Diffusion through a Membrane

A student fi lled two Petri dishes with a clear gel made with corn starch. He was given two unknown solutions (A and B) and was asked to determine which solution contained a chemical that digests starch. Using a clean cotton swab, he dipped it into solution A and wrote a “?” invisibly onto the gel in one of the Petri dishes. He repeated the same procedure on the second Petri dish with a clean cotton swab he dipped in solution B. Twenty minutes later, he added starch-indicator solution to the surface of both Petri dishes. The surface of the Petri dish with solution A added turned completely blue. Most of the surface of the Petri dish to which solution B was added was blue, except the “?” was clear. The results are illustrated in the attached picture.

An observation that supports the student’s conclusion that solution B contained a chemical that digests starch is that the

• damp cotton swab absorbed some of the starch where it touched the gel

• starch indicator changed the color of the gel to blue

• area swabbed with solution B remained clear

• chemical in the starch indicator reacted with the chemical in B

A student placed artificial cells, each containing a 25% sugar solution, into three different beakers containing sugar solution which varied in concentration from 0% to 25%. The setups are shown in the picture.

The student collected data on the mass of each artificial cell. The student predicted that the cell in the beaker with 25% sugar solution would have the greatest change in mass after 24 hours. Would his prediction be correct? Support your answer.

• yes because it has the highest sugar concentration for both inside and outside the cell.

• no because the concentration of sugar is the same inside and outside the cell, so the mass will stay the same.

• Yes because more sugar will move into the cell since it is small enough.

• No because the cell will shrink in the sugar solution.

The diagram represents a sugar cube being dropped into an undisturbed beaker of water at room temperature. One sugar molecule is labeled.

• 
• 
• 
• 

The diagram represents a lab setup. The artificial cell (dialysis tube) contains a starch solution and the beaker contains a solution of starch indicator and water. The setup is left undisturbed for twenty minutes. Identify one molecule, present in this setup, that will be able to pass through the dialysis tubing

• starch

• dialysis tubing

• glucose

• starch indicator

The diagram represents a lab setup. The artificial cell (dialysis tube) contains a starch solution and the beaker contains a solution of starch indicator and water. The setup is left undisturbed for twenty minutes. Describe one observation that could be made that would confirm that the molecule you identified in the previous question had passed through the membrane.

• I would see a color change in the environment outside of the cell

• I would see a color change in both the inside and the outside of the cell

• I would see a color change on the inside of the cell

• There would be an increase in the mass.

A cube cut from a potato is placed in a beaker of distilled water. The potato cells have a relatively high concentration of starch and a relatively low concentration of water. The diagram represents the water and starch molecules in and around one of the potato cells in contact with the water in the beaker. Which row in the chart correctly describes what would be expected to occur in the potato cells, with regard to both the starch and water molecules?

• 
• 
• 
• 

Which statement correctly describes a possible result if starch indicator is added to the water in the beaker one hour after the potato cube was added?

• The indicator solution would turn to an amber color in the water if starch molecules were present in the water in the beaker.

• The indicator would remain amber in color if starch molecules were not present in the water in the beaker

• The indicator would change to a black color if starch molecules were not present in the water in the beaker.

• The indicator solution would remain black in color if starch molecules were present in the water in the beaker.

Before placing the potato in the beaker, the student used an electronic balance to determine the mass of the potato cube. The mass of the cube was determined again after it was in the beaker for an hour. Describe how this information could specifically be used to determine if water moved during the investigation.

• If there was a decrease in mass, the water moved into the cell.

• If there was a decrease in mass, the starch moved out of the cell.

• If there was a decrease in mass, the starch indicator moved into the cell.

• If there was an increase in mass, water moved into the cell.

Some students tested two samples of a mixture of starch and water with two different indicators. The results of these tests are shown in Table 1.

Next, a specifi c protein was added to two new samples of the starch and water mixture. After waiting 30 minutes, the students tested these samples with the same two indicator solutions. The results are shown in Table 2.

• a salt solution

• a new indicator

• a pancreatic hormone

• a biological catalyst

The diagram represents one of many microscopic air sacs in a human lung. The alveolus (air sac) is the place where oxygen (O2) and carbon dioxide (CO2) move into or out of the blood, as represented in the diagram. Alveolus CO2 O2 Out In Capillary Which statement best explains why these gases are able to move in the directions shown in the diagram?

• The CO2 moves out of the capillary and into the alveolus to make more room for the blood to carry O2.

• The O2 is needed by the cells, so it is actively transported into the blood. The CO2, which is not needed, is actively transported out of the blood.

• The blood coming to the lungs is low in CO2 and high in O2, so the gases each diffuse from a lower to a higher concentration in this area

• The blood coming to the lungs is high in CO2 and low in O2, so the gases each diffuse from a higher to a lower concentration in this area.