Mar 10, 2009 ... homeostasis. ▫ Provides protection and support for the cell. Victoria Gómez
Ceballos. IES Pedro Jimenez Montoya. Structure of cell membrane.
03/10/2009
Cell Membrane
All cells have a cell membrane Functions: Controls what enters and exits the cell to maintain an internal balance called homeostasis Provides protection and support for the cell
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Structure of cell membrane It is a: Lipid Bilayer -2 layers of phospholipids a. Phosphate head is polar (water loving) b. Fatty acid tails nonpolar (water fearing) c. Proteins embedded in membrane
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Fluid mosaic model of the cell membrane
Actual theory Polar heads love water & dissolve.
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
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Structure of the Cell Membrane Outside of cell
Carbohydrate chains
Proteins
Lipid Bilayer Transport Protein
Phospholipids Inside of cell cytoplasm
(
)
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Go to Section:
Transport in cells After studying this section you should be able to Understand how substances pass in and out of cells including: Passively
by diffusion osmosis, which is a special type of diffusion By active transport, which requires energy By
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
CELL TRANSPORT
Passive Transport cell doesn’t use energy 1. Diffusion 2. Facilitated Diffusion 3 3. Osmosis
Weeee!! ! high low
Active Transport cell does use energy 1. Protein Pumps 2. Endocytosis 3. Exocytosis
This is gonna be hard work!!
high
low Victoria Gómez Ceballos IES Pedro Jimenez Montoya
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What is a solution? Solutions are made of solute and a solvent
Solvent - the liquid into which the solute is poured and dissolved. Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Methods of Transport Across Membranes 1.
Passive transport 1. 2. 3.
2.
Diffusion Osmosis Facilitated Diffusion
Active Transport 1. 2. 3.
Protein pumps Endocytosis exocytosis Victoria Gómez Ceballos IES Pedro Jimenez Montoya
DIFUSSION I Passive transport
Diffusion is the net movement of a substance from an area of high concentration to an area of low concentration. This is down a diffusion gradient How does it work? Diffusion works because particles are always moving about in a random way. This means that the particles will spread out evenly after a while.
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Diffusion II
How fast does it work?
The rate of diffusion depends on how fast the particles move. The warmer it is , the faster they move. Smaller S ll paticles ti l also l move faster. f t Examples Oxygen diffuses into the red blood cells in the lungs and carbon dioxide diffuses out of the blood. Carbon dioxide enters leaves and leaf cells by diffusion. Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Osmosis I
Osmosis is a very special kind of diffusion. It involves the movement of water molecules. It needs a:
Selectivelyy p permeable membrane
The cell membrane is selectively permeable because it lets certain molecules through and not others
Different concentration of solution on each side of the membrane
Water will move from the high concentration of water(weak solution) to the low concentration of water(strong solution) Victoria Gómez Ceballos IES Pedro Jimenez Montoya
OSMOSIS II TONICITY IS A RELATIVE TERM Hypotonic Solution - One solution has a lower concentration of solute than another.
Hypertonic Solution - one solution has a higher concentration of solute than another. Isotonic Solution - both solutions have same concentrations of solute.
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OSMOSIS III
DEFINITION It is the diffusion of water through a selectively permeable membrane. Water moves from high to low concentrations
Water moves freely through pores. Solute (green) to large to move across.
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
OSMOSIS IV
Remember:
Semi-permeable means permeable to solvents (WATER), but not to large molecules Movement High [water] to low [water] Dissolved molecules (i.e. glucose, starch) are called solutes Water = solvent Glucose, Starch = solutes Victoria Gómez Ceballos IES Pedro Jimenez Montoya
OSMOSIS V
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OSMOSIS VI
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OSMOSIS VII
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Facilitated Diffusion I Definition: Diffusion of specific particles through transport proteins
f found d in i the th membrane b a. Transport Proteins are specific – they “select” only certain molecules to cross the membrane b. They transport larger or charged molecules Victoria Gómez Ceballos IES Pedro Jimenez Montoya
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Facilitated Diffusion II A cellular transport from a:
Glucose molecules
High
High Concentration
Cell Membrane
Low Concentration
Through a Æ
Transport Protein
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Go to Section:
Active Transport I
Cell uses energy Actively moves molecules to where they are needed Movement from an area of low concentration to an area of high concentration (Low Æ High) Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Active transport II
Protein Pumps transport proteins th t require that i energy to do work
Example: Sodium / Potassium Pumps are important in nerve responses
Protein changes shape to move molecules: this requires energy
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Active transport III Endocytosis: taking bulky material into a cell • Uses energy • C ll membrane Cell b in-folds i f ld around food particle • “cell eating” • forms food vacuole & digests food • This is how white blood cells eat bacteria!
Victoria Gómez Ceballos IES Pedro Jimenez Montoya
Active Transport IV Exocytosis: Forces material out of cell in bulk • membrane surrounding the material t i l fuses f with ith cellll membrane • •
Cell changes shape – requires energy EX: Hormones or wastes released from cell Victoria Gómez Ceballos IES Pedro Jimenez Montoya
