Mass transport

• Micelle formation+lipid absorption: fatty acids+monoglycerides leave micelles and enter epithelial cell, fatty acids form triglyceride, fatty globules combine with proteins and form chylomicrons, chylomicrons are removed from cell and lymph transports chylomicrons away from intestine
• tissue fluid forms at the atrial end of capillary, high hydrostatic pressure forces fluid from blood plasma out of capillary, forming tissue fluid
• tissue fluid contains few proteins as most are to large to move out of gaps in capillary walls
• haemoglobin is a quaternary protein made up of 4 polypeptide chains with a haem group
• haemoglobin has a high affinity for oxygen
• the process which haemoglobin binds with oxygen is called oxygen loading or oxygen associating
• the process which haemoglobin releases oxygen is called unloading or dissociation-this takes place in respiring tissues
• on an oxygen dissociation graph, the further to the left the curve is, the greater the affinity for oxygen, meaning oxygen is loaded more readily but inloaded less readily.
• on an oxygen dissociation graph, if the curve is further to the right, there is a lesser affinity for oxygen meaning oxygen is less readily loaded but readily unloaded.
• larger mammals (like elephant) have a higher affinity for oxygen as they have a low SA:VOL ratio and low metabolic rate per G, so doesn’t need to release as much oxygen
• xylem structure: made of dead cells, has lignin and thick cell wall to withstand pressure,
• xylem is used to transport water and dissolved minerals from roots to the rest of the plant
• transpiration pull= negative pressure at the top of xylem pulls water up, caused by the loss of water through evapouration on the leaf
• adhesion- water forms hydrogen bonds with cellulose in xylem lining
• cohesion- water form hydrogen bonds with each other, helping to hold the water molecules together and pull them up the xylem
• The factors effecting transpiration are: Light intensity, Temperature, Air movement and humidity
• rate of transpiration is measured using a potometer
• translocation= the movement of dissolved substances such as sucrose and amino acids from the leaves to the rest of the plant
• the source- (leaves) the part of the plant that loads assimilates into phloem sieve tubes
• the sink-(roots) the part of the plant that removes assimilates from phloem sieve tubes
• structure of phloem cells= living cells, sieve plate at ends of cells, have companion cells
• process of translocation- water potential is effected by concentration of sugars, osmosis creates changes in w.p and create a pressure gradient, active transport is then involved with movement of sucrose
• digestion of lipids- bile emulsifies lipids and breaks them down to smaller drop of fat so it is easier for lipase to hydrolyse them
• The Bohr effect is when an increase in co2 levels pushes the line on the oxygen dissociation graph further right meaning more oxygen is release to respiring tissues
• Cohesion tension theory- transpiration of water through stomata occurs when the water potential of the leaf is lower than the water potential of the air so water is pulled up from xylem creating negative pressure, a water column is formed by hydrogen bonds between water molecules
• the mass flow hypothesis is : Sucrose moves from companion cells into sieve tube elements by active transport. This reduces the water potential of the sieve tube element.
• how is the sieve tube element adapted for mass transport?

  • it has few organelles and very little cytoplasm so there is an easier flow of substances
• How is companion cell adapted for transport of sugars between cells? - mitochondria release energy from ATP for active transport to take place
• explain how water from tissue fluid is returned to circulatory system

  • plasma remains in the blood, creating a water potential gradient
  • water moves via osmosis and returns to blood by lymphatic system
• how is pressure generated in the phloem?

  • sucrose is actively transported out of phloem
  • causing a lower water potential
  • so water moves into phloem by osmosis
• what is digestion?


  the hydrolysis of large insoluble molecules into smaller molecules that can be absorbed across membranes
• how can tracers be used to show transport in plats?

  radioactive substances are supplies to the leaf got the plant, we can then detect the movement of the substances throughout the plant
• a limitation of the mass flow hypothesis is the fact that not all solutes move at the same speed, like mass flow hypothesis believes
• Explain why oxygen uptake is a measure of metabolic rate in organisms?

  Oxygen is used in respiration, which provides

  energy in the form of ATP
• describe the process of translocation/transport of sugars in plants:

  • sucrose is actively transported into the phloem/sieve element
  • By companion cell
  • This Lowers water potential in phloem/sieve element
  • water enters by osmosis
  • This Produces high pressure
  • Mass transport towards sink/roots
  • At sink/roots sugars are unloaded