HOMEOSTASIS AND THE PLASMA MEMBRANE

Section 4 Cellular Transport 1. Diffusion,

2. Dynamic equilibrium,

3. Facilitated diffusion,

4. Osmosis,

5. Isotonic solution,

6. Hypotonic solution,

7. Hypertonic solution,

8. Active transport,

9. Endocytosis,

10. exocytosis

SC.912.L.14.2

• Relate structure to function for the components of plant and animal cells.

• Explain the role of cell membranes as a highly selective barrier (passive and active transport) (as 14.3)

•  

PLASMA MEMBRANE

• SEPARATES THE INSIDE CONTENTS OF THE CELL FROM THE OUTSIDE ENVIRONMENT AND CONTROLS WHAT GOES IN AND OUT OF THE CELL

A real cell membrane

FLUID MOSAIC MODEL• FLUID BECAUSE IT MOVES

• MOSAIC BECAUSE IT CONTAINS SEVERAL DIFFERENT PARTS

SELECTIVELY PERMEABLE

• SELECTIVE: PICK OR CHOOSE

• PERMEABLE: CAN PASS THROUGH OR GETS IN OR OUT OF SOMETHING

• The plasma membrane is not like a sieve because it can change what goes in and out from time to time depending upon the cells “needs”.

Diffusion and osmosis

• http://www.youtube.com/watch?v=AYNwynwaALo&feature=youtube_gdata_player

• Selective permeability is a property of the cell membrane that allows the cell to maintain homeostasis by taking in some substances, letting out some substances and being able to alter this function as needed.

• Predict what will happen• sugar• water• salt

endocytosis

• When a cell brings something into the cell across the cell membrane

• Phagocytosis is cell “eating”

• http://wolfbat359.com/phagocytosis1.html

• See favorites: cells link

• Pinocytosis is cell “drinking”

exocytosis

• When the cell moves something out of the cell across the cell membrane.

exocytosis• Exit cell

• things going out of the cell

diffusion• movement of particles from an area of

higher concentration to an area of lower concentration.

•            net movement- movement which changes concentrations

Diffusion

• Diffusion is the movement from a high concentration of molecules to a low concentration of molecules. 

factors that affect diffusion

•            particle size and shape

•            temperature

•            concentration gradient- difference in concentrations

          

• cytoplasmic streaming- continuous movement of materials in cytoplasm

•  

Diffusion interactive

• http://www.wisc-online.com/objects/index.asp?objID=AP1903

http://www.wisc-online.com/objects/index_tj.asp?objID=AP1903

Facilitated diffusion

• using a protein to move particles down the conc. gradient

Passive transport

• Molecules can diffuse across membranes through the phospholipid bilayer or using a special protein. 

• Either kind of diffusion does not need energy from the cell. 

osmosis

• diffusion of water across a selectively permeable membrane

•         - water moves from an area of high water concentration.

• to an area of low water concentration .

low solute high solute

• In this picture a red blood cell is put in a glass of distilled water (all water with no salt or sugar in it).  Because there is a higher concentration of water outside the cell, water enters the cell by OSMOSIS.  In this case too much water enters and the cell swells to the point of bursting open.  In the end pieces of cell membrane are left in the water.  

•  

Dynamic equilibrium• When the overall movement is not in any

one direction.

• Things are evenly spread out but continue to randomly move.

Active Transport• When energy is required to move

molecules against a concentration gradient

Active Transport

• Some special proteins move certain molecules across cell membranes only with the help of cell energy (either directly or indirectly). 

• Moving molecules with cell energy is called active transport. 

Contractile vacuoleFresh Water Protists -

Adaptation: Contractile Vacuole Store & Expel H2ORequires energy

Maintain homeostasis

Passive and active transport

• http://www.youtube.com/watch?v=1ZFqOvxXg9M&feature=youtube_gdata_player

tonic

• Hypo

• Iso

• hyper

ISOTONIC

• WHEN THE CONCENTRATION OF SOLUTES OUTSIDE AND INSIDE THE CELL ARE EQUAL, THE OUTSIDE SOLUTION IS SAID TO BE ISOTONIC TO THE CYTOSOL. UNDER THESE CONDITIONS. WATER DIFFUSES INTO AND OUT OF THE CELL AT EQUAL RATES, SO THERE IS NO NET MOVEMENT OF WATER.

