Transport in Cells (AQA GCSE Biology: Combined Science)

Sugar molecules are moved from the gut to the blood by active transport.

What is involved in active transport?

Outline two ways in which the intestine is specialised for exchanging materials.

Figure 1 shows two plant cells.

Figure 1

Which of the plant cells above was placed in a solution with a lower solute concentration than the cell contents?

Explain what has happened to the plant cell you identified in part (a).

When placed in different solutions, animal cells will also change.

Figure 2 below shows a red blood cell.

Figure 2

Describe what would happen if a red blood cell was put into a solution with a lower solute concentration than the cell contents and explain why this would be different from what would happen to a plant cell.

Hereditary spherocytosis is a rare inherited condition that produces red blood cells with an abnormal spherical shape, as shown in Figure 3.

Figure 3

Suggest the possible impact of this condition on a sufferer.

All living organisms exchange substances with the environment. Plant roots use two different methods to absorb water and ions from the soil.

Explain why roots have two different methods to absorb water and ions.

Table 1 shows the concentrations of three mineral ions in the roots of a plant and in the surrounding soil.

All three mineral ions are essential to the healthy functioning of a plant.

Table 1

Explain why the plant roots can not absorb these mineral ions by diffusion.

Waterlogged soil has a lower oxygen concentration than non-waterlogged soil.

Suggest the impact of waterlogged soil on the activity of root cells.

A student decided to investigate the effect of different salt solutions on the mass of chicken eggs.

They used the following method:

1. 5 eggs were placed in 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 salt solution of a particular concentration and one with water (0.0 mol dm^-3).
4. An egg was placed in each of the beakers.
5. After 1 hour, the eggs were removed and dried with a paper towel.
6. The mass of each egg was measured and recorded.

Their results are shown in the table in Table 2 below:

Table 2

Calculate the percentage change of the egg placed in the 0.4 mol dm^-3 salt solution.

Show your working.

Give your answer to two significant figures.

Explain why in some of the solutions the mass of the eggs decreased.

Explain what the student would need to do to determine an estimate of the concentration of the solution inside an egg.

A group of scientists investigated the rates of absorption of different sugars using two pieces of the intestine.

One piece of the intestine was poisoned with cyanide which stops cellular respiration.

The results are shown in Table 3 below.

Table 3

Which of the sugars in Table 3 are absorbed by active transport?

Explain why you chose these sugars, using evidence from Table 3.

One of the scientists states ‘All four of the sugars we investigated can be absorbed by diffusion.

Determine whether the statement is correct or incorrect. Justify your answer.

One of the sugars absorbed by active transport is glucose.

Xylose is a sugar that is the same size as glucose, but it is not absorbed by active transport.

Suggest a reason why.

The wall of the small intestine contains smooth muscle cells.

Muscle cells convert soluble glucose into glycogen which is insoluble in water.

Suggest an explanation as to why it is essential that muscle cells store glucose as glycogen.

The statements in Table 1 refer to processes occurring in an organism.

Table 1

Complete Table 1 to show which transport mechanism is being used for each of the processes described.

During digestion, glucose is absorbed from the partially-digested food in the lumen of the small intestine, across the cells lining the small intestine (the epithelial cells) and into the bloodstream.

It is a two-stage process, shown in Figure 1.

Process A - glucose moves from the partially digested food in the small intestine into the epithelial cell (lining the small intestine) using energy from ATP.

Process B - glucose moves passively from the epithelial cell into the the bloodstream.

Use the information in Figure 1 and your knowledge of transport across cell membranes to describe the mechanisms used in process A and process B for the absorption of glucose into the bloodstream.

Process B (in Figure 1) relies on the presence of a concentration gradient.

Explain how a steep concentration gradient is maintained in order to continually support Process B.

Absorption of glucose may not always occur through the transport mechanism shown in Process A in Figure 1.

Suggest a situation when glucose may be absorbed into the epithelial cell through an alternative transport mechanism different to that shown in Figure 1.

You should refer to concentration gradients in your answer.

Particulate matter (PM) refers to the small particles in air pollution which can irritate the airways and caused damage to the alveoli.

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 could lead to reduced gas exchange in the lungs of humans.

Figure 2 shows the results of an investigation into the concentration of particulate matter and the percentage of dead alveolar epithelium cells after 48 of exposure.

Figure 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.

Compare, with examples, the different transport processes involved in moving substances across the cell membrane.

Monoglycerides are molecules made up of glycerol and one fatty acid tail. They are absorbed into the epithelial cells of the small intestine by diffusion across the cell membrane.

A scientist measured the uptake of monoglycerides in the epithelial cells of mice. In the investigation, the scientist provided the mice with different concentrations of monoglycerides and measured the uptake into the epithelial cells of the small intestine.

Complete Table 1 to show which variables the scientist used in this investigation.

Table 1

The graph in Figure 3 shows the results of the investigation from part (a).

Figure 3

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.

Figure 4 shows the concentration of sugars in three different cells. X, Y and Z.

Figure 4

Which of the following statements is correct?

A student wanted to investigate the transport of water across a partially permeable membrane. Figure 5 shows how the student prepared the beaker at the start of the investigation.

Figure 5

Complete Figure 5 to show what the student would observe after 15 minutes.

Explain your answer to part (a).

The student carried out a further investigation into the effect of osmosis on plant tissue. 

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

Figure 6 shows the results the student obtained from one cube of potato.

Describe and explain the trend shown on the graph.

The potato cube from Figure 6 had an initial mass of 2.3g.

Calculate the percentage increase that the potato cube had shown after 10 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.

Explain your line drawn for part (e)

Glucose is a soluble sugar molecule. It can be stored in cells once it has been converted to an insoluble form.

In plants, glucose is stored as starch grains and in animals, glucose is stored as glycogen.

Cells in the roots of a clover plant contain the following specialised adaptations

• Large quantities of mitochondria
• Many stored starch grains
• Nodules on the roots which contain bacteria

Explain how these adaptations assist with the absorption of mineral ions and water from the soil into to cells of the clover root.

A student places an animal cell and a plant cell into distilled water and examines both under a microscope.

Explain the differences in observations that the student would have made of the animal cell and plant cell.