Topic 4) Gas exchange and transport

Topic 4) Gas exchange and transport

1. 4. 1 – Surface area to volume ratio

   • Smaller, single-celled organisms
     • Surface area : volume = large
       • Surface area in contact with outside is very large, in comparison to volume inside organism
         • Big surface area where diffusion can occur
   • Bigger, multi-cellular organisms
     • Surface area : volume = smaller
       • Increased distance between outside and inside of organism
         • Substances do not diffuse to cells fast enough
           • Need specialised gas exchange (eg. lungs) + mass transport system (eg. circulatory system)
     • Higher metabolic rate
   • Determines whether diffusion alone will allow substances to move in and out of cells

2. 4.2 – Cell transport mechanisms

   • Fluid mosaic model of cell membrane
     • Lipoprotein bilayer
       • Mosaic = scattered proteins
       • Fluid = lipids + proteins able to move past each other in linear plane
     • COMPONENTS
       • Carbohydrate polymers
         • Glycolipids when attached to phospholipids
         • Glycoproteins when attached to proteins
       • Enzymes
         • Attached to membrane → carry out metabolic reactions
       • Cholesterol molecules
         • Disturbs the close-packing of the phospholipids → increasing flexibility of membrane
       • Proteins
         • TYPES
           • Integral proteins
             • Partially or totally buried within lipid bilayer
           • Peripheral proteins
             • Superficially attached to lipid bilayer
         • FUNCTIONS
           • Channel proteins
             • Allow movement of molecules that are too large/too hydrophilic to pass through membrane directly
           • Carrier proteins
             • Use E (= ATP) to actively move substances across the membrane
   • Movement
     • BY PASSIVE TRANSPORT
       • Diffusion
         • Free movement of particles (l or g state) down a concentration gradient
       • Facilitated diffusion
         • Diffusion that takes place through carrier proteins/protein channels
           • Protein-line pores of cell membrane make it possible
       • Osmosis
         • Movement of solvent molecules down a concentration gradient, through partially permeable membrane
       • E = kinetic
     • BY ACTIVE TRANSPORT
       • Active transport
         • Movement of substances across cell membranes, against a concentration gradient, using proteins in the bilayer which act as carrier proteins – these use energy in the form of ATP.
       • ATP
         • Common intermediate between energy-yielding reactions + every-requiring reactions/processes
         • Formed from ADP through phosphorylation, which requires E (E used = energy released in respiration/ energy trapped in illuminated chloroplasts)
         • Hydrolysis of ATP → provides accessible E for biological processes
     • BY BULK TRANSPORT
       • Occurs through movement of vesicles of matter across cell membrane = cytosis
         • Vesicles = membrane-bound organelles containing liquid or solid particles
       • Uptake = endocytosis
       • Export = exocytosis
   • Properties of transported material
     • Size
       • Molecules too big to pass through carrier proteins/through membrane itself (eg. some proteins) → bulk transport
     • Solubility
       • Particles with limited solubility → transported slowly
       • When dissolved → dissociate into charged ions (= mobile + smaller)
     • Charge
       • Structure of cell membrane makes it difficult for charged particles to pass through → electrostatic attractions/repulsions → prevents free movements
       • Most ions + charged particles pass through membrane using specialised protein channels

3. 4.3 – Gas exchange

   • Insects
     • Insects have no transport system so gases need to be transported directly to the respiring tissues.
     • Exoskeleton → made of chitin → impermeable to oxygen → barrier for gas exchange
       • Spiracles in trachea (= valves connected to outside atmosphere)
         • Gas exchange along trachea occurs in tracheoles → v thin walls → allows diffusion
           • Oxygen
             • High concentration of O2 in external atmosphere ≠ Low concentration O2 in tracheoles
           • Carbon Dioxide
             • Low concentration of CO2 in external atmosphere ≠ High concentration CO2 in tracheoles
   • Fish
     • Gills (specialised gas-exchange organs) → composed of thousands of filaments → covered in feathery lamellae (few cell thick + contain blood capillaries)
       • Large surface area + short distance for gas exchange
       • Blood flows through capillaries in opposite direction to flow of water over gills = counter-current flow system
         • Maintains a concentration gradient along whole length of blood-water boundary
   • Mammals

