Mass transport Flashcards
What does it mean when the heart is a ‘double pump system’?
This means that blood stays in the vessels and passes through each circuit of the heart twice
Describe the structure of the atria
Thin muscled wall
Elastic tissue to stretch and expand to collect as much as possible
Describe the structure of the ventricles
Thick muscled walls to withstand high-pressure so it can contract strongly to pump blood around the body and lungs
What are the names of the atrioventricular valves?
Left AV = Bicuspid valve
Right AV = Tricuspid valve
What is systole and diastole
Systole - When the heart is pumping blood
Diastole - When the heart is relaxing as blood fills the chambers
Describe the steps of the cardiac cycle
- The heart is in atrial diastole as blood flows from the vena cava into the pulmonary vein. Volume and pressure start to increase in the atria
- The heart is now in atrial systole as the atria are at their full capacity, the pressure difference between the ventricle and atria causes the atrioventricular valves to open and the atria does a weak contraction as most blood falls naturally into the ventricles. Volume and pressure increases in the ventricles cause the atrioventricular valves to close
- The heart is now in ventricular systole, pressure is highest in the ventricles causing AV valves to shut and causing the semilunar valves to open, as blood is forced up above the semilunar valves causing the pressure difference to cause the semi lunar valves to shut
Describe how a heartbeat is initiated and coordinated
The Sinoatrial node sends an electrical impulse across both atria causing atrial systole and forcing blood down to the ventricles, however, a delay is needed to allow all blood to empty the atria so then the electrical impulse is cut off by the Non conducting tissue between the atria and ventricle. Atrioventricular node delays the impulse whilst blood leaves the atria and fills up the ventricle, first contraction is from base to top at high pressure. A new impulse is sent out from the Atrioventricular node down the bundle of His and up and around the Purkinje fibres.
Describe the structure of arteries
Thicker muscular walls than veins which can be dilated and constricted to control volume of blood flowing through them.
Thicker elastic wall, when pressure gets to high it can reach extremities, wall stretches at each systole and recoils back at each diastole to create a slight delay for the atria to fully empty
Describe structure of arterioles and their job
Controls blood flow from arteries to capillaries. Thicker muscle layer than in arteries to control rate of blood flow
Elastic layer is thinner because it has lower pressure.
Describe the structure of capillaries
Endothelial lining is 1 cell thick providing a short diffusion pathway. Very narrow lumen, red blood cells travel in single file which allows more time for exchange
Narrow diameter to permeate the tissues
Spaces between endothelial cells which allow WBC to escape and deal with infections .
Describe the structure of veins
Thinner muscular walls as pressure is lower and doesn’t need to withstand high pressure
Wider lumen so it can collect as much blood as possible to send back to the heart
Thinner elastic walls as blood travels at low-pressure and won’t need to regulate rate of blood flow
How is tissue fluid formed?
High hydrostatic pressure in the arterial end of the capillary is caused by contractions in the left ventricle. This forces out small molecules like water and other molecules out of the capillary (ultra filtration). Large proteins remain inside the capillary as they are too large to leave the capillary which lowers the water potential at the venous end of the capillary. This allows most water to move back into the capillary by osmosis.
The lymphatic system collects any excess tissue fluid and returns it back to the blood.
What is tissue fluid and what does it do?
Tissue fluid is a watery fluid containing water glucose amino acids and other molecules. Tissue fluid allows materials to be exchanged between blood and cells
Describe the structure of the xylem and how its beneficial
No end walls - Creates a continuous hollow tube permitting water flow
Xylem cells are dead - Have very few organelles to minimise chemical reactions taking place and slowing down water flow
Xylem vessels covered in lignin - Provides structural support and makes xylem waterproof minimising water loss
Pits in the walls - Allows lateral movement of water in case one xylem vessel gets blocked and water can no longer flow through
What is cohesion and adhesion?
Cohesion - Hydrogen bonds between water molecules allow each other to stick to one another creating a continuous water column
Adhesion - Water molecules also stick to the walls of the xylem and pull them inwards
Describe cohesion tension theory of water transport in the xylem
Transpiration is the movement of water up a xylem vessel and evaporation through the stomata
This temporarily lowers the w.p. in the mesophyll cells
This pulls water molecules up and as a result moves every water molecule up (transpiration pull)
Water molecules have hydrogen bonds between each other allowing water molecules to stick to each other creating cohesion
This allows for thr formation of a continuous water column pulling water molecules up the plant
Water molecules also stick the sides of the xylem vessel pulling the walls inward creating adhesion
What factors affect transpiration?
Temperature - Water molecules have more kinetic energy so travel up the plant faster and so they evaporate out f the stomata faster
Light intensity - Presence of light cause stomata to open for longer allowing gas exchange and more evaporation of water
Humidity - Air surrounding stomata containing water can decrease the concentration gradient between water about to leave stomata and water surrounding stomata.
Wind speed - Air containing water surrounding lead is carried away faster creating a stronger concentration gradient allowing water o evaporate faster
What evidence is there that supports cohesion tension theory?
If a xylem vessel is broken and air enters then that part of the tree can no longer pull up water because the hydrogen bonds between water molecules have been broken which looses cohesion between water molecules
Changes in diameter of tree trunk more transpiration = more cohesion between water molecules and more adhesion between xylem walls and water molecules meaning a decreased diameter in the morning
Describe the structure of the phloem and why it is beneficial
Companion cells attached to sieve tube elements - provide nutrients keeping them alive and are also packed with mitochondria releasing energy for translocation as its an active process
Contain very few organelles - Doesn’t restrict flow of sucrose up and down the sieve tube elements
Describe the processes involved in the transport of sugars in plant stems
At the source, sucrose is produced from photosynthesis and moved by active transport to the sieve tube elements which make them more concentrated and lowering the water potential
Water from the neighbouring xylems move into the sieve tube elements by osmosis which creates an area of high hydrostatic pressure
At the sink sucrose is either used for aerobic respiration or stored away in the roots as starch which lowers the concentration making the sieve tube elements more dilute causing the water to move back into the xylem vessels by osmosis which decreases the hydrostatic pressure
WHICH RESULTS IN MASS FLOW
What evidence is there for and against the mass flow hypothesis
FOR - Concentration of sucrose is greater in the source than in the sink. Companion cells contain a lot of mitochondria for the release of energy as translocation is an active process
AGAINST - Function of sieve plates is unclear as they would seem to hinder mass flow. Not all solutions move at the same speed which they should if its moved by mass flow
Describe the structure of haemoglobin
Quaternary structure 2 beta polypeptide chains and 2 alpha polypeptide chains each polypeptide chain contains a ferrous ion Fe2+ which is the binding site for oxygen
Describe why the sigmoid graph is shaped how it is
Stage 1, shape of Hb makes it hard for any O2 to bind to the haem group in the polypeptide chain. Stage 2, after one O2 molecule has binded to the haem group the quaternary structure changes shape which maks it easier for a second and third O2 molecule to bind to Hb this is called positive co operativity. Fourth O2 molecule usually never gets binded as 3 is usually enough
Describe a left shift in the sigmoid graph
Hb has a higher affinity for O2 at low ppO2 meaning it can load O2 more readily, however it cant unload O2 as readily because of its higher affinity for O2. This is beneficial for people who loive in higher altitudes where ppO2 is lower. However is a disadvantage for organisms with a higher metabolism as they need O2 more quickly.
