Chapter 4

• Heart


  Organ that pumps blood around the body
• Heart


  • Made from cardiac muscle tissue
  • Supplied with oxygen by the coronary artery
• Heart rate


  Controlled by a group of cells in the right atrium that generate electrical impulses, acting as a pacemaker
• Artificial pacemaker


  Used to control irregular heartbeats
• Artery


  • Carries blood away from the heart (high pressure)
  • Thick, muscular, and elastic walls
  • Walls can stretch and withstand high pressure
  • Small lumen
• Vein


  • Carries blood to the heart (low pressure)
  • Have valves to stop blood flowing the wrong way
  • Thin walls
  • Large lumen
• Capillary


  • Carries blood to tissues and cells
  • Connects arteries and veins
  • One cell thick - short diffusion distance for substances to move between the blood and tissues
  • Very narrow lumen
• Double circulatory system


  • Blood passes through the heart twice for every circuit around the body
  • Right ventricle pumps blood to the lungs where gas exchange takes place
  • Left ventricle pumps blood around the rest of the body
• 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
• 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)
• Oxygen then diffuses into the blood in the network of capillaries over the surface of the alveoli
• Transpiration


  Movement of water from the roots to the leaves through the xylem
• Translocation


  Movement of dissolved sugars from the leaves to the rest of the plant through the phloem
• Factors affecting the rate of transpiration

  • Temperature
  • Humidity
  • Wind speed
  • Light intensity
• Higher temperature


  Increases the rate of transpiration
• Lower humidity


  Increases the rate of transpiration
• More wind


  Increases the rate of transpiration
• Higher light intensity


  Increases the rate of transpiration
• Xylem


  Transports water and mineral ions from the roots to the rest of the plant
• Xylem


  • Made of dead cells
  • No end wall between cells
  • Walls strengthened by lignin to withstand water pressure
• Phloem


  Transports dissolved sugars from the leaves to the rest of the plant
• Stomata


  Tiny openings on the lower surface of the leaf that allow gases to move into and out of the leaf
• Guard cells


  Control the opening and closing of the stomata
• Leaf


  • Contains many tissues that work together to perform photosynthesis
• Upper epidermis


  • Single layer of transparent cells allow light to pass through
  • Cells secrete a waxy substance that makes leaves waterproof
• Palisade mesophyll


  • Tightly packed cells with lots of chloroplasts to absorb as much light as possible for photosynthesis
• Spongy mesophyll


  • Air spaces increase the surface area and allow gases to diffuse quickly
• Most stomata are found on the underside of leaves, which reduces water loss through evaporation