Diffusion, Osmosis, active transport

• Movement of molecules or ions from an area of high concentration- area of low concentration-Diffuse down a concentration gradient.
• Process used in oxygen entering a cell, and carbon dioxide leaving a cell. 
• Requiresno energy as always down the concentration gradient. (Natural kinetic energy causes then to move around randomly)

• Movement of water.
• from a high water potential(less concentrated solution) to a low water potential (more concentrated solution)
• needs only the kinetic energy of the particles themselves. 
• move through a semi-permeable membrane-only allows certain molecules through ie water molecules= they will cross until an equilibration is reached. 

In cells

if water potential higher= gain water swell and bursts.

If lower-will  lose water shrivel up and burst. 

Movement of specific molecules across cell membranes through protein channels.

Channel Protein:

• Line a water-filled pore in the membrane so water soluble molecules can easily pass through. 
• particular shapes so only particular molecules move through. 
• e.g chloride ions.

Carrier Protein:

• Can change its shape to make diffusion possible. 
• has binding sites for particular solute molecules, these can enter and leave the site randomly. 
• moving down the conc. gradient so no energy required. 
• eg glucose, sodium ions

• Active transport is the energy-demanding transfer of a substance across a cell membrane against its concentration gradient eg low to high. .
• Special proteins within the cell membrane act as specific protein ‘carriers’. 
• The energy for active transport comes from ATP generated by respiration (in mitochondria).
•  
• eg Na ions diffuse from the gut lumen in small intestine >cell (taking glucose with it)> concentration. of gradient inside cell increases and glucose diffuses out of the cell by facilitated diffusion. 

Endocytosis

Into the cells

Involves engulfing of the material by the cell surface membrane. 

Exocytosis

Out of cells

Process by which materials are removed from the cells.