Exchange and Transport Systems

• A large surface area to volume ratio means a very large surface area per unit volume
• Smaller animals have a larger SA:V. 
• We, as large animals, have a large SA:V, which means that we need to have a specialised exhcange surface i.e. lungs and blood
• SA:V is calculated by doing SA divided by volume.
• Smaller animals tend to lose more water due to their high SA:V, and larger organisms have heat loss that is too slow. 

• A fish uptakes oxygen using gills. These gills have thousands of gill filaments which help increase SA. They also have gill lamallae at right angles to thef low, again increasing SA
• There are lots of blood capillaries running through the lamallae to increase concentration gradient.
• There is a countercurrent exchange system
  • This is where blood flows in the opposite direction to water
  • This means that highly concentrated water meets highly concentrated blood, and low concentrated water meets low concentrated blood
  • If it was a parallel system, low concentrated water will meet highly concentrated blood, and diffusion will occur the other way, meaning that only 50% uptake will occur. 

• Insects have trachae which are used for gas exchange
• Air can move in and out of the system through holes called spiracles
• Tracheoles (branches) have thin walls to allow for a small diffusion pathway. The circulatory system doesn't transport oxygen.
• Insects uses abdominal movements to move air over the spiracles (RAM ventilation)
• Insects can control water loss by closing their spiracles using muscles. They also have a waxy cuticle and hairs around the spiracles. 

• Gas exchange surface is the mesophyll cells, which have a large surface area
• Gas moves in and out through the stomata
  • They can open and close to control water loss, which is controlled by the turgidity of gaurd cells
• Xerophytes are plants which are adapted for warm/dry habitats
  • Stomata sunk in pits
  • Hairs around stomata
  • Curled leaves to protect from wind
  • Reduced number of stomata
  • Waxy cuticle to reduce evaporation 

• Inspiration
  • External intercostal muscles contract and diaphragm muscles contract, moving ribs up and outwards and increasing volume in thoracic cavity
  • This decreases lung pressure, which causes air to be forced into the lungs (pressure outside higher)
  • Is an active process [requries energy]
• Expiration
  • Internal intercostal muscles contract and the external intercostal muscles relax (antagonistic) and the diaphragm relaxes, causing the ribs to be moved down and inwards.
  • This decreases the volume in the thoracic cavity, which forces air out of the lungs.
  • Is a passive process [doesn't require energy]
• The alveoli are adapted in having a thin exchange surface, a large surface area and lots of blood vessels. 

• Pulmonary tuberculosis is damage to the exchange surface, leading to a reduced tidal volume (Volume of air in each breath) 
• Fibrosis is scar tissue which stops the lungs from expanding properly, this reduces tidal volume and increases ventilation rate (number of breaths per minute) as more oxygen is needed to overcome this
• Asthma is inflamed airways which decreases forced expiratory volume (maximum volume of air breathed out in one second)
• Emphysema is an infammation, loss of elasticity, and destruction of alveoli in the lungs. It leads to shortness of breath and increased ventilation rate
  • Forced vital capacity = the maximum amount of air that can be breathed forcefully out of the lungs. 

• Food is broken down from large to small molecules by hydrolysis for ease of absorption
• Carbohydrates are broken down into maltose by amylase and then glucose by maltase. 
  • There are two types of amylase: salivary and pancreatic
  • Membrane bound disaccharidases in the ileum break down disaccharides into monosaccharides
  • Glucose & sucrose absorbed by co transport, fructose by facilitated diffusion
• Lipids are broken down into glycerol and fatty acids by lipases
  • Firstly, bile salts surround the lipid, emulsifying it (forming smaller droplets, with a larger SA:V)
  • These are then broken down into monoglycerides and free fatty acids by lipases
  • bile salts then surround these to form micelles
  • These help the components move towards the epithelium, where the monoglycerides an fatty acids are absorbed. they are then reformed into lipids and surrounded by a membrane (produced by RER). These packages are called chylomicrons, which are secreted into a lacteal
• Endopeptidases hydrolyse internal peptide bonds; exopeptidases hydrolyse terminal peptide bonds; Dipeptidases hydrolyse dipeptide bonds [ these are membrane bound ]

• Haemoglobin combines with oxygen to form oxyhaemoglobin. (Hb + 02 -> HbO2)
• The partial pressure of oxygen measures [oxygen] - the higher the concentration, the greater the partial pressure.
• Oxygen asscociates with haemoglobin when there is a high partial pressure and vice versa
• At a high partial pressure, haemogobin has a high affinity, and there is a maxium affinity of 4 O2 molecules, so the curve looks like an 's'. 
  • In the middle of the curve, it is steep because it is very easy for oxygen to join.
• Haemoglobin has a lower affinity at a higher partial pressure of CO2
  • So at a higher partial pressure of CO2, the curve will shift to the right [for a set partial pressure of oxygen change, the saturation will change greater == greater unloading of oxygen] // Bohr Effect
• Organisms in environments with a low oxygen concentration have a higher affinity for oxygen, so the curve is further to the left
• Organisms that are very active must have a lower affinity to oxygen, and so their curve is to the right of a human curve. 

