Water Potential and Osmosis

Flashcards covering key concepts related to water potential, osmosis, and their effects on cells.

What is solvation?

The combination of a solvent with the molecules or ions of a solute, dependent on water's polarity.

Why do polar solutes dissolve in water?

Because of the attraction between partial positive and negative charges on water molecules and solute molecules.

What happens to positively charged ions in water?

They are attracted to the partial negative oxygen pole of water.

What happens to negatively charged ions in water?

They are attracted to the partial positive hydrogen pole of water.

Why is the dissolving property of water important in the cytoplasm?

Water molecules separate many ions and charged molecules and prevent them from clumping, which is important for metabolic reactions.

Describe the movement of water in solutions with different concentrations.

Water moves from a solution with more water (less concentrated) to one with less water (more concentrated).

What is osmosis?

The movement of water across a membrane due to the attractions between solutes and water.

What are osmotically active solutes?

Solutes that have intermolecular forces with the solvent, such as sodium ions, potassium ions, chloride ions, and glucose.

Describe the net movement of water between hypotonic and hypertonic solutions.

There is a net movement of water from a hypotonic solution to a hypertonic solution due to a higher concentration of osmotically active solutes.

Describe the net movement of water between isotonic solutions.

There is no net movement of water because there is no difference in the concentrations of osmotically active solutes.

What is dynamic equilibrium in the context of water movement across a membrane?

Equal numbers of water molecules moving between a membrane, resulting in a steady concentration on either side.

Define concentration in the context of solutions.

The amount of solute per volume of solution, measured in moles per dm³ (1 dm³ = 1 liter = 1000 mL).

How do cells change the rate of osmosis?

By changing the permeability of the membrane to water.

How do cells change the direction of osmosis?

By raising or lowering the concentration of osmotically active solutes inside the cell.

What happens to plant tissues when bathed in salt or sugar solutions?

Any increase or decrease in mass is almost entirely due to water entering or leaving the cells by osmosis.

If plant tissue is placed in 0.0 mol dm³ sodium chloride solution, does water move into or out of the tissues?

Water moves into the tissues.

If plant tissue is placed in 1.0 mol dm³ sodium chloride solution, does water move into or out of the tissues?

Water moves out of the tissues.

What might a low solute concentration in cactus tissue indicate?

It might act as a water store.

What might a high solute concentration in pine kernel tissue indicate?

It might have dried out to become dormant.

Why is percentage mass change used rather than actual mass change in osmosis experiments?

The starting masses might have been different in different tissue samples, and percentage change is a better measure of relative change.

Describe how the osmolarity of potato tissues in sucrose solution could be determined in a lab practical.

Prepare solutions of different concentrations, prepare samples of plant tissue to give similar results (controlling variables), ensure the surface of the tissue sample is dry when finding the mass, keep other variables constant, and determine the optimal length of time to bathe the solutions.

What is sampling in a biological context?

Taking a sample with a method that ensures it is representative of the whole population.

Describe a normal distribution (bell curve).

It is symmetrical around the mean, with values concentrated near the mean and decreasing in frequency as the distance from the mean increases.

What is standard deviation?

A measure of the range of variation from the mean (average).

What does a large standard deviation indicate?

That the data is very variable.

What percentage of measurements fall within one standard deviation of the mean in a normal distribution?

68%

What percentage of measurements fall within two standard deviations of the mean in a normal distribution?

95%

Is standard deviation affected by sample size?

No

What is standard error?

A measure of how reliably the mean of a sample estimates the mean of the whole population.

How is standard error calculated?

By dividing the sample standard deviation by the square root of the sample size.

What does the following statement illustrate: 68% of the sample cell width values are in the range of 3.1 ± 0.91?

It illustrates the range of variation in the sample.

What does the following statement illustrate: There is a 68% probability that the population mean cell width is 3.1±0.14?

It illustrates the reliability of the sample mean as an estimate of the population mean.

How do plant and animal plasma membranes differ in materials?

Plasma membranes are made of phospholipids.

How do plant and animal cell walls differ in materials?

Cell walls are made of cellulose.

What are the thickness differences between plant and animal plasma membranes?

Plasma membranes are thin, 5 nm or less.

What are the thickness differences between plant and animal cell walls?

Cell walls are much thicker, 250 nm to 5 µm or more.

What are the differences in tensile strength between plant and animal plasma membranes?

Plasma membranes have very low tensile strength and are easily torn.

What are the differences in tensile strength between plant and animal cell walls?

Cell walls have high tensile strength, stronger than steel.

What are the differences in permeability between plant and animal plasma membranes?

Plasma membranes are semi-permeable, with some solutes scarcely able to pass through.

What are the differences in permeability between plant and animal cell walls?

Cell walls are freely permeable unless waterproof material is present.

Why are animal cells more likely to burst in hypotonic solutions?

Because they lack a cell wall and are unsupported.

In an Osmometer experiment, why does the height of the solution increase during the first ten minutes?

Solute concentration is higher inside the bag than in the beaker; so water enters the bag by osmosis, increasing the solution volume.

In an Osmometer experiment, describe the trends over the two-hour period.

Increases in height continue but get smaller and smaller until there is equilibrium.

In an Osmometer experiment, explain why the trends in the results occur?

Solute concentration is still higher in the bag so water continues to move from beaker to bag, the solution in the bag is diluted by water entry so rate of entry gets less and pressure rises in the bag as solution rises in tube

What effect does closing stomata have on water loss in plants?

They can prevent water loss.

What happens to plants when plasmolyzed?

The cell wall is permeable, and the membrane loses water because of the osmotically active solutes in the solution which is damaging and often causes cell death.

Why must solutions be isotonic in medical applications?

To create dynamic equilibrium so cells can remain healthy.

What is the typical concentration of isotonic saline solutions?

9 g of NaCl per L (0.9%, 0.154 mol dm-3).

What are some medical applications of isotonic saline solutions?

Safely introduced to patient’s blood via IV (intravenous) drip, Used to rinse wounds and abrasions, Used to keep areas of damaged skin moist before skin grafts, Basis of eye drops and Frozen to consistency of slush to cool hearts, kidneys, & other donor organs during hospital transport