Sample Exam in Passive Transport

DIFFUSION & OSMOSIS

Diffusion is the result of the random motion of molecules.

According to Newton's laws of motion, objects will remain in motion and travel in a straight line unless acted upon by an unbalanced force. Thus we have molecules constantly moving back and forth, colliding with each other, bouncing off, and spreading outward away from the middle. This results in a gradual spreading of molecules from areas of great concentration to areas of lesser concentration. Many things can diffuse. Odors diffuse through the air. Salt diffuses through water. Nutrients diffuse from the blood to the body tissues.

The difference between the greater concentration and the lesser concentration is called a concentration gradient. Just as water will always flow from high to low, molecules will always diffuse down the gradient, from high to low. However, when there are equal numbers of molecules in each area, a state of equilibrium has been reached. At this point molecules continue to move, but they now move back and forth in equal amounts.

Diffusion of substances and their absorption by the body is an important part of many of our body functions. The regulation and maintenance of a steady balance of substances in the body is referred to as homeostasis. The cell membrane is the most important part of the cell in regard to homeostasis of substances. In living organisms diffusion is sometimes complicated by the fact that the cell membrane will allow some substances to pass through it but not others. If a substance can pass through the membrane we say that the membrane is permeable to it. So the cell membrane is described as being selectively permeable. Water can almost always diffuse through the membrane although its dissolved solutes may not always do so. This may create concentration gradients (areas of high and low concentration) on either side of the membrane. This diffusion of water through a cell's selectively permeable membrane is termed osmosis.

The main direction in which the water flows is determined by the concentration gradient. The concentration gradient of solutions is indicated by use of the terms hypotonic, hypertonic, and isotonic.

The prefix hypo means "less than". The prefix hyper means "greater than". The prefix iso means "equal".

ANSWER QUESTIONS 1-6

In a hypotonic solution the concentration of dissolved solutes is less than that of the cell. This means that the water concentration will be higher outside the cell and more water will move into the cell. Cells placed in this type of solution may swell, build up pressure, or burst. The bursting of cells, cytolysis, happens more often in animal cells because they have no thick cell walls. In order to prevent this, some unicellular organisms pump out the extra water using organelles called contractile vacuoles. Plant cells, with their thick cell walls, may build up a pressure called turgor.

EXAMPLE:

Blood cells have a salt concentration of 0.9% salt. This means that they are approximately 99% water (This is higher than most cells). When blood cells are placed in distilled water (pure water, 100% water), more water diffuses into the membrane than diffuses out. Think of it in this way. Since the substance outside the membrane is 100% water molecules (and the membrane is permeable to water) all of the molecules that try to diffuse through, will be able to pass into the cell. However, only 99% of the molecules on the inside of the cell are water molecules. Thus only 99% of the molecules that try to diffuse out will be able to. Therefore there are 100 molecules going in, for every 99 that come out. Eventually the increase in water may cause the blood cells to burst (cytolysis.)

ANSWER QUESTIONS 7-11

In a hypertonic solution, the concentration of dissolved solutes is greater than that of the cell. This means that the water concentration outside the cell will be less than the concentration inside. More water will diffuse out of the cell than in. When this occurs the cell shrinks or shrivels. This is called plasmolysis.

Example: When salt is poured on a snail, a hypertonic solution is created because the concentration of salt is greater outside his body than inside the cells. If the salt solution outside is 20% salt, then the water concentration is 80%. If the water concentration inside the snail's cells is in the 90% range, more water diffuses out of the cell than in. In reality water diffuses both directions. But for every 80 molecules that diffuse in, 90 molecules diffuse out. As a result the cells of the snail shrink or shrivel (plasmolysis).

In an isotonic solution, the concentration of the dissolved solutes is the same inside and outside the cell. If the water concentration of the snail cells is 90% (10% solutes) and they are placed into a 10% salt solution (90% water), then equal numbers of water molecules will diffuse in and out of the cells.

ANSWER QUESTIONS 12-16

OTHER TYPES OF TRANSPORT:

Substances may pass through the membrane by diffusion, moving from areas of higher concentrations to lower concentrations without using any energy from the cell. These types of movment requiring no use of cell energy are called Passive Transport. They include simple diffusion, osmosis, and a type of assisted diffusion called Facilitated Diffusion. To "facilitate" means to make easier. Facilitated diffusion is used to speed up the diffuion of larger molecules, like glucose, through the membrane. In order to do this, special protein molecules imbedded in the lipid membrane combine with glucose and then change shape, pulling the glucose through the membrane. These special protein molecules are called carrier molecules. Facilitated diffusion works only when the diffusion is from high to low.

Cells also have special protein molecules called "gated-channels" that can be turned on or off as needed to make the membrane permeable or impermeable to certain substances. These open up at specific times to allow substances to diffuse through.

