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