biology

• Heart

  Double pump
• Oxygenated blood flow

  1. Enters left side of heart

  2. Pumped to rest of body (systemic circuit)
• Left ventricle

  • Thicker muscle wall than right ventricle
  • Pumps blood at high pressure around entire body
• Deoxygenated blood flow

  1. Enters right side of heart

  2. Pumped to lungs (pulmonary circuit)
• Right ventricle

  • Pumps blood at lower pressure to the lungs
• Septum

  • Muscle wall that separates the two sides of the heart
• Blood flow

  • Pumped towards heart in veins
  • Pumped away from heart in arteries
• Coronary arteries

  Supply cardiac muscle tissue of the heart with oxygenated blood
• Heart is a muscle

  Needs constant supply of oxygen and glucose for aerobic respiration to release energy to allow continued muscle contraction
• Valves

  • Present to prevent blood flowing backwards
• Pathway of blood through the heart

  1. Deoxygenated blood flows through vena cava into right atrium

  2. Atrium contracts, blood forced through tricuspid valve into right ventricle

  3. Ventricle contracts, blood pushed through semilunar valve into pulmonary artery

  4. Blood travels to lungs, moves through capillaries past alveoli for gas exchange

  5. Low pressure blood flow prevents damage to lung capillaries

  6. Oxygenated blood returns via pulmonary vein to left atrium

  7. Atrium contracts, blood forced through bicuspid valve into left ventricle

  8. Ventricle contracts, blood forced through semilunar valve out through aorta

  9. Thicker muscle walls of left ventricle produce high pressure for blood to travel around body
• Platelets

  • Involved in blood clotting
  • Involved in forming scabs where the skin has been cut or punctured
• Platelets' role when skin is broken

  1. Platelets arrive

  2. Series of reactions occur within the blood plasma

  3. Platelets release chemicals

  4. Soluble fibrinogen proteins convert into insoluble fibrin

  5. Insoluble mesh forms across the wound, trapping red blood cells

  6. Clot forms
• Clot

  Eventually dries and develops into a scab to protect the wound from bacteria entering
• The importance of blood clotting

  • Blood clotting prevents continued / significant blood loss from wounds
  • Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that could cause infection
  • It remains in place until new skin has grown underneath it, sealing the skin again
• Main types of blood vessel

  • Arteries
  • Veins
  • Capillaries
• Arterioles

  Smaller vessels that branch off from arteries
• Venules

  Smaller vessels that branch into veins
• Each vessel has a particular function and is specifically adapted to carry out that function efficiently
• Arteries

  • Carry blood at high pressure away from the heart
  • Carry oxygenated blood (except the pulmonary artery)
  • Have thick muscular walls containing elastic fibres
  • Have a narrow lumen
  • Blood flows through at a fast speed
• Structure of an artery is adapted to its function

  1. Thick muscular walls containing elastic fibres withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through

  2. A narrow lumen also helps to maintain high pressure
• Veins

  • Carry blood at low pressure towards the heart
  • Carry deoxygenated blood (other than the pulmonary vein)
  • Have thin walls
  • Have a large lumen
  • Contain valves
  • Blood flows through at a slow speed
• Structure of a vein is adapted to its function

  1. A large lumen reduces resistance to blood flow under low pressure

  2. Valves prevent the backflow of blood as it is under low pressure
• Capillaries

  • Key features:
  • Carry blood at low pressure within tissues
  • Carry both oxygenated and deoxygenated blood
  • Have walls that are one cell thick
  • Have ‘leaky’ walls
  • Speed of blood flow is slow
  • The structure of a capillary is adapted to its function in the following ways:
  • Capillaries have walls that are one cell thick (short diffusion distance) so substances can easily diffuse in and out of them
  • The ‘leaky’ walls allow blood plasma to leak out and form tissue fluid surrounding cells
• Arterioles and venules

  • As arteries get further away from the heart, they divide more and get narrower
  • The narrow vessels that connect arteries to capillaries are called arterioles
  • Veins also get narrower the further away they are from the heart
  • The narrow vessels that connect capillaries to veins are called venules
• Trophic levels

  Used to describe the feeding relationships between organisms
• Energy flow

  1. From the sun to the first trophic level (producers) in the form of light

  2. Producers convert light energy into chemical energy

  3. Energy flows in this form from one consumer to the next

  4. Eventually, all energy is transferred to the environment

  5. Energy is passed on from one level to the next with some being used and lost at each stage
• Energy flow is a non-cyclical process - once the energy gets to the top of the food chain or web, it is not recycled but 'lost' to the environment
• This is in direct contrast to the chemical elements that organisms are made out of, which are repeatedly recycled
• • Animals (known as consumers) can be at different trophic levels within the same food web as they may eat both primary, secondary and/or tertiary consumers