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 1. All matter is made of particles 2. The particles of matter are constantly moving or

vibrating3. the particles of matter are attracted to one

another 4. 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 DiffusionOsmosisFacilitated 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. nutrientsPhagocytosis: Bringing in a large particle (animation)Pinocytosis: Brining in many small particlesReceptor 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