6. The Membrane

Osmosis

Osmosis and Tonicity

What would you expect to happen to the cell under the following conditions?<img class="fr-dib" src="https://static.studychannel.pearsonprd.tech/courses/biology/thumbnails/images/01f7468d" style="width: 300px;" title="">

Osmosis Example 1

Animation: Osmosis and Water Balance in Cells

Direction of Osmosis

 No. If the cell were in a hypotonic solution, you would expect water to enter the cell. 

 No. If the membrane is permeable to urea, then urea will simply diffuse through the membrane until it reaches equilibrium. This will increase the solute concentration inside the cell relative to outside, and water will enter osmotically. 

 No. If the outside of the cell were hypotonic, you would expect water to enter the cell. Furthermore, if the membrane is permeable to urea, then urea will quickly diffuse through the membrane, causing more water to enter the cell. 

 No. Pure water is the most hypotonic environment possible. Water will enter any cell placed in a hypotonic solution. 

Consider both osmosis and the passive movement of solutes.

The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?

A Level Biology Revision "Osmosis and Water Potential"

 No. Distilled water is hypotonic to the plant; thus, water will enter the plant cell and make the cell more turgid. 

 No. This solution is hypotonic to the plant cell. Water will move into the cell via osmosis and the cell will become more turgid. 

 No. This solution is isotonic to the plant cell. The cell will become flaccid, but it will not plasmolyze. 

No. This concentration is equivalent to 0.15 M, and it is less than the solute concentration of the cell's cytoplasm, so water will move into the cell.

Consider the direction of water movement based on the relative tonicity of solutions.

The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?

A cell that is placed in salty seawater will                   .
a. take sodium and chloride ions in by diffusion;
b. move water out of the cell by active transport;
c. use facilitated diffusion to break apart the sodium and chloride ions;
d. lose water to the outside of the cell via osmosis

 The added salt would enter the cell, causing the cell to take up water and swell. 

 No. The permeability of the plasma membrane is greater to water than it is to salt. Water will cross the membrane before salt does. 

 Water would enter the cell by osmosis, and the cell would swell. 

 No. The added salt makes the solution hypertonic compared to the cell. 

 There would be no osmotic movement of water in response to the added salt. 

 The added salt makes the solution hypotonic compared to the cell. Water will enter the cell by osmosis. 

 Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease. 

Consider the effect of added salt on the osmotic movement of water.

A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition?

Hypertonic, Hypotonic and Isotonic Solutions!

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

Based on your reading of this chapter, propose at least five traits that you think might have been most important in triggering diversification within phyla (examples: origin of hearing, origin of internal fertilization).

Into the cell and out of the cell at equal rates

Water will not move across the cell membrane

Which direction would you expect water to move across the cell membrane?<img class="fr-dib" src="https://static.studychannel.pearsonprd.tech/courses/biology/thumbnails/images/7e275c63" style="width: 300px;" title="">

Short Video: Plasmolysis

Which traits do not correlate strongly with diversification rate within phyla, but are likely to have been important in the original diversification of animal phyla during the Cambrian? Select True or False for each trait.
T/F presence of a head
T/F mobile lifestyle
T/F terrestrial lifestyle
T/F bilateral symmetry


The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

Jezkova and Wiens used a type of graph called a linear regression to find correlations between variables such as the proportion of species per phylum with legs (on the y-axis) and the diversification rate per phylum (on the x-axis). Sketch a graph to show what a strong positive correlation between these two variables would look like and what the absence of a correlation would look like.

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora?

A sample of Jekova and Wiens’ results is shown here. The R2 value represents the strength of the correlation (where 0.00 is lowest and 1.00 is highest). The P value represents the statistical significance. Which five traits look most important? <IMAGE>

Plants become turgid when placed in this type of solution:

GCSE Biology - Osmosis  #8

DRAW IT An artificial “cell” consisting of an aqueous solution enclosed in a selectively permeable membrane is immersed in a beaker containing a different solution, the “environment,” as shown in the accompanying diagram. The membrane is permeable to water and to the simple sugars glucose and fructose but impermeable to the disaccharide sucrose.
a. Draw solid arrows to indicate the net movement of solutes into and/or out of the cell.
b. Is the solution outside the cell isotonic, hypotonic, or hypertonic?
c.  Draw a dashed arrow to show the net osmosis, if any.
d. Will the artificial cell become more flaccid, more turgid, or stay the same?
e. Eventually, will the two solutions have the same or different solute concentrations?

Osmosis and Water Potential (Updated)

 Bacterial cells shrivel up in high salt solutions, causing the cell to burst. 

 High salt concentration lowers the pH, thus inhibiting bacterial metabolism. 

 No. High salt concentration does not directly affect the pH of a solution. 

 High salt concentration raises the pH, thus inhibiting bacterial metabolism. 

 A 30% salt solution is hypotonic to the bacteria, so they gain too much water and burst. 

 No. Thirty percent is a rather high concentration of salt; it is not hypotonic to bacteria. 

 A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis. 

Consider how such a salt solution relates to the interior of a microorganism and subsequently affects water movement.

Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives?

Water molecules across a semi-permeable membrane into a region of low solute concentration

Solute molecules from an area of high concentration to an area of lower concentration

Water molecules across a semi-permeable membrane into a region of high solute concentration

Water molecules inside a cell that can’t be transported out

Solute molecules from an area of low concentration to an area of higher concentration

Osmosis is best defined as the movement of:

Environmental Tonicity Affects Cells

Cell Membrane Transport - Transport Across A Membrane - How Do Things Move Across A Cell Membrane

 Water will enter the sucrose solution because the sucrose molecule is a disaccharide and, thus, larger than the monosaccharide glucose. 

 No. The individual size of the molecule does not affect osmotic pressure. 

 Water will leave the sucrose solution because the sucrose molecule is a disaccharide and, thus, larger than the monosaccharide glucose. 

 The sucrose solution is hypertonic and will gain water because the total mass of sucrose is greater than that of glucose. 

 No. The mass of the molecule does not affect osmotic pressure. Each solution has the same number of particles, so they are isotonic. 

 After the sucrose dissociates into two monosaccharides, water will move via osmosis to the side of the membrane that contains the dissociated sucrose. 

 No. Disaccharides do not dissociate spontaneously. 

 Nothing will happen because the two solutions are isotonic. 

Consider the relative solute concentration in each of the solutions and how their relative concentrations will affect solute movement.

A selectively permeable membrane separates two solutions. Water is able to pass through this membrane; however, sucrose (a disaccharide) and glucose (a monosaccharide) cannot pass. The membrane separates a 0.2-molar sucrose solution from a 0.2-molar glucose solution. With time, how will the solutions change?

 The red blood cell would burst, and the plant cell would shrink. 

 No. Both cells would lose water by osmosis. 

 Both cells will gain water, but cell walls will prevent both cells from bursting. 

 No. Both cells will lose water; in any case, red blood cells do not have cell walls. 

 Both cells would gain water by osmosis; the red blood cell would burst, and the plant cell would increase in turgor pressure. 

 The red blood cell would shrink, and the plant cell would gain water. 

 Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall. 

Consider the relative solute concentrations of the cells' cytoplasm and seawater.

Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?

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