Sometimes the cell needs to move substances through the membrane against the concentration gradient (from low to high). Going against the concentration gradient requires the use of energy (like paddling upstream). The use of energy to transport substance across the membrane is called Active Transport. One common use of active transport is used to maintain high levels of sodium ions outside the cell and high levels of potassium ions inside the cell. This is called the sodium-potassium pump. During active transport ATP molecules cause carrier molecules to move 3 sodium molecules out of the cell and bring 2 potassium molecules into the cell. This unequal distribution positive ions creates an electrical potential that is responsible for the generation of nerve impulses. Other pumps are also used elsewhere in the body.

ANSWER QUESTIONS 17-20

Molecules that are too large for gated channels, pores, or carrier molecules, such as food materials and waste materials may enter and leave the cell through processes called Endocytosis and Exocytosis. During endocytosis, the membrane encloses a large object (such as food) in an inward pouch and then pinches off to the inside where cellular enzymes may digest the food. When endocytosis involves large solid particles it is referred to as phagocytosis. If endocytosis involves movement of dissolved solutes or fluids into the cell, it is referred to as pinocytosis. Amebas feed by using phagocytosis. White blood cells may also destroy bacteria in the body by phagocytosis.

Exocytosis is the process of transporting substances out of the cell that are too large to pass through the membrane. It is the exact reverse of endocytosis. One common example is the export

of packaged proteins out of the cell. The ribosome manufactures the proteins which are transported to the golgi apparatus where they are surrounded by a membrane forming a bubble or vesicle. These vesicles move to the membrane, fuse with it, and empty their contents out of the cell.

ANSWER QUESTIONS 21-25

Osmosis Tutorial

Click on the correct answer

1 Which of the following would be an example of simple diffusion?the smell of ammonia spreading throughout the room

water being poured into a glass

blood cells shrinking when placed in salt water

turgor pressure in plant cells

2 Which of the following would be an example of osmosis?the smell of ammonia spreading throughout the room

the shriveling of a snail after salt is poured on it

water being poured into a glass

the absorption of water by a bathroom sponge

3 A state of biological balance maintained by living organisms is called .....phagocytosis

osmosis

cytolysis

homeostasis

4 The part of the cell that is most important in maintaining homeostasis with the cell's environment is the ...

nucleus

cytoplasm

DNA

cell membrane

5 Which prefix means "greater than"?hypo

hyper

iso

plasmo

cyto

6 When the process of diffusion reaches an equilibrium state:the movement of all molecules stops

molecules continue to move but in equal amounts

a further exchange of molecules ceases

a hypotonic solution is formed

7 Red blood cells contain 0.9% salt. Which of the following solutions would be hypotonic to the blood?

9%

0.9%

0.09%

1.9%

8 The bursting of cells due to osmosis is called ....plasmolysis

hypertonic

cytolysis

turgor

9 The pressure that builds up in plant cells due to osmosis and the strength of the cell walls is called ...

plasmolysis

hypertonic

cytolysis

turgor

10 Sea water is approximately 3% salt. Sea water is hypertonic to the tissues of freshwater fish. Therefore we can conclude that the tissues contain .......% salt.

3%

greater than 3%

less than 3%

none of these

11 Unicellular freshwater organisms find themselves in a hypotonic solution. In order to get rid of excess water that diffuses into the cells, these organisms use .....

plasmolysis

turgor

cytolysis

contractile vacuoles

12 Red blood cells contain 0.9% salt. Which of the following solutions would be isotonic solutions to the blood?

9% salt

0.9% salt

0.09% salt

0% salt

none of these

13 Carrot sticks that are left in a dish of freshwater for several hours become stiff and hard. Similar sticks left in a saltwater solution become limp and

solf. From this we can deduce that the freshwater is ______ and the saltwater is ________ to the cells of the carrot sticks.

hypotonic / hypotonic

hypertonic / hypotonic

hypotonic / hypertonic

hypertonic / hypertonic

14 In an attempt to replenish the body fluids, a patient (who has had serious hemorrhage) accidentally receives a large transfusion of distilled water directly into one of his veins. This would probably .....

have no unfavorable effect as long as the water was sterile

have serious, perhaps fatal effects because there would be too much fluid for the heart to pump.have serious, perhaps fatal effects because the red blood cells would tend to shrivelhave serious, perhaps fatal effects because the red blood cells would tend to burst

15 A solution that contains a higher level of salts than found in cells is said to be .....

hypertonic

hypotonic

isotonic

catatonic

16 A beacher is divided into two halves, A & B by a membrane freely permeable to the water but not to glucose. Side A is filled with a solution of water with 2% glucose, while side B is filled with water and 4% glucose. Which best describes what will happen to this system.

