7 3 Cell Boundaries Cell Membrane Cell membrane

7 -3 Cell Boundaries

Cell Membrane • Cell membrane = – controls what enters and leaves the cell – provides protection and support – Receives chemical signals • All cell membranes are made up of a double layer known as a lipid bilayer.

The of the Cell Membrane Section Structure 7 -3 Outside of cell Proteins Carbohydrate chains Cell membrane Inside of cell (cytoplasm) To concept map Protein channel Lipid bilayer

Cell Walls • Cell wall = provides support and protection for the cell • the cell wall is found in plant and fungi cells not animal cells

Measuring concentration • The cytoplasm of a cell contains many different substances in water • The substances dissolved in the solution are called solutes • The concentration of a solution is the mass of the solute in the volume of solution – Example: 12 grams of salt in 4 liters of water is 12 g/3 L – The concentration is 3 g/L

Diffusion • In a solution molecules move constantly and randomly • Diffusion = molecules tend to move from an area of high concentration to an area of low concentration to spread out • When the concentration in the solution is the same throughout it is at equilibrium • Diffusion happens without having to use energy

Osmosis • Many substances can diffuse across the membrane bus some are too large or strongly charged and cannot cross. – Water moves easily across the membrane • Osmosis = is the diffusion of water through a selectively permeable membrane • Water will move across the membrane until equilibrium is reached, at that point the concentration of water and solute will remain the same. This will mean they are isotonic

• Isotonic = same strength (equal amounts) • Hypertonic = above strength (more solute) • Hypotonic = below strength (less solute)

Effects of Osmosis on Cells

Facilitated Diffusion • Some molecules, such as Glucose, move across the cell membrane through protein channels • Facilitated diffusion= is when a protein in the cell membrane helps a molecule move across it

Section 7 -3 Facilitated Diffusion Glucose molecules High Concentration Cell Membrane Low Concentration To concept map Protein channel

Active Transport • Active transport is when a cell uses energy to “pump” molecules across the membrane against the concentration gradient • Moving molecules from a low concentration to a high concentration • Requires energy!!

Molecule to be carried Section 7 -3 Energy Molecule being carried To concept map Active Transport

Endocytosis • Endocytosis = is the process of taking material into the cell by means of infoldings, or pockets of the cell membrane • Endo = In

Endocytosis – two types • Phagocytosis: extensions of cytoplasm surround a particle and package it within a food vacuole • Pinocytosis: tiny pockets form around the cell membrane, fill with fluid, and pinch off to form vacuoles

Exocytosis • exocytosis: the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell. • Exo = Out