Mass transport - Yr 1 Flashcards
Haemoglobins
A group of chemically similar molecules found in a wide variety of organisms. Protein molecules with a quaternary structure that has evolved to make it efficient at loading oxygen under one set of conditions but unloading it under a different set of conditions. It has four polypeptide chains which are linked together to form a spherical molecule – each polypeptide is associated with a haem group which contains a ferrous (Fe2+) ion which can combine with an oxygen molecule (O2).
Oxygen loading
The process by which haemoglobin binds with oxygen is called loading or associating. In humans this takes place in the lungs.
Oxygen unloading
The process by which haemoglobin releases its oxygen is called unloading or dissociating. In humans this takes place in the tissues.
High affinity
Haemoglobins with this for oxygen take up oxygen more easily, but release it less easily.
Low affinity
Haemoglobins with this for oxygen take up oxygen less easily, but release it more easily.
Oxygen dissociation curve
The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen. Shows how at low oxygen concentrations little oxygen binds to haemoglobin (shallow gradient initially). After the first oxygen molecule binding the quaternary structure of the haemoglobin molecule changes, making it easier for the other subunits to bind an oxygen molecule, therefore it takes a smaller increase in the partial pressure of oxygen to bind the second molecule and third molecule so the gradient steepens. After the binding of the third molecule, it is less likely that a single oxygen molecule will find an empty site to bind to so the gradient of the curve reduces and the graph flattens off.
Positive cooperativity
Binding of the first molecule makes binding of the second easier and so on, so the gradient of the curve steepens.
Partial Pressure
The amount of a gas that is present in a mixture of gases is measured by the pressure it contributes to the total pressure of the gas mixture.
Bohr Shift
The greater the concentration of carbon dioxide the more readily the haemoglobin releases its oxygen because the more carbon dioxide there is, the lower the pH, the greater the haemoglobin shape change, the more readily oxygen is unloaded, the more oxygen is available for respiration.
Transport System
Required to take materials from cells to exchange surfaces and from exchange surfaces to cells. They must have a suitable medium to carry materials, a form of mass transport in which the transport medium is moved around in bulk over large distance, a closed system of tubular vessels and a mechanism for moving the transport medium within vessels.
Circulatory System
Contains a pump (heart), vessels (arteries, capillaries and arteries) and a medium (blood) to transport substances around the body.
Double circulatory system
Blood is confined to vessels and passes twice through the heart for each complete circuit of the body (to the lungs and tissues).
Heart
A muscular organ that lies in the thoracic cavity behind the sternum. It operates continuously and tirelessly throughout the life of the organism. Made of four chambers – left and right atria and left and right ventricle.
Atria
The upper chambers of the heart which are thin-walled and elastic and stretches as it collects blood.
Ventricles
The lower chambers of the heart which have a much thicker muscular wall as it has to contract strongly to pump blood some distance, the left side to the rest of the body (and therefore has a thicker muscular wall) and the right side to the lungs.
Vena Cava
A vein connected to the right atrium and brings deoxygenated blood back from the tissues of the body (except the lungs).
Pulmonary Artery
An artery connected to the right ventricle which carries deoxygenated blood to the lungs where its oxygen is replenished and its carbon dioxide is removed.
Pulmonary Vein
A vein which is connected to the left atrium and brings oxygenated blood back from the lungs.
Aorta
An artery which is connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs.
Atrioventricular Valves
The valves found between the atrium and ventricle which prevent the backflow of blood into the atria when the ventricles contract and the ventricular pressure exceeds atrial pressure. The left is also known as the bicuspid and the right is also known as the tricuspid.
Semilunar valves
The valves found in the aorta and pulmonary artery which prevent the backflow of blood into the ventricles when the pressure in these vessels exceeds that in the ventricles.
Coronary Artery
The blood vessels which branch off the aorta and supply the heart muscle with oxygenated blood.
Myocardial infarction
Blockage of these coronary arteries (for example by a blood clot) leads to this. Also known as a heart attack.
Diastole
Stage of the cardiac cycle when the atria and ventricles are relaxed. Blood returns to the atria of the heart. Atrial pressure increases as they fill with blood, causing the atrioventricular valves to open, which allows blood to flow into the ventricles. The semi-lunar valves are closed (‘dub’) because the pressure in the ventricles is lower than that in the aorta and the pulmonary artery.
Atrial systole
A stage of the cardiac cycle when the atrial walls contract, forcing the remaining blood into the ventricles from the atria. Ventricle walls remain relaxed.
Ventricular systole
A stage of the cardiac cycle when the ventricle walls contract simultaneously (after a short delay to allow the ventricles to fill with blood) which increases the blood pressure and causes the atrioventricular valves to shut (‘lub’). Ventricle pressure rises further and forces the semilunar valves open as pressure exceeds that in the aorta and the pulmonary artery, allowing blood to be pumped blood into these vessels.
Heart rate
The rate at which the heart beats in beats per minute.
Stroke volume
The volume of blood pumped out at each beat measured in dm3.
Cardiac output
The volume of blood pumped by one ventricle of the heart in one minute. It is usually measured in dm3min-1.
Arteries
Carry blood away from the heart and into arterioles. They have a thicker muscular layer, thicker elastic layer and overall thicker wall than veins. They also do not contain valves (apart from the aorta and pulmonary artery).