4. 4.4 –Circulation

   • Advantages of a double circulation
   • The Blood
   • Arteries, Veins and Capillaries
     • ELASTIC ARTERIES
     • VALVES IN VEINS
     • ARRANGEMENT OF ARTERIES AND VEINS
   • The Heart
     • CARDIAC CYCLE
       • Periods of contraction = systole
       • Periods of relaxation = diastole
       • 1) Diastole
         • ATRIA + VENTRICLES are RELAXING
           • Blood flows from major veins (VENA CAVA + PULMONARY VEINS) into ATRIA, then into VENTRICLES, via ATRIOVENTRICULAR VALVES
             • OPEN atrioventricular valves → PRESSURE in the ATRIA is GREATER than that in the VENTRICLES
               • CLOSED semi-lunar valves → PRESSURE in VENTRICLES is LOWER than that in MAIN ARTERIES
       • 2) Atrial Systole
         • BEGINNING of the MUSCLE CONTRACTION
           • ATRIA CONTRACT → pushes MORE BLOOD into the VENTRICLES
       • 3) Ventricular Systole
         • VENTRICLES CONTRACT → increase in VENTRICULAR PRESSURE → blood pushes against ATRIOVENTRICULAR VALVES → snap shut → PREVENTS blood from FLOWING BACK into ATRIA
         • PRESSURE in VENTRICLES continues to INCREASE until it is GREATER than that in MAIN ARTERIES → SEMILUNAR VALVES are forced OPEN → blood RUSHES OUT of VENTRICLES out of heart into ARTERIES
         • VENTRICLES finished contracting → MUSCLES relax + PULLED BACK by ELASTIC TISSUE → DECREASES the PRESSURE in VENTRICLES → causes SEMILUNAR VALVES to SHUT + ATRIOVENTRICULAR VALVES to OPEN → so DIASTOLE PHASE can proceed once more → CARDIAC CYCLE restarts
     • CONTROL OF THE CARDIAC CYCLE
     • STRUCTURE
       • Right hand side → pumps deoxygenated blood to the lungs in the pulmonary artery → to pick up O2 + release CO2
         • Left hand side → oxygenated blood returns here via the pulmonary vein
       • Blood pumped to the body in the aorta → returning to the right hand side of the heart in the vena cava → to start the cycle again
       • 4 chambers → 2 atria above 2 ventricles (eg. Left atrium + Left ventricle)
         • Atria = receive blood as it enters heart
         • Ventricles = pump blood out heart
       • Valve between left atrium + left ventricle = tricuspid valve
         • Valve between right atrium + right ventricle = bicuspid valve
           • Valves = prevent backflow of blood
           • Valves are held open or closed by tendons → attached at the other end to the papillary muscles in ventricle walls
       • Muscle of the heart = cardiac muscle
         • Made of tightly connecting cells → allows rapid ion transport from cell to cell → allows smooth, efficient waves of depolarisation → to produce contractions (and repolarisation to bring about relaxation), which pass through the heart
           • ∴ tissue = myogenic (doesn't need electrical impulses from nerve to make it contract)
         • Supplied with O2 + nutrients by coronary arteries
   • Exchange in tissues –Tissue Fluid & Lymph

5. 4.5 – Transport of gases in blood

   • Haemoglobin
   • Partial pressures
   • Oxygen dissociation curves
     • BOHR EFFECT
     • MYOGLOBIN
     • FETAL HAEMOGLOBIN

6. 4.6 – Transfer of materials between the circulatory system and cells

7. 4.7 – Transport in plants

   • Xylem
   • Phloem