Transport Across the Cell Membrane

The Particle Model of Matter In order to survive and function properly cells need to move gases, ions, nutrients, and waste material across their selectively permeable membrane.

Understanding how particles move Particle Model All matter is made of particles The particles of matter are constantly moving or vibrating the particles of matter are attracted to one another particles have spaces between them Particle Movement is described by Brownian motion: the random movement of microscopic particles suspended in a fluid. Applet

Particle Movement

Methods of Transport Passive Transport: The movement of particles across the membrane without the cell expending energy Simple Diffusion Osmosis Facilitated Transport

Diffusion the movement of particles down their concentration gradient - from an area of high concentration to an area of low concentration. (animation) Ex. O2, CO2

Osmosis diffusion of water molecules down their concentration gradient across a semi-permeable membrane. (animation) Ex. H2O Only Isotonic, Hypotonic & Hypertonic Solutions

Isotonic solution solution outside the cell has the same amount of solute particles as found in the cell no net movement of water particles

Hypertonic solution solution outside the cell has a higher concentration of solute than found in the cell lower concentration of water outside water moves out of cell

Hypotonic solution solution outside the cell has a lower concentration of solute higher concentration of water ouside net movement of water into cell

Facilitated Diffusion movement with the concentration gradient, but assisted by carrier proteins in the membrane. (animation) Ex. Glucose and Ions

Active Transport Moving molecules against their concentration gradient using energy (ATP). (animations 2) Ex. Na+, K+, & H+ Pumps

The Na+ K + Pump

Endocytosis and Exocytosis movement of larger molecules in and out of the cell with transport vesicles. (animation)

Endocytosis: Bringing substances into the cell by wrapping them in part of the cell membrane Ex. nutrients Phagocytosis: Bringing in a large particle (animation) Pinocytosis: Brining in many small particles Receptor Mediated Endocytosis: process is triggered by a receptor on the surface of the membrane

Exocytosis Removing/secreting large substances or groups of particles from the cell. Ex. Waste products, enzymes, chemical messengers, hormones