i.e. the number of cardiac cycles per minute.

The volume of blood pumped out of the heart during one cardiac cycle.

cardiac output = heart rate × stroke volume

heart rate = cardiac output ÷ stroke volume

stroke volume = cardiac output ÷ heart rate

Cardiac output = heart rate × stroke volume

Fitter individuals tend to have thicker and stronger ventricular muscles, so a greater volume of blood can be pumped with each contraction (a larger stroke volume).

So that the blood supply can match the increased metabolic demands of the cells during exercise (e.g. delivering more oxygen and glucose and removing more waste).

Step 1: Find the heart rate

1 cardiac cycle = 1 second, and 1 minute = 60 seconds, so heart rate = 60 ÷ 1 = 60 bpm

Step 2: Apply the equation

cardiac output = heart rate × stroke volume = 60 × 73 = 4380 cm³ per minute

Step 3: Convert to dm³

4380 ÷ 1000 = 4.38 dm³ per minute

You must use the change in volume of the ventricle, not the change in pressure.

Roughly 4.7 litres of blood per minute.

Most cardiac cycle graphs plot pressure changes in the left ventricle, atrium and aorta, so students often mistakenly try to read stroke volume from a pressure graph instead of a volume graph.

True

False — that describes heart rate; stroke volume is the volume of blood pumped out per cardiac cycle.

Describes muscle that contracts and generates its own rhythm without an external (nervous) stimulus. The heartbeat is myogenic.

The heart will beat by itself, without any external stimulus. This intrinsic rhythm causes the heart to beat at around 60 times per minute.

A group of cells in the wall of the right atrium that acts as the heart's pacemaker, initiating a wave of depolarisation that spreads across the atria.

The SAN initiates a wave of depolarisation that spreads across both atria, causing the atria to contract (atrial systole).

It is a region of non-conducting tissue that prevents the wave of depolarisation spreading straight from the atria to the ventricles.

This ensures the atria and ventricles do not contract at the same time.

The AVN is a region of conducting tissue between the atria and ventricles.

After a slight delay, it passes the wave of depolarisation on to the bundle of His.

The delay means the ventricles contract after the atria.

This gives the atria time to empty their blood fully into the ventricles before ventricular contraction.

A collection of conducting tissue in the septum (middle) of the heart.

It divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them.

They spread around the ventricles and initiate the depolarisation of the ventricles from the apex (bottom) of the heart.

This makes the ventricles contract, forcing blood out of the pulmonary artery and aorta.

The Purkyne fibres carry the wave of excitation to the apex first, so contraction starts at the base.

This pushes blood upwards and outwards into the pulmonary artery and aorta.

• SAN initiates a wave of depolarisation, causing the atria to contract

• The annulus fibrosus stops this spreading directly to the ventricles

• The AVN receives the wave and, after a delay, passes it to the bundle of His

• The bundle of His carries it through the septum to the Purkyne fibres

• The Purkyne fibres spread depolarisation from the apex, causing the ventricles to contract

The bundle of His is a collection of conducting tissue in the septum (middle) of the heart.

Non-conducting tissue, which prevents depolarisation spreading straight to the ventricles, is called the annulus fibrosus.

False — myogenic means the heart generates its own beat without any external (nervous) stimulus.

True

A trace that records the electrical activity of the heart, produced by electrodes placed on the skin. It shows a series of distinctive waves generated by the activity of the heart.

Electrodes placed on the skin detect the electrical activity of the heart and produce the ECG trace.

The P wave is caused by the depolarisation of the atria, which results in atrial contraction (systole).

The QRS complex is caused by the depolarisation of the ventricles, which results in ventricular contraction (systole).

The T wave is caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole).

The QRS complex is caused by the depolarisation of the ventricles, resulting in their contraction.

The cause of the U wave is uncertain, but some scientists think it is caused by the repolarisation of the Purkyne fibres.

Some heart problems produce characteristic shapes or waves in an ECG, so a doctor can use the trace as a diagnostic tool to identify the specific problem.

A condition in which the heart beats too fast. A resting heart rate of over 100 bpm is classed as tachycardia.

A condition in which the heart beats too slowly. A resting heart rate below 60 bpm is classed as bradycardia.

Many fit individuals or athletes have lower heart rates, which is usually not dangerous.

A condition caused by an early heartbeat followed by a pause. It is common in the population and usually requires no treatment unless very severe.

An irregular heartbeat that disrupts the rhythm of the heart. Severe cases can be very dangerous, even fatal.

• The speed of the heartbeat (too fast or too slow)

• The rhythm / regularity of the heartbeat

Because the ventricles have the largest muscle mass, so their depolarisation produces the largest deflection.

False — the P wave represents depolarisation of the atria; it is the QRS complex that represents the ventricles.

