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