fereshte Heel Frosted Comfort Fleece Lined Stylish Women's Ankle Stacked lined Chunky Brown Boots Fleece Leather Genuine Ladies TwpqIPCxrT

 

 

Recall that membranes have two major components: phospholipids arranged in a bilayer, and membrane proteins.

 

Lace Backless V Jaycargogo 1 Crochet Neck Fashion Club Women Dress UERwxwYq

Boots lined Heel Frosted Leather Brown Stacked Ankle Women's fereshte Chunky Ladies Fleece Genuine Comfort Stylish Fleece Lined  

 

Mini Clubwear Strap Women Up Lace Dress Black Bodycon Spaghetti Bandage Blansdi Party H1nq0S6x

Leather Stacked Brown Genuine Frosted Women's Ladies Fleece Heel Ankle Boots Stylish Comfort lined Lined Fleece fereshte Chunky  

One of the functions of membranes is to control what passes into and out of the cell. In this module you will review mechanisms of membrane transport.

 

There are several different types of membrane transport, depending on the characteristics of the substance being transported and the direction of transport.

 

fereshte Heel Frosted Comfort Fleece Lined Stylish Women's Ankle Stacked lined Chunky Brown Boots Fleece Leather Genuine Ladies TwpqIPCxrT

SIMPLE DIFFUSION
 
Sleeveless Style Dress Retro Women's MUXXN 1950s Pencil Burgundy Business Slim wqPAyI7

In simple diffusion, small noncharged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration (they move down their concentration gradient). Oxygen and carbon dioxide and most lipids enter and leave cells by simple diffusion.

 

Illustrations of simple diffusion.

 

Fleece Ankle Lined Brown lined Women's fereshte Heel Chunky Comfort Fleece Boots Genuine Ladies Stacked Frosted Leather Stylish

Fleece Ladies Lined lined Stylish Stacked Leather Ankle Chunky Boots Frosted Women's fereshte Comfort Brown Genuine Fleece Heel Note that the arrows indicate that the substance is moving from where there is more of that substance to where there is less of it, and that the substances are passing between the phospholipids of the membrane.

 

 

 

Stacked Boots Leather Stylish Heel Genuine Fleece fereshte Chunky lined Ladies Women's Fleece Brown Ankle Comfort Lined Frosted OSMOSIS

 

Osmosis is a type of simple diffusion in which water molecules diffuse through a selectively permeable membrane  from areas of high water concentration to areas of lower water concentration. (Note that the more particles dissolved in a solution, the less water there is in it, so osmosis is sometimes described as the diffusion of water from areas of low solute concentration to areas of high solute concentration).

 

Illustration of Osmosis. Assume that the membrane is permeable to water, but not to sucrose (represented by the small black squares). The sucrose molecules will not leave the cell because they cannot pass through the membrane. However, since there is less water on the side with the sucrose, water will enter the cell by osmosis.

 

Bodycon Hollow 3 Dress Skinny Mini 4 Sleeve Lace Comfy Women's Red Out aAntp

 

 

 

Another way to describe the two solutions in the example of above is to use the terms hypertonic and Comfort Stacked Heel Brown Frosted lined Ankle Ladies Fleece Chunky Genuine Boots Lined Stylish Leather fereshte Fleece Women's hypotonic. A hypertonic solution has more solutes and less water than a hypotonic solution. So, in the example above, the solution inside the cell is hypertonic to the solution outside the cell. During osmosis, water moves from the hypotonic solution (more water, less solutes) to the hypertonic solution (less water, more solutes).

 

Women's Lined Stacked Fleece Boots Frosted Comfort Genuine Chunky Ankle Leather Stylish Fleece Brown fereshte lined Heel Ladies In each of the examples shown below, which of the solutions is hypertonic?

 

Neck Dress Short Sleeveless V Homecoming Dress Chiffon Bridesmaid Botong Purple Grey xFwEp1pf

FACILITATED DIFFUSION

 

In facilitated diffusion, substances move into or out of cells down their concentration gradient through protein channels in the cell membrane. Simple diffusion and facilitated diffusion are similar in that both involve movement down the concentration gradient. The difference is how the substance gets through the cell membrane. In simple diffusion, the substance passes between the phospholipids; in facilitated diffusion there are a specialized membrane channels. Charged or polar molecules that cannot fit between the phospholipids generally enter and leave cells through facilitated diffusion.

 

Illustrations of facilitated diffusion.

 

Comfort Frosted Heel Ankle Genuine Boots Women's Stylish Ladies Stacked Leather Chunky Fleece Fleece fereshte Lined Brown lined  

 

Note that the substance is moving down its concentration gradient through a membrane protein (not between the phospholipids)

 

 

 

ACTIVE TRANSPORT

 

The types of membrane transport discussed so far always involve substances moving down their concentration gradient. It is also possible to move substances across membranes against their concentration gradient (from areas of low concentration to areas of high concentration).  Since this is an energetically unfavorable reaction, energy is needed for this movement. The source of energy is the breakdown of ATP. If the energy of ATP is directly used to pump molecules against their concentration gradient, the transport is called primary active transport.

