Cellular Transport

Homeostasis In order for a cell to function properly, it must maintain homeostasis In order for this to happen, a cell must take in materials and while getting rid of others.

All cellular transport can be classified into 2 different categories 1. Passive Transport 2. Active Transport

Passive Transport does not require energy input to move molecules. There are two types of Passive Transport. Simple & Facilitated Diffusion 2. Osmosis

DIFFUSION The movement of molecules from an area of high concentration to an area of lower concentration.

Diffusion Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells. In your cells Oxygen Gas diffuses from the red blood cells and Carbon Dioxide gas diffuses into the red blood cells. X = Oxygen Gas Y = Carbon Dioxide Gas Z = Glucose

Simple Diffusion Diagram

Simple Diffusion Molecules (other than water) move from an area of high concentration to a area of lower concentration. This occurs due to the Brownian movement: Random movements and collisions. Diffusion follows a concentration gradient. (High  Low)

Facilitate Diffusion Diagram

Facilitate Diffusion Uses structures (Intrinsic proteins) to move large molecules from an area of high concentration to a lower area of concentration. The Intrinsic proteins act as doorways to allow molecules that might be too large to fit through the phospholipids. Faster than simple diffusion. Glucose has it’s own Protein channel which allows glucose to enter the cell quickly. These carriers can move up to 100 glucose molecules per second across the cell membrane.

Facilitated Diffusion Polar and charged molecules tend to have difficulty diffusing through the membrane Typically they would have a protein channel to help in their diffusion Examples are – water (aquaporin proteins), amino acids, nucleotides, etc.

Factors that Affect Diffusion Temperature Higher temperature, the greater the motion of particles and the faster rate of diffusion. Concentration Levels A larger concentration of molecules will increase the rate of diffusion. Size and Shape A molecule’s size and shape can increase/decrease it’s rate of diffusion. Lipid Solubility Lipid soluble molecules can move through the lipid bilayer faster.

OSMOSIS The diffusion of WATER molecules across a semi- permeable membrane from an area of low solute concentration to an area of high solute concentration.

Osmosis Water molecules move from an area of high concentration of water to an area of low concentration of water If no membrane was present the solute particles (molecules dissolved in water) would move due to simple diffusion. There are 3 types of Osmosis.

Iso tonic Solutions “Equal” “Liquid Mixture” The solute concentration outside of the cell is equal to the solute concentration inside of the cell. Water is diffusing into the cell at the same rate it is diffusing out of the cell.

Hypotonic Solutions The water concentration outside of the cell is higher than the concentration of water inside the cell. A net movement of water is going into the cell. Cells would tend to swell up and burst if it didn’t have some mechanism to counteract this trend.

Hypertonic Solution The water concentration outside the cell is lower than the water concentration inside the cell. The net movement of water is flowing out of the cell. Tends to shrink the cell because water exits to the external environment.

Active Transport Energy-requiring movement of molecules across a membrane from a region of lower concentration to a region of higher concentration.

Active Transport (diagram)

Active Transport Intrinsic proteins also help with some types of active transport. The carrier proteins serve as “pumps” because they move substances against the flow of diffusion. (Low conc.  High conc.) Active transport is powered by chemical energy (ATP) from the cell.

Active Transport Active transport is powered by chemical energy (ATP) from the cell. Active Transport moves molecules AGAINST a concentration gradient (Low conc.  High conc.) Active transport occurs through transport protein pumps (intrinsic proteins). Cells use active transport to maintain homeostasis.

Other Forms of Active Transport A cell can import and export large materials or large amounts of material (food), that cannot fit through intrinsic proteins in the plasma membrane, in vesicles during the processes of endocytosis and exocytosis. Both require cell energy to transport materials in vesicles.

Endocytosis Used to take in large molecules which cannot enter through intrinsic proteins. The plasma membrane starts to surround the molecule. Membrane completely surrounds the molecule and then pinches off making a vesicle. When the vesicle encounters a lysosome, the molecule proceeds to be broken down.

Endocytosis - continued Two types of Endocytosis Phagocytosis – when a solid substance is absorbed into the cell (cell eating). Pinocytosis – when dissolved molecules (in a solution) are absorbed (cell drinking)

Exocytosis The process of expelling material from the cell. This is how cellular wastes, hormones, etc. are released from the cell Molecules are enclosed within a double membranous vesicle. The vesicle fuses with the cell membrane. The vesicles contents are then release into the environment or in multicellular organisms into the blood stream.