Exchange and Transport

Exchange and Transport

1. Circulatory System

   • Cardiac Cycle
     • 1) Filling Phase- atria and ventricles relaxed, internal vol increases and blood flows into ventricles through open AV valves (DIASTOLE)
     • 2) Atrial contraction- both contract, small pressure increase pushes all blood into ventricles, (ATRIAL SYSTOLE) Ventricles begin to contract and snap AV valves shut.
     • 3) Ventricular contraction- all 4 valves closed, ventricles contract from apex to top (VENTRICULAR SYSTOLE), pressure raised fast and blood pushed up, semilunars open and blood pushed out of heart. SHORT contraction then relaxation & no. 1
   • Structure of heart
     • Left Oxygenated Right Deoxygenated
     • Coronary arteries on surface provide blood for muscle contraction. Blocks=angina and heart attacks (myocardial infarction)
     • 4 chambers- 2 ventricles 2 atria. Deox blood from body--> vena cava into right atrium Ox blood from lungs --> pulmonary vein into left atrium
     • Atria-->atrioventircular valves (thin flaps tissue) -->ventricles-->up into arteries
       • Tendinous cords in ventricles- attach valves to walls and prevent valves turning inside out (blood never flows back)
     • Atria- thin muscle (little pressure)
       • Right ventricle- thicker than atria, deox blood to lungs (not very far so less pressure), pressure low to prevent bursting alveoli capillaries
       • Left ventricle- 2/3x thicker than right, must pump to whole body, must overcome systemic circulation pressure
   • Gases
     • Haemoglobin-erythrocytes contain haem group, affinity for O2 and becomes oxy
       • Oxy dissociates into respiring tissue
       • low tension=low uptake (haem hard to reach), tension rises=1 O2 binds and shape change (conformational) of haem =easier for 2nd O2, hard for 4th so 100% satn is rare even at high tension THIS ALL CREATES S SHAPED CURVE
         • Fetal haemoglobin- higher affinity for O2, must be able to pick up in areas where adult has dissociated (placenta) . S curve is to left of adult curve
     • Partial pressure/O2 tension measures amount of O2
     • Carbon Dioxide- H+ competes with O2, more O2 to respiring tissue Bohr effect (S shifts down and right)
     • 5% dissolved in plasma, 10% with haemoglobin (carbamimo..), 85% as HCO3-
       • CO2+water (in red blood cells) = carbonic acid (catalysed by carbonic anhydrase)
         • Acid dissociates to H+ and HCO3-. Carbonate diffuses into plasma and Cl- move into red blood cells (Cl shift) to keep charge
           • Haemoglobin takes up H+ to prevent acidity = haemoglobinic acid (buffer)
   • Vessels & Fluids
     • Open system=blood not always in vessels Closed system=remains in vessels
       • Open system not good for large animals- flow is slow and low pressure
     • Peristalsis- blood pumped to head (in insects) and pours into body
     • Artery- small lumen, thick wall (with collagen), elastic tissue, smooth muscle to control lumen, folded endothelium
     • Veins- large lumen, thin layers of collagen etc, valves to prevent backflow
     • Capillaries- single layer flattened cells, narrow lumen (diameter=to red blood cell)

2. Respiratory System

   • Exchange surfaces
     • Living things need: O2, glucose, proteins, fats, water, minerals
       • Absorbed from surrounding or made in cell metaboliism
     • Must remove: CO2, oxygen, other waste e.g. ammonia
     • Single cell/small LARGE SA:vol exchange via normal surface
       • Large organism = small SA;vol so diffusion is too slow and has to travel further into centre MUST HAVE AN EXCHANGE (& transp) SYSTEM
     • Properties: large SA, thin barrier, removal of waste, constant supply (last 2 maintain gradient)
     • E.g. alveoli, small intestine, root hairs, hyphae (fungi)
   • Lungs
     • Tissues
       • Airway requirements: 1)larger airways allow flow without obstruction 2)divide into smaller airways 3)strong to prevent collapse 4) flexible 5) stretch and recoil
       • Trachea and bronchi- cartilage walls, incomplete C rings (less regular in bronchi), cartilage surface has layers of glandular tissue, elastic fibres, connective tissue, smooth muscle & blood vessels (LOOSE TISSUE), epithelium layer (ciliated and goblet)
       • Bronchioles- no cartilage (unless v large), made of smooth muscle/elastic, alveoli clusters at ends
       • Roles of tissue
         • Elastic fibres- reverses effect of muscle contraction by recoiling as muscles relax (dilates airway)
         • Smooth muscle- contracts to narrow lumen, prevents harmful substances entering lungs (involuntary allergic reactions like asthma)
         • Cartilage- supports and prevents collapse when low pressure, neck moves without constriction (C rings flexible), oesophagus can expand (C rings)
         • Ciliated epithelium- hair like projections waft in time to move mucus to throat (swallowed and killed by acid or expectorated)
         • Goblet cells/glandular tissue- secret mucus to trap particles (pollen/bacteria)
     • Air in via nose, trachea, bronchi, bronchioles and alveoli (exchange site)
     • Ribs protect
     • Exchange
       • In alveoli, O2 into blood, CO2 into air
       • Adaptions
         • small alveoli (100-300 microm) but many= huge SA (70m2)
         • Barrier- plasma membranes surround thin cytoplasm, gas exchange=easy
           • Alveolus 1 cell thick, capillary 1 cell thick, squamous epithelium (flat), capillaries pushed against alveoli, narrow capillaries=red blood cells closer to air in alveoli + slower flow
           • moisture (from ctyo) lines alveoli --> evaps when air out SO surfactant produced to reduce cohesion and prevent collapse
         • Gradient- blood transp system and ventilation
           • blood brings CO2 to lungs so blood>air and CO2 diffuses out blood takes away O2 so blood<air and O2 diffuses in
             • blood pumped in PULMONARY artery -->smaller vessels -->capillaries on alveoli
           • used air replaced = fresh O2 and CO2 taken away
           • Ventilation process: IN 1)diaphragm contracts (flatter) 2) external intercostals contract & raise ribs 3) volume of cavity increases 4) pressure drops below atmos 5) air moves in OUT 1)diaphragm relaxes 2) external intercostals relax & ribs fall 3) volume decreases 4) pressure increases above atmos 5) air moves out
   • Lung measurements
     • TIDAL VOL=moved in/out with each breath at rest (0.5) VITAL CAPACITY= largest vol moved in/out in 1 breath (5dm- varies with fitness, age etc. ) RESIDUAL VOL=vol left in lungs (about 1.5dm) DEAD SPACE=air in bronchioles, trachea etc INSPiRATORY RESERVE VOL=vol of air that can be breathed in over normal tidal vol (used in exercise) EXPIRATORY RESERVE VOL=vol of air that can be breathed out over the normal tidal vol
     • Spirometer- chamber with medical grade O2, air in=chamber sinks air out=chamber floats. Recorded by datalogger to form spirometer trace.
     • CO2 increases to danger level if spirometer used for long time.SODA LIME used to absorb CO2 (this is same as O2 being taken in )

