Transport Across the Cell Membrane http://www.youtube.com/watch?v=moPJkCbKjBs

fcp://@kenton.k12.ny.us,%231016084/%2311127825

Cell Membrane

Functions:1. Gatekeeper2. Protects and controls the substances going in and out of the cell

Structure•bilayer of phospholipids •with proteins imbedded

3. Cell membrane is Semi-permeable only allow certain things to pass through the membrane.

•Things they want to let in:

•Things they do not want to let out:

•Things they DO NOT want to let in:

The cell tries to let in good things and keep out bad things. Often based on size…small things are allowed in and larger things are kept out or have to be pumped in.

sugar, oxygen, water

carbon dioxide, waste

viruses, bacteria

Question 1. Which statement regarding the functioning of the

cell membrane of all organisms is not correct?

A) The cell membrane forms a boundary that separates the cellular contents from the outside environment.

B) The cell membrane forms a barrier that keeps all substances that might harm the cell from entering the cell.

C) The cell membrane controls the movement of molecules into and out of the cell.

D) The cell membrane is capable of receiving and recognizing chemical signals.

Question 2.

In the given diagram of a single-celled organism, that arrows indicate various activities taking place.

Which systems perform these same activities in humans?

1) Respiratory, nervous and endocrine

2) Excretory, respiratory, and reproductive

3) Digestive, circulatory, and immune

4) Respiratory, excretory, and digestive

Receptor Molecules-“cell receptors”• Communication between

cells to maintain homeostasis• Protein molecules on the

surface of the membrane with specific shapes.

• Certain chemicals (i.e. hormone) will match up with shape on the cell membrane signaling that cell to produce a desired product

• Target cell is the cell that is a correct match and is influenced by that hormone or enzyme Click on image

Question 3.Cellular communication is illustrated in the diagram below

Information can be sent from

A) Cell A to Cell B because cell B is able to recognize signal 1

B) Cell B to Cell A because cell B is able to recognize signal 2

C) Cell B to Cell A because cell A is able to recognize signal 1

D) Cell A to Cell B because cell A is able to recognize signal 2

Question 4.

Which substance are found on cell surfaces and respond to nerve and hormone signals?

A) Vitamins and minerals

B) Subunits of DNA

C) Receptor molecules

D) Starches and simple sugars

Question 5.

Hormones and secretions of the nervous system are chemical messengers that

A) Store genetic information

B) Extract energy from nutrients

C) Coordinate system interactions

D) Carry out the circulation of materials

Question 6.

In multicelluar organisms, cells must be able to communicate with each other. Structures that enable most cells to communicate with each other are known as

A) Chloroplasts

B) Pathogenic agents

C) Receptor molecules

D) Antibiotics

TRANSPORT ACROSS THE CELL MEMBRANE http://www.youtube.com/watch?v=kfy92hdaAH0

• Passive Transport– No energy required (ATP)– Includes diffusion, osmosis, and Facilitated

Diffusion (carrier proteins “help” molecules across the membrane ie. Like a revolving door)

• Active Transport– Energy required– Requires ATP

Diffusion http://www.youtube.com/watch?v=SSS3EtKAzYc

• molecules move from an area of high concentration to an area of low concentration

• Molecules tend to “spread out”• Requires NO energy• Substances that may diffuse:

• Oxygen, carbon dioxide, amino acids, water

Click on image

Facilitated Diffusion (uses protein carriers)

• Many cell membranes have special channels (carrier proteins) that allow molecules to cross it.

• These channels help or facilitate diffusion to happen.

• Like regular diffusion, will ONLY occur if there is a higher concentration of molecules on one side of the membrane.

• Let’s see!

Osmosis

• Water molecules move from HIGH to LOW concentration

across a SEMI-PERMEABLE membrane– Only certain molecules,

like water, can move freely across the membrane

– They want to BALANCE OUT a solution

– Therefore, water moves OPPOSITE of other molecules

Low High

water

Watch How osmosis works; http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Example of Osmosis #1Example of Osmosis #1

• Condition #1: More Water outside of cell– Inside cell = 98% Water, 2% salt– Outside cell = 100% Water, 0% salt

Water moves into cell, salt moves out to balance

CELL SWELLS orCELL SWELLS orBURSTS!BURSTS!

Example of Osmosis #2Example of Osmosis #2

• Condition #2: More water inside of cell– Inside cell: 98% Water, 2% Salt– Outside cell: 95% Water, 5% Salt

Water moves out of cell, salt moves in to balance

CELL SHRIVELS!CELL SHRIVELS!

Basic Rule for Determining types of Osmostic conditions…..

If the area outside the cell has more salt – then water will be “pulled” out of the cell

•Watch the animation

Osmotic PressureOsmotic Pressure

• Cells behave differently when placed in different solutions!

• This is due to OSMOSIS!– Most cells are ~ 98% water!

• Three types of osmotic pressure:– Hypotonic– Hypertonic– Isotonic

Isotonic - "ISO" means the same

Hypotonic (Hypo = below)– Solution outside of cell has MORE water,

less of other materials (i.e., salt)• Therefore, solution is below strength (hypo)

• Examples– Animal cells may burst– “contractile vacuoles” remove excess water

Let’s see…Hypotonic ConditionLet’s see…Hypotonic Condition

• Cell is placed in 100% water– Solution outside of cell has MORE water,

less of other materials (i.e., salt)• Therefore, solution is below strength (hypo)

98%

Water ENTERS cell100%

CELLSWELLS!

Why is it dangerous to drink sea water?

Why does pouring salt on a slug kill it?

• Solution outside of cell has LESS water, more of other materials (i.e., salt)

• Therefore, solution is above strength (hyper)

• Water moves out of cell - Cell will shrink (Plasmolysis) or die, plants wilt

HYPERTONIC – “Hyper = above”

Let’s see….Hypertonic ConditionLet’s see….Hypertonic Condition

• Cell is placed in 95% water– Solution outside of cell has LESS water, more

of other materials (i.e., salt)• Therefore, solution is above strength (hyper)

Water LEAVES cell

98%

95%

CELL SHRINKS!

Isotonic - "ISO" means the same

• Solution outside of cell has SAME water, same amount of other materials (i.e., salt)• Therefore, solution is equal strength

(iso)

Let’s see….Isotonic ConditionLet’s see….Isotonic Condition

• Cell is placed in 98% water– Solution outside of cell has SAME water,

same amount of other materials (i.e., salt)• Therefore, solution is equal strength (iso)

Water moves equally; Equilibrium exists

98%

98%

CELLSTAYSTHE SAME!

Water relations and Cell shape in blood cells

HYPERTONICHYPOTONIC

Water relations in a plant cell.

Active Transport

• Sometimes, materials will move across the cell membrane AGAINST a concentration gradient.

• LOW HIGH• THIS REQUIRES ENERGY!!!

Just like pulling something uphill!• Cells get this energy from ATP

(Adenosine Triphosphate)

Low High

ATP

Types of Active Transport

– Phagocytosis = “phood”, taking in food particles– Pinocytosis = liquid substances

• Removing large particles (waste) from the cell

Exocytosis

Endocytosis - Taking “in” large molecules by the cell

Endocytosis

Exocytosis