Mass transport - Yr 1

Question 1

Haemoglobins

Answer 1

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).

Question 2

Oxygen loading

Answer 2

The process by which haemoglobin binds with oxygen is called loading or associating. In humans this takes place in the lungs.

Question 3

Oxygen unloading

Answer 3

The process by which haemoglobin releases its oxygen is called unloading or dissociating. In humans this takes place in the tissues.

Question 4

High affinity

Answer 4

Haemoglobins with this for oxygen take up oxygen more easily, but release it less easily.

Question 5

Low affinity

Answer 5

Haemoglobins with this for oxygen take up oxygen less easily, but release it more easily.

Question 6

Oxygen dissociation curve

Answer 6

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.

Question 7

Positive cooperativity

Answer 7

Binding of the first molecule makes binding of the second easier and so on, so the gradient of the curve steepens.

Question 8

Partial Pressure

Answer 8

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.

Question 9

Bohr Shift

Answer 9

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.

Question 10

Transport System

Answer 10

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.

Question 11

Circulatory System

Answer 11

Contains a pump (heart), vessels (arteries, capillaries and arteries) and a medium (blood) to transport substances around the body.

Question 12

Double circulatory system

Answer 12

Blood is confined to vessels and passes twice through the heart for each complete circuit of the body (to the lungs and tissues).

Question 13

Heart

Answer 13

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.

Question 14

Atria

Answer 14

The upper chambers of the heart which are thin-walled and elastic and stretches as it collects blood.

Question 15

Ventricles

Answer 15

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.

Question 16

Vena Cava

Answer 16

A vein connected to the right atrium and brings deoxygenated blood back from the tissues of the body (except the lungs).

Question 17

Pulmonary Artery

Answer 17

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.

Question 18

Pulmonary Vein

Answer 18

A vein which is connected to the left atrium and brings oxygenated blood back from the lungs.

Question 19

Aorta

Answer 19

An artery which is connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs.

Question 20

Atrioventricular Valves

Answer 20

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.

Question 21

Semilunar valves

Answer 21

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.

Question 22

Coronary Artery

Answer 22

The blood vessels which branch off the aorta and supply the heart muscle with oxygenated blood.

Question 23

Myocardial infarction

Answer 23

Blockage of these coronary arteries (for example by a blood clot) leads to this. Also known as a heart attack.

Question 24

Diastole

Answer 24

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.

Question 25

Atrial systole

Answer 25

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.

Question 26

Ventricular systole

Answer 26

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.

Question 27

Heart rate

Answer 27

The rate at which the heart beats in beats per minute.

Question 28

Stroke volume

Answer 28

The volume of blood pumped out at each beat measured in dm3.

Question 29

Cardiac output

Answer 29

The volume of blood pumped by one ventricle of the heart in one minute. It is usually measured in dm3min-1.

Question 30

Arteries

Answer 30

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).

Question 31

Arterioles

Answer 31

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.

Question 32

Capillaries

Answer 32

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.

Question 33

Veins

Answer 33

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.

Question 34

Valves

Answer 34

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.

Question 35

Lumen

Answer 35

The central cavity of the blood vessel through which the blood flows.

Question 36

Tough fibrous outer layer

Answer 36

Resists pressure changes from both within and outside arteries, arterioles and veins.

Question 37

Elastic Layer

Answer 37

Helps to maintain blood pressure by stretching and recoiling (springing back) in arteries, arterioles and veins.

Question 38

Muscle layer

Answer 38

Can contract and so control the flow of blood in arteries, arterioles and veins.

Question 39

Endothelium

Answer 39

Thin inner lining which is smooth to reduce friction in all vessels.

Question 40

Plasma

Answer 40

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.

Question 41

Tissue fluid

Answer 41

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.

Question 42

Ultrafiltration

Answer 42

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.

Question 43

Lymphatic system

Answer 43

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.

Question 44

Xylem vessels

Answer 44

Hollow thick-walled tubes which transport water through flowering plants.

Question 45

Transpiration

Answer 45

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.

Question 46

Stomata

Answer 46

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.

Question 47

Cohesion

Answer 47

Attraction between molecules of the same type - how water molecules form hydrogen bonds between one another and hence tend to stick together.

Question 48

Transpiration pull

Answer 48

How a column of water is pulled up the xylem as a result of transpiration.

Question 49

Cohesion-tension theory

Answer 49

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.

Question 50

Potometer

Answer 50

A piece of apparatus which enables the rate of water loss in a plant to be measured.

Question 51

Phloem

Answer 51

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.

Question 52

Translocation

Answer 52

The process by which organic molecules and some mineral ions are transported from one part of a plant to another.

Question 53

Sieve tube element

Answer 53

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.

Question 54

Companion cell

Answer 54

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.

Question 55

Mass-flow theory

Answer 55

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).

Question 56

Ringing

Answer 56

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.

Question 57

Tracer

Answer 57

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.