3. Plants

   • Xylem vessels
     • Long cells,thick walls (lignified), end walls and contents decay = long column dead cells
       • Lignin strengthens vessel and keeps open even when little/no water
       • Lignin patterns- spiral, annular (rings) or reticulate (broken rings = flexibilty
       • Incomplete lignification --> bordered pits where water can leave/enter vessels
     • Adaptations
       • Dead cells end to end =continuous
       • Narrow so water column does not break and capillary action works
       • Flow of water not impeded: no end walls, no contents, no nucleus
   • Phloem vessels
     • Sieve tubes
       • little cytoplasm, no nucleus, end-end SIEVE TUBE (5/6 sides) transports sucrose (dissolved in water=sap), perforated cross walls at intervals (SIEVE PLATES)
     • Companion cells
       • Small cells, large nucleus, dense cytoplasm, lots of mitochondria (for ATP)
         • Perform metabolic processes needed by sieve tubes ('loading' sucrose)
         • Plasmodesmata (gaps in cell walls) link tube elements to cells
   • Water Movement
     • Apoplast- water moves through spaces in cellulose (does NOT pass through plasma membranes) Salt/minerals also carried
       • Vacuolar-Water not confined to cytoplasm, can pass through vacuoles
       • Symplast- Enters cytoplasm through plasma membrane and passes through plasmodesmata between cells
     • Endodermis cells move minerals by AT from cortex-xylem so water moves into xylem down gradient
       • Water potential in endodermis decreases so water moves across symplast from root to cortex
       • Water moves through Apoplast path across cortex and joins symplast (Casparian strip)
     • Up the Stem
       • Root pressure- Minerals --> xylem drives water intro xylem. Water pushed upwards (few m - not all the way for tall trees)
         • Transpiration pull- Water attracted to itself by cohesion (forms column). Molecules lost at top=all molecules pulled up. Column breaks-->enters other vessel by pits
           • Capillary action- molecules attracted to sides of narrow vessel (adhesion) and pulled up
     • Transpiration
       • osmosis into mesophyll--> evaps from surface of mesophyll --> fills air spaces --> potential rises and diffuses out of leaf
       • No. of leaves, position of stomata, cuticles, light, temp, humidity, wind and water levels all effect rate of transpiration
       • Xerophytes= well adapted to dry/arid conditions
     • Translocation/Mass Flow
       • Translocation= movement of assimilates
         • Evidence: Radioactive CO2 appears in phloem after entry, tree ringing (removing phloem) = sugars collect above ring, translocation can be stopped by metabolic poison (stops ATP production), ph of companion cells is higher than others, concentn of sucrose higher in source than sink
           • Evidence against: Not all solutes in sap move at same rate, sucrose is moved everywhere at same rate (not more quickly to areas with low concentn) sieve plate role is unclear
       • Source-releases sucrose Sink-removes sucrose
       • Companion cells move H+ into surrounding tissue=gradient H+ diffuse back into cells and bring sucrose (via cotransporter proteins) More sucrose in cell=diffusion into sieve tubes through plasmodesmata
       • Hydrostatic pressure increases at source due to water moving into sieve tubes --> sucrose into cells around tubes (stored as starch or used)-->Water potential increase in tubes so water enters cells and reduced pressure at sink
         • Water flows along phloem (high --> low pressure) and brings assimilates (MASS FLOW) in any direction.
         • Summer/Autumn- source is leaves sink is roots Spring- sink is growing leaves source is roots (stored carbs)