Transpiration & Translocation (Cambridge O Level Biology)

Fig. 1 shows a photomicrograph of a section of a root.

Fig. 1

Structure J is a xylem vessel.

The xylem vessels conduct water from the roots to