Chapter 5

Homeostasis and Transport

What part of a cell maintains it homeostasis? Cell Membrane is selectively permeable

Regulates what goes in and out of a cell

Passive transportPassive transport

– movement of molecule across a cell membrane w/o energy expenditure.

Types of Passive transport– Diffusion– Osmosis– Facilitated Diffusion– Ion Channels

1. Diffusion – movement of molecules from an area of [High] to an area of [low].

Concentration gradient - No energy is required to go from High to low [ ].

Totally driven by molecules’ kinetic energy – constant motion.

Demos with Air freshener, Potassium Permangenate

Low

HighThe steeper the slope, the faster the rate of diffusion.

Therefore, the greater the concentration differential, the faster the rate of diffusion

• Movement of molecules continues until they reach Equilibrium

• An increase in temperature, > the kinetic energy of the molecules therefore diffusion occurs faster. – Why sugar “melts” faster in hot water over cold

• May occur across the cell membrane• Dependant on:

– size of molecules– size of pores

– & solubility of molecules (CO2 & O2) easily go into solution into bilipid layer.

Demo with Ammonia and phenolphthalein

2. Osmosis - [ ] means concentration

- net movement of water from [high] ---> [low] through a membraneDirection of water movement depends on the [ ] of solutes on 2 sides (inside the cell and outside the cell

Water Molecules move from where there is a lower solute concentration to a higher solute concentration

Demonstration of osmosis

What is happening to:

the water (blue)

and the dissolved substances (green and red). What is the same?

What is different?

Hypertonic• Hypertonic Solution:

[Solute] outside the cell is higher than inside the cytosol– More dissolved particles outside of cell than

inside of cell • Hyper = more; • Tonic = dissolved particles/solutes

– Water moves out of cell into solution – Cell shrinks – What happens when you put salt on a slug?

Red Blood Cells in a normal Red Blood Cells in a normal solute concentation, freshwater solute concentation, freshwater

and then saltand then salt

Elodea

Plasmolysis*

-  loss of cytoplasmic structure due to water.

Hypotonic

Hypotonic Solution:

[Solute] concentration outside is lower than cytosol

– Less dissolved particles outside of cell than inside of cell

• Hypo = less, under • Tonic = dissolved particles/solute

– Water moves into cell from solution – Cell expands(and may burst)

Hypotonic

• Turgidity -  swollen cells due to water gain. Plant cells depend on this!

• Cytolysis (bursting) may result.

• Isotonic Solution:– Solute

concentration of solution equal to that of cell

• No net water movement

• Most cells exists in an isotonic external environment

PlasmyolysisTurgor Pressure

• Plants usually exist in a hypotonic environment.

• Cells don’t burst due to flexible & strong cell wall.

• Turgor pressure – pressure exerted by water on a plant’s cell wall.

Part 2 of Diffusion/Osmosis lab

A B

Glucose-Starch Solution

Iodine Solution

Iodine Solution Glucose-Starch Solution

Glucose- Starch

Iodine Solution

 Day 1 Mass

(grams)

Day 2 Mass

(grams)

Difference in Mass (grams)

Percent Percent ChangeChange

Net Movement of

water(Into grape, out of grape

or no net movement)

Type of Solution

(Hypotonic, Isotonic,

Hypertonic)

Distilled water

      

   

Grape Juice

      

   

Salt Water

      

   

Osmosis Grape Lab

Percent Change = Day 2 – Day 1 Mass x 100 Day 1 Mass

QuizParamecium live in freshwater. They

have a 3% salt internal environment. How do they keep from exploding in this hypotonic environment?

Contractile VacuolesContractile Vacuoles – Organelles found in unicellular organisms that collect, then pump out excess water that enters through osmosis. Does require energy.

Like a sump pump in your basement!

Contractile Vacuoles

Facilitated diffusionFacilitated diffusionDiffusion with assistance from Carrier proteins.

Can’t occur fast enough on their own or too large to pass through pores.

May occur into or out of cell.

Carrier proteins are specific to 1 type of molecule.

Animation

Steps in Facilitated Diffusion:

1. Carrier protein binds to molecule to be transported.

2. Carrier protein changes shape (shielding it from hydrophobic interior of bilipid layer).

3. Carrier protein releases molecule & goes back to its original shape.

Occurs with glucose & amino acids (that can’t pass through cell on their own).

Diffusion thru Ion ChannelsDiffusion thru Ion Channels

– Na+, K+, Ca2+, & Cl- cannot pass thru themembrane.

Ions can not pass since ions aren’t soluble in lipids.

Therefore, they need ion channels to provide a small passageway for each ion.

Conditions for ion channel gates to open.1. Stretching of cell membrane

2. Electrical signals

3. Chemicals in cytosol

or external environment.

Active TransportActive Transport • Movement of molecules from [Low] to [High].

Energy is needed• Cell Membrane PumpsCell Membrane Pumps

– Use Carrier Proteins and becomes cell membrane pumps

• Sodium – Potassium pump - Transports Na+ and K+ up [ ] gradient

– 3 Na+ from cytosol bind to the carrier protein– Carrier proteins breaks ATP to ADP + P, P group binds to

Carrier protein– 3 Na+ are released to environment. Carrier protein changes

shape.– 2 K+ from outside cell bind to Carrier protein– With release of P group, K+ ions released into cytosol– Cycle repeats– Top speed – 450 Na+ & 300 K+ per second– Inside of cell membrane is now negatively charged,

outside is positive. Difference is necessary for electrical impulses along nerve cells.

– McGraw Hill video

http://www.google.com/url?sa=i&source=images&cd=&cad=rja&docid=UTAjNVMwmTq5DM&tbnid=N3S4g2zdYfiD0M:&ved=&url=http%3A%2F%2Fibbio.pbworks.com%2Fw%2Fpage%2F59801063%2FMembranes&ei=HgJ9Up6XDcnpkAec6IDIDg&psig=AFQjCNGP8RA0RBgyGZesGvxB4fVMCV5Kzw&ust=1384010654288808

EndocytosisEndocytosis and ExocytosisExocytosis Engulfing of macromolecules & food Engulfing of macromolecules & food particles into the cell membraneparticles into the cell membrane

Animation 1Animation 2

Endocytosis

– Cells ingest external fluids, macromolecules & large particles.

• Cell membrane surrounds material into a pouch.

• Cell membrane around pouch pinches together to form a vesicle.

• Vesicle may fuse with lysosome for digestion

2 Types of Endocytosis– Pinocytosis (cell drinking) if solutes or

fluids are involved– Phagocytosis (cell eating) if large particles

or whole cells are involved

Another animation

Occurs with bacteria, viruses or phagocytes (WBC)

Exocytosis – Release of vesicles thru cell membrane. May be proteins, waste materials, or indigestibles.

• Vesicles fuse with membrane, release contents into environment

• Proteins packaged by Golgi Apparatus into vesicles which fuse with membrane to release excess proteins

• Animation

VocabularyVocabulary• Carrier protein Diffusion• Hypotonic Passive transport• Concentration gradient Equilibrium• Ion channel Plasmolysis• Contractile vacuole Facilitated

Diffusion• Isotonic Turgor pressure• Cytolysis Hypertonic• Osmosis Active transport• Phagocytosis Sodium – K pump• Vesicle• Endocytosis Exocytosis• Pinocytosis Phagocytosis