mass transport

• Single Circulatory System


  A system where blood is not confined to blood vessels and only passes through the heart once, smaller animals have this system
• Mass Transport System


  This system exists when organisms have:

  - A large surface area to volume ratio (simple diffusion cannot accommodate for the organisms)

  - A large activity of the organism (require more substances at one time than smaller organisms)
• Arteries


  Vessels that carry blood away from the heart and to arterioles at a high pressure. Most layers are thick so that they can function correctly and efficiently
• Arterioles


  Vessels that control blood flow from arteries to capillaries. Layers are thinner than arteries due to lower blood pressure
• Capillaries


  Tiny vessels that link arterioles to veins. These have branched networks to allow for a larger total surface area across the body, as they are so thin but have a vast network, no cell is too far away from one
• Veins


  Vessels that carry blood towards the heart from capillaries. Layers are very thin with a large lumen to ensure pressure is very low
• Basic Structure of Arteries, Arterioles and Veins

  Consist of:

  - Tough fibrous outer layer which resists internal and external pressure changes

  - Muscle layer which can contract to control blood flow

  - Elastic layer which maintains blood pressure by stretching and springing back (recoiling)

  - Endothelium which is a smooth layer that reduces friction

  - Lumen which is the central cavity
• Contents of Blood


  Contains:

  - Oxygen

  - Glucose

  - Platelets (proteins)

  - Plasma

  - Red blood cells

  - White blood cells

  - Hormones

  - Antibodies

  - Urea

  - Amino acids
• Fluid in Circulatory System

  These are all associated with the circulatory system:

  1) Blood

  2) Tissue fluid

  3) Lymph
• Tissue Fluid


  A fluid that allows cells to receive the contents of blood and utilise these products to stay alive and functioning. It is formed due to hydrostatic pressure and osmosis
• Capillary Network


  Where tissue fluid is formed
• Hydrostatic Pressure


  The pressure of the blood as the heart beats. This forces fluid and nutrients from the capillaries. A small amount of this pressure forces some fluid back into the network. But the net movement is out of the capillary network
• Osmotic Pressure


  The pressure that occurs due to sudden changes in water potential, moving water back into the capillary network via osmosis, where the water potential is lower
• Lymph Vessel


  The location where excess tissue fluid is drained, this is where tissue fluid is converted into lymph
• Swelling


  If you have fewer lymph nodes, then there is a lower likelihood of you being able to drain tissue fluid which could lead to this problem. The only way to heal this is by giving the body time to drain the tissue fluid
• Xylem


  The part of a plant which brings water up through the roots of the plant and transports the water and nutrients to different parts of the plant; mainly to the leaves
• Transpiration


  The loss of water from a leaf via the stomata (evaporation)
• Cohesion


  What allows for water to "stick together" and form unbroken columns across the mesophyll layer
• Transpiration Pull


  The reason water is pulled up through the plant when the plant has undergone transpiration
• Cohesion-Tension Theory


  The theory in which the xylem is put under pressure due to tension which creates a negative pressure in the xylem
• Mass Flow Theory


  The theory by which sucrose molecules move from the source to the sink via various mechanisms throughout the phloem, this is the overall theory behind the mechanism of translocation
• Sink


  The location which requires sucrose in a plant, which is received from the source
• Source


  The location that produces sucrose (the leaf) and transports this sucrose to the sink
• Transfer of Sucrose into Sieve Tubes

  Sucrose is produced by the leave due to photosynthesis at the chloroplasts. The sucrose then travels via facilitated diffusion into the companion cells of the source.

  Hydrogen ions then move via active transport from the companion cells into the spaces within cell walls.

  The sucrose and hydrogen ions then undergo co-transport and travel into the sieve tube elements
• Mass Flow of Sucrose through Sieve Tubes


  As the sucrose and hydrogen ions are transported into the sieve tube elements, the sieve tubes now have a lower water potential.

  This stimulates water movement from the xylem, into the phloem via osmosis - increasing the hydrostatic pressure within this sieve tube element.

