BIOL 1406 LAB Unit 7 Review

Define diffusion

DIffusion is the movement of molecules from an area where their concentration is high to an area where their concentration is low

Describe how temperature and size of a molecule can affect the rate of diffusion

1. Higher temp = faster diffusion

2. Smaller molecules = faster diffusion

3. Larger molecules = slower diffusion

Describe how rate of diffusion is calculated

Rate of Diffusion = Distance/Time

Define a selectively permeable membrane

A selectively permeable membrane (also called a semipermeable membrane) is a membrane that allows certain molecules or ions to pass through it, while blocking others.

Explain why certain molecules can freely diffuse across the plasma membrane of a cell while some others cannot

They can’t because of the different structure and properties of the molecules.

For example, water cannot easily cross a membrane because of the hydrophobic phospholipid tails that make up the bilayer’s interior

Explain why certain molecules can freely diffuse across the dialysis tubing “membrane” while some others cannot

Dialysis bags have microscopic pores of a specific size which only allow molecules of a certain size to pass across.

For example, a dialysis bag may have a 14,000 Dalton (Da) cut off indicating it will not allow molecules that are larger to pass across.

Predict what will happen to the color of the bag and beaker in the following scenarios

a. Dialysis bag filled w/ 1% starch placed in a beaker filled w/ iodine/water

b. Dialysis bag filled w/ 1% starch and 1% amylase placed in a beaker filled with iodine/water

A. Bag is blue-black and beaker is yellow

B. Bag will just remain yellow and beaker will also remain yellow

Identify the product of the following reaction: amylase + starch —>

Maltose

Describe which of the following substances were permeable across the dialysis membrane and which were not and why

a. Iodine

b. Starch (Identify the detection reagent for this molecule)

c. Maltose (Identify the detection reagent for this molecule)

A. Iodine is permeable because it is a small molecule

B. Starch is not permeable because it is a large molecule and the reagent is blue-black

C. Maltose is permeable in most cases because it is a disaccharide and the reagent is DNS

Compare diffusion and osmosis

Diffusion goes from high to low concentration whereas osmosis goes from low to high concentration in water.

Describe the physical property of dialysis tubing that allows it to function as a selectively permeable membrane

The microscopic pores allow it to function as a selectively permeable membrane

Describe the movement of water across a semi-permeable membrane if there is a solute imbalance between the two solutions on opposite sides of the membrane

1. When a cell is placed in a solution of higher solute concentration (like water for example) compared to the inside of the cell, water will exit the cell in order to equalize the concentration of solutes within and outside of the cell.

2. If a cell is placed in a solution of a very low solute concentration (like diH₂O), in comparison to the inside of the cell the cell will take up water for the same reason

Define aquaporin

Aquaporins reside in the membrane to facilitate the movement of water

Describe the difference between hypertonic, hypotonic, and isotonic solutions

1. Hypertonic = higher solute concentration

2. Hypotonic = lower solute concentration (less)

3. Isotonic = equal levels of solute concentration

Explain why water moves out of a cell when the cell is placed in a hypertonic solution

The reason why water moves out of a cell when the cell is placed in a hypertonic solution is because water will exit the cell in order to equalize the concentration of solutes within and outside of the cell

Explain why water moves into a cell when the cell is placed in a hypotonic solution

Same reason as hypertonic

Describe what physically happens to a plant and animal cell when water moves out of the cell by osmosis

1. For plant cells, they lose water and the plasma membrane pulls away from the cell wall at several places. This is known as plasmolysis

2. For animal cells, they shrivel up (shrink) and this is known as crenation

Describe what physically happens to a plant and animal cell when water moves into the cell by osmosis

1. For plant cells, it takes up water and expands until the water contained in the cell exerts a force on the cell wall known as turgor. This makes the cell rigid and it becomes turgid (healthy)

2. For animal cells, the cell will swell and burst (lyse)

Use the following terms appropriately: (turgid, plasmolyzed, crenated/shriveled, and lysed).

1. Turgid = healthy and hypotonic for plants

2. Plasmolyzed = plant dying and hypertonic

3. Crenated = animal cell shrinking and hypertonic

4. Lysed = animal cell bursting and hypotonic