Membranes

• Seperates cell contents from the outside environment 
• Cell recognitions and signalling
• Regulating transport of materials in and out of cells 
• Maintain integrity of the cell 

• Hydrophobic head
• Hydrophilic tail, fatty acid.
• They are fluid so the component can move around freely 
• They are permable to small, non - polar molecules 
• But impermeable to large molecules and ions

• Gives the membrane mechanical stability 
• Sits between the fatty acid tails, making the barrier more complete and preventing molecules like water and ions from passing through the membrane

• Phospholipid molecules that have a carbohydrate part attached 
• Used for cell signalling
• Cell surface antigens
• Cell adhesion

• Channel : 

Allow movementof some subtances, such as the large molecule sugar, into and out of the cell as they can't travel directly through the cell surface membrane.

• Carrier: 

Actively moves substances across the cell surface membrane

• Increase in temp = molecules have more kinetic energy 
• Increased movement = membrane leaky 
• Unfamiliar molecules move in and out as a result

The communication and coordination between cells and their surrounding envronment 

Eg. hormones binding to their receptors on the cell surface membrane

Requires no energy 

Diffusion - THE NET MOVEMENT OF PARTICLES FROM HIGH TO LOW CONCENTRATION DOWN A CONCENTRATION GRADIENT

Facilitated Diffusion - process by which substances are transported across cell membranes by means of protein carrier molecules, such as large and charged molecules 

Transport of molecules from an area of low to high concentration, against a concentration gradient

• Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell.
• The membrane folds over the substance and it becomes completely enclosed by the membrane. At this point a membrane-bound sac, or vesicle, pinches off and moves the substance
• EG Phagocytosis and Pinocystosis 

= Active transport process, requires energy

• Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
• Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell,. Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin.

Osmosis - The movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane

Water Potential - The amount of pressure exerted by water molecules as they collide with a membrane/container, measured in kPa or Pa. 

Pure water has a water potential of 0kPa, this is the highest possible value for water potential, the presence of a solute lowers it to below 0. 

Higher water potential = Less concentrated - which moves to areas of Lower water potential = More concentrated. 

Endoplasmic Recticulum --> Packaged into Vesicle --> Modified in Golgi --> Vesicle --> Merges with membrane --> Release