Topic 4) Gas exchange and transport

4. 1 – Surface area to volume ratio
1. Smaller, single-celled organisms
  1. Surface area : volume = large
    1. Surface area in contact with outside is very large, in comparison to volume inside organism
      1. Big surface area where diffusion can occur
2. Bigger, multi-cellular organisms
  1. Surface area : volume = smaller
    1. Increased distance between outside and inside of organism
      1. Substances do not diffuse to cells fast enough
        Need specialised gas exchange (eg. lungs) + mass transport system (eg. circulatory system)
  2. Higher metabolic rate
3. Determines whether diffusion alone will allow substances to move in and out of cells
4.2 – Cell transport mechanisms
1. Fluid mosaic model of cell membrane
  1. Lipoprotein bilayer
    1. Mosaic = scattered proteins
    2. Fluid = lipids + proteins able to move past each other in linear plane
  2. COMPONENTS
    1. Carbohydrate polymers
      1. Glycolipids when attached to phospholipids
      2. Glycoproteins when attached to proteins
    2. Enzymes
      1. Attached to membrane → carry out metabolic reactions
    3. Cholesterol molecules
      1. Disturbs the close-packing of the phospholipids → increasing flexibility of membrane
    4. Proteins
      1. TYPES
        Integral proteins
        Partially or totally buried within lipid bilayer
        Peripheral proteins
        Superficially attached to lipid bilayer
      2. 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
2. Movement
  1. BY PASSIVE TRANSPORT
    1. Diffusion
      1. Free movement of particles (l or g state) down a concentration gradient
    2. Facilitated diffusion
      1. Diffusion that takes place through carrier proteins/protein channels
        Protein-line pores of cell membrane make it possible
    3. Osmosis
      1. Movement of solvent molecules down a concentration gradient, through partially permeable membrane
    4. E = kinetic
  2. BY ACTIVE TRANSPORT
    1. Active transport
      1. 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.
    2. ATP
      1. Common intermediate between energy-yielding reactions + every-requiring reactions/processes
      2. Formed from ADP through phosphorylation, which requires E (E used = energy released in respiration/ energy trapped in illuminated chloroplasts)
      3. Hydrolysis of ATP → provides accessible E for biological processes
  3. BY BULK TRANSPORT
    1. Occurs through movement of vesicles of matter across cell membrane = cytosis
      1. Vesicles = membrane-bound organelles containing liquid or solid particles
    2. Uptake = endocytosis
    3. Export = exocytosis
3. Properties of transported material
  1. Size
    1. Molecules too big to pass through carrier proteins/through membrane itself (eg. some proteins) → bulk transport
  2. Solubility
    1. Particles with limited solubility → transported slowly
    2. When dissolved → dissociate into charged ions (= mobile + smaller)
  3. Charge
    1. Structure of cell membrane makes it difficult for charged particles to pass through → electrostatic attractions/repulsions → prevents free movements
    2. Most ions + charged particles pass through membrane using specialised protein channels
4.3 – Gas exchange
1. Insects
  1. Insects have no transport system so gases need to be transported directly to the respiring tissues.
  2. Exoskeleton → made of chitin → impermeable to oxygen → barrier for gas exchange
    1. Spiracles in trachea (= valves connected to outside atmosphere)
      1. 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
2. Fish
  1. Gills (specialised gas-exchange organs) → composed of thousands of filaments → covered in feathery lamellae (few cell thick + contain blood capillaries)
    1. Large surface area + short distance for gas exchange
    2. Blood flows through capillaries in opposite direction to flow of water over gills = counter-current flow system
      1. Maintains a concentration gradient along whole length of blood-water boundary
3. Mammals
4.4 –Circulation
1. Advantages of a double circulation
2. The Blood
3. Arteries, Veins and Capillaries
  1. ELASTIC ARTERIES
  2. VALVES IN VEINS
  3. ARRANGEMENT OF ARTERIES AND VEINS
4. The Heart
  1. CARDIAC CYCLE
    1. Periods of contraction = systole
    2. Periods of relaxation = diastole
    3. 1) Diastole
      1. 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
    4. 2) Atrial Systole
      1. BEGINNING of the MUSCLE CONTRACTION
        ATRIA CONTRACT → pushes MORE BLOOD into the VENTRICLES
    5. 3) Ventricular Systole
      1. VENTRICLES CONTRACT → increase in VENTRICULAR PRESSURE → blood pushes against ATRIOVENTRICULAR VALVES → snap shut → PREVENTS blood from FLOWING BACK into ATRIA
      2. 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
      3. 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
  2. CONTROL OF THE CARDIAC CYCLE
  3. STRUCTURE
    1. Right hand side → pumps deoxygenated blood to the lungs in the pulmonary artery → to pick up O2 + release CO2
      1. Left hand side → oxygenated blood returns here via the pulmonary vein
    2. 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
    3. 4 chambers → 2 atria above 2 ventricles (eg. Left atrium + Left ventricle)
      1. Atria = receive blood as it enters heart
      2. Ventricles = pump blood out heart
    4. Valve between left atrium + left ventricle = tricuspid valve
      1. 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
    5. Muscle of the heart = cardiac muscle
      1. 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)
      2. Supplied with O2 + nutrients by coronary arteries
5. Exchange in tissues –Tissue Fluid & Lymph
4.5 – Transport of gases in blood
1. Haemoglobin
2. Partial pressures
3. Oxygen dissociation curves
  1. BOHR EFFECT
  2. MYOGLOBIN
  3. FETAL HAEMOGLOBIN
4.6 – Transfer of materials between the circulatory system and cells
4.7 – Transport in plants
1. Xylem
2. Phloem

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Topic 4) Gas exchange and transport

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