Cell Boundaries

7-3

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.

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Section 7-3The Structure of the Cell Membrane

To concept map

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 12g/3L– The concentration is 3g/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

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

Section 7-3 Facilitated Diffusion

To concept map

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 tobe carried

Moleculebeing carried

Energy

Section 7-3

Active Transport

To concept map

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