Movement into & out of Cells (CIE AS Biology)

Some membranes are described as semi-permeable; this means that only water and a few small solutes can pass through the membrane.

However, the preferred term to describe most biological membranes is selectively permeable. 

Explain why selectively permeable is the preferred term for biological membranes. 

Diffusion can be studied using visking tubing. Visking tubing (or dialysis tubing) is a plastic-like material that water and small solute molecules can pass through.

Students set up an investigation in which equal volumes of each of the following solutions were placed into separate visking tubings:

0.7 mol dm^-3 sodium chloride

0.7 mol dm^-3 glucose

The visking tubings, each of the same size, were placed in distilled water and maintained at a constant temperature of 23°C. The volume and mass of the bags were measured at 5 minute intervals for 160 minutes.

The data recorded is shown below.

Calculate the rates of increase in mass and in volume for the visking tubing containing glucose solution during the first 30 minutes.

Compare and contrast the rates of change in mass for the two visking tubings.

Explain why the volumes of both visking tubings increases over time.

The graph in Fig.1 shows the increase in mass of a potato chip when placed into a solution.

Fig.1 

Describe the water potential of the solution at 25 minutes.

Explain the trend shown in Fig.1 from 0-24 minutes.

Contrast the processes of osmosis and exocytosis.

Explain the role of exocytosis in the digestion of starch in the small intestines.

Design an experiment to estimate the glucose concentration of the cell contents of sweet potato tuber. The following equipment has been provided. 

• Sweet potato
• 1 mol dm³ glucose solution
• Cork borers
• Other common laboratory supplies and reagents.

Outline the steps you would take and the way that you would process the data that you would generate. 

Sketch a graph of the expected results from the experiment in question 3a). 

Define the term, ‘water potential’ and explain why values of water potential are expressed in kilopascals (kPa).

Explain why an aqueous solution has a lower water potential than pure water. 

A plant palisade mesophyll cell is 4 μm in width and depth, and 25 μm in length.

Its shape is approximately cuboid. 

Calculate the surface area to volume ratio of this cell. Show your working.

If the palisade cell in part (a) has a large central vacuole, so that the cytoplasm (not including the vacuole) extends inward 500 nm from the plasma membrane of the cell. 
    
Calculate the surface area to cytoplasmic volume ratio. Show your working.

Explain the importance of the surface area to volume ratio to a growing bacterial cell.

Palisade mesophyll cells and bacterial cells are both approximately cuboid in shape. 

Explain the benefit of this shape for the functioning of the cell. 

An investigation was conducted to estimate water potential in plant tissue. The following method was used:

• The investigators made a range of dilutions of a 1 mol dm^-3 solution of sodium chloride.
• A cork borer was used to cut three potato cylinders for each sodium chloride concentration.
• The initial mass of each potato cylinder was recorded.
• The potato cylinders were placed in boiling tubes, each containing 10 cm³ of sodium chloride solution of a different concentration. One of the boiling tubes contained only distilled water.
• The boiling tubes were placed in a water bath at 25 °C and left for a period of 5 hours.
• The final mass of each potato cylinder was measured and recorded for each sodium chloride solution.
• The mean initial and final mass was calculated for each sodium chloride solution.

The results for this investigation is shown in Table 1

Table 1

Calculate the mean percentage change in mass of the potato cylinders in the 0.75 mol dm^-3 sodium chloride solution. Show your working.

Explain why there was no change in mass for the potato cylinders in the 0.5 mol dm^-3 sodium chloride solution.

Explain the change in mass that occurred in the potato cylinder placed in the boiling tube containing distilled water.

Sketch one of the potato cells that was kept in the 1.00 mol dm^-3 sodium chloride solution. Label the cell wall, cell membrane and cytoplasm in your diagram.

Active transport plays an important role in the absorption of the products of digestion in the small intestine.

Compare the process of active transport with the process of facilitated diffusion.

Fig.1 illustrates another type of membrane transport.

Fig. 1

Identify the type of transport that is illustrated in Fig. 1

[1]

[2]

A gastric chief cell is a type of gland cell that secretes pepsinogen and other digestive enzymes in the stomach.

Fig. 2 shows a diagram of a gastric chief cell.

Fig. 2

Gastric chief cells contain a large number of structure X.

Explain the reason for this.

Describe the process by which gastric chief cells will release these digestive enzymes into the stomach.

Fig.1 shows a light micrograph of a series of onion cells that have been placed in distilled water for several hours.

Fig. 1

Describe the events that led to the appearance of the cells in Fig. 1

Fig.2 shows another set of onion cells.

Fig. 2

Explain why the cells in Fig.2 differ in appearance from the cells shown in Fig. 1.

Emphysematous pyelonephritis (EPN) is a very rare complication that can develop as a result of an untreated kidney infection. It is a severe infection during which bacteria destroy kidney tissue, eventually leading to kidney failure. If kidney failure is left untreated the kidneys are unable to regulate the amount of water in the body and the blood plasma becomes more dilute than normal.

Describe the effect that this would have on red blood cells.

Explain why changes in cell volume affect animal cells more severely than plant cells.

Some scientists investigated the uptake of magnesium ions in rice plants. They divided the plants into two groups and placed their roots in solutions containing radioactive magnesium ions.

   Group Y: plants had a substance that inhibited respiration added to the solution
   Group Z: plants did not have the respiratory inhibitor added to the solution

The scientists calculated the total amount of magnesium ions absorbed by the plants every 5 minutes. Their results are shown in the graph in Figure 1 below:

Figure 1 

Calculate the ratio of the mean rate of uptake of magnesium ions in the first 20 minutes to the mean rate of uptake of magnesium ions in the second 20 minutes for group Z plants. Show your working.

Consider the graph in Figure 1. Explain the results of the students’ investigation.

Using the graph in Figure 1, calculate the rate of uptake of magnesium ions for group Y plants during the investigation. Give suitable units.

State the names of three other substances that would not be absorbed into the group Y plants.