Cell Boundaries and Transport Unit 4 Cell Boundaries

Cell Boundaries and Transport Unit 4

Cell Boundaries: Plasma Membrane • All cells are bordered by this thin, flexible and selectively permeable lipid bilayer barrier that has two functions The “Bou ncer ” of t he ce ll

Cell boundaries Two Functions of the PM: 1. Regulates what enters and leaves the cell 2. Provides protection and support for the cell

Cell Boundaries: Cell Wall • Plants, algae, fungi and many prokaryotes have this additional barrier outside their plasma membrane. It provides additional protection and support for the cell. The wall is made of carbohydrate and protein fibers like cellulose. Cellulose is the principle component of wood and paper! Which of the four organic compounds does a book belong to? !! ! s e t a r d y h o b r a C

Cell Limitations • Recall: – A solution is a mixture of 2 or more substances – The liquid doing the dissolving is the solvent (usually water) – The solid being dissolved is the solute – The concentration is the amount of solute in the solution

Cell Limitations • Cells are limited in their size because of 3 things: 1. Diffusion 1. Osmosis 2. Facilitated Diffusion 2. DNA 3. Food Requirements

Diffusion • Does not require use of cell’s energy (passive transport) • Particles move constantly in a solution, colliding with each other. As a result they tend to spread out to areas where they are less concentrated (have more “elbow room”) • Equilibrium is reached when the concentration of solute is the same on both sides of the membrane

Osmosis • Does not require cell’s energy (passive transport). The water can move freely through the selectively permeable plasma membrane. High Concentration Low Concentration – Isotonic-concentration the same on both sides – Hypertonic-solution with greater concentration of solutes – Hypotonic-solution with the lesser concentration of solutes Video Link: http: //www. pearsonsuccessnet. com/ snpapp/i. Text/products/0 -13 -1811185/bm/vaosmosi. html

Osmosis and Cells • Osmosis plays an important role in maintaining homeostasis through the intake and loss of water. Osmosis exerts osmotic pressure on the hypertonic side causing a cell surrounded by fresh water to be flooded. The cell will burst (lysis) if it gains too much volume.

Blood cells in animals are isotonic and have roughly the same amount of dissolved materials inside the cell as surrounding the cell Plant cells have cell walls that prevent the cell from swelling and bursting when in contact with water

Facilitated Diffusion • Does not require cell’s energy (passive transport) • The cell’s plasma membrane has protein channels that help larger solute molecules who wouldn’t normally be allowed in, pass through more easily. - Red blood cells have a protein channel that facilitates the diffusion of glucose in and out Oxygen diffusion through the blood for transport to mitochondria for cellular respiration Video Link: http: //www. pearsonsuccessnet. c om/snpapp/i. Text/products/0 -13181118 -5/bm/vapassi. html

Active Transport • Cell’s sometimes need to move materials against a concentration gradient (low to high) • This process requires much of the cell’s daily energy • Generally carried out at PM by protein “pumps” or by processes called endocytosis and exocytosis

Endocytosis and Exocytosis Endocytosis (active transport) “Cell eating” – The PM engulfs food particles and package them in a food vacuole called a vesicle. Pinocytosis (active transport) “Cell drinking” – Tiny pockets form along PM and fill with water. They pinch off inside the cell Exocytosis The membrane of a contractile vacuole carrying waste or cellular material fuses with the PM and forces its contents

Jump In: Transport and Diffusion Complete all 3 sections. We will go over the answers as a class.

What kind of membrane is this? Which direction will the water flow? 1. Which cell is in an isotonic, a hypertonic and a hypotonic solution? 3. 2.

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