Unit 2.3 a

• The interventrucular septum is the muscular wall seperating the left and right chambers of the heart
• The coronary sinus brings blood from the coronary arteries.
• Veins bring blood to the heart
• Arteries bring blood away from the heart and around the body
• Papillary muscles are muscles controlling the opening and closing of the valves
• The bicuspid valve is between the left atrium and ventricle. It has 2 'flaps' to prevent the backlog of blood.
• The tricuspid valve is found between the right atrium and right ventricle. It has 3 'flaps' which prevents the backflow of blood.
• The heart is myogenic, meaning that it needs no nervous stimulation to contract and relax. Cardiac muscle is a specialised tissue which is capable of rhythmical contraction.
• Atrium recieve blood from the veins
• Ventricles have thick muscle walls to increase pressure and force blood into the arteries.
• Valve tendons keep the valves shut and prevent them from being Inverted.
• Coronary arteries supply the heart with blood. They are responsible for the heart's oxygen and glucose supply.
• The sinoatrial node (SAN) in the right atrium is the pacemaker. The SAN is spontaneously active, it is a region of specialised cells which initiates waves of electrical excitation that spreads across the atria causing them to contract at the same time.
• The wave of electrical excitation is prevented from spreading to the ventricles by a thin layer of connective tissue, which acts as a layer of insulation.
• The AVN (atrioventricular node) is another specialised region of cardiac cells between the 2 atria. The excitation wave travels through the nerves of Bundle of his, to the apex of the ventricles. Bundle branches of purkinje fibres (specialised cardiac muscle fibres) in the ventricle walls carry the wave of excitation upwards through the ventricles muscle. Ventricular contraction starts from the apex (the bottom of the ventricles) upwards through the ventricles muscle.
• The AV node provides the only pargway for the transition of the electric excitation wave from artia to ventricles. This means that there will always be a delay between the atria and ventricles contracting.
• The SA node initiates the heartbeat however the rate can very due to hormones (such as adrenaline) and the nervous system. If blood pressure is too high, impulses are sent to and from the brain (the medulla) to decrease the heart rate which in turn lowers the blood pressure.
• Atrial systole refers to the atria contracting. It lasts approximately 0.1 seconds. The ventricles relax, and the atria contracts, increasing the blood pressure in the atria and therefore forcing blood through the valve to the ventricles.
• Ventricular systole refers to the contraction of the ventricles, which occur after atrial systole. Ventricular systole lasts for 0.3 seconds. The atria relax, and the ventricles contract. This increases the blood pressure in the ventricles

  The atrioventricula valves close once the pressure in the ventricles exceeds the pressure of the atria. The semilunar valves open once the pressure in the ventricles exceed the pressure in the arteries. Blood is pumped into the arteries and through the valves.
• Diastole refers to the relaxation of the heart. It lasts for approximately 0.4 seconds. Blood pressure in the ventricles decreases and so semilunar valves close once the pressure in the arteries exceeds the ventricular pressure. The atria relaxes, allowing blood to enter. The atrioventricular valves open once the atrial pressure exceeds the ventricular pressure.
• The first sound of the heartbeat, referred to as 'lub' is the sound of blood pushed against the atrioventricular valves after the close due to the pressure difference in the atria and ventricles.
• The second sound of the heartbeat, referred to as 'dub' is the sound of blood pushing against the seminar valves right after they close due to pressure differences between the ventricles and the arteries.
• Multicellular organisms must have transport systems to transport oxygen and nutrients to all cells, and to transport carbon dioxide and waste away from cells.
• Transport system features:

  A medium to carry materials, a pump to move the medium, valves to maintain blood flow in one direction, a respiratory pigment to increase the oxygen carrying capacity of the blood, a system of vessels to distribute the medium to all cells.
• Open circulatory systems are found I insects. It consists of a dorsal, tube shaped body that runs the length of the body. Pumps blood at low pressure into a space called a haemocoel within the body cavity. The blood is in direct contact with tissues for the exchange of materials. Little control is had over the direction of circulation. Blood returns to the heart.
• Insects have no respiratory pigments in the blood to carry oxygen as insects have trachea as the respiratory surface.
• Closed circulatory systems are used in earthworms. They contain blood within tubes (vessels) and organs are not in direct contact with the blood unlike in open circulatory systems. Materials diffuse through the vessel walls into the cells. A muscular heart pumps blood at high pressure
• Survival of a plant depends on balancing water uptake and water loss
• Root hair cells increase surface area for absorbtion. The more surface area, the more absorbtion.
• Epidermis is present in root hairs to protect them as they grow through the soil. It is the outer layer of the root hair.
• Cortex parenchyma can act as a storage organ of the root tissue. Intercellular spaces allow movement of water and ions.
• The endothermic has a waterproof layer that forces water and ions into the cytoplasm of the endometrial cells and controls transport into the xylem.
• Pericycle has a role in controlling transport into the zylem. It is the site of lateral growth.
• The xylem transports water and ions from the roots to the stem and leaves. Provides support for the plant.
• The phloem transports the products of phtoosynthesis to the root from the leaves
• The cambium is a meristematic tissue that can undergo mitosis to produce more xylem and phloem
• An open circulatory systems is when blood 'bathes' cells amd organs and is not enclosed in blood vessels. There is no haemoglobin as oxygen is transported in the tracheal system.
• All arthropods have an open circulatory system
• A closed circulatory system is when blood is enclosed in blood vessels. Blood contains haemoglobin from which oxygen will diffuse into cells.
• Fish, mammals and earthworms have a closed circulatory system