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- Which of the following ways of expressing a solution’s concentration is written as a number without units? A. % concentration B. Molarity C. Osmotic pressure D. Specific gravity Answer is D: Specific gravity of a solution is the ratio of the density of the solu- tion to the density of water (which is 1.0). Consequently the density units “can- cel out”.
- A solution of 5 % glucose is infused over a period of three hours. If 250 ml of solution was used, how many grams of glucose was infused? A. 5 g B. 12.5 g C. 15.0 g D. 50 g Answer is B: 5 % glucose means 5 g per 100 ml of solution. 250 ml was used, therefore 2.5 × 5 = 12.5 g
- A solution is prepared by dissolving 10 g of glucose in 250 ml of water. What will be the concentration of this solution expressed as a percentage? A. 4 B. 6 C. 25 D. 40 Answer is A: % concentration states how many grams of solute are in 100 ml of solution. 10 g per 250 ml is the same as 10 ÷ 2.5 per 100 ml. This is 4 %
4.3 Diffusion and Osmosis
Ions and molecules in a solution are continually bumping into each other and mov- ing independently in random directions. This continual motion results in the solute particles and solvent molecules being evenly distributed. Because if there is a greater concentration of one type of molecule in one place compared to elsewhere, the random motion will result in more molecules moving away from that place than are moving towards the place. Diffusion is the name given to this random motion of molecules and ions. If water is the molecule that is moving and it is passing through a semi-permeable membrane from one solution to the solution on the other side, the movement is called “osmosis”. If it is a solute molecule or ion that is passing through a semi-permeable membrane, the movement is called “dialysis”. The result of osmosis is that the more concentrated solution becomes more dilute.
Another way to describe the concentration of a solution is to state its “osmotic pressure” (in pressure units). The osmotic pressure of blood is about 7.3 atmo- spheres (740 kPa). Osmotic pressure is described as the tendency of water to move into a solution via osmosis. The higher the solution’s concentration, the higher is its osmotic pressure. Osmotic pressure may be measured by determining the amount of pressure that must be applied to a solution to prevent water from entering the solu- tion by osmosis.
- Consider two aqueous solutions of different concentration separated by a semi- permeable membrane. In this situation, osmosis results in: A. water molecules moving to the side where the solution concentration is lower. B. the more concentrated solution becoming even more concentrated. C. the more dilute solution becoming even more dilute. D. the more concentrated solution becoming more dilute. Answer is D: The result of osmosis is that the more concentrated solution becomes more dilute.
- Osmosis may be defined as which of the following? A. The diffusion of water molecules across a semi-permeable membrane from the solution with higher water concentration into the solution of lower water concentration. B. The movement of water molecules across a semi-permeable membrane from the solution of higher concentration into the solution of lower concentration. C. The diffusion of solute particles across a semi-permeable membrane from the solution of higher concentration into the solution of lower concentration. D. The movement of water molecules across a semi-permeable membrane from the solution of lower concentration into the solution of higher concentration. Answer is D: The definition should include: “water”; movement through an SP membrane; direction of water flow from more dilute solution into the solution of higher concentration.
- What is the movement of water molecules across a plasma membrane from the side where the solution concentration is more dilute to the side where the solu- tion is more concentrated called? A. osmosis B. reverse osmosis C. diffusion D. hydration Answer is A: Osmosis is the diffusion of WATER molecules through a mem- brane, from where there is a higher concentration of water molecules to where
Answer is C: dialysis refers to movement of solutes (not water). Choice D is wrong as filtration refers to movement due to hydrostatic pressure difference from the solution under higher pressure to low pressure.
- A suitable definition of osmosis would be movement: A. of solute particles through a plasma membrane from the side where their concentration is greatest to the side where it is lower. B. of water molecules through a plasma membrane from the side where their concentration is greatest to the side where it is lower. C. of a substance from a region where it is in high concentration to where its concentration is lower D. caused by a hydrostatic pressure difference. Answer is B: osmosis refers to movement of water molecules (not other mole- cules), by diffusion.
- The difference between dialysis and diffusion is that A. dialysis involves the movement of water molecules. B. diffusion involves movement against the concentration gradient. C. dialysis involves passive movement through a cell membrane. D. diffusion is caused by a hydrostatic pressure difference. Answer is C: diffusion is passive and occurs in the direction of the concentra- tion gradient. Diffusion can occur within a solution or across a membrane. Dialysis on the other hand, requires a membrane and is a term applied to sol- utes, not water molecules.
- Osmosis involves the movement of:
A. water molecules through a membrane from a region of higher concentration of water molecules to a region of lower water molecule concentration. B. solute particles from a region of higher solution concentration to a region of lower solution concentration. C. water molecules from a region of lower concentration of water to a region of higher water molecule concentration. D. solute particles through a membrane from a region of lower solute concen- tration to a region of higher solute concentration. Answer is A: osmosis involves water molecules (not solutes) moving down their concentration gradient into a solution of lower concentration of water molecules.
- What does “osmosis” refer to?
A. the constant random motion of ions and molecules. B. the movement of ions and molecules from regions of high concentration to regions of low concentration. C. the movement of water molecules through a semi-permeable membrane.
D. the movement of water molecules through a semi-permeable membrane from the side with higher water concentration to the side with lower water concentration. Answer is D: the definition must include water molecules; crossing a SP mem- brane; a correct direction of movement.
- What is the difference between filtration and diffusion?
