2.3 - transportation

• Adhesion


  The formation of hydrogen bonds between carbohydrates in the xylem vessel walls and water molecules. This contributes to the capillarity of water and transpiration pull.
• Adult haemoglobin


  Haemoglobin in an adult that has a lower affinity for oxygen than fetal haemoglobin. This enables the fetus to obtain oxygen from the mother's blood.
• Aorta


  The artery that takes oxygenated blood away from the heart to the body.
• Aphid


  A small insect that sucks sap through a mouthpart (known as a stylet) which is inserted into a sieve tube. The sap exuding from the stylet can provide evidence that sugars are carried in the phloem.
• Apoplast route

  One of three pathways by which water and minerals move across the root. Water moves through intercellular spaces between cellulose molecules in the cell wall.
• Arteriole

  A type of blood vessel that connects the arteries and capillaries. The walls of the arterioles contain large amounts of smooth muscle, some elastic fibres and some collagen.
• Artery


  A type of blood vessel that carries blood away from the heart to the tissues, under high pressure. The walls of the arteries contain collagen, smooth muscle and elastic fibres.
• Atrial systole

  The stage of the cardiac cycle in which the atria contract, pushing blood into the ventricles. The AV valves are pushed open fully and the atria are emptied of blood.
• Atrioventricular node (AVN)


  A group of cells located between the atria that slow down the wave of excitation and pass it between the ventricles, along the bundle of His.
• Atrioventricular (AV) valves

  The valves found between the atria and ventricles. They prevent the backflow of blood from the ventricles into the atria. There are two types of atrioventricular valves: bicuspid and tricuspid.
• Autoradiography


  A technique used to record the distribution of radioactive material within a specimen. Autoradiographs produced using carbon dioxide labelled with radioactive carbon can provide evidence for translocation occurring in the phloem.
• Bicuspid valves

  The atrioventricular valves found between the left atrium and left ventricle.
• Blood

  The transport medium in the mammalian circulatory system. It consists of plasma, red blood cells, white blood cells and platelets.
• Bohr effect

  The loss of affinity of haemoglobin for oxygen as the partial pressure of carbon dioxide increases.
• Bundle of His

  A collection of Purkyne fibres which run from the AVN down to the apex of the ventricles.
• Capillaries

  Microscopic blood vessels that form a large network through the tissues of the body and connect the arterioles to the venules. They are the site of exchange of substances between the blood and the tissues.
• Capillarity


  The tendency of water to move up the xylem, against gravity, due to adhesive forces that prevent the water column dropping back.
• Carbaminohaemoglobin


  A compound of carbon dioxide and haemoglobin that enables the transport of carbon dioxide in the blood.
• Carbonic acid


  A compound formed from water and carbon dioxide in the blood that dissociates to hydrogen and hydrogencarbonate ions.
• Carbonic anhydrase


  An enzyme that catalyses the reversible reaction between water and carbon dioxide to produce carbonic acid.
• Cardiac cycle


  Describes the sequence of events involved in one complete contraction and relaxation of the heart. There are three stages: atrial systole, ventricular systole and diastole.
• Casparian strip


  A waterproof strip surrounding the endodermal cells of the root that blocks the apoplast pathway, forcing water through the symplast route.
• Chloride shift


  The process by which chloride ions move into the erythrocytes in exchange for hydrogen carbonate ions which diffuse out of the erythrocytes. This is a one-to-one exchange and it maintains the electrochemical equilibrium of the cell.
• Circulatory system

  The transport system in animals.
• Closed circulatory system

  A circulatory system in which the blood pumped by the heart is contained within blood vessels. The blood does not come into direct contact with the cells. Closed circulatory systems are found in earthworms.
• Cohesion


  The formation of hydrogen bonds between water molecules. This contributes to the capillarity of water and plays an important part in maintaining the transpiration stream.
• Cohesion-tension theory


  The model that explains the movement of water from the soil to the leaves, in a continuous stream.
• Companion cells


  The active cells of the phloem located adjacent to the sieve tube elements. They retain their nucleus and organelles, producing ATP for metabolic processes in both themselves and the sieve tube elements.
• Cytoplasmic strands


  Small extensions of the cytoplasm between adjacent sieve tube elements and companion cells that allow communication and the exchange of materials. They also hold the nucleus in place.
• Diastole

  The stage of the cardiac cycle in which the heart muscle relaxes. The atria and ventricles fill with blood.
• Dicotyledonous plants

  Plants that produce seeds that contain two cotyledons. They have two primary leaves.
• Double circulatory system


  A circulatory system in which the blood flows through the heart twice in two circuits. Blood is pumped from the heart to the lungs before returning to the heart. It is then pumped around the body, after which it returns to the heart again. Double circulatory systems are found in mammals.
• Electrocardiogram (ECG)


  A technique used to indirectly measure the spread of electrical activity through the heart by measuring tiny changes in the skin's electrical conductivity. This produces a trace which is used to detect abnormalities in heart rhythm.
• Endodermis

  The innermost layer of the cortex of a dicotyledon root. It is impregnated with suberin which forms the Casparian strip. Endodermal cells actively transport mineral ions into the xylem.
• Erythrocyte

  A type of blood cell that is anucleate and biconcave. It contains haemoglobin which enables the transport of oxygen and carbon dioxide to and from the tissues.
• Fetal haemoglobin


  Haemoglobin in a fetus that has a higher affinity for oxygen than adult haemoglobin due to the presence of two different subunits that allow oxygen to bind more readily. This enables the fetus to obtain oxygen from the mother's blood.
• Haemoglobin


  The red pigment found in erythrocytes that binds reversibly with four oxygen molecules to form oxyhaemoglobin. It is a globular protein that consists of four polypeptide chains, each with a prosthetic haem group.
• Hydrophytes


  Plants that are adapted to live and reproduce in very wet habitats, e.g. water lilies.
• Hydrostatic pressure


  The pressure exerted on the sides of a vessel by a fluid.
• Inferior vena cava


  The vein that returns deoxygenated blood to the heart from the lower body.