  Sucrose is then actively transported into the sieve tube elements (due to the hydrostatic pressure gradient) closer to the sink, decreasing the hydrostatic pressure in the other sieve tube elements.

  From there, the sieve tube elements transport the sucrose into the sink via active transport. Water also moves into these sieve tubes via osmosis due to the water potential gradient.

  The sink can then break down the sucrose in respiration or store the sucrose for later respiratory functions
• Supporting Mass Flow


  Evidence surrounding mass flow theory include:

  - There is a pressure within sieve tubes that is shown when sap seeps out of cut stems

  - Sucrose levels increase in the source, then the sink shortly after

  - There is a higher concentration of sucrose in the source than the sink

  - Downward flow in the phloem only occurs in daylight

  - Companion cells contain many mitochondria so readily produce ATP
• Opposing Mass Flow


  Evidence surrounding mass flow theory include:

  - The function of sieve plates is unclear as they seem to slow down the mass flow process

  - If mass flow was true, then the solutes should move at a constant speed

  - Sucrose is delivered throughout the plant, regardless of how much sucrose is required at each sink, rather than having a subjective amount of sucrose delivered to the cells that require more sucrose
• Rigging Experiment


  An experiment in which:

  - The phloem and protective layer of a woody stem is removed

  - The stem above the removed contents swells with fluid containing sugars and dissolved molecules

  - The stem below wither and die

  - Suggesting that the phloem, not the xylem, is responsible for the transport of nutrients
• Tracer Experiment


  An experiment in which:

  - The plant is grown in an area containing the radioactive isotope, carbon-14, within the carbon dioxide (14CO2)

  - This means that the sugars that are manufactured by the plant are radioactive and can be traced using auto-radiography

  - An X-Ray film would show where these radioactive substances have travelled and show that the phloem is responsible for this transport
• Evidence of Translocation in the Phloem

  Evidence includes:

  - Organic molecules flow out of the phloem when cut

  - When plants absorb radioactive carbon, the phloem then has this radioactivity present within it moments later

  - Aphids that feed on plants have needle-like mouths so can extract the contents of sieve tube elements

  - The removal of the ring of phloem around the circumference of the stem leads to a build up of organic molecules and sugars above that ring
• Using a Potometer


  An experiment in which:

  - A leafy shoot is cut under water, without the leaves getting wet

  - The potometer is completely filled with water (no bubbles)

  - All joints are sealed with waterproof jelly when the potometer is removed

  - One air bubble is introduced in the capillary tube

  - The distance moved by this bubble over a set amount of time is measured

  - Using the mean value we can calculate how much water is lost within the set time, including plotting a graph

  - To start the experiment again, the water from a "reservoir" pumps the air bubble back into its starting position

  
• Haemoglobin


  A molecule within blood that is comprised of four polypeptide chains with four ferrous groups, also known as haem groups.

  There are different types of these depending on the animal, some can load oxygen better than others, whilst some can unload oxygen better than others

  
• Association


  The loading of oxygen onto a haemoglobin molecule
• Dissociation


  The unloading of oxygen from a haemoglobin molecule
• Oxygen Dissociation Curve


  A graph which shows how oxygen is saturated onto haemoglobin molecules

  
• High Affinity


  Haemoglobin that can load oxygen very easily, has a shift to the left of the oxygen dissociation curve as it is easier to load and takes less time to become saturated
• Low Affinity


  Haemoglobin that can unload oxygen very easily, has a shift to the right of the oxygen dissociation curve as it is harder to load and takes more time to become saturated
• Positive Cooperativity


  As oxygen binds to the first haem group, a change in the quaternary structure of the haemoglobin makes association easier for the other oxygen molecules (other than the final one which rarely associates)
• Probability


  The reason why the fourth haem group isn't always saturated despite positive cooperativity making the haemoglobin a more ideal quaternary structure for association
• Partial Pressure


  A way in which you measure the concentration of a specific gas within an area where there is a range of molecules