Rate of diffusion

A student uses this apparatus to investigate osmosis in a non-living system.

This is the student’s method.

• tie partially permeable tubing at one end with string to make a bag

• fill the bag with sugar solution

• tie the bag at the other end with string

• measure the mass of the bag, string, and sugar solution

• place the bag into a test tube filled with pure water

• after 5 minutes remove the bag and measure the mass

• return the bag to the test tube

• repeat the measurement of mass every 5 minutes for 30 minutes in total

The table shows the student’s results.

Draw a line graph to show the student’s results. Join your points with straight lines.

Describe the change in mass of the bag during the 30 minutes.

Explain the change in mass of the bag during the 30 minutes.

The student decides to investigate how increasing the temperature would affect the results.

Describe how the student could repeat the experiment safely at a higher temperature.

Explain how repeating the experiment at a higher temperature would affect the results.

The diagram shows a plant cell with some structures labelled.

Which structure is the cell vacuole?

Which structure is the site of photosynthesis?

Which structure is the cell wall?

Structure U is the site of protein synthesis in the cell. What is the name of structure U?

A cell is shaped like a cube. Each side has a length of 0.053 mm. Calculate the surface area to volume ratio of this cell. Give your answer in the form n: 1

surface area to volume ratio =_........

Animal cells, unlike plant cells, do not have a cell wall.

Explain how this difference affects red blood cells when placed in distilled water.

Explain how this difference affects red blood cells when placed in a concentrated salt solution.

A student uses this method to investigate osmosis in potato tissue.

• cut three 5.0 cm long cylinders from a raw potato

• dry the cut surfaces using filter paper

• measure the mass of each cylinder using a balance

• place one cylinder in a test tube containing 10 cm³ of concentrated sucrose solution, one cylinder in a test tube containing 10 cm³ of distilled water and one cylinder in an empty test tube

• put a bung in each test tube and leave them for one hour

• remove the cylinders and dry them with filter paper

• measure the mass of each cylinder again

• measure their lengths using a ruler

Describe what is meant by the term osmosis.

State the independent variable in the student’s investigation.

Osmosis is affected by the surface area and volume of the cylinders, so the student keeps the original surface area and volume of each cylinder the same.

At the start of the experiment each cylinder had a radius of 0.25 cm and a length of 5.0 cm.

Calculate the surface area of each cylinder using this formula.

[ l = length of cylinder, r = radius of cylinder and π = 3.14]

Explain how surface area would affect the rate of osmosis.

State another variable the student should control in the investigation.

The table shows the student’s results for the mass of the cylinders.

Explain the changes in the mass of the potato cylinder in each test tube.

The student also measured the change in length of each potato cylinder.

Assuming the length has the same percentage change as the mass, calculate the final length of the cylinder in the concentrated sucrose solution.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Treating Kidney Disease

Chronic kidney disease affects approximately 12% of the world’s population and many people are unable to obtain treatment. One method of treating chronic kidney disease is by dialysis. The diagram shows how kidney dialysis is done.

During dialysis, blood is taken from an artery in the arm and is pumped through a dialyser. In the dialyser, the blood passes through a long, coiled dialysis tube made of a thin partially permeable membrane. The tube is surrounded by dialysis fluid. The dialysis fluid contains glucose and ions at concentrations normally found in blood plasma, but does not contain urea. The urea passes from the blood into the dialysis fluid. The temperature in the dialyser is kept at 40C. After passing through the dialyser, the blood is returned to a vein in the arm. Kidney dialysis can take up to three hours and must be done three times a week.

Scientists have now designed a new bioartificial kidney. This artificial kidney is a combination of engineering and living cells. This artificial kidney has a haemofilter made from artificial membranes that filter the blood. The substances filtered out of the blood then pass through a device called a bioreactor. This bioreactor absorbs useful substances back into the blood. The bioreactor is made of living nephron cells that are grown from stem cells. These cells are separated from the patient’s blood by a silicon membrane to prevent the immune system rejecting them. Bioartificial kidneys are the same size as a human kidney and will be fitted inside the body to replace a kidney. The bioartificial kidney can react to changes in the body in the same way as a normal kidney.

In 2021, the world’s population was 7 900 000 000.

Calculate the number of people in the world who have chronic kidney disease (Lines 1 and 2).

Give your answer in standard form.

Urea is an excretory product that is released by the kidneys.

Give the name of an excretory product that is released by the lungs.

Explain two ways that the dialyser is designed to increase the rate of removal of urea from the blood (Lines 5 to 11).

The haemofilter in the bioartificial kidney filters the blood (Lines 13 and 14).

Where does ultrafiltration occur in a nephron?

The cells in the bioreactor absorb glucose from the filtrate in a way that is similar to the cells in a nephron (Lines 14 to 17).

Describe how the nephron absorbs glucose back into the blood from the filtrate.

The bioartificial kidney is connected to blood vessels and to the tube that transports urine to the bladder in the same way as the human kidney.

Which row of the table is correct?

Explain how the pituitary gland and the nephron cells in the bioreactor will respond in a patient who is dehydrated (Lines 20 and 21).

The table lists values that can be obtained in practical investigations.

Complete the table by naming pieces of laboratory apparatus that can be used to help obtain these values.

The first one has been done for you.

The diagram shows a red blood cell viewed through a microscope.

The actual width of this red blood cell is 8 µm.

The magnification of this red blood cell can be calculated using this formula.

Calculate the magnification of this red blood cell.

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.

This apparatus can be used to show osmosis.

Explain what happens to the level of the sucrose solution in the glass tube.

Describe how this apparatus could be modified to measure the rate of osmosis at different temperatures.