Transport in & out of cells

A student uses this apparatus to investigate the effect of nitrate ions on the growth of plants.

● A young plant is grown in a sterile solution containing all the mineral ions needed for growth.

● The student repeats the experiment with other young plants.

● The student also carries out the experiment with young plants grown in a sterile solution that contains all the mineral ions except nitrate.

● The student measures the length of the stem of each plant every five days. Some of the student’s results are shown in the table.

Describe the growth of the plants in each solution.

Explain why young plants absorb more mineral ions when air is bubbled through the solutions.

Suggest why each solution is sterilised at the start of this investigation.

Suggest why the glass jar is surrounded by cardboard during this investigation.

Identify the dependent variable in this investigation.

Name one biotic (living) variable that should be controlled in this investigation.

This question is about the effect of salt on plant growth.

Explain what happens to a plant cell if it is put into a concentrated salt solution.

In the UK, salt is spread over road surfaces in winter to prevent ice from forming. When it rains this salt is washed on to the soil by the side of the road. Design an investigation to find out if plant growth is affected by the increased salt concentration in the soil. Your answer should include experimental details and be written in full sentences.

A student carries out an experiment to investigate the effect of different concentrations of a food dye on diffusion.

Describe what is meant by the term diffusion.

The student adds a different concentration of coloured food dye to each of five wells in an agar plate. The diagram shows the agar plate at the beginning of the experiment and after 24 hours.

The student does the experiment using three plates. For each plate he measures the diameter of each circle to see how far the food dye has diffused. The table shows his results.

Calculate the average diameter for 0.2% concentration of food dye.

average diameter =_........

Describe the effect of food dye concentration on diffusion.

Explain the relationship between food dye concentration and diffusion.

State two variables that the student should control in this experiment to ensure that the results are valid.

A student carries out an experiment to investigate the factors affecting the rate of diffusion.

In her first experiment she makes three agar jelly cubes, one with sides of 4.0 cm, one with sides of 2.0 cm and one with sides of 1.0 cm she covers each cube in a solution of a coloured dye for three minutes she then cuts the cubes to see how far the dye has diffused The diagram shows a cross-section through the largest cube after three minutes.

Describe what is meant by the term diffusion.

Measure the distance that the dye has diffused into the large cube.

Complete the diagram below to show how far the dye will have diffused in the smallest cube after three minutes.

The student then carries out a second experiment but this time she leaves the cubes in the dye for six minutes. Draw the results you would expect to see when the largest cube is cut open after six minutes.

Other factors may affect the rate of diffusion of the dye. Explain two factors that the student should keep constant in her investigation.

Explain how the results of the student’s investigation support the idea that large organisms need a circulation system.

The table shows the concentration of sodium ions and chloride ions inside a plant root hair cell and in the water in the soil.

The ratio for the concentration of sodium ions in the root hair cell compared to the water in the soil is 71:1

Calculate the ratio for the concentration of chloride ions in the root hair cell compared to the water in the soil.

Adding too much water to soil will fill all the air spaces in the soil with water. Suggest why this will prevent root hair cells from absorbing sodium or chloride ions.

The table lists two other mineral ions. Complete the table by naming a molecule that is made in plants using the mineral ion.

A chicken egg is a single cell protected by a shell on the outside. A student puts three chicken eggs into dilute acid and leaves them for three days. The acid dissolves the egg shells, leaving the contents of the eggs surrounded by the cell membrane. The diagram shows the student’s method.

egg shell surrounded by cell membrane

The student removes the eggs from the dilute acid and uses water to wash the surface acid away. The student then uses the eggs for this osmosis experiment. • he measures the mass of each egg • he then puts one egg into a beaker containing distilled water • he puts another egg into a beaker containing 5% salt solution • he puts a third egg into a beaker containing 15% salt solution • after 15 minutes he removes each egg from its beaker and measures its mass again

The bar graph shows the results obtained by the student from the osmosis experiment.

Name the dependent variable in this experiment.

Explain the result for the egg placed in distilled water.

The student calculates the percentage change in mass for the eggs placed in distilled water and in 5% salt solution.

Use the data from graph 1 to calculate the percentage change in mass for the egg placed in 15% salt solution. Show your working.

Percentage change in mass =_........

The student plots the percentage change in mass on graph 2. Complete the bar graph to show the percentage change in mass for the egg placed in 15% salt solution.

distilled water salt solution salt solution Bar graph 2

Give one way in which osmosis differs from diffusion.

A student investigated the effect of size on the movement of molecules. He cut three different sized cubes from a block of clear agar jelly. Cube A was 2 × 2 × 2 cm. Cube B was 1 × 1 × 1 cm and cube C was 0.5 × 0.5 × 0.5 cm.

The student wore safety glasses and placed the cubes in a beaker of red dye solution for five minutes. He then poured the solution into another beaker, washed the surface of the cubes and dried them with blotting paper. He then cut each cube in half and examined the newly cut surfaces. Diagram 1 shows what the cubes looked like.

Why did he wear safety glasses?

Explain how the red dye molecules entered the jelly.

Use a ruler to measure the distance the red dye has entered each cube in diagram 1.

Calculate the surface area of cube A.

surface area =_........ unit_........

Calculate the volume of cube A.

The student was told by his teacher that the cubes have different surface area to volume ratios. Complete the table by putting one tick () in each row to show whether the statement applies to cube A, B or C.

Explain how this experiment can be used to understand the need for transport systems in larger organisms such as humans.

A student prepared some plant cells taken from an onion. She placed the cells in a few drops of distilled water. She then used a camera attached to a microscope to photograph the cells. She then added a few drops of concentrated salt solution to the cells and waited a few minutes. She then took another photograph of the same cells.

photograph of cells in concentrated salt solution

Describe the differences in the appearance of the cells in concentrated salt solution compared with the cells in distilled water.

The student thought that the differences in the cells were caused by osmosis. What is meant by the term osmosis ?

Explain what happens to the cells in concentrated salt solution to change their appearance.

Another student investigated the appearance of red blood cells in distilled water and in concentrated salt solution. Use your knowledge of osmosis and the structure of red blood cells to describe and explain what the red blood cells would look like

in distilled water

in concentrated salt solution.

Lily investigated the effect of concentration of a substance on the rate of diffusion. In a fume cupboard she set up a glass tube with small squares of damp red litmus paper spaced at 4 cm intervals along its length. She added 1 drop of ammonia solution to some cotton wool and used tweezers to place the cotton wool at one end of the tube. She closed the tube with a bung. She timed how long it took for each square of litmus paper to change colour. She then set up an identical tube and repeated the experiment, but this time she used 3 drops of ammonia solution.

Her results are shown in the table.

Describe what is meant by the term diffusion.

Plot these results on the grid. Use straight lines to join the points.

Describe the results shown by the graph.

Calculate the average rate of diffusion, in centimetres per second of ammonia, from the 3 drops of ammonia solution between the litmus papers at 4 cm and 24 cm. Show your working.

Explain the difference in the rate of diffusion between the experiment using 1 drop of ammonia and the experiment using 3 drops of ammonia.

Suggest how Lily could modify her experiment to investigate the effect of temperature on the rate of diffusion.

The diagram shows the apparatus used to investigate how quickly water passes through two different types of soil.

Each funnel contained 200 g of dry soil. Water was poured into each funnel to make the soil completely wet. Then 100 cm³ of water was poured on to the wet soil in each funnel and allowed to drain into the measuring cylinders. The volume of water collected in the cylinders was measured every two minutes until all 100 cm³ had been collected. The table shows the results.

Soil type is an independent variable in this investigation. What is meant by the term independent variable ?

What is the dependent variable in this investigation?

Tick the box to show the correct controlled variable in this investigation.

Calculate the average rate in cm³ per minute at which water drained through the clay soil. Show your working.

_........ cm³ per minute

The photographs show two stop clocks, A and B, that could be used to measure the time taken for water to drain through the soil in this investigation.

Which of these two stop clocks would give a more precise reading? Explain your answer.

Sandy soil contains large soil particles with big air spaces between them. Clay soil contains very small soil particles with small air spaces between them and most of these air spaces are filled with water.

Suggest why many plants may find it difficult to grow in sandy soil.

Use your knowledge of how plant roots absorb mineral ions to suggest why some plants may find it difficult to grow in clay soil.

The diagram shows the nitrogen cycle. Different stages have been numbered 1 to 8.

The table lists the stages involved in the nitrogen cycle. Complete the table by giving the correct number, or numbers, corresponding to each stage. The first one has been done for you.

Explain how nitrates are absorbed into plants at stage 8.