8.2 TRANSPORT ACROSS CELL MEMBRANES

TERMS… Selective Transport: the movement of

only certain substances across the cell membrane

Particle Model of Matter – all matter is made of tiny particles

Brownian motion – in a liquid or a gas, particles are in constant, random motion

Brownian motion video: http://www.youtube.com/watch?v=2Vdji

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TERMS… Concentration Gradient – the difference

in concentration between two areas for any given molecule produces a gradient or path of movement in which molecules move toward areas where the concentration of particles is lower.Molecules move down a concentration gradient

Equilibrium – a state at which molecules are evenly distributed (the concentration is equal throughout the medium)Molecules continue moving but equilibrium is

maintained

TYPES OF TRANSPORT ACROSS MEMBRANESA. Passive Transport – movement

across cell membranes without an input of energy

Q. Name 2 reasons molecules move1. Brownian Motion2. Concentration gradients

THREE TYPES OF PASSIVE TRANSPORT1. Diffusion – the net movement of

particles from an area of high concentration to an area or low concentration (down the gradient)- no energy is expended- In a cell, very small particles can cross the cell membrane by moving between the phospholipid molecules

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

- Match demo- Handout, do first diagram

DIFFUSION Q: Why does oxygen diffusion into

the cell never reach equilibrium? A: your cells continually consume

oxygen for cellular respiration, making the concentration inside always lower than the outside

Q: describe the concentration gradient of carbon dioxide.

A: higher concentrations in the cell so net movement is out of the cell

PASSIVE TRANSPORT: 2. OSMOSISOsmosis: the diffusion of water

molecules across a membrane (water molecules move from where they are more highly concentrated to where they are less concentrated; down their concentration gradient) Water molecules will go to the side that more solute is on.

Solutions are described in terms of their concentration relative to another solution.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

OSMOSISa) Hypotonic solution – has a lower

concentration of solute compared to outside the cell

Water is therefore more concentrated inside the cell and water will leave the cell (cell shrinks).

b) Hypertonic solution – has a higher concentration of solute compared to the outside of the cell

Water is therefore less concentrated inside the cell and water will enter the cell (cell swells)

OSMOSISc) Isotonic solution – has the same

solute concentration on both sides of the cell membrane. Equilibrium has been reached.

Q: What happens when a cell is placed into distilled water?

A: The cell is hypertonic and water moves into the cell & the cell may burst

OSMOSISQ: what is turgor pressure?A: the cell wall of a plant resists the pressure of a

water-filled vacuole keeping the plant firm.Q: What happens when a cell is placed into a

strong salt water?A: the solution is hypertonic and water leaves the

cell. The cell shrinks and may die (plasmolysis)Q: What is plasmolysis?A: loss of water in a plant cell resulting in wilting (cell

shrinks)Q: Why would drinking saltwater pose a

problem?A: Hypertonic solution outside cells would cause cells

to lose water, shrink and die (dehydration)

PASSIVE TRANSPORT: 3. FACILITATED DIFFUSION

Facilitated Diffusion: diffusion of molecules across the cell membrane by way of transport proteins.- necessary for glucose, ions and other substances that cannot cross the membrane by simple diffusion

Transport proteins have 3-D shapes that make them highly selective, recognizing atoms or molecules by shape, size or charge.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

TWO TYPES OF TRANSPORT PROTEINS:a) Carrier proteins – facilitate the

diffusion of glucose across the cell membrane

Q: Explain how glucose enters the cell.

A: Glucose fits into a groove on the carrier (like a lock and key), the protein’s shape changes, and glucose is released on the inside of the cell.

b) Channel proteins – have tunnel-like pores filled with water that allow charged ions in and out of the cell

ACTIVE TRANSPORT …The movement of molecules and ions

against the concentation gradient which requires ATP energy and carrier proteins to pump these molecules from an area of low solute concentration to an area of high solute concentration. (UP or against the concentration gradient)used to accumulate nutrients, or remove

toxic materials or wastes

ACTIVE TRANSPORThttp://

www.coolschool.ca/lor/BI12/unit4/U04L03/active%20transport_jeffedit.swf

Most cells use 40% of their energy on active transport; kidney cells use 90% of their energy on active transport

Example: Plants and potatoes

C. BULK TRANSPORT- The use of vesicles to facilitate movement of

substances that are too large to enter or exit the cell via transport proteins.

Two types:1. Endocytosis – the cell membrane forms a

pocket around the material to be transported, then either pinches off as a vesicle or a vacuole.

Q: Differentiate between a vacuole & vesicle.A: Vesicle transports contents; vacuole stores the

ingested material.

ENDOCYTOSISTwo Types of Endocytosis:a) Phagocytosis – when cells “eat” by

taking in large particles or other cellshttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.htmlQ: What happens after a new vesicle

enters the cytoplasm of a cell?A: It fuses with a lysosome and the

enzymes would digest the materialb) Pinocytosis – when cells “drink: by

taking in droplets of fluid

ENDOCYTOSIS Receptor – mediated endocytosis (RME) –

receptors, like antennae, detect specific compounds or cells and bind with them, triggering endocytosis.

Q: Give 2 examples of molecules entering by RME

A: cholesterol & HIV

2. EXOCYTOSIS- The reverse of endocytosis, whereby the

membrane of vesicles or vacuoles fuses with the cell membrane and the stored contents are expelled from the cell.

Q: Give 2 examples of expelled materials.

A: wastes, enzymes, hormoneshttp://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf

MEMBRANES AT WORK: APPLICATIONS1. Water Purification

Reverse osmosis – uses pressure to force contaminated water through a membrane with fine pores that will not allow bacteria, salts, and other dissolved molecules through, resulting in water with fewer impurities.

WATER PURIFICATION: REVERSE OSMOSIS

MEMBRANES AT WORK: APPLICATIONS2. Kidney Dialysis – filters toxic wastes

that accumulate in the blood while retaining necessary proteins, glucose, amino acids & ions

- The patient’s blood is pumped through dialysis tubing, a synthetic, semi-permeable membrane.

- When immersed into a salt solution, needed salts don’t diffuse, but wastes, which are hypertonic to the dyalysate diffuse out of the blood.

KIDNEY DIALYSIS

CONTROLLED DELIVERY OF MEDICATIONS

a) Medication can be placed in a flat transdermal patch that sticks to the skin. A semi-permeable membrane lining the inner surface allows drugs to diffuse out of the patch at a slow, constant rate.

Q: give 4 examples of medications available in patches

A: - nicotine, hormones, motion sickness drugs, contraceptives, pain reducers, weight loss

CONTROLLED DELIVERY OF MEDICATIONSb) Liposomes – artificial vesicles that can

safely transport medications from one part of the body to another

Two Examples:1) Used to transport anti-cancer

medications to tumors in cancer patients

2) Liposomes, coated with the gene needed to cure cystic fibrosis, are sprayed into the patients nostrils