True

Another name for a red blood cell, the cell in which the majority of oxygen is transported bound to haemoglobin.

The molecule formed when oxygen binds to haemoglobin.\n\nOxygen + Haemoglobin $\rightleftharpoons$ Oxyhaemoglobin

Bound to the protein haemoglobin inside red blood cells (erythrocytes).

Each haemoglobin molecule can carry four oxygen molecules (eight oxygen atoms).

The binding of the first oxygen molecule causes a conformational change in the haemoglobin molecule.\n\nThis makes it easier for each successive oxygen molecule to bind.

• A very small percentage dissolved in the blood plasma (in solution)\n\n- Bound to haemoglobin as carbaminohaemoglobin\n\n- The largest percentage as hydrogen carbonate ions (HCO₃⁻)

The compound formed when carbon dioxide binds to haemoglobin.

• Carbon dioxide diffuses from the plasma into red blood cells\n\n- It combines with water to form carbonic acid (H₂CO₃), catalysed by carbonic anhydrase\n\n- Carbonic acid dissociates into hydrogen carbonate ions (HCO₃⁻) and hydrogen ions (H⁺)

It catalyses the reaction between carbon dioxide and water to form carbonic acid (H₂CO₃).\n\nWithout it the reaction proceeds very slowly, so carbonic acid forms more slowly in plasma than in red blood cells.

Hydrogen ions (H⁺) from the dissociation of carbonic acid combine with haemoglobin to form haemoglobinic acid.\n\nThis prevents the H⁺ ions from lowering the pH of the red blood cell.

Hydrogen ions combine with haemoglobin to form haemoglobinic acid, which prevents a fall in pH inside the red blood cell.

The movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed.\n\nAs HCO₃⁻ ions move out of the cell, negatively charged chloride ions (Cl⁻) move in via the same transport protein to prevent an electrical imbalance.

• The Bohr shift occurs when a high partial pressure of carbon dioxide causes haemoglobin to release oxygen into respiring tissues\n\n- The chloride shift is the movement of chloride ions into red blood cells when hydrogen carbonate ions are formed

Because it contains four haem groups, each able to bind one molecule of oxygen.

True

False — the largest proportion is transported as hydrogen carbonate ions (HCO₃⁻).

A graph showing the rate at which oxygen associates with, and dissociates from, haemoglobin at different partial pressures of oxygen (pO2).

The pressure exerted by oxygen within a mixture of gases; it is a measure of oxygen concentration.

The ease with which haemoglobin binds to and dissociates from oxygen.

• High affinity: binds oxygen easily and dissociates slowly

• Low affinity: binds oxygen slowly and dissociates easily

When all of its oxygen binding sites are taken up with oxygen, i.e. when it contains four oxygen molecules.

Because oxygen binds to haemoglobin at different rates as the pO2 changes, rather than at a constant rate.

This reflects the changing affinity of haemoglobin for oxygen at different partial pressures of oxygen.

• Shallow bottom-left: due to haemoglobin's shape, it is difficult for the first oxygen molecule to bind, so binding is slow

• Steep middle: after the first oxygen binds, haemoglobin changes shape (conformation), making it easier for further oxygen molecules to bind

• Levelling off top-right: as haemoglobin approaches saturation there are few remaining binding sites, so the fourth oxygen molecule takes longer to bind

The shape (conformation) change of haemoglobin after the first oxygen molecule binds, which makes it easier for the subsequent oxygen molecules to bind.

Respiring tissues have a medium/lower pO2, which corresponds to the steep region of the curve.

Here a small decrease in pO2 causes a large decrease in percentage saturation, so plenty of oxygen dissociates and is released to the cells for respiration.

In the lungs the pO2 is high, so haemoglobin has a high affinity for oxygen and becomes almost fully saturated.

There is very little dissociation of oxygen from haemoglobin at high pO2.

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.

It allows the foetus to obtain oxygen from its mother's blood at the placenta.

Foetal haemoglobin can bind oxygen at the low pO2 at which the mother's haemoglobin is releasing (dissociating with) oxygen.

The curve for foetal haemoglobin lies to the left of the curve for adult haemoglobin.

This means that at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin.

After birth, a baby begins to produce adult haemoglobin, which gradually replaces foetal haemoglobin.

The partial pressure of oxygen is lower at higher altitudes.

Haemoglobin with a high affinity that binds oxygen very readily allows llamas to achieve a sufficient level of oxygen saturation in their blood even when the pO2 in the air is low.

Haemoglobin is a quaternary protein of four globin polypeptides and four haem groups; the haem structure is identical in all types.

However, the globin chains can differ substantially, and these determine the precise oxygen-binding properties of the haemoglobin.

False — the haem structure is identical in all types; it is the globin chains that differ.

True