3.6 Mass Transport in Plants

A potometer can be used to investigate the water uptake of plants under different conditions. Students investigated how covering the leaves from plant shoots with grease affects the water uptake of the shoots. All of the shoots were from the same plant and had 7 leaves. The set up of their experiment is shown in Figure 1 below.

Figure 1

When setting up the potometer shown in Figure 1 one of the precautions the students took to ensure reliable measurements of water uptake was to cut the shoots underwater. Give two other precautions the students should take when setting up the potometer apparatus to ensure reliable results.

Using your knowledge of plant processes, discuss whether the measurements taken from a potometer represents the true rate of transpiration in a plant.

The results for the experiment are shown in Table 1.

Table 1

Sketch a graph to illustrate the results in Table 1. 

What can you conclude about the effect of covering plant leaves with grease from the data in Table 1 and your graph? Explain how you reached your conclusions.

A scientist is investigating two substances X and Y,  which may affect the growth of new roots from a cut plant stem. They used a ringing experiment to investigate the transport of substances X and Y through the plant stems taken from a grapefruit plant. A length of stem was cut from each grapefruit plant and a small block of agar was placed at the top of each stem. Substance X or Y was added to some of the agar blocks.

                                                                        Figure 1

The stems were grown in the same environmental conditions for 5 weeks and then the number of roots per stem was recorded. The roots grew at the opposite end to where the agar block was located. Table 1 below shows the results of the experiment. 

Table 1

Agar delivers substances X and Y in treatments 2-5. Suggest one other reason why agar is present in all of the treatments.

What can you conclude about the action of substance Y in plants from Figure 1 and Table 1?

The movement of substances through the phloem can be explained using the mass flow hypothesis. Evaluate if the data from this experiment supports the mass flow hypothesis. No statistical analysis is required.

Upon further research it was discovered that substance Y could be sprayed onto the leaves of a plant and it would be absorbed into the phloem sap. Using this information, discuss the mechanism by which substance Y could act as weed control.

Figure 1 shows a cross section of a stem.

Figure 1

Label I and J from Figure 1 and state their function

I   ________________________

Function of I ________________

J  ________________________

Function of J _______________

Figure 2 shows how the changes in environmental temperature and light intensity throughout the day can cause the diameter of a spruce tree to fluctuate.

Figure 2

Describe and explain the trunk diameter measured at midday in Figure 2. Use your knowledge of the cohesion-tension theory.

Upon further analysis of the results the scientist noticed a trend. At 12 noon the trees closer to the edge of the forest showed a greater change in trunk diameter compared to the trees in the centre of the forest. They determined the mean change in trunk diameter at 12 noon for both groups of trees.

What statistical test should the scientist use to determine if the mean changes in trunk diameter for the two groups of trees are significantly different? Give the reason for your choice.

Suggest why the trees on the edge of the forest could show a greater change in trunk diameter at 12 noon. 

Privet and Holly are both common types of evergreen plants that can be found in British gardens. The leaves of holly bushes possess particularly thick waxy cuticles. A  student wants to investigate the rate of transpiration in privet and holly leaves.

For set X he cut 10 privet leaves and for set Y he cut 10 holly leaves. After weighing each set of leaves he attached the leaves in each set to a separate wire. He then weighed each set of leaves at 30-minute intervals for a duration of 3 hours. His results are seen in Figure 1.

Figure 1

Environmental conditions can affect the rate of transpiration in plants. Name one of these conditions and state its effect on transpiration.

In Figure 1, the starting mean mass of the leaves in Set X was 0.1 grams. After 90 minutes the mean mass was 0.096 grams. Calculate the rate of change in mass per hour.

Explain the change in mass for the leaves in sets X and Y shown in Figure 1.

Predict what would happen if the experiment were to carry on for 12 hours.

Figure 1 shows the cross-section of a phloem in a plant.

Figure 1

Cell type B is characterised by a large number of mitochondria. Suggest why this is advantageous.

Using Figure 1, suggest and explain two ways in which the intracellular space and walls of the sieve cells are adapted to mass transport.

Describe the mechanism of sugar transport in plant stems.

Most of the sugars produced by plants are used up rapidly in respiration. However, sometimes plants can overproduce sugars during photosynthesis. Describe what happens to excess sugars in plants.

A potometer can be used to investigate the water uptake of plants under different conditions. Figure 1 shows how a student investigated the effect of covering the leaves from plant shoots with grease on the water uptake of the shoots. All of the shoots were from the same plant and had 7 leaves.

Figure 1

When setting up the potometer one of the precautions the students took to ensure reliable measurements of water uptake was to dry off the leaves. Suggest a reason for this.

Give two other precautions the students should take when setting up the potometer apparatus to reliable results.

A potometer measures the water uptake of a plant in a given time. Give three reasons why the measurements taken from a potometer do not represent the true rate of transpiration in a plant.

The results for the experiment are shown in Table 1.

Table 1

Describe and explain the results seen in Table 1.

Figure 1  below shows a transection of a stem.

Figure 1

Name the vessel J and state its function.

Figure 1 shows how the changes in environmental temperature and light intensity throughout the day can cause the diameter of a spruce tree to fluctuate.

Figure 1

Using Figure 1, state the time range that environmental factors have the greatest impact on trunk diameter?

Using the data represented in Figure 1 and your knowledge of the cohesion-tension theory, explain the changes in trunk diameter throughout the day.

The scientist wanted to investigate the effect of wind on the transpiration rate of the spruce trees. He identified and labelled trees in the forest that were exposed to more windy conditions and ran the experiment again. Predict what his results will show and suggest why.

A scientist is investigating two substances X and Y,  which may affect the growth of ne roots from a cut plant stem. They used a ringing experiment to investigate the transport of substances X and Y through the plant stems taken from a grapefruit plant. A length of stem from each grapefruit plant was cut and then placed a small block of agar at the top of each stem as a food source. Substance X or Y was added to some of the agar blocks.

Figure 1

Table 1

Treatment 1 was used as a control for the experiment. Explain how the result from treatment 1 is used by the scientist.

Using Figure 1 and Table 1, explain the effects of substance X on root growth.

Substance Y is known to be transported through the plant via the phloem. Suggest a value for J from the table in part (a) and justify your answer.

During the experiment the scientist ensured that the temperature was constant for all the leaf stems. Suggest why this is important.