Diffusion & Osmosis (Cambridge O Level Biology)

They used the following method:

1. Five eggs were placed in hydrochloric acid for 24 hours to dissolve the eggshell.
2. The mass of each egg was measured and recorded.
3. Five beakers were set up; four with 200 cm³ of sugar solution of different concentrations (0.2, 0.4, 0.6 and 0.8 mol dm^-3) and one with distilled water (0 mol dm^-3).
4. An egg was place in each of the beakers for 1 hour.
5. The eggs were removed and dried with a paper towel whereafter the mass of each egg was measured and recorded.
6. The percentage change in the mass of each egg was calculated and a graph was drawn from these results.

Fig. 1 represents the graph that was drawn of the percentage change in mass.

Fig. 1

Use the information in Fig. 1 to describe the results obtained in each beaker.

Use the graph in Fig. 1 to identify the concentration of the sugar solution where the mass of the egg would not change.

[1]

Explain why the mass of the egg would not change at the concentration identified at part (i).

[2]

Diffusion and osmosis are two ways in which molecules can move.

Compare diffusion and osmosis with each other.

Fig. 1

Which of the plant cells above (A or B) was placed in a solution that was more dilute than the cell contents?

Fig. 2 below shows a red blood cell.

Fig. 2

Describe what would happen if a red blood cell was placed in a solution that was more dilute than the cell contents.

[2]

Explain why the description at part (i) would be different from what would happen to a plant cell.

[2]

Fig. 1 shows the structure of an alveolus with a capillary running next to it.

Fig. 1

If concentrations of PM are high, the epithelium cells of the alveoli may be killed and replaced with unspecialised cells resulting in:

• Fewer functioning alveoli
• Thickening of alveolar walls

Explain how particulate matter would affect the process of gas exchange in human lungs.

Fig. 2

Scientists studied 31 080 alveolar epithelium cells in this study.

Calculate how many more cells died after 48 hours of exposure to 1 000 µg cm^-3 of particulate matter than after 48 hours of exposure to 50 µg cm^-3 of particulate matter.

They cut a potato into cubes and recorded the change in mass over a 30 minute period.

Fig. 1 shows the results the student obtained from one cube of potato.

Describe and explain the trend shown on the graph.

The potato cube from Fig. 1 had an initial mass of 2.5 g.

Calculate the percentage increase that the potato cube had shown after 15 minutes.

The student repeated the investigation but with the beaker placed in a water bath at 30°C.

Draw a second line on the graph to show the trend expected from these results.

Diabetes insipidus is a disease that results in a large amount of dilute urine being excreted by the kidneys. This leads to blood which is more concentrated than normal.

Explain the effect that diabetes insipidus may have on red blood cells.

One of the symptoms of diabetes insipidus is blue fingernails, which indicates a lack of oxygen.

Suggest an explanation for this.

Central diabetes insipidus is a form of the disease that is believed to have a negative effect on the bone density of a sufferer which may leave them with an increased risk of sustaining fractures.

A study was conducted on the effect of central diabetes insipidus on the risk of sustaining fractures.

• The study was done at a hospital and included men and women between the ages of 45 and 65 that were admitted with bone fractures.
• Men and women were divided up into two groups each; those with diabetes insipidus and those without.
• Each of the four groups consisted of 250 individuals.
• The data gathered was used to calculate the percentage prevalence of fractures in each group.

Fig. 1 shows the results of this study.

Fig. 1

Calculate the difference in the number of men suffering from fractures between those with diabetes insipidus and those without. Show your calculations.

[3]

The scientists concluded that diabetes insipidus does increase the risk of sustaining fractures.

Evaluate this conclusion.

[4]

Some people suffer from coeliac disease that affects the lining of their small intestine.

Fig. 1 compares the lining of the small intestine of a healthy person and a person suffering from coeliac disease.

Fig. 1

Based on the information provided, explain the effect that coeliac disease would have on the absorption of monoglycerides.

Fig. 2

Describe and explain what the graph shows.

Human body temperature is approximately 37 °C, which provides the optimum temperature for activity of protein molecules such as enzymes. 

Suggest why a temperature of 37 °C helps to maximise the rate of transport of substances across the cell membrane.

Fig. 3

Describe and explain the movement of water between the cells in Fig. 3.