Complete A level Biology Flashcards

• Why cant complex multi cellular organisms rely on diffusion to transport substances around the body?

  They are too large for diffusion to transport substances quickly enough
• Open circulatory system


  Blood is not contained in blood vessels but circulates in large spaces
• How does blood circulate in an open circulatory system


  A simple heart pumps blood out into the cavities surrounding the organs. The heart muscle relaxes so the pressure decreases and blood is drawn from the cavity back into the heart through open valves
• Closed circulatory system


  Blood is enclosed in tubes.
• Why is a closed circulatory system more efficient


  The blood is forced through fairly narrow tubes so it travels faster and under pressure.
• Valves


  Prevent the backflow of blood
• Single closed circulatory system


  The blood is pumped through the heart once for each complete circuit
• Double closed circulatory system

  The blood is pumped through the heart twice for each complete circuit
• Why is a double closed circulatory system good


  Substances needed can be delivered rapidly to cells as the blood is given an extra boost which decreases the time taken for the blood to circulate around the whole body.
• Mass transport system


  Carries raw material from specialised exchange organs to the body cells to remove metabolic waste
• Mass flow


  The process where all the particles are transported in one direction
• Why is water a polar molecule


  Oxygen is more electronegative than Hydrogen so there is a slight difference in charge between the atoms.
• Why does water remain a liquid over a wide range of temperatures

  Hydrogen bonding holds water molecules together and collectively they make water very stable
• Why is water cohesive


  the delta positive H is attracted to the delta negative O. This helps water to flow so it is good at transporting substances
• Why is water a good solvent


  Polar molecules and ionic substances dissolve in water because water is dipolar. The forces of attraction between the delta positive H and the delta negative O are stronger than the ionic bonds so the ions become hydrated and completely surrounded by water molecules
• Why is the left ventricle thicker than the right


  It needs more muscle to contract so it can pump blood powerfully to the whole body. The right ventricle only pumps blood to the nearby lungs
• Why are the atria walls thinner than the ventricles?


  The atria pump blood to the ventricles which is nearby but the ventricles pump blood out of the heart
• Where do the arteries and veins pump blood

  Arteries pump blood away from the heart and the veins pump blood towards the heart
• Structure of the arteries

  Thick walls, muscular, elastic tissue in walls, narrow lumen, no valves. No valves as it carries blood under high pressure. Elastic tissue allows them to recoil
• Structure of the veins


  Thinner walls, very little elastic or muscle tissue because the blood is not being carried under high pressure. Valves and wide lumen
• Structure of the capillaries

  Very narrow lumen for short diffusion distance, single layer of cells so it can lie very close to the cells. joins the arteries and venules together, medium pressure, large surface area
• What is the function of the capillaries

  Where metabolic exchange occurs so substances are exchanged between cells and the capillaries
• Describe the stretch and recoil in arteries

  Heart contracts and blood is forced into the arteries. The elastic walls stretch a little to accommodate the blood. The heart relaxes and the elasticity of the walls causes them to recoil a lot behind the blood pushing it forward. This causes a pulsing flow through the arteries
• Describe how blood flows in veins

  Blood flow is assisted by the contraction of skeletal muscles during movement of limbs and breathing. Low pressure in thorax when breathing draws blood back into the heart from veins
• Cardiac cycle


  The ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating around the body
• When are the atrioventricular valves open


  During Atrial systole and Cardiac diastole
• When are the semilunar valves open


  During Ventricular systole
• Atrial Systole


  Blood returns to the heart due to the contraction of skeletal and gaseous exchange muscles. Blood under pressure flows into the atria from the pulmonary vein and vena cava. As atria fills, the pressure against the atrioventricular valves pushes them open so blood leaks into the ventricles
• Ventricular systole


  Ventricles contract after a short delay from the base upwards so the pressure in the ventricles increases as the volume decreases. Pressure becomes higher in the ventricles than the atria so the AV valves close to prevent blood flowing back into the atria. The pressure in the ventricles is higher than in the aorta and pulmonary artery so the SL valves are forced open. Blood is forced into the arteries
• Cardiac Diastole


  Ventricles and atria relax. Higher pressure in the arteries close the SL valves to prevent backflow into the ventricles. Blood returns to the heart and the atria fill again due to higher pressure in the veins which increases the pressure in the atria. As ventricles continue to relax, pressure falls below the pressure in the atria so the AV valves open. Blood flows passively into the ventricles from the atria. Atria contracts and process starts again
• Atherosclerosis


  The hardening of arteries due to build up of plaque which blocks/narrows the arteries
• Endothelium dysfunction


  The endothelium becomes damaged. Damage could be due to high blood pressure or toxins from cigarette smoke.
• Inflammatory response


  White blood cells leave the blood vessel and move into the artery wall
• How does an atheroma form


  White blood cells accumulate chemicals especially cholesterol and this deposit builds up
• Plaque formation


  Calcium salts and fibrous tissue also build up forming a hard swelling called a plaque on the inner artery wall. This build up of fibrous tissue causes the artery wall to lose some elasticity so it hardens.
• Dangerous positive feedback


  Plaque makes the arteries narrower so blood flow is restricted and the blood pressure increases
• How can an atheroma increase the risk of thrombosis in arteries

  An atheroma can rupture the endothelium fo an artery, damaging the wall and leaving a rough surface. This triggers thrombosis at the rupture site
• How can blood clots cause heart attacks, stroke or DVT


  Blood clot can cause a complete blockage of the artery or it can become dislodged and block a blood vessel elsewhere. The blood flow is restricted so less oxygen can reach tissues causing damage
• Thrombosis


  Used by the body to prevent lots of blood from being lost when a blood vessel is damaged
• Where is thromboplastin released from


  It is a protein released from the damaged blood vessel and from platelets which have stuck to the damaged blood vessel wall