Diffusion 5.3 Flashcards
What’s the difference between active and passive in terms of exchange of substances
Active transport requires metabolic energy
passive (still requires energy) however, utilises energy from the natural motion of particles, rather than energy from an another source
what is diffusion
Diffusion is the net, or overall, movement of particles (atoms, molecules or ions, of the same species) from a region of higher concentration to a region of lower concentration, It is a passive process and it will continue until there is a concentration equilibrium between the 2 areas
Equilibrium means a balance or no difference in concentrations
why does diffusion occur and explain the movement of particles undergoing diffusion
diffusion happens because the particles in a gas or liquid have kinetic energy (they are moving)
This movement is random and an unequal distribution of particles will eventually become an equal distribution. Equilibrium doesn’t mean the particles stop moving, just that the movements are equal in both directions
explain the difference in speed between diffusion over a short and long distance
Particles move at high speeds and are constantly colliding, which slows down their overall movement.
This means that over short distances diffusion is fast, but as diffusion distance increases the rate of diffusion slows down because more collision have taken place
explain how diffusion has influenced the size of cells
Cells are microscopic - The movement of particles within the cells depend on diffusion and a large cell would lead to slow rates of diffusion. Reactions would not get the substrates they need quickly enough or ATP would be supplied too slowly to energy requiring processes
how does temperature affect the rate of diffusion
The higher temperature the higher the rate of diffusion. This is because the particles have more kinetic energy and move at higher speeds
how does a concentration difference affect the rate of diffusion
The greater the difference in concentration between 2 regions the faster the rate of diffusion.
Because the overall movement from the higher concentration to lower concentration will be larger
Diffusion takes place down a concentration gradient
what is simple diffusion
simple diffusion is diffusion in the absence of a barrier or membrane
explain the steps to investigate how surface area affects the rate of diffusion
Different sized agar blocks are used to investigate how the rate of diffusion is affected the surface area
The agar used to make the blocks contained the indicator phenolphthalein with turns pink in the present of an alkali
The agar blocks were immersed in a solution of sodium hydroxide for 10 mins. The blocks were removed and the distance the sodium hydroxide had diffused was measured with a ruler
when can diffusion across a membrane occur
- can only happen if membrane is permeable to molecules
- non-polar molecules such as oxygen (O2) diffuse through freely down a concentration gradient
can polar substances pass through a membrane
The hydrophobic interior of the membrane repels substances with a positive or negative charge (ions), so they cannot easily pass through.
Polar molecules, such as water with partial charges can diffuse through membranes, but only at a very slow rate.
small polar molecules pass through more easily than larger ones. Membranes are therefore described as partially permeable
what affects the rate at which molecules or ions diffuse across membranes
surface area - the larger the area of an exchange surface, the higher the rate of diffusion
thickness of membrane - the thinner the exchange surface, the higher the rate of diffusion
what is facilitated diffusion
Diffusion across a membrane through protein channels is called facilitated diffusion
facilitated diffusion can also involve carrier proteins
in facilitated diffusion the movement of the molecules is down a concentration gradient and does not require external energy
what are membranes with protein channels called
Membranes with protein channels are selectively permeable as most protein channels are specific to 1 molecule or ion
Membranes contain channel proteins which are polar molecules and allow ions to pass thought it.
what is the rate of facilitated diffusion dependent on
The rate of facilitated diffusion is dependent on the temperature, concentration gradient, membrane surface area and thickness, but is also affected by the number of channel proteins present. The more protein channels, the higher the rates of diffusion overall
