Cell Transport

Passive transport (requires no ATP as molecules move along a concentration gradient):

• Simple Diffusion
• Facilitated Diffusion
• Osmosis

Active transport (requires ATP as molecules move against a concentration gradient):

•  Endocytosis
•  Exocytosis
•  Pinocytosis (“drinking”)
•  Phagocytosis

Simple Diffusion

• Net movement of molecules in and out of the cell along a concentration gradient
• Eg. gas exchange during photosynthesis, gas exchange at the alveoli 

Facilitated Diffusion

• Movement of specific molecules down a concentration gradient through specific carrier proteins
• Molecules that move by facilitated diffusion include glucose and amino acids

Osmosis

• Net movement of water molecules from a region of higher water potential to a region of lower water potential, across a partially permeable membrane
• Eg. absorption of water by plant roots

credits to: http://www.biologymad.com/resources/diffusionrevision.pdf

Cell membrane structure

Function of cell membranes:

•      To compartmentalize the cell --> separate different enzymes of different organelles and prevent autolysis
•      Control entry and exit of substances
•      Increases surface area for exchange of substances
•      Cell recognition
•      Cell communication
•      Site of chemical reactions (eg. light reactions of photosynthesis)

Fluid mosaic model

The cell membrane consists of:

• phospholipids --> head is polar while tail is non-polar 
• proteins --> peripheral/integral proteins 
• glycoproteins (consists of carbohydrate chains bound to peripheral proteins and hydrophilic regions of integral proteins) 
• cholesterol --> maintains membrane fluidity

Cell Structure — Animal cell vs Plant cell

Animal Cell structure

Plant Cell structure

credits to: http://www.diffen.com/difference/Animal_Cell_vs_Plant_Cell