Transport of Materials Across Cell Boundaries Part I

Cell Boundaries All cells are in a liquid environment Cytoplasm is a solution of many substances Cell Boundaries help maintain constant stable environment inside cell = homeostasis Must regulate substances moving into & out of cell

Cell Membrane: Thin flexible barrier that surrounds all cells (phospholipid bi-layer) –Regulates what enters and leaves the cell –Provides protection and support – Hydrophyllic = water-loving –Hydrophobic = water-fearing

Cell Membrane Cell Membranes also contain other embedded molecules with specific jobs Protein channels for transport (doorways) Carbohydrate receptors (security guard)

Cell Wall: Strong supporting layer around the cell membrane in plant cells and prokaryotes –Provides support and protection for the cell –Porous enough to allow some substances to pass through

Solution: Mixture of 2 or more substances –Solute: Dissolved substances Example = Kool-Aid –Solvent: Dissolving substance Example = Water

Dissolved particles (solute) move around in space to reach equilibrium –Diffusion: Movement of particles from an area of high concentration to an area of low concentration –Equilibrium: Concentration of the solute is the same throughout the system

Concentration Gradient High Concentration Low Concentration

Diffusion Depends on random particle movement down a concentration gradient (cg) –CG = Measurement of concentration change over a distance Requires no energy = passive transport Small particles = able to pass through cell membrane

Permeability Permeable: A substance can pass across it Impermeable: A substance cannot pass across it Most cell membranes are semi or selectively permeable –Some substances can pass through

Cells regulate water exchange to maintain homeostasis –Osmosis: The diffusion of water through a selectively permeable membrane –Water will move across the membrane until equilibrium is reached = isotonic

Isotonic: Equal concentration –Same strength –Water moves equally –Cell stays the same

Hypertonic: Higher concentration of solute outside the cell –“Above Strength” –Water moves out of the cell –Cell shrinks

Hypotonic: Lower concentration of solute outside the cell –“Below strength” –Water moves into the cell –Cell expands

Osmotic Pressure Pressure difference across a membrane caused by different concentrations of particles in and out of the cell

Facilitated Diffusion Molecules that are too large to cross the cell membrane must use special “doorways” Protein Channels – designed to allow specific molecules to diffuse across the membrane easily Example - Glucose

Transport of Materials Across Cell Boundaries Part II

What if a cell needs to move particles against a concentration gradient? –From low to high concentration –Allows cells to concentrate molecules in a particular location regardless of concentration gradient

–Requires energy = Active Transport Examples –Transport proteins –Endocytosis –Exocytosis

Transport Protein: Transmembrane protein that helps a certain class of substances cross the membrane –Think of them like doors

Endocytosis: Materials are moved into the cell via folds in the cell membrane –Endo = Within –Two examples Phagocytosis: Extensions of cytoplasm surround a particle and package it within a food vacuole Pinocytosis: Tiny pockets form along the cell membrane, fill with liquid, and pinch off to form vacuoles within the cell

Phagocyte: “Eating Cell” –Important white blood cell –Consumes and destroys cellular debris & pathogens (germ)

Endocytosis

Exocytosis: Materials are moved out of the cell via folds in the cell membrane –Exo = Outside

Cell Differentiation & Life Organization Ch. 7 Section 4 In Textbook

Cell Differentiation In unicellular organisms the single cell will develop the structures necessary to live its life. Some may grow appendages for movement: 1)Cilia – tiny hairs on cell surface that move to allow mobility of the cell 2)Flagella – whip-like appendage used for movement

What about multi-cellular eukaryotes? Some cells develop differently than others for specific jobs: 1) Muscle Fiber Cells: Highly developed cytoskeleton for movement (remember actin?) 2) Pancreatic Cells: Need to produce enzymes for digestion so the Rough ER and Ribosomes are more highly developed 3) Red Blood Cells: No nucleus, oxygen transport