The movement of substances into or out of a cell depends upon something called a CONCENTRATION GRADIENT. A concentration gradient is a difference in concentration across a space. Not as much here. Lots here.

Two Main Types of Cell Transport 1.Passive Transports – Move substances DOWN a concentration gradient. (From high concentration to low concentration.) 2.Active Transports – Move substances UP a concentration gradient. (From low concentration to high concentration.) Passive transports require NO energy. High Low Active transports require energy!!

Diffusion Osmosis Facilitated Diffusion Diffusion through Ion Channels The movement of molecules from an area of greater concentration to an area of lesser concentration. Driven entirely by the kinetic energy of the molecules Down the concentration gradient. Substances will diffuse across a membrane as long as the membrane is permeable to those substances!

Equilibrium When the concentration of a substance is the same throughout a space.Equilibrium All passive transports move substances towards equilibrium. The molecules DO NOT stop moving! The molecules still move but there is no net movement in any direction.

Diffusion Osmosis Facilitated Diffusion Diffusion through Ion Channels The process by which water molecules diffuse across a cell membrane from an area of greater concentration to an area of lesser concentration. It’s not the volume of water that is important – it’s the concentration of solutes or the amount of PURE water. 8% Saltwater 5 gallons 8% Saltwater 5 gallons 25% Saltwater 15 gallons 25% Saltwater 15 gallons Where will water move?

Terms describing concentration Hypotonic – The concentration of solutes outside the cell is LESS than the concentration of solutes inside the cell. Hypertonic – The concentration of solutes outside the cell is GREATER than the concentration of solutes inside the cell. Isotonic – The concentration of solutes is the same inside and outside the cell. 2% NaCl 98% Water 2% NaCl 98% Water 8% NaCl 92% Water 8% NaCl 92% Water Where will water move? Into the cell? Out of the cell? Where will water move? Into the cell? Out of the cell? In a hypotonic environment. Water moves into the cell. 3% NaCl 97% Water 3% NaCl 97% Water 8% NaCl 92% Water 8% NaCl 92% Water In a hypertonic environment water moves out of the cell Water will still move into and out of the cell but there is NO NET MOVEMENT

Concentration can have ill effects on cells The cell bloats and can explode (cytolysis) The cell shrivels up and cannot function (plasmolysis) The cell shrivels up and cannot function (plasmolysis) Contractile Vacuole – An organelle some freshwater cells have to pump excess water out of the cell.

Plant Cells and Concentration Most of the time, plants are in a hypotonic environment. Water moves into the cells and causes them to swell until the cell membrane pushes against the cell wall = turgor pressure After a lot of hot, dry days, the water evaporates out of the soil and the plant is in a hypertonic environment and the plant cells enter plasmolysis and wilt.

Diffusion Osmosis Facilitated Diffusion Diffusion through Ion Channels Used for molecules that cannot diffuse rapidly across the cell membrane. (too large, not able to dissolve in lipids, etc) These substances use a carrier protein to transport them into or out of the cell. The carrier proteins only work for ONE type of substance. They still move things DOWN the concentration gradient.

Diffusion Osmosis Facilitated Diffusion Diffusion through Ion Channels Membrane proteins which allow IONS to travel across the cell membrane down their concentration gradient. Each type of ion channel can only allow ONE type of ion to pass through. Gated Ion Channels – Open and close in response to stimuli like electrical signals or stretching of the cell membrane. Other ion channels are always open

Review Passive transports move substances DOWN their concentration gradients and require NO energy – Diffusion – Osmosis – Facilitated Diffusion – Diffusion through Ion Channels

Active Transports Move substances UP their concentration gradients. Require the cell to input energy. Cell Membrane Pumps Endocytosis Exocytosis Cell membrane proteins which “pump” substances UP their concentration gradient while consuming energy.

Active Transports Cell Membrane Pumps Endocytosis Exocytosis The process by which cell ingest external fluid, macromolecules and large particles. The material is surrounded by a portion of the membrane which folds in on itself, pinches off and becomes a VESICLE. The vesicles fuse with lysosomes which digest the membrane and release the contents into the cell. There are 2 types of Endocytosis: 1.Pinocytosis – “cell drinking” When the cell takes in fluids. 2.Phagocytosis – “cell eating” When the cell takes in large particles There are 2 types of Endocytosis: 1.Pinocytosis – “cell drinking” When the cell takes in fluids. 2.Phagocytosis – “cell eating” When the cell takes in large particles

Active Transports Cell Membrane Pumps Endocytosis Exocytosis The process of a cell REMOVING large particles A vesicle inside the cell fuses with the cell membrane and releases its contents to the external environment.

Review: Passive Transports Passive Transports DiffusionOsmosis Facilitated Diffusion Diffusion through ion channels

Review: Active Transports Active Transports Cell Membrane Pumps Endocytosis Pinocytosis Phagocytosis Exocytosis