B4 Organisation in animals

• Levels of organisation in living organisms


  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organisms
• Tissue


  A group of cells with similar structures and functions
• Organ


  A group of tissues working together to perform a specific function
• Organ system


  Groups of organs working together, forming an organism
• Digestive system


  • Pancreas makes enzymes: amylase, lipase, and protease
  • Liver makes bile
• Small intestine


  • Where digested food is absorbed into the blood
• Large intestine


  • Where water and minerals are absorbed into the blood
• Breathing in


  1. Air moves into the body through the mouth and nose

  2. Down the trachea

  3. Into the bronchi

  4. Through the bronchioles

  5. Into the alveoli (air sacs)
• Lungs


  • Oxygen diffuses into the blood in the network of capillaries over the surface of the alveoli
• Components of blood


  • Red blood cells
  • Plasma
  • Platelets
  • White blood cells
• Red blood cells


  Bind to oxygen and transport it around the body
• Plasma


  Transports substances and blood cells around the body
• Platelets


  Form blood clots to create barriers to infections
• White blood cells


  Part of the immune system to defend the body against pathogens
• Blood


  A tissue made up of the four main components
• Arteries


  • Carry blood away from the heart (high pressure)
  • Have thick, muscular, and elastic walls
  • Have a small lumen
  • Often have valves to stop blood flowing the wrong way
• Veins


  • Carry blood to the heart (low pressure)
  • Have thin walls
  • Have a large lumen
• Capillaries


  • Carry blood to tissues and cells
  • Connect arteries and veins
  • Have a one cell thick wall for short diffusion distance
  • Have a very narrow lumen
• Heart


  • Pumps blood around the body
  • Made from cardiac muscle tissue
  • Supplied with oxygen by the coronary artery
• Double circulatory system


  Blood passes through the heart twice for every circuit around the body
• Heart rate is controlled by a group of cells in the right atrium that generate electrical impulses, acting as a pacemaker
• Artificial pacemakers can be used to control irregular heartbeats