• Components of the heart: RIGHT; Vena Cava; right atrium; tricuspid (av) valve; right ventricle; semi lunar valve; pulmonary artery // LEFT; Pulmonary vein; left atrium; bicuspid (av) valve; left ventricle; semi lunar valve; aorta
• There are many different types of blood vessel:
  • Artery - Thick and muscular walls with elastic tissue, so it can stretch, maintaing pressure
  • Arterioles - Can constrict and relax to control blood flow
  • Veins - Large lumen and lots of valves, bloood flow helped by valves. 
  • Capillaries - The site of substance exchange
    • Adaptations - very near cells; one cell thick; large number of capillaries
    • When blood enters the capillary there is a higher hydrostatic pressure than in the surrounding tissue, so fluid is forced out of the capillary, forming tissue fluid. 
    • As fluid leaves, hydrostatic pressure decreases, so water potential of tissue fluid is less negative, so water re-enters the capillary at the venule end by osmosis
    • Excess tissue fluid is drained into the lymphatic system, which is like a drain. 

• The Cardiac cycle:
  • 1. The atria contract (systole), which is caused by the SAN, forcing blood into the ventricle. AV VALVES ARE OPEN
  • 2. The ventricals contract (systole), increasing ventricle presure, so the AV VALVES ARE SHUT, blood forced into the aorta and pulmonary artery, where pressure is hgih, so SEMI LUNAR VALVES ARE OPEN. [This is caused by the AVN, which sends an impulse down the fibres of his. 
  • 3. Everything relaxes (diastole) and blood flows into the atria ALL VALVES ARE CLOSED 
• Adaptations of the heart; left ventricle has thicker walls; valves precent backflow; cords stop av valves being forced up into atria

• Layers of artery:
  • Lumen; endothelium; muscle layer; elastic tissue
• If endothelium damaged white blood cells and liopids clump together to form fatty streaks, Over time, these harden to form plaque [atheroma]
• This plaque blocks the lumen causing an increase in blood pressure. 
• Diseases:
  • Aneurysm
    • An atheroma causes damage and weakens arterys, so the high pressure pushes inner layer through elastic layer, causing a swelling (aneurysm)
    • This could burst and cause a haemorrhage
  • Thrombosis
    • atheroma can rupture endothelium, creating a rough surface
    • Platelets and fibrin form a blood clot. This can cause complete blockage or be dislodged
    • Debris can casue the formation of another blood clot
  • Myocardial infarction
    • Blood cuts off blood supply, no O2, so heart attack
    • Can cause death and heart damage, symptons are chest pain/sweating

• Risk Factors:
  • High blood cholesteral is dangerous as it is a component of atheromas.
    • See previous card.
    • This is cause by dioet high in saturated fat and salt
  • Cigarette smoking is dangerous due to nicotine and carbon monoxide
    • Nicotine increases blood pressure and also smoking decreases antioxidants
  • High blood pressure is dangerous as it increases the risk of damage to artery walls
    • Increases risk of atheroma

• The xylem transports water and mineral ions in solution. They are long and tube like and are made up completely of dead cells.
• Cohesion tension theory
  • Water evapourates from the leaves at the 'top' of the xylem through transpiration
  • This creates tension which pulls more water into the leaf
  • Water molecules stick together due to cohesion, so a whole column of water in the xylem is pulled up
  • Water therefore enters the stem through the roots
• Transpiration
  • Water evapourates from cell walls and accumulates between leaf cells. When the stomata open, the vapour moves out of the cell down a concentration gradient
  • Factors that affect transpiration:
    • Humidity - If there is water in the air, the concentration gradient is reduced less Transp.
    • Wind - If it is very windy, water vapour is blown away, increasing [concentration] more Transp.
    • Heat - If it is hotter water evapourates more quickly, more Transp.
    • Light - When it is lighter, more photosynthesis occurs so the stomata open to gain CO2, more Transp. 

• A potometer measures rate of water uptake, not transpiration, because some water may be used for photosynthesis or to maintain turgidity
• You cut a shoot at a slant (increased SA) underwater (no trapped air in xylem)
• Assemble the potometer and form a bubble by removing the cappilary tube from the beaker
• Record starting position and then position per unit time using a stopwatch.
• Layout: 

Test tube with plant in                            Reservoir to return bubble to start with tap (on to return)

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Beaker  (cappilary tube)----------------------------------------------

• Dissecting a Plant
  • Cut thin sections and place them in water. Put on dish with stain (toluidine blue=lignin in xylem blue green) 
  • rinse in water and mount it using a coverslip 

• The phloem transports solutes
• Seive tube elements form the backbone with the seive plates at right angles, but they don't have organelles so companion cells carry out processes such as providing energy for active transport
• Translocation is the movement of solutes from where they are to where they're needed. Solutes are assimilates
• Enzymes maintain the concentration gradient because they convert solutes into something else at the sink, increasing [concentration]
• The Mass Flow Hypothesis:
  • Active transport loads solutes into the seive ubes from companion cells, lowering water potential in seive tubes, so water osmoses in from xylem
  • This increases the pressure, which causes movement of solutes to the sink, where solutes are removed, increasing water potential in seive tube, so water osmoses out, lowering pressure.
  • This causes a pressure gradient to be created, which causes the mass movement of solutes. 
• Higher concentration of source sucrose===higher rate of translocation

• Evidence For
  • A ring of bark including the phloem is removed (not xylem). A bulge forms there with a high concentration of solute, showing mass movement
  • A tracer can track the movement (see below)
  • Aphids, which pierce phloem, can be decapitated and sap flows out. Quicker flow near leaves so high pressure gradient
  • An inhibitor stops mass flow, showing that there is active transport involved
• Evidence Against
  • Sieve plates could create a barrier to mass flow and many different sinks are travelled to
• Tracers explained
  • e.g. carbon dioxide with carbon 14
  • Sugars produced by photosynthesis will have this incourporated
  • Movement tracked by autoradiography.
  • Shows movement of solutes from leaves to roots