Movement of substances into and out of cells. Flashcards
What is diffusion?
The spreading of a particular gas or substance in solution, resulting in a net movement from a region where they are of a higher concentration, into a region where they are in a lower concentration.
This happens along the concentration gradient.
How can the speed of diffusion be increased?
Increasing the concentration - particals will diffuse into the lower concentration area.
Increasing the temperature - the higher the temperature the greater the energy so the particals will move around quicker and diffuse faster
Give a practical example of diffusion.
Oxygen diffuses from a high concentration in a red blood cell to a lower concentration in a tissue cell.
What is osmosis?
The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane.
It is a type of diffusion.
What is a partially permeable membrane?
A membrane that lets through small molecules such as water, but not larger molecules like glucose.
Give an example of a partially permeable membrane.
Cell membrane
visking tube
Why does osmosis happen?
Osmosis happens because of random movement of molecules.
Molecules in a solution bump into the membrane and bounce off.
If water molecules bump into the part of a membrane with a small hole they are small enough to pass through. Glucose molecules are too big so bounce back.
The more dilute the solution the more water molecules there are = more chance of finding a hole.
Water will always flow towards a more concentrated solution
What is active transport?
Active transport moves substances in and out of cells against the concentration gradient using energy released during respiration.
Lower concentration –> higher concentration
Give an example of when active transport is used.
When there are nutrients in the gut but in too low concentration to diffuse into the blood. Active transport uses energy from respiration to allow nutrients to be taken into the blood.
What 4 factors affect the movement of substances?
- Surface area to volume ratio
- Distance
- Temperature
- Concentration Gradient
How does surface area to volume ratio affect the movement of substances?
The higher the surface area to volume ratio the higher the rate of movement.
How does distance affect the movement of substances?
Substances with only a short distance to move do so faster.
e.g. moving through thinner cell membranes
How does temperature affect the movement of substances?
As the particles in a substance get warmer they have more energy and so move faster
How does the concentration gradient affect the movement of substances?
If there is a big difference in concentration substances move quicker.
NB does not affect active transport - only diffusion and osmosis.
