4.2 Movement into & out of Cells

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.

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.