Worksheet. Passive Transport Diffusion & Osmosis - PMA SCIENCE

Name:___________________________________________ Date: _________________________ Period:___________

Worksheet: Passive Transport Diffusion and Osmosis

All cells are enclosed by a cell membrane that consists of a double layer of phospholipids interspersed with proteins. Its unique characteristic is described as selectively permeable because it permits some substances to cross it rapidly, while others are unable to cross it, or cross it slowly. Naturally, molecules move from an area of high concentration to low concentration without the need of energy. Movement across the membrane without the need for energy is called passive transport. Diffusion is defined as the movement of molecules from an area of high concentration (more crowded) to an area of low concentration (less crowded).

Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly.

Molecules with strong electrical charges such as ions cannot simply diffuse across the cell

membrane. Irrespective of their size, their charge prevents them from moving freely across the cell

membrane. Other molecules such as proteins, starch and sugar are simply too large to diffuse

across the membrane. Sometimes, some of these large molecules are transported across the cell

membranes by carrier proteins; this does not require energy and as a result is a form of passive

transport.

There are three types of passive transport: simple diffusion, osmosis, and facilitated diffusion. The

term simple diffusion refers to a process whereby a substance passes through a membrane

without the help of an intermediary such as an integral membrane protein. Hydrocarbons, carbon

dioxide, and oxygen are hydrophobic substances that can pass easily across the cell membrane by

simple diffusion and travel down the concentration gradient (from high concentration to low

concentration). This type of diffusion relies on the thermal motion energy intrinsic to the molecule

in question. It is a form of passive transport because the cells use no energy in moving the

substances.

The movement of water across a selectively permeable membrane is osmosis. A cell has one of

three water relationships with the environment around it:

? In an isotonic solution there will be no net movement of water across the plasma

membrane. Water crosses the membrane, but at the same rate in both directions.

? In a hypertonic solution the cell will lose water to its surroundings. The hyper -- prefix

refers to more solutes in the water around the cell, hence, the movement of water to the

higher (hyper--) concentration of solutes. In this case the cell loses water to the

environment, shrinks, and may die.

? In a hypotonic solution water will enter the cell faster than it leaves. The hypo -- prefix

refers to fewer solutes in the water around the cell, hence, the movement of water into the

cell where the solutes are more heavily concentrated. In this case the cell will expand and

may burst, unless protected by a cell wall such as that found in bacteria and plant cells.

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Ions and polar molecules cannot pass easily across the membrane. The process by which ions and

hydrophilic substances call travel across the cell membrane with the help of transport proteins

facilitated diffusion. Transport proteins are for the substances they transport. They work in one of

two ways:

? They provide a hydrophilic channel through which the molecules in question can pass.

? They bind loosely to the molecules in question and carry them through the membrane.

Passive Transport Reading Comprehension Questions

1. The plasma membrane will allow oxygen and carbon dioxide to pass through the membrane

while other substances are blocked from passing through the membrane; its unique characteristic

is described as _______________________________________________.

2. Naturally, molecules move from an area of _______________________________________________to

_______________________________________________ without the need of energy.

3. Movement across the membrane without the need for energy is called

______________________________.

4. Define diffusion.

5. What are three types of passive transport that occur in the body?

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6. What is simple diffusion? What types of molecules can pass easily across the plasma membrane by simple diffusion?

7. Define osmosis.

8. What would happen to a cell if placed in each of the following solutions:

a. Isotonic solution:

b. Hypotonic solution:

c. Hypertonic solution:

9. What is facilitated diffusion? What structure assists with this process?

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Passive Transport Reading Application Questions

10. Use arrows to indicate the direction of diffusion in each case.

is a molecule that can pass through the cell membrane and

is a cell membrane.

A)

B)

11. For each of the situations below use an arrow to indicate the net movement of sugar into or out of the

cell (Assume that the sugar molecules can pass through the cell membrane in each case.).

1% sugar

3% sugar

1% sugar

5% sugar

1% sugar

1% sugar

12. Use arrows to show the direction of water movement into or out of each cell.

Color and label the cell in an isotonic environment light blue, the hypotonic environment yellow, and the

hypertonic environment light green.

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13. Label the tonicity for each solution (isotonic, hypotonic, or hypertonic):

________________________________

_______________________________

_______________________________

Below are semi--permeable bags filled with various concentrations of solutions placed in

beakers with various concentrations of solutions. Use this information to help answer the

questions below for each set--up.

? The solutions are prepared with distilled water.

? The semi--permeable membrane bag is permeable to glucose, a very small sugar

? molecule.

? The semi--permeable membrane bag is NOT permeable to sucrose, a larger sugar

? molecule.

For each set--up, you must:

1. Indicate whether the solution in the bag is isotonic, hypertonic, or hypotonic to the

solution in the beaker.

2. Draw a blue arrow for the net movement of water by osmosis (do not draw any

arrow if there would be no net movement of water).

3. Draw a green arrow for the net movement of solute by diffusion (do not draw any

arrow if there would be no net movement of solute).

4. Explain why you drew the arrows you did in terms of the properties of diffusion,

osmosis, and semi--permeable membranes. Be sure to include concentrations of

solutions in your explanation.

14.

Beaker Set--Up # 1

The solution in the bag is ______________________

compared to the solution in the beaker.

Explain your arrows:

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