water will move from A to B

water will move from B to A

water will move equally in both directions

water will move in both directions but mostly from A to B

water will move in both directions but mostly from B to A

17 Movement of substances across the membrane without the use of cellular

energy is termed ......active transport

carrier transport

passive transport

the sodium-potassium pump

18 The process of facilitated diffusion requirescarrier proteins

no input of energy from the cell

a downhill gradient

all of these

none of these

19 One common example of active transport is ....the diffusion of glucose across a membrane

the sodium-potassium pump

osmosis

plasmolysis

20 Both facilitated diffusion and active transport make use of carrier molecules that change shape and move substances through the membrane. These molecules are made of .....

hydrophobic lipids

carbohydrates

proteins

hydrophilic lipids

21 Substances that are much too large to pass through the cell membrane may still get into the cell through the process of .....

endocytosis

exocytosis

facilitated diffusion

active transport

osmosis

22 The engulfing or swallowing of large objects by amebas or white blood cells is called .....

exocytosis

pinocytosis

phagocytosis

oxytosis

23 Which one of the following DOES NOT BELONG?Passive

Active

Facilitated diffusion

Osmosis

24 Which of the following cell structures are involved in exocytosis involving packaged proteins?

cell membrane

golgi apparatus

ribosomes

all of these

25 A beaker is divided into two halves, A & B, by a membrane that is freely permeable to the water and NaCl but not to protein. Side A is half-filled with a solution of 8% protein, while side B is half filled with a 2% protein solution. After time goes by, it is found that in side A ......

the number of protein molecules has increased

the number of water molecules has decreased

the number of water molecules has increased

the percentage of water has decreased

WelcomeType your answers and click on "Check". There are words to choose from at the bottom of the page.

Osmosis Review

Gap-Fill Exercise

1. "Hypo" means " than".

2. transport requires the use of cell energy to move materials through the cell membrane against the concentration gradient.

3. is a specific term referring to the movement of small particles or liquids into the cell.

4. diffusion moves substances passively through the membrane from high concentrations to low concentrations using carrier proteins.

5. is a specific term referring to the movement of large particles or solids into the cell.

6. solutions have equal concentrations of solutes inside and outside the cell.

7. solutions have lower concentrations of solutes outside the cell.

8. solutions have higher concentrations of solutes outside the cell.

9. transport allows substances to enter the cell without any energy being used from the cell.10. A cell that is 70 percent water is placed into a 30 percent sugar water solution, what will

happen to the cell? Water will move of the cell .

11. A concentration refers to the difference between the high and low concentrations.12. A cell that is 60 percent water is placed into a 30 percent sugar solution in water. What will

happen to the cell? Water will move the cell.

13. A general term that refers to the bulk transport of large objects into the cell is .14. Animal cells have no cell walls. When placed in hypotonic solutions animal cells may

or burst.

15. Because of osmosis, plant cells build up water pressure inside. This pressure is called .

16. Bulk movement of materials out of the cell is referred to as .

17. Cell membranes are selectively , which means that they allow only certain substances to pass through.

18. Diffusion rates may be affected by: concentration, temperature, and .

19. Distilled water has no solutes and is therefore to all cells.

20. Glucose enters cells through the process of diffusion.

21. Hypertonic solutions cause water to flow of a cell. (like putting salt on a snail)

22. Hypotonic solutions cause water to flow the cell.23. If a cell that is 80 percent water is placed into a 30 percent sugar in water solution, what will

happen to the cell? Water will move the cell.24. If a cell that is 80 percent water is placed into a distilled water solution, what will happen to

the cell? Water will move the cell.

25. and diffusion are examples of passive transport which take place without cell energy.26. Osmosis depends on the concentration gradient on each side of the membrane which is

determined by the concentration of dissolved in the water.

27. Some cells may pump out excess water through special organelles called vacuoles.

28. Special protein molecules called molecules move some larger molecules through the membrane.

29. The bursting of cells due to osmosis is referred to as .

30. The cell membrane is composed of a double layer of with some proteins embedded in and through it.

31. The current model of membrane structure is called the Fluid Model.

32. The diffusion of water through a selectively permeable membrane is termed .

33. The prefix "hyper" means " than".

34. The prefix "iso" means " ".

35. The random motion of molecules (when first observed) was referred to as motion.36. The random motion of molecules that occurs from a region of higher concentration to a

region of lower concentration is called .

37. The shrinking of cells due to osmosis is referred to as .

38. Water flows in and out of cells until it reaches (equal concentrations). Then itcontinues to flow both directions in equal amounts.

Top of Form

  Active     brownian     carrier     contractile     cytolysis     diffusion     endocytosis     equal to     equally     equilibrium     exocytosis     Facilitated     facilitated     gradient     greater     

Hypertonic     hypotonic     Hypotonic     in and out     into     into     into     Isotonic     less     lipids     lyse     Mosaic     Osmosis     osmosis     out     out of     Passive     permeable     

Phagocytosis     Pinocytosis     plasmolysis     pressure     solutes     turgor