The movement of particles from an area of higher concentration to an area of lower concentration.
What is a concentration gradient?
The difference in concentration.
The bigger the concentration gradient...
the faster the diffusion rate.
What will give a faster diffusion rate?
Hightemperature- the particles have more energy so will move faster.
A biggerconcentration gradient.
How do dissolved substances move in and out of cells?
By diffusion through the cell membrane.
What happens to the rate of diffusion if the surface area of the membrane increases?
It increases because more particles can pass through at once.
What is osmosis?
Osmosis is the movement of water molecules from a
region of higher water/solute concentration to an region of lower water/solute concentration across a partially/semi-permeable membrane.
What is a partially permeable membrane?
One with very small holes in it, only tiny molecules can pass through it e.g water.
Can the water pass through both ways of the membrane?
Yes, as water molecules move randomly all the time.
Osmosis required practical.
Cut up a potato into identical cylinders.
Then get some beakers and fill them differentsugar solutions (one should be pure water and another should be a very concentrated sugar solution e.g 1mol/dm3)
Measure the mass of each cylinder and record it on a table then place one potato cylinder in each beaker for 24 hours.
Then take them out and dry them using a bluepapertowel and measure their newmass.
Repeat the experiment and calculate a mean percentage rate of each concentration.
How does the mass of the potato change?
If water has been drawn in by osmosis the mass increases.
If water has been drawn out the mass decreases.
What is the dependent variable of the of the practical?
The mass of the potato.
What is the independent variable of the osmosis practical?
The concentration of the sugar solution.
What are the control variables of the osmosis practical?
The volume of the solution.
The time each cylinder has been in the solution for.