Please enable JavaScript.

Coggle requires JavaScript to display documents.

Movement of substances - Coggle Diagram

- - - - eg. Large ions and hydrophilic molecules
    - - Carrier Proteins
        
        Carrier proteins undergo conformation (shape) changes
        
        Shape change occurs when polar molecules and ions bind at their respective binding sites on the carrier protein.
        
        This results in the facilitated movement of the molecules and ions across the cell membrane from high concentration to low
        
        Transport Molecules that change shape to allow molecules to pass across the membrane
        
        Transmembrane proteins
        
        with the concentration gradient (High to Low) passive
        
        Specific to different molecules
        
        Also transport proteins across intracellular compartment membranes
        
        Transport sugars, amino acids and nucleosides and other molecules
        
        Gated channel proteins have a binding site that opens a gate to allow a protein to pass.
        
        Insulin is the key that opens the gate to allow glucose to flow through a channel protein
      - There is some degree of specificity in terms of the type of molecule and type of Channel/Carrier Protein
      - Channel proteins
        
        A channel protein is a special arrangement of amino acids which embeds in the cell membrane
        
        This provides a hydrophilic passageway for water and small, polar ions.
        
        Like all transport proteins, each channel protein has a size and shape which excludes all but the most specific molecules.
        
        Passive (no energy) molecules moving from high concentration to low
        
        Transport ions (a charged atom or molecule)
        
        Transmembrane
        
        Passive
        
        Each type of channel protein is a specific size
        
        Facilitated diffusion - always passive
        
        No energy required
        
        Channel that remain open to outside (extracellular) and inside (intracellular) environments are called pores
        
        Water channel proteins are called aquaporins
    - - small, hydrophobic molecules:
        
        Oxygen and carbon dioxide are small, hydrophobic molecules which means they are able to pass through the lipid layer easily.
        
        They diffuse through the cell membrane without the need for energy, which is passive movement.
      - small, hydrophilic molecules:
        
        Although water is a small molecule it finds it difficult to move through the lipid layer.
        
        There is a special channel protein called an aquaporin which allows water to move rapidly across the membrane.
        
        This is facilitated diffusion.
      - Ions:
        
        Atoms or molecules that have a permanent charge are called ions.
        
        Because of their charge they are unable to move through the lipid bilayer.
        
        Instead they use a channel protein. The protein opens in response to extracellular signals, to allow the movement of ions across the membrane.
        
        This is Channel Mediated - facilitated diffusion.
      - large, hydrophilic molecules:
        
        Glucose and amino acids are too large to pass through the membrane.
        
        Instead they use specific carrier proteins.
        
        These proteins selectively bind to the specifically shaped protein, which allows it to move across the membrane.
        
        This is Carrier Facilitated Diffusion.
  - - - Water can also diffuse across the cell membrane by diffusion but the process is very slow
      - Diffusion of water molecules from a high concentration to a low concentration continues until equilibrium of solute concentration occurs
      - Tonicity refers to the ability of an extracellular solution to make water move into or out of the cell by osmosis.
      - Osmosis is the diffusion of water across the cell membrane.
      - The movement of water is dependent on the concentration of water molecules and solutes.
      - In the example below the water wants to diffuse from the left side into the right side as there is a higher solute concentration on the right, and therefore a lower concentration of water.
      - the membrane down the middle prevents solute molecules moving
      - Osmosis is a passive process where the water particles move with the concentration gradient, through aquaporins (proteins that act as channels).
    - - A hypotonic solution has a lower solute concentration than the cell, moving water into the cell.
        
        Effect: Animal cells will lyse, whist plant cells are protected by their cell wall (turgor pressure) and do not become lysed.
      - An isotonic solution has the same solute concentration as the cell, and therefore there is no net movement of water across the membrane.
        
        Effect: No change
      - A hypertonic solution has a higher solute concentration than the cell, causing water to move out of the cell.
        
