2d Transport in and out of cells Flashcards
Osmosis definitions
a form of passive transport (does not require energy) of water molecules from an area of high solute concentration to low solute concentration across a semi-permeable membrane until equilibrium is reached
Diffusion definition
a form of passive transport (does not require energy) from an area of high concentration to low concentration until equilibrium is reached
Osmosis in potatoes practical (method)
- Cut potato into small pieces of equal size (e.g 2cm diameter).
- Blot the potato pieces gently with tissue paper to remove excess water.
- Measure the initial mass of each piece.
- Place the pieces in sucrose solutions of different concentrations (1%, 2% etc)
- Blot with tissue paper again and record new mass.
- Find difference in mass (end mass - start mass) and use the percentage change
equation to calculate percentage gain or loss of mass.
Osmosis in potatoes practical (variables)
- Independent variable (what you are changing) = the concentration of the sucrose solution
- Dependent variable (what you are measuring) = the change in mass of the potato
- Control variable (what you are controlling) = the size of the potato pieces
What is happening in the potato osmosis practical
Water is moving by osmosis from a more dilute solution (in the potato) to a more
concentrated solution (the sucrose solution) across a selectively permeable membrane
(the cell membranes of all the potato cells holding water).
Active transport definition
a form of transport that requires energy from ATP to move molecules against a concentration gradient (i.e from an area of low
concentration to an area of high concentration)
What affects movement into and out of cells
- temperature
- concentration gradient
- distance
- surface area to volume ratio
How does temperature affect diffusion/osmosis
the higher the temperature, the higher the rate because the molecules have more kinetic energy thus are moving faster
How does concentration gradient affect diffusion/osmosis
the higher the concentration gradient, the higher the rate
if there is almost an equal concentration, the rate will be very slow
How does distance affect diffusion/osmosis
the shorter the distance the molecules have to move, the faster the rate
How does surface area to volume ratio affect diffusion/osmosis
as the surface area of the membrane increases, the rate increases, as there is more space for molecules to move across the membrane
What happens in equilibrium
concentrations are equal and molecules are still moving around the space but there is no net movement of molecules from one area to another (also known as dynamic equilibrium)
