15: Transport systems

• Diffusion

  The net movement of substances from a region of higher concentration to a region of lower concentration, without requiring energy
• Osmosis

  The net movement of water molecules from a solution of higher water potential to a solution of lower water potential, through a partially permeable membrane, without requiring energy
• Concentration gradient

  The higher the concentration gradient, the higher the rate of diffusion
• Temperature

  The higher the temperature, the higher the rate of diffusion
• Mass of particle

  The higher the mass of a particle, the slower it diffuses
• Medium

  Diffusion is faster through a gas than a liquid, and very slow or impossible through a solid
• Surface area to volume ratio

  The larger the surface area to volume ratio, the faster the rate of diffusion
• Unicellular organisms


  Organisms consisting of a single cell, which can obtain nutrients and remove waste directly from/to their surrounding environment by diffusion and osmosis
• Multicellular organisms


  Organisms consisting of many cells, which require a transport system to distribute substances around the body as simple diffusion and osmosis are not sufficient
• Transport systems


  • Necessary for multicellular organisms to:

  1. Obtain nutrients for cells
  2. Remove metabolic waste from cells
• Xylem

  Plant transport tissue that transports water and mineral salts from the roots to the rest of the plant
• Phloem

  Plant transport tissue that transports sucrose and amino acids from the leaves to the other parts of the plant
• Human circulatory system


  • Consists of the heart, blood vessels, and blood, which transport nutrients and metabolic waste around the body
• Components of human blood

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

  Blood vessels that carry blood away from the heart
• Capillaries


  Blood vessels that are the site of exchange of substances between blood and body cells
• Veins


  Blood vessels that carry blood back into the heart
• Drug abuse


  Can affect the nervous system, cardiovascular system, and lead to addiction
• Platelets


  Triggers a series of chemical reactions to form blood clot to prevent excessive bleeding
• white blood cells


  protects the body against harmful organisms
• red blood cells

  transport oxygen from the lungs to the rest of the body
• red blood cells adaptations

  contains haemoglobin- binds to oxygen & no nucleus- RBC more space to contain more haemoglobin thus carry more oxygen & biconcave shape increases surface area to volume ratio for faster diffusion of oxygen into and out of RBCs & flexible cell surface membrane to allow RBC to bend to move through narrow capillaries
• plasma


  transports dissolved substances around the body
• artery structure


  thick, muscular elastic wall to withstand high pressure and has narrow lumen
• capillary structure

  has one cell thick wall to shorten diffusion distance of substances
• vein structure


  thinner and less muscular wall and wide lumen and also contains semilunar valves to prevent back flow of blood
• xylem structure

  xylem vessels have thick lignified walls to provide mechanical support to the plant. have hollow lumen to all water to pass through without obstruction. narrow lumen to allow water to pass through quickly
• Is the xylem and phloem inside or outside

  Xylem inside

  phloem outside
• Examples of movement of substances by diffusion in multicellular organisms (plants )

  root hair cells of plants absorb oxygen and mineral salts by diffusion
• Examples of movement of substances by diffusion in multicellular organisms (Humans)

  • oxygen gas diffuses from the lungs into the bloodstream
  • carbon dioxide gas diffuses from the bloodstream into the lungs
  • digested food diffuses from the illeum to the bloodstream
• Examples of movement of substances by osmosis in multicellular organisms (plants)

  Root hair cells of plants absorb water molecules from the surrounding soil by osmosis
• Examples of movement of substances by osmosis in multicellular organisms (humans)

  Water molecules are absorbed into the bloodstream at the ileum and the colon by osmosis
• Osmosis in the root cells

  There are more water molecules present in the soil than in the root cells of plants. Root hair cells have cell membranes that are partially permeable. Water molecules enter the root hair cells through osmosis
• Diffusion in the roots

  As the xylem in the plant transports mineral salts away from the roots to the rest of the plants, the root cells have lower concentration of mineral salts. Thus the root cells get a continuous supply of mineral salts from the soil via diffusion