        Effect: Animal cells will shrivel, whist in plant cells the cell membrane shrivels, but the overall shape of the cell is not effected due to the cell wall.
    - - Cell Wall
        
        Cell walls are fully permeable to all molecules!
        
        The wall is strong and pushes against the cytoplasm of the cell which is pushing against the cell wall.
        
        This causes the plant cell to develop high internal pressures in the right conditions!
      - Turgor pressure
        
        Definition: Turgor Pressure (also called turgidity) is the main pressure of the cell contents against the cell wall in plant cells.
        
        Water moves into and out of the vacuole by osmosis!
        
        The vacuole when normally full presses against the cytoplasm which presses against the cell wall creating a normal internal cellular pressure (turgor pressure).
        
        Turgor pressure in young and soft parts of plants provide support! Reduced turgor pressure results in the plant wilting.
      - Flaccid
        
        The water potential inside the vacuole and outside the cell is the same!
        
        There is no net movement of water in or out of the cell!
        
        The turgor pressure is low but not extremely low!
        
        The cell is said to be flaccid!
      - Plasmolysis
        
        Water leaves the vacuole by osmosis. .
        
        The vacuole reduces in size and no longer pushes against the cytoplasm (eventually having the same water potential as the surrounding solution).
        
        The cytoplasm pulls away form the cell wall.
        
        The cell wall has no internal pressure acting on it, so turgor pressure is extremely low!
        
        The cell is plasmolyzed!
      - Turgid
        
        Water enters the plant vacuole by osmosis
        
        The vacuole swells and expands pushing against the cytoplasm.
        
        The cytoplasm pushes against the cells wall!
        
        The cell wall does not burst or stretch which causes the plant internal pressure to increase!
        
        The cell is turgid when the pressure is high enough it prevents water entering the cell.
        
        The water potential inside and out of the cell is the same
    - - Single cell organisms that live in fresh water, fresh water will constantly enter the organisms by osmosis
      - To resolve this issue water is actively pumped out from the body by 2 contractile vacuoles which fill and empty alternately, (one then the other)
      - The amount of water entering leaves at the same rate.
      - This is osmoregulation – keeping a constant water concentration
- - - - small molecules like oxygen and carbon dioxide can be freely exchanged,
      - large molecules such as proteins cannot pass through
    - - Most atoms or molecules with a charge (or ions) must enter or leave cells through specific membrane proteins
    - - Hydrophobic molecules can enter or leave cells by passing straight through the phospholipid bilayer
        
        e.g. ethanol/ and steroids,
      - Most hydrophilic molecules need to use membrane proteins to pass through
        
        eg. Glucose
- - - - 2 Types:
        
        Phagocytosis
        
        is the intake of particles and is sometimes called ‘cell eating’.
        
        Once the vesicle (food vacuole) is within the cell, a lysosome, containing digestive enzymes, attaches, to break down the contents.
        
        Pinocytosis,
        
        ‘cell drinking’, is the intake of liquids.
        
        It can be non-selective, such as the intake of extra-cellular fluid, or selective in the intake of fat droplets.
      - info
        
        A type of vesicular transport (Vesicular - presence of one or more vesicles.)
        
        Requires energy
        
        It is where the cell surrounds some extracellular material with a fold in the cell membrane (it engulfs it)
        
        Into the cell
        
        The enfolding membrane then breaks away and the material is enclosed within the cell in the form of a small membrane bound vesicle (Vesicles - vesicle is a structure within a cell, or extracellular, consisting of liquid enclosed by a lipid bilayer)
    - - Exit the cell
      - is the secretion of materials produced by the cell.
      - The substance, eg. saliva, to be secreted is packaged by the Golgi apparatus into a vesicle.
      - This vesicle then moves to the cell membrane, which it fuses with and then releases its contents.
      - Where the contents of a vesicle is pushed out through the cell membrane
      - Requires energy
      - The membrane around the vesicle fuses with the cell membrane and the vesicle contents are passed to the exterior