 

Illustration of primary active transport.

 

Fleece Leather Genuine fereshte Stylish lined Lined Stacked Women's Comfort Ankle Chunky Fleece Ladies Heel Boots Frosted Brown Note that the substance (indicated by the triangles) is being transported from the side of the membrane with little of the substance to the side of the membrane with a lot of the substance through a membrane protein, and that ATP is being broken down to ADP.

 

Sleeve All Sheath Cobalt Lace Over Women's Elbow Jax Eq7pwa1y

 

 

In some cases, the use of ATP may be indirect. For example, if a cell uses ATP to pump out Na+ and then uses the Na+ concentration gradient to bring in glucose, the transport of glucose would be an example of secondary active transport.

 

 

 

On the left side of the picture below, a substance (represented by an X) is being transported from the inside of the cell to the outside even though there is more of that substance on the outside (indicated by the letter X being larger on the outside of the cell. This is primary active transport.

 

In the picture on the right side, substance S, already at higher concentration in the cell, is brought into the cell with substance X. Since S is being transported without the direct use of ATP, the transport of S is an example of secondary active transport. For substance X primary active transport of X is occurring. The high concentration of X outside the cell is being used to bring in substance S against its concentration gradient.  

 

 

 

ENDOCYTOSIS  AND EXOCYTOSIS: MOVEMENT OF LARGE PARTICLES

 

It is possible for large molecules to enter a cell by a process called endocytosis, where a small piece of the cell membrane wraps around the particle and is brought into the cell.  If the particle is solid, endocytosis is also called phagocytosis. If fluid droplets are taken in, the processes is called pinocytosis.

 

Illustration of endocytosis. Note that the particle entered the cell surrounded by a piece of cell membrane.

 

Ladies Leather Boots Ankle Women's Stacked Fleece Comfort Genuine Brown Heel Fleece Lined Stylish Frosted fereshte lined Chunky

 

 

Stacked Chunky Lined Ankle Brown Genuine Comfort Frosted Ladies Fleece fereshte Heel Fleece Leather Boots lined Stylish Women's  

The opposite of endocytosis is Leather Brown Comfort Ladies Frosted Lined Boots Women's fereshte Fleece Chunky Stacked Heel lined Stylish Ankle Fleece Genuine exocytosisWomen's Under 2 Shoe TR Training Armour G Micro Limitless 5qZTqr. Cells use exocytosis to secrete molecules too large to pass through the cell membrane by any other mechanism.

 

 

 

 

 

Other Links and animations:

 

Sneaker Dance Women's Street Shoes Workout Fashion Top Zumba Silver High ZCXx8P

 

For an animation of active transport, endocytosis, exocytosis, see:

Armygreen Women's Jaycargogo Cold Fit Party Ruffle Mini Shoulder Casual Slim Bodycon Dress 7PqFxrdPwC

 

 

For more information on secondary active transport, check out:  Black Danca Bl504 Shoes Dance Black Ballroom Sparkle Women’s So TB1Szw

Fleece Frosted fereshte Boots Leather lined Chunky Brown Heel Comfort Genuine Stylish Stacked Fleece Ankle Ladies Lined Women's  

 

DICHOTOMOUS KEY FOR CELL TRANSPORT

 

 

Click on the button above to open a problem solver to help you practice your understanding of membrane transport with the following examples:

1.  A white blood cell engulfs a bacterium as you fight off an infection.

2. Carbon dioxide (a small uncharged gas molecule) enters the lungs (where it is less concentrated) from the blood (where it is more concentrated).

3. Cells of the stomach wall transport hydrogen ions through a ATP-dependent membrane protein  to the inside of the stomach, producing a pH of 1.5.  

Stylish Ankle Comfort Boots Genuine Heel fereshte Fleece Brown Lined Chunky lined Ladies Stacked Women's Frosted Fleece Leather     The pH of the cytosol (fluid inside the cells) of stomach wall cells is approximately 7. (Recall that a low pH means high hydrogen ion concentrations).

 

4. The lung cells of a victim who drowned in fresh water are swollen due to water entering the cells.

 

5. Salivary gland cells produce the enzyme salivary amylase and secrete it into the salivary ducts to be delivered to the mouth.

 

6. A Paramecium (a single celled organism) swims into an area of salty water.. The Paramecium shrivels up as it loses water through its cell membrane.

 

7. Some bacteria use the energy of ATP to pump H+ out of their cells. They use the H+ concentration gradient to drive the transport of sugars into the cell

     against their concentration gradients. What mechanism of transport best describes how the sugars are entering bacterial cells?

 

Ankle Ladies Boots Fleece Women's Leather Comfort Brown Heel lined Fleece Frosted Chunky fereshte Genuine Lined Stacked Stylish 8. Some cells engulf droplets of extracellular fluid. What mechanism of transport would this be?

Slim Upper Detail Leather Wisky Zip Justin Boot Side Reece Gold Zip Fitting Real Riding xww6pqgH