1.4 Membrane transport Flashcards
Types of transport
passive transport
active transport
Passive transport
involves the movement of material along a concentration gradient (high to low concentration) thus do not require energy
Main types of passive transport
simple diffusion
osmosis
facilitated diffusion
Diffusion
the net movement of molecules from a region of high concentration to a region of low concentration
What factors affect the rate of diffusion + how?
temperature - affects kinetic energy of particles in solution
molecular size - larger particles are subjected to greater resistance within a fluid medium
steepness of gradient - rate of diffusion will be greater with a higher concentration gradient
Osmosis
the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
Osmolarity
a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)
Hypertonic
solutions with a relatively higher osmolarity (high solute concentration ⇒ gains water)
Hypotonic
solutions with a relatively lower osmolarity (low solute concentration ⇒ loses water)
Isotonic
solutions that have the same osmolarity (same solute concentration ⇒ no net water flow)
How do we estimate osmolarity?
The osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities
The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
Water loss or gain may be determined by weighing the sample before and after bathing in solution
Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)
What are the effects of uncontrolled osmosis?
In hypertonic solutions, water will leave the cell causing it to shrivel (crenation)
In hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis)
How are the effects of uncontrolled osmosis present in plant tissues?
In hypertonic solutions, the cytoplasm will shrink (plasmolysis) but the cell wall will maintain a structured shape
In hypotonic solutions, the cytoplasm will expand but be unable to rupture within the constraints of the cell wall (turgor)
Facilitated diffusion
the passive movement of molecules across the cell membrane via the aid of a membrane protein
What are the two types of transport proteins?
channel proteins
carrier proteins
Carrier proteins
carrier proteins will bind to a specific molecule that needs to be transported, similar to an enzyme-substrate interaction
Channel proteins
channel proteins contain a pore in which ions may cross from one side of the membrane to another
Active transport
uses energy to move molecules against a concentration gradient
How does active transport work?
involves the use of carrier proteins (protein pumps)
- a specific solute will bind to the protein pump on one side of the membrane
- hydrolysis of ATP causes a conformational change in the protein pump
- the solute molecule is translocated across the membrane and released
Vesicular transport
the movement of particles or fluid droplets through the plasma membrane by the process of endocytosis or exocytosis
Endoplasmic reticulum
Rough ER is embedded with ribosomes and synthesises proteins destined for extracellular use
Smooth ER is involved in lipid synthesis and also plays a role in carbohydrate metabolism
Golgi apparatus
Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face
While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.)
Plasma membrane
Released immediately into the extracellular fluid (constitutive secretion)
Stored within an intracellular vesicle for a delayed release in response to a cellular signal (regulatory secretion)
Endocytosis
The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane
