Movement of Substances Into & Out of Cells (Edexcel IGCSE Biology: Double Science)

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 a 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 below:

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

Give your answer to two significant figures.

(2)

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.

State one safety precaution the student would need to carry out during this experiment. 

A student carried out an experiment to study diffusion.

A cube of beetroot was placed in a test tube of distilled water at room temperature as shown in the diagram.

The beetroot was left in the water for ten minutes.

Describe what the student should expect to see.

Give one variable that must be controlled and explain why this control is necessary to provide valid results.

The student found that more of the beetroot pigment leaked out at higher temperatures.

Explain why this result was different at higher temperatures compared to room temperature.

During a science lesson a student writes down the following statement about osmosis.

Using your knowledge of osmosis, suggest what is wrong with this statement.

The diagram shows two human red blood cells. The cell labelled B had been placed in concentrated salt solution.

Describe the changes to the cell labelled B.

Explain why the cell labelled B has changed shape.

A student placed a sample of red blood cells into pure water for 30 minutes. When they checked the blood/water solution under a microscope they could not identify any intact cells.

Explain what is likely to have happened to the red blood cells after being in water.

Define the term diffusion.

Substances diffuse into simple organisms, like bacteria, across their cell surface. The rate of diffusion is affected by surface area to volume ratio.

(i)

State two other factors that affect the rate of diffusion.

(2)

(ii)

Explain how these two factors affect the rate of diffusion.

(2)

A student was investigating the effect of surface area to volume ratio on cubes of agar jelly containing phenolphthalein indicator. Phenolphthalein indicator turns from pink to colourless in acidic conditions. 

The student cut the cubes into the following size.

Complete the table by calculating the missing numbers showing the dimensions of the three cubes. 

The student placed each of the cubes in beakers of acid, as shown in the diagram. 

The acid diffused into the cubes and reacted with the phenolphthalein indicator, changing it to colourless. 

The student timed how long it took for the three cubes to become fully colourless.  

The results are as follows:

Explain the results of the experiment shown in the table.

(2)

The student concluded that the experiment explains why bacteria can rely on diffusion to transfer waste and nutrients, but larger organisms, such as humans, require complex transport systems. 

Explain how the results support this conclusion. 

(1)

How could the student improve their experiment to increase the reliability of the conclusion? 

(1)

The cell shown in the diagram below is an epithelial cell found in the lining of the small intestine. 

It is specially adapted to transport nutrients from the digested food into the blood. 

Explain two adaptations of this cell for the transportation of nutrients. 

This cell carries out both diffusion and active transport. 

Explain why it is necessary for the epithelial cell to be able to carry out both types of transport, and not just diffusion.  

Glucose is an example of a nutrient that is transported by active transport through the epithelial cell. 

Explain what is happening along the folded membrane of the epithelial cell during the process of active transport of glucose. 

Compare and contrast active transport and osmosis.

Substances can move into and out of cells by a variety of mechanisms.

Explain the factors that affect the rate of movement of substances into and out of cells.

Describe the differences between diffusion and active transport.

A teacher carries out a demonstration to show the effect of different concentrations of salt solution on red blood cells.

This is the teacher’s method.

• Dilute a sample of blood using a salt solution that has the same concentration as blood plasma
• Place 1 cm³ of the diluted blood into each of three test tubes labelled A, B and C
• Add 10 cm³ of water to tube A
• Add 10 cm³ of 1 % sodium chloride solution to tube B 
• Add 10 cm³ of 5 % sodium chloride solution to tube C
• Leave each tube for 5 minutes
• Compare the cloudiness of the solutions in the three test tubes
• Take a drop of liquid from each tube and put on separate microscope slides
• Observe each slide under a microscope

State the independent variable in this investigation.

Give one variable that the teacher controls in this investigation.

After 5 minutes, these are the teacher’s observations.

• Tube A – a clear red solution
• Tube B – a cloudy red suspension
• Tube C – a cloudy red suspension

Explain the differences in the teacher’s observations.

(2)

When the teacher looks down a microscope for cells on each slide, these are the teacher’s observations.

• Slide from tube A – no cells are seen
• Slide from tube B – normal biconcave red cells are seen
• Slide from tube C – red cells are seen but the cells have shrunken edges

The photographs show the teacher’s observations.

Zephyris, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Explain the differences between the teacher’s observations of the slides from each tube.

(2)

Blood samples can be separated into different layers using a centrifuge.

This is a machine that spins blood at a high speed.

A new sample of blood is shown after it has been spun in a centrifuge.

Describe how the blood in tubes A, B and C from the teacher’s demonstration would look after they had been spun in a centrifuge.

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 the table below.

Which of the sugars in the table are absorbed by active transport?

Explain why you chose these sugars, using evidence from the table in part (a).

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

Is this statement 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.

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

Complete the diagram 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.

The graph shows the results the student obtained from one cube of potato.

Describe and explain the trend shown on the graph.

The potato cube from the graph in part (c) 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)

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.

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

The diagram compares the lining of the small intestine of a healthy person and a person suffering from coeliac disease.

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

The graph shows the rate of uptake of monoglycerides in the small intestine.

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.

A student investigated the effect of different concentration of sugar solution on osmosis in potato tissue.

This is the method they used:

1. Add 20 cm³ of distilled water to a boiling tube. 
2. Repeat step 1 with equal volumes of 0.2, 0.4, 0.6 and 0.8 mol dm⁻³ sugar solutions.
3. Cut five cylinders of potato of equal size using a cork borer, cutting off the ends to remove the skin.
4. Weigh each potato cylinder and place one in each tube.
5. Remove the potato cylinders from the solutions after 12 hours.
6. Dry each potato cylinder with a paper towel.
7. Reweigh the potato cylinders.

The table below shows the results:

(2)

(1)

The student analysed the data from the experiment.

In the space below, plot a graph of the results from this experiment.

(5)

Use your graph to estimate the concentration of the solution inside the potato cells. 

Give your answer in mol dm^-3.

(1)

Design an investigation to compare the sugar content of sweet potato to the sugar content of normal potato.

Your answer should include experimental details and be written in full sentences.