# 5: Diffusion and Osmosis

Question 1

Describe the scientific methods

Answer 1

The scientific method investigates problems in an interative fashion, using hypothesis testing to explain observations.

*hypothesis: an educated guess or prediction that explains the reason for an observation and can be written in an “if…, then.. because” format

Question 2

what are the control groups and experimental groups?

Answer 2

1. control group: the reference to compare with the results of an experiment
   » helps to interpret your experiment and ensure that the effects seen are due to the independent variable and not another factor
2. experimental group: the group in an experiment that receives the variable being tested

Question 3

what are these variables? (e.g. independent, dependent, controlled variables)

Answer 3

1. independent variable: the variable being tested in the “if” statement of the hypothesis
2. dependent variable: represents the experiment’s result
   - you will look for changes in the variable stated in the “then” statement by measuring the dependent variable
3. controlled variable:the variable in the experiment are kept the same, in the experiments on the control and test groups

Question 4

What are the negative/ positive control groups?

Answer 4

1. negative group: an experiment in which you do not expect an effect to occur, typically b/c you intentionally left out the independent variable (e.g., giving patients a placebo instead of antibiotic)
2. positive control group: an experiment in which you know that the expected effect will occur (e.g., giving patients an antibiotic known to treat a bacterial infection» treated with the new antibiotic)

Question 5

What does a replicate mean?

Answer 5

:each repeat of the experiment
» each experiment should be repeated (or replicated) multiple times to ensure that the results are consistent and not the result of a random event

Question 6

Explain the process of diffusion.

Answer 6

• the higher the temperature, the faster the molecules move
• the higher concentration (of that molecule) to one of low concentration (molecules move down their concentration gradient)
  = diffusion (occurs in gases, liquids, and solids)
  *larger/ heavier the molecules, the more slowly it will diffuse

Question 7

Explain the process of osmosis

Answer 7

Diffusion of water across a selectively permeable membrane = osmosis
- water will continue to present net osmotic movement across a membrane until the concentration of water is equal on both sides unless an opposing pressure prevents the movement
- movement of a solute through a membrane is limited by the selective permeability of the membrane
> Small molecules (e.g. water, dissolved salts) can cross easily but large (e.g. starch) cannot

Question 8

What is the osmotic pressure?

Answer 8

the osmotic pressure of a solution is equal to the pressure that must be applied to prevent the net movement of water molecules across the membrane
(iso/ hypo/ hypertonic)

Question 9

How diffusion and osmosis are applied in the human body using appropriate terminology?

Answer 9

Diffusion: in the lungs
- O2/ CO2 diffuses in and out of the lungs
- oxygen molecules move from the lungs into the blood vessels, and carbon dioxide moves from the blood plasma into the air breathed out

Osmosis: in the digestive system and the kidney
= helps you get nutrients out of food you consume and also gets waste products of your blood

Question 10

Discuss factors that alter the rate of diffusion and/or osmosis

Answer 10

1. particle size
- the smaller molecules, the faster diffuses
2. concentration gradient
- higher concentration to lower concentration
3. temperature
- higher temp = the particles with more energy, faster diffuses
4. viscosity of the medium
- more density packed, slower diffuses

Question 11

Hypotonic solution or hypertonic solution?

Answer 11

a) In hypotonic solution..
- there will be an osmotic gain of water, and the cells will swell; the osmotic pressure causes the cell membrane to tear, resulting in hemolysis (e.g. RBC)
- relatively higher concentration of water outside of cell goes into the cell, eventually burst

b) In hypertonic solution…
- will be an osmotic loss of water, and the cell will shrink &raquo_space; cell is crenated

Question 12

Identify the correct movement of a substance during diffusion.
1. from a low solute concentration to high solute
2. from a high concentration to a low solute concentration
3. from a high solute concentration to a low solute concentration
4. from a low solvent concentration to a high solute concentration

Answer 12

3. from a high solute concentration to a low solute concentration

Question 13

Identify the correct movement of water during osmosis
1. from a low solvent concentration to a high solute concentration
2. from a high solvent concentration to a low solvent concentration
3. from a high solvent concentration a low solute concentration
4. from a low solvent concentration to a high solvent concentration

Answer 13

2. from a high solvent concentration to a low solvent concentration

Question 14

Identify ALL of the features of a molecule that would allow it to cross the plasma membrane.
1. large
2. non-polar
3. polar
4. small

Answer 14

2. non-polar/ 4. small

Question 15

Identify ALL of the location(s) in the body where you would expect a large amount of diffusion.
1. aorta
2. blood capillaries
3. kidneys
4. lungs
5. bones
6. skin

Answer 15

2. blood capillaries/ 4. lungs/ 6. skin

Question 16

Identify the type of tissue that you would expect the largest amount of diffusion to occur in.
1. simple squamous epithelia tissue
2. bone
3. transitional epithelial tissue
4. stratified squamous epithelial tissue

Answer 16

1. simple squamous epithelia tissue