A. Diffusion can occur through a biological membrane whereas filtration cannot. B. Filtration can occur through a biological membrane whereas diffusion cannot. C. Filtration is the movement of molecules caused by a pressure difference but diffusion does not involve a difference in pressure. D. Diffusion is the movement of molecules caused by a pressure difference but filtration does not involve a difference in pressure. Answer is C: filtration requires a pressure difference, diffusion does not. Both diffusion and filtration can occur through a membrane.
- What is the difference between osmosis and dialysis?
A. Dialysis involves the movement of solute molecules whereas osmosis refers to water molecules. B. Osmosis involves the movement of solute molecules whereas dialysis refers to water molecules. C. Osmosis involves movement of molecules across a membrane but dialysis does not involve a membrane. D. Dialysis involves movement of molecules across a membrane but osmosis does not involve a membrane. Answer is A: osmosis refers to the movement of water molecules (only) through a membrane. Only choice A is consistent with this.
- Which one of the following processes that describe movement of the particles in a solution does NOT require passing through a membrane? A. diffusion B. filtration C. dialysis D. osmosis Answer is A: While diffusion can occur through a membrane, its presence is not required in order to define diffusion.
- Which statement about the osmotic pressure of an aqueous solution is correct? Osmotic pressure: A. is an indication of the force with which pure water moves into that solution. B. is a measure of the tendency of water to move into the solution.
A. bicarbonate will flow from patient’s blood to dialysing liquid, urea will flow from patient’s blood into dialysing liquid. B. bicarbonate will flow from dialysing liquid to patient’s blood, urea will flow from dialysing liquid into patient’s blood. C. bicarbonate will flow from dialysing liquid to patient’s blood, urea will flow from patient’s blood into dialysing liquid. D. bicarbonate will flow from patient’s blood to dialysing liquid, urea will flow from dialysing liquid to patient’s blood. Answer is C: molecules will flow from areas of high concentration towards areas of low concentration. Hence bicarbonate will flow from the dialysing liquid at 32 to blood at 14 mmol/L, while urea will flow from blood at 23 mmol/L to the dialysing liquid at 0 mmol/L.
- Which is the best description for the osmotic pressure of a solution?
A. A: the pressure that needs to be applied to the solution while it is separated from pure water by a membrane, to prevent a net flow of water through the membrane into the solution. B. B: the force with which pure water moves through a membrane into that solution as a result of its solute concentration. C. C: the movement of particles through a membrane, where the movement is caused by a hydrostatic pressure. D. D: it is the force of attraction for water by undissolved particles in the solution. Answer is A: the application of a hydrostatic pressure to a solution in order to oppose and prevent the osmotic flow of water into that liquid is the basis for assigning a value to that solution for its “osmotic pressure”. Osmotic pressure is the value of this externally applied hydrostatic pressure. Choice C describes filtration. Choices B & D are nonsense.
- In which of the following situations would the osmotic pressure of blood be the greatest? A. in a patient whose blood osmolarity is 290 mosmol/L B. in a patient whose blood osmolarity is 280 mosmol/L and whose urine spe- cific gravity is 1. C. in a patient with hyperthermia D. in a patient who is dehydrated Answer is D: the healthy range for blood osmolarity is 280–300 mosmol/L. a dehydrated person would have a blood osmolarity approaching or exceeding 300 mosmol/L.
- Osmosis involves movement of water from where the:
A. water concentration is lower to where it is higher B. solute concentration is higher to where it is lower
C. solution is more concentrated to where it is less concentrated D. water concentration is higher to where it is lower Answer is D: in osmosis water molecules flow down their concentration gradi- ent (and from weaker solutions to more concentrated ones).
- What is “osmotic pressure”?
A. the pressure exerted by a solution due to its concentration B. a measure of solution concentration expressed in the units of pressure C. the pressure exerted by the blood colloidal plasma proteins D. the pressure that drives water movement out of the arterial end of capillaries Answer is B: Osmotic pressure is a way of expressing solution concentration. The word pressure in the term “osmotic pressure” makes it tempting to errone- ously think of the solution exerting some type of pressure due to its solutes.
- If a red blood cell (rbc) is placed in a solution that has a greater concentration than that inside the rbc, what will happen? A. the rbc will crenate B. the rbc will haemolyse C. there will be a net movement of water out of the rbc into the solution D. there will be no net movement of water out of the rbc Answer is C: water will flow by osmosis from the rbc into the surrounding solu- tion. If the difference in concentration is large enough, the outflow of water will be large, and the rbc will also shrivel (crenate) as a result of this outflow.
- One of the following is an example of osmosis. Which one?
A. water moving from the glomerulus of a nephron into the Bowman’s capsule B. water leaving a blood capillary from close to its arteriole end, to enter the interstitial fluid C. water entering a red blood cell that is in a 0.8% sodium chloride solution, by passing through its plasma membrane D. water evaporating from perspiration on the skin Answer is C: Osmosis refers to the movement of water through a membrane in the direction of its concentration gradient. A 0.8 % solution is hypotonic to the contents of the rbc, so water would enter the cell. In both choice A & C, the water is moving due to a hydrostatic pressure difference.
- The Na+/K+ ATPase pump in the plasma membrane moves Na out of the cell and K into the cell against their concentration gradient. Then Na reenters the cell and K leaks out of the cell, along their concentration gradients through their membrane channels. What is the movement of Na and K along their concentra- tion gradients called?
