CIE IGCSE Biology Unit 3: Movement in and Out of Cells

Diffusion

the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient, as a result of their random movement

Importance of diffusion of gases and solutes

To move in nutrients and removal of waste products from the cells

Importance of water as a solvent

universal solvent that dissolves most solutes

Factors that affect diffusion

- surface area: larger surface area higher rate of diffusion

- temperature: particles gain kinetic energy therefore move faster and diffusion increases

- concentration gradients: higher concentration gradients causes a larger difference in concentration therefore increasing until net movement is 0

- distance: shorter distance particles have to travel between membrane the higher the rate of diffusion

Osmosis

the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower

water potential (concentrated solution), through a partially permeable membrane

Osmosis test

1. cut potato into equal strips

2. measure initial mass of each potato strip

3. prepare 3 salt solutions of concentrated, dilute and pure water

4. immerse potato strips into solution for 3 hours

5. remove potato strips from solution and record mass and texture of potato

Osmometer

Used for measuring the osmotic pressure in water

Importance of Osmosis in Animal Cells

Intake of glucose

Importance of Osmosis in Plants

uptake of water

Water potential

The potential energy of water

Effects on cells in solutions of different concentrations

Animal cells:

Concentrated solution of salt/glucose

-crenation: shrinking of animal cell due to osmosis

Pure water

-lysis: bursting due to intake of water due to osmosis

Plant cells:

Pure water

-turgid: absorbing of water causes plant cell to be full of water causing it to be inflated

Salt solution

-flaccid: losing of water causes plant cell to be soft

Concentrated salt solution

-plasmolysed: due to too much water diffusing out of plant cell causing cell membrane to pull away from cell wall

Turgor pressure

plants are supported by the pressure of water inside the cells pressing outwards on the cell wall

Active Transport

the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Importance of Active Transport

- Plants: ion uptake by root hairs

- Animals: uptake of glucose by epithelial cells of villi and kidney tubules

How protein molecules move particles across a membrane during active transport

Plant and animals: Through rough endoplasmic reticulum

Role of water as a solvent in organisms with respect to digestion, excretion and transport

Proteins: water can dissolve amino acids

Osmosis: movement of nutrients in and out of cells