diffusion

applications of osmosis

How do marine animals keep their cells from shrinking? How do you keep your blood cells from bursting? Both of these questions have to do with the cell membrane and osmosis. Marine animals live in salt water, which is a hypertonic environment; there is more salt in the water than in their cells. To prevent losing too much water from their bodies, these animals intake large quantities of salt water and then secrete the excess salt. Red blood cells can be kept from bursting or shriveling if put in a solution that is isotonic to the blood cells. If the blood cells were put in pure water, the solution would be hypotonic to the blood cells, so water would enter the blood cells, and they would swell and burst ( Figure 1.2). Osmosis causes these red blood cells to change shape by losing or gaining water.

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osmosis

The diffusion of water across a membrane because of a difference in concentration is called osmosis. Lets explore three different situations and analyze the flow of water. 1. A hypotonic solution means the environment outside of the cell has a lower concentration of dissolved material than the inside of the cell. If a cell is placed in a hypotonic solution, water will move into the cell. This causes the cell to swell, and it may even burst. 2. A hypertonic solution means the environment outside of the cell has more dissolved material than inside of the cell. If a cell is placed in a hypertonic solution, water will leave the cell. This can cause a cell to shrink and shrivel. 3. An isotonic solution is a solution in which the amount of dissolved material is equal both inside and outside of the cell. Water still flows in both directions, but an equal amount enters and leaves the cell.

diffusion

Small molecules can pass through the plasma membrane through a process called diffusion. Diffusion is the movement of molecules from an area where there is a higher concentration (larger amount) of the substance to an area where there is a lower concentration (lower amount) of the substance ( Figure 1.1). The amount of a substance in relation to the total volume is the concentration. During diffusion, molecules are said to flow down their concentration gradient, flowing from an area of high concentration to an area of low concentration. Molecules flowing down a concentration gradient is a natural process and does not require energy. Diffusion can occur across a semipermeable membrane, such as the cell membrane, as long as a concentration gradient exists. Molecules will continue to flow in this manner until equilibrium is reached. At equilibrium, there is no longer an area of high concentration or low concentration, and molecules flow equally in both directions across the semipermeable membrane. At equilibrium, equal amounts of a molecule are entering and leaving a cell. Diffusion is the movement of a substance from an area of a higher amount toward an area of lower amount. A concentra- tion gradient initially exists across the cell membrane. Equilibrium is reached when there is an equal amount of the substance on both sides of the membrane.

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questions

diffusion is the movement of molecules from an area of low amount to an area of high amount.

a. true

-->  b. false

diffusion does not require energy.

-->  a. true

b. false

during diffusion, which way to molecules move?

-->  a) molecules flow down the concentration gradient.

b) molecules flow against the concentration gradient.

c) from an area of low concentration to an area of high concentration.

d) none of the above

which best describes an hypertonic solution?

a) the solution outside of the cell has a lower concentration of dissolved material than the inside of the cell.

-->  b) the solution outside of the cell has a higher concentration of dissolved

c) the solution outside of the cell has an equal concentration of dissolved material as the inside of the cell.

d) none of the above

what should happen to cells in a hypotonic environment?

a) water will flow through the cell in both directions.

-->  b) cells should swell and may burst.

c) cells should shrink and shrivel.

d) nothing, the cells should be fine.

which of the following statements about diffusion is not true?

a) diffusion is a natural process.

b) molecules flow down their concentration gradient.

-->  c) molecules cannot move at equilibrium.

d) all of the above statements are true.

which is more likely to diffuse through the cell membrane?

a) a starch molecule

b) a protein

-->  c) a sodium ion

d) dna

diagram questions

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