Arterioles
Smaller arteries that control blood flow from arteries to capillaries. Their muscular layer is relatively thicker than in arteries and elastic layer is relatively thinner than in arteries.
Capillaries
Tiny vessels that link arterioles to veins. Their walls consist mostly of the lining layer making them extremely thin, they are numerous and highly branched, they have a narrow diameter and narrow lumen and there are spaces between the lining (endothelial) cells.
Veins
Carry blood from capillaries back to the heart. They have a thinner muscular layer, thinner elastic layer and overall thinner wall than arteries. They contain valves at intervals throughout to ensure that blood does not flow backwards.
Valves
Ensure that blood does not flow backwards and that when body muscles contract, compressing veins, pressurising the blood within them, they ensure the blood flows in one direction only: towards the heart.
Lumen
The central cavity of the blood vessel through which the blood flows.
Tough fibrous outer layer
Resists pressure changes from both within and outside arteries, arterioles and veins.
Elastic Layer
Helps to maintain blood pressure by stretching and recoiling (springing back) in arteries, arterioles and veins.
Muscle layer
Can contract and so control the flow of blood in arteries, arterioles and veins.
Endothelium
Thin inner lining which is smooth to reduce friction in all vessels.
Plasma
Yellow liquid inside blood vessels, which carries red blood cells, platelets, white blood cells and also dissolved substances such as proteins, water, glucose, amino acids and hormones. Composition is controlled by various homeostatic systems.
Tissue fluid
A watery liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen. It supplies all of these substances to the tissues and receives carbon dioxide and other waste materials from tissues. It is the means by which materials are exchanged between blood and cells and bathes the cells of the body. It is formed from blood plasma.
Ultrafiltration
Filtration under pressure at the arterial end, assisted by blood pressure (a hydrostatic pressure) which causes small molecules to be forced out of the capillaries, leaving all cells and proteins in the blood because they are too large to cross the membranes.
Lymphatic system
A system of vessels which begin in the tissues. Initially they resemble capillaries (except that they have dead ends), but they gradually merge into larger vessels that form a network throughout the body. These larger vessels then drain their contents back into the bloodstream via two ducts that join veins close to the heart. It is how the remainder of tissue fluid (which cannot return to the capillaries) is carried back.
Xylem vessels
Hollow thick-walled tubes which transport water through flowering plants.
Transpiration
The main force that pulls water through the xylem vessels in the stem of a plant is the evaporation of water from leaves through stomata.
Stomata
Tiny pores which guard cells control the opening and closing of. If the stomata are open, water vapour molecules diffused out of the air spaces into the surrounding air.
Cohesion
Attraction between molecules of the same type - how water molecules form hydrogen bonds between one another and hence tend to stick together.
Transpiration pull
How a column of water is pulled up the xylem as a result of transpiration.
Cohesion-tension theory
The main factor that is responsible for the movement of water up the xylem, from the roots to the leaves. Transpiration pull puts the xylem under tension (there is negative pressure within the xylem) and because of the cohesive nature of water (due to hydrogen bonds between water molecules) there is a continuous stream of water being pulled across the mesophyll cells and up the xylem.
Potometer
A piece of apparatus which enables the rate of water loss in a plant to be measured.
Phloem
The tissue which transports biological molecules in flowering plants. It is made up of sieve tube elements, long thin structures arranged end to end. Their end walls are perforated to form sieve plates. Associated with the sieve tube elements are cells called companion cells.
Translocation
The process by which organic molecules and some mineral ions are transported from one part of a plant to another.
Sieve tube element
These are living, tubular cells that are connected end to end. The end cell walls have perforations in them to make sieve plates. The cytoplasm is present but in small amounts and in a layer next to the cell wall. It lacks a nucleus and most organelles so there is more space for solutes to move. The cell walls are made of cellulose so solutes can move laterally as well as vertically. Next to each sieve tube element is a companion cell.
Companion cell
Since the sieve tube element lacks organelles, the companion cell with its nucleus, mitochondria, ribosomes, enzymes etc., controls the movement of solutes and provides ATP for active transport in the sieve tube element. Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell.
Mass-flow theory
The bulk movement of a substance through a given channel or area in a specified time. Sucrose is transferred into sieve elements from photosynthesising tissue and there can be mass flow of sucrose solution down a hydrostatic gradient in sieve tubes (caused by active transport of sucrose into sieve tubes at the source and out of sieve tubes at the sink, and osmosis – movement of water into sieve tubes near source and out of sieve tubes near sink).
Ringing
An experiment when a section of outer layers (protective layer and phloem) is removed around the complete circumference of a woody stem while it is still attached to the rest of the plant. This results in the region of the stem immediately above the missing ring of tissue swelling because the sugars of the phloem accumulate above the ring and it leads to tissues dying below the ring because of the interruption of flow of sugars to this region. It shows that the phloem is responsible for translocating sugars.
Tracer
Radioactive isotopes can be used to trace the movement of substances in plants. 14CO2 is used so plants incorporate this isotope into the sugars produced during photosynthesis. These radioactive sugars can then be traced as they move within the plant using autoradiography. This shows that sugars are found where phloem tissue is in the stem.
