Gas Exchange, Cell Membranes & Transport

Cards (96)

  • Properties of Gas Exchange Surfaces

    • Surface area to volume ratio
    • Diffusion pathway
    • Concentration gradient
  • Surface area to volume ratio (SA:V ratio)
    The surface area of an organism in relation to its volume
  • As the overall size of the organism increases, the surface area becomes smaller in comparison to the organism's volume, and the organism's surface area: volume ratio decreases
  • Single-celled organisms

    • Have a high SA:V ratio which allows the exchange of substances to occur by simple diffusion
    • The large surface area allows for maximum absorption of nutrients and gases and removal of waste products
    • The small volume within the cell means the diffusion distance to all organelles is short
  • Large multicellular organisms

    • Have evolved adaptations to facilitate the exchange of substances with their environment
    • The gas exchange systems are adapted to increase the surface area available for the exchange of gases
  • Adaptations to increase surface area
    • Alveoli increase the surface area of mammalian lungs
    • Fish gills have structures called lamellae which provide a very large surface area
    • Leaves have a spongy mesophyll layer within which a large area of leaf cell surface is exposed to the air
  • Diffusion pathway

    The diffusion distance across an exchange surface is very short
  • Concentration gradient
    The difference in concentration of the exchange substances on either side of the exchange surface
  • A greater difference in concentration means a greater rate of diffusion as the gas molecules move across the exchange surface
  • The continued movement of exchange substances away from the exchange surface mean that a concentration gradient is maintained
  • Fick's Law of Diffusion

    Relates the rate of diffusion to the concentration gradient, the diffusion distance and the surface area
  • Fick's Law of Diffusion

    1. Rate = P x A x ((C1 - C2)÷ T)
    2. P = Permeability constant
    3. A = Surface area
    4. C1 - C2 = Difference in concentration
    5. T = Thickness of exchange surface
  • The lungs of air-breathing animals provide an ideal exchange surface for the diffusion of gases
  • Mammalian lungs

    • Located in the thorax
    • Enable efficient gas exchange
  • Structures of the mammalian lung

    • Trachea
    • Bronchi
    • Bronchioles
    • Alveoli
  • Trachea
    • Tube that allows air to travel to the lungs
    • Contains C-shaped rings of cartilage
    • Lined with mucus and cilia
  • Bronchi
    • Similar structure to trachea but thinner walls and smaller diameter
    • Cartilage rings are full circles
  • Bronchioles
    • Narrow, self-supporting tubes with thin walls
    • Larger ones have elastic fibres and smooth muscle
    • Smaller ones have no smooth muscle but elastic fibres
  • Alveoli
    • Groups located at ends of bronchioles
    • Alveolar wall is a single layer of flattened epithelium
    • Surrounded by extensive capillary network
    • Lined with moisture to facilitate gas diffusion
  • Membranes are vital structures found in all cells
  • Cell surface membrane
    Creates an enclosed space separating the internal cell environment from the external environment
  • Intracellular membranes

    Form compartments within the cell such as the nucleus, mitochondria, and endoplasmic reticulum
  • Membranes
    • Control the exchange of substances from one side to the other
    • Act as an interface for communication
  • Phospholipids
    • Consist of a glycerol molecule, a phosphate group, and two fatty acid tails
    • Phosphate head is polar (hydrophilic)
    • Lipid tails are non-polar (hydrophobic)
  • Phospholipid bilayer

    • Forms the basic structure of the cell membrane
  • Phospholipids
    Molecules that form the basic structure of cell membranes
  • Representations of phospholipids

    • Simple representation of phosphate head and lipid tails
    • Chemical structure showing glycerol, phosphate group, and ester bonds
    • Diagrammatic representation of chemical structure
  • Phospholipid monolayer
    Phospholipids spread over surface of water with hydrophilic phosphate heads in water and hydrophobic fatty acid tails sticking up away from water
  • Phospholipid bilayer

    Two-layered structures that form in sheets
  • Phospholipid bilayers form the basic structure of the cell membrane
  • Components of cell membranes

    • Phospholipid bilayers
    • Proteins
    • Cholesterol
  • Intrinsic (integral) proteins
    Embedded in the membrane with their precise arrangement determined by their hydrophilic and hydrophobic regions
  • Extrinsic (peripheral) proteins

    Found on the outer or inner surface of the membrane
  • Cholesterol
    • Regulates membrane fluidity by increasing fluidity at low temperatures and stabilising the membrane at higher temperatures
    • Increases the mechanical strength and stability of membranes
  • Glycolipids and glycoproteins

    Present on the surface of the cell, aid cell-to-cell communication
  • Fluid mosaic model

    Describes the scattered pattern and fluid movement of components within the phospholipid bilayer
  • The cell membrane is partially permeable
  • Small, non-polar molecules
    Can pass through the gaps between the phospholipids
  • Large, polar molecules
    Must pass through specialised membrane proteins called channel proteins and carrier proteins
  • The distribution of proteins within the membrane gives a mosaic appearance