ISOTONIC

HYPERTONIC

• WHEN THE CONCENTRATION OF SOLUTE MOLECULES OUTSIDE THE CELL IS HIGHER THAN THE CONCENTRATION IN THE CYTOSOL, THE SOLUTION OUTSIDE IS HYPERTONIC TO THE CYTOSOL. IN THIS SITUATION, WATER DIFFUSES OUT OF THE CELL UNTIL EQUILIBRIUM IS ESTABLISHED.

HYPERTONIC

  plasmolyzed

The plasma membrane

• http://www.youtube.com/watch?v=moPJkCbKjBs&feature=youtube_gdata_player

HYPOTONIC

• WHEN THE CONCENTRATION OF SOLUTE MOLECULES OUTSIDE THE CELL IS LOWER THAN THE CONCENTRATION IN THE CYTOSOL, THE SOLUTION OUTSIDE IS HYPOTONIC.  IN THIS SITUATION, WATER DIFFUSES INTO THE CELL UNTIL EQUILIBRIUM IS ESTABLISHED.

HYPOTONIC

Quiz

• The job of the ___________ is to control what enters and exits the cell.   

• Molecules can enter a cell across the cell membrane by going through the _______________  ___________ or by using a special protein.   

•                     Cell membranes are made up of _________  and _________.  

• The _____________ makes up the rest of the space in the cell and is what the other organelles are suspended in.   

• The heads of phospholipids are __________ so they like to  be with water.

• A molecule that needs energy to move across a cell membrane moves by ____________ ___________.

1. I n what direction do molecules move by diffusion? From areas of greater to less concentration or lesser to greater concentration? Greater to lesser concentration____ why? The 2nd law of thermodynamics says things move towards more entropy/disorder

2. Do they ever stop moving? no

3. When the net movement stops what is reached? _dynamic equlibrium

4. When a “helper molecule” is needed to move something across a cell membrane, what is this called? _facilitated diffusion_

5. What is osmosis? The diffusion of water across a membrane ( from high concentration of water to low concentration of water)

6. What happens to a cell placed in a hyper tonic solution? It shrinks

7. What does active transport use as its energy source? ATP

8. What is passive transport? Movement from high to low concentration without energy needed. Osmosis, diffusion and facilitated diffusion are examples

9. How does an increase in temperature affect the rate of diffusion? It increases it

• Why?_molecules move faster at hig temperatures, so the process occurs faster._____________

• How does a decrease in temperature affect the rate of diffusion? __it will slow down

• Why? Molecules move slower at cold temperatures so the process will go slower.  

10. How is facilitated diffusion different from diffusion? _Facilitated requires a transport protein to move the molecules across the cell membrane.___

11. Differentiate between passive and active transport. Passive requires no energy and moves high to low, active requires energy and moves low to high

12. What happens to a cell in an isotonic solution? It remains the same size why? molecules move in and out at the same rate.

13. What happens to a cell in a hypertonic solution? It will shrink• why? Water is removed from the cells to move into the surrounding

solution that has less water.

14. What happens to a cell in a hypotonic solution? The cells will swell• why? _water will move into the cells because there is more water in

the surrounding solution than in the cells.

15. Why would a cell need to use endocytosis? The bring in by pinocytosis liquids in large quantities too large to cross the cell membrane or large solids by phagocytosis too large to cross.

16. Why would a cell need to use exocytosis? to remove large molecules for transport or waste materials too large to pass across the cell membrane.

Review of cells video

• http://www.cleanvideosearch.com/media/action/yt/watch?v=1Z9pqST72is&list=PL7A750281106CD067&index=5&feature=plpp_video

Diffusion Video Review

• http://www.cleanvideosearch.com/media/action/yt/watch?v=RPAZvs4hvGA