Cell Transport Passive Transport and Osmosis Cell Size

Cell Transport Passive Transport and Osmosis

Cell Size Large cells: there are few because the larger the cell the more food and waste produced and there is a smaller areas (1 door) to go through Small Cells: have lots of surface areas (doors) to have food and waste pass through – so its easier to survive Surface to volume ratio. The more surface area a cell has compared to the cell’s volume the easier it is to get nutrients .

Cell Wall Plants & Prokaryotes. (not animals) Structural (plant support) & protective role Cellulose Freely permeable

Cell walls of onion skin…

Cell Membrane/Plasma Membrane Cell membrane In ALL cells 1. Function: ▫ Regulates materials entering and exiting the cell. Water Nutrients Waste products 2. Structure: Two layers of phospholipids, proteins Support/protection

The Cell Membrane • Is composed of a phospholipid bilayer • • A barrier; reg. what passes in/out Supports and protects Selectively permeable – only certain things pass through. About 5 nanometers thick (1 nm = 1 Billionth of a meter)

Cell membrane - Structure • A phospholipid contains▫ one head; negatively charged phosphate group that is hydrophilic (water-loving) ▫ two tails of fatty acid chains that are hydrophobic (water fearing)

Cell membrane features • The fluid mosaic model ▫ ▫ it is fluid in nature allowing cell mobility Scattered in the membrane are various proteins which perform various functions: enzyme activity, cell attachment, communicating with other cells, Transporting substances in and out of cell

Permeability • A material is permeable if it allows molecules to pass through. • The cell membrane (plasma membrane) is semipermeable

Passive Transport • Passive transport require NO ENERGY. Molecules move from high to low concentration through the cell membrane. • There are three types of passive transport ▫ Diffusion & Facilitated Diffusion ▫ Osmosis

Diffusion • Diffusion is the movement of small molecules from high concentration to low concentration. (example: Oxygen, CO 2) ▫ Molecules are not stationary, they are constantly moving ▫ Collisions between moving molecules will spread the molecules apart until the molecules are evenly distributed in the available space

Solution - the mixture formed when a substance dissolves in it Solute - the substance that dissolves Solvent - the liquid in the solution

Osmosis • Osmosis is the diffusion of WATER through a permeable membrane

Osmosis • There are three types of solutions you can have ▫ Hypotonic – lower concentration of solutes outside the cell ▫ Isotonic – equal concentration of solutes inside and outside the cell ▫ Hypertonic – higher concentration of solutes outside the cell

Osmosis in Animal Cells

Equilibrium Plasmolysis Animal Lysis Plant Turgid Flaccid Plasmolysis

Facilitated Diffusion • Some molecules are too large for diffusion so they use facilitated diffusion (example: glucose) ▫ In facilitated diffusion there are proteins the plasma membrane that pass the molecule through �Channel Proteins �Carrier Proteins

Active transport • Active transport - Transportation of molecules against a concentration gradient (from regions of low concentration to regions of high concentration) with the aid of proteins in the cell membrane • and energy from ATP

Other types of active transport Endocytosis – import of materials into cell by infoldings of the cell membrane. A. phagocytosis – “cell eating”; extensions of the cell membrane surround the food and make a vacuole. Lysosomes then secrete enzymes into vacuole to digest food. B. pinocytosis – “cell drinking”; smaller infoldings allowing droplets of liquid to enter cell.

Endocytosis in general

Exocytosis – reverse of endocytosis v. Dumping of excretions or wastes outside by discharging them from waste vacuoles. v. Also can result in secretion of substances (ex: gland cells secreting hormones into the bloodstream)