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Transport Across the Cell Membrane
Cell Membrane
The cell membrane is selectively permeable.This means that some molecules are able to
pass through more easily.The molecules that can easily pass through are
Lipids (nonpolar) Small molecules (glucose, water, amino acid,
carbon dioxide, oxygen and neutral molecules)
It is very hard for large molecules and charged molecules.
Structure of the Cell Membrane
It is made up of lipids, proteins, carbohydrates and some cholesterol!
It is a phospholipid bilayer!That means it is made up of 2 layers
of phospholipids!
Structure of the Cell Membrane
Proteins in the membrane! Proteins can go through the whole membrane
(integral) or just be attached to one side of the membrane (peripheral)!
Proteins that go through the membrane acts as channels or pumps for molecules to move through.
Carbohydrates in the membrane! The carbohydrates chains here act as
identification cardsCholesterol in the membrane!
This keeps the fluidity of the membrane.
Outsideof cell
Cellmembrane
Insideof cell(cytoplasm)
Proteinchannel Lipid bilayer
Proteins
Carbohydratechains
“Mosaic”
The membrane is said to be mosaic because of the proteins, carbs and lipids that make it up!!!!
Cell Wall
• The main function of the cell wall is to provide support and protection for the cell.
• Cell walls lie outside the cell membrane and are porous enough to allow H2O, O2, CO2 and other substances through
Plant cell walls are made from cellulose, a tough carbohydrate fiber.
Movement Through Cell Boundaries
•EVERY LIVING CELL EXISTS IN A LIQUID
ENVIRONMENT.
Movement Through Cell Boundaries
One of the most important functions of a cell membrane is to regulate the movement of dissolved
molecules from the liquid on one side of the membrane to the liquid on the other side
Types of Movement
PassiveDiffusionOsmosisFacilitated Diffusion
Active Transport
Passive Transport
No energy is needed for movement across the membrane
Molecules of liquids and gases are in constant motion
Therefore, the molecules move from where there is a high concentration to where there is a low concentration
Passive Transport
Diffusion Movement of molecules from an area of
high concentration to an area of lower concentration
Occurs because molecules are in constant motion
Will eventually reach an equilibrium where the concentration of the solute is the same throughout
So substances use the concentration gradient to move across the membrane without using any energy
Seen with copper sulfate
Passive Transport
Facilitated Diffusion Uses transport proteins found in the cell
membrane for diffusion So the molecules still move from a higher
concentration to a lower concentration but do so through a protein.
Transport protein - a passage for molecules to go through by diffusion
Two types of transport proteins Channel proteins – pores that certain ions can pass through
Carrier proteins – molecules bind on one side and are released onto the other side of the membrane when the protein change shape
Passive Transport
Osmosis Diffusion of water through a selectively permeable
membrane from a high concentration to a lower concentration
Isotonic solution – one that has the same concentration of dissolved substances as the living cell placed in it. The two solutions are the same strength.
Hypertonic solution – “above strength”; solution has a higher solute concentration than the cell. Usually water moves OUT of the cell Plasmolysis – shrinking of the cytoplasm
Section 7-3
Figure 7-15 Osmosis
Passive Transport
Hypotonic solution – there is a lower concentration of dissolved substances than in the cell. Concentration of water molecules is
higher in the hypotonic solution than in the cell so water will move INTO the cell.
Turgor pressure in plants – makes the plant look firm and healthy
In a solution, particles move constantly and tend to spread out where there is less of them.
When the concentration is the same throughout the solution the system has reached…..Equilibrium!!!!!!!
Review - Isotonic, Hypertonic, Hypotonic
Isotonic: When concentrations are the same on both sides of a membrane
Hypertonic: The more concentrated side.
Hypotonic: The less concentrated or diluted side.
http://www.linkpublishing.com/video-transport.htm#Elodea_-_Hypertonic_Solution
Organisms and Osmotic Pressure
Osmotic pressureOrganisms have to balance osmosisOsmotic pressure on the hypertonic
side of the membrane could cause the cell to burst
Most cells are bathed in an isotonic solution
Plants and bacteria have cell walls to help protect them
Active Transport
Molecules move against the concentration gradient
In order for transport across the membrane, transport proteins (carrier proteins) or pumps are needed
So the pumps use energy to move molecules across the membrane
Endocytosis – taking materials into the cell by infoldings of the cell membrane. Large molecules can be taken in this way Phagocytosis – cell eating -
http://www.edumedia-sciences.com/a82_l2-phagocytosis.html
Pinocytosis – cell drinking - http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/pinocyt.html
Receptor mediated endocytosis This is seen with cholesterol Sometimes molecules bind to receptors on the membrane
Once many molecules have bonded to the membrane, the membrane than pinches in and the enters the cell.
Active Transport
Exocytosis – the membrane of a food vacuole fuses with the cell membrane and the contents are released from the cell.
Molecule tobe carried
Moleculebeing carried
Energy
Organization of Cells
Unicellular organisms – one cell that performs all the functions necessary for life
Multicellular organisms – made up of more than 1 cellThe cells most communicate and work
together with each otherCell specialization- cells throughout the
organism can develop in different ways to perform different tasks
4 Levels of Organization
1) Cells (muscle cells)2) Tissue (smooth muscle
tissue)3) Organ (stomach)4) Organ System (digestive
system)
Muscle cell Smooth muscle tissue Stomach Digestive system
Section 7-4
Levels of OrganizationLEVELS OF ORGANIZATION