Transport in Plants (Cambridge (CIE) IGCSE Biology)

A student investigated the effect of temperature on water uptake in celery stalks.

Water is transported in the xylem tissue in plant stems.

Step 1

One celery stalk was placed into a beaker containing warm red stain. Another celery stalk was placed into a beaker containing cool red stain.

This is shown in Fig 1.

Fig. 1

Step 2

Both celery stalks were left in the red stain for 10 minutes.

Step 3

After 10 minutes the celery stalks were removed from the red stain.

Step 4

A 5 mm section was cut from the end of the celery stalk which had been in the warm red stain, as shown in Fig. 2.

Fig. 2

Step 5

The section was inspected for the presence of the red stain in the xylem tissue in the celery stalk, as shown in Fig. 3.

Fig. 3

Step 6

If the red stain was visible in the cut section, another 5 mm section was cut and the process repeated until no red stain was visible in the cut section. This allowed the student to estimate how far the red stain had moved up the celery stalk.

Step 7

Steps 4 to 6 were repeated for the celery stalk which had been in the cool red stain.

(i)

State one safety precaution that should be taken while carrying out this method.

[1]

(ii)

The student’s results are shown in Fig. 4.

Fig. 4

Prepare a table and record your results in your table, in the space provided.Your table should include:

• the temperature (cool or warm) of the red stain

• the number of sections that were stained in 10 minutes

• the total distance moved by the red stain in 10 minutes.

[3]

(iii)

Use the data to calculate the rate of movement of the red stain in the celery stalk at each temperature.

Give your answers in mm per minute.

[2]

(iv)

State a conclusion for these results.

[1]

State two variables which were kept constant in this experiment.

One way of improving the method used in this investigation would be to repeat it a number of times.

Identify two other sources of error in this investigation.

For each error, suggest an improvement to minimise the effect of the error.

Some farmers wanted to investigate the effect of humidity on the rate of transpiration in celery plants.

Fig. 5 shows celery plants being harvested. 

Fig. 5

One method of measuring the rate of transpiration is to record how long it takes a red stain to travel up the xylem tissue in a celery stalk that still has its leaves attached.

Plan an investigation to determine the effect of humidity on the rate of movement of water through leafy celery stalks.

Some students decided to investigate the effect of wind speed on the rate of transpiration from leaves. For this, they used a potometer as shown in Fig. 1.

Fig.1

They selected a beech tree from the grounds of their school. Beech was selected because it is a species with a thin waxy cuticle. 

In the laboratory, they filled a sink with water, placed the small branch underwater and cut a shoot off the branch. This shoot contained ten leaves. 

Petroleum jelly (e.g. Vaseline™) was smeared around the edges of the cut end of the shoot prior to inserting the shoot into the potometer, as shown in Fig. 2.

Care was taken to avoid petroleum jelly getting onto the cut end of the shoot.

Fig. 2

(i)

Suggest why a species with a thin waxy cuticle was chosen for this experiment.

[2]

(ii)

Explain why the shoot with ten leaves was cut from the branch under water and not in air. 

[2]

(iii)

Explain the purpose of petroleum jelly being smeared on the areas shown in Fig. 2.

[1]

(iv)

Explain why the students should avoid petroleum jelly getting onto the cut end of the shoot as shown in Fig. 2.

[2]

Before the first experiment, the leaves were dried carefully by blotting excess water from the sink off them using pieces of paper towel. 

The students used an electric fan with three speed settings to adjust the speed of air flowing over the leaves. The speed settings were numbered 0 (fan switched off), I (slowest setting), II and III (fastest setting).

At each wind speed they measured the time taken for the air bubble to move a set distance of 50 mm in the potometer. 

(i)

Explain why the leaves were first dried using a paper towel. 

[2]

(ii)

Suggest and explain an experimental step that the students should take after drying the leaves and before beginning to take measurements. 

[2]

(iii)

Draw a blank results table that the students could fill in with their experimental data.

[3]

The capillary tube in the potometer used in this experiment (see Fig. 1) has a diameter of 1mm. 

(i)

Calculate the volume of water transpired by the piece of plant in the time taken for the bubble to move a distance of 50mm. 

The volume of a cylinder = πr²h, where r is the radius and h is the length of capillary tube. 

Give your answer in appropriate units. 

[3]

(ii)

The piece of beech under zero wind speed conditions took 7 minutes and 45 seconds to move the bubble 50mm.

Calculate the rate of transpiration in mm³ minute^-1.

[2]

(iii)

Suggest two reasons why the answer you calculated in part (ii) might be an under-estimate of the rate of transpiration that the plant may experience in its natural habitat. 

[2]

In a similar experiment using a piece of shoot and leaves from a different species of tree, the students achieved the following results.

Fan setting 0 = transpiration rate 45 mm³min^-1

Fan setting I = transpiration rate 57 mm³min^-1

Fan setting II = transpiration rate 68 mm³min^-1

Fan setting III = transpiration rate 70 mm³min^-1

Plot the results on a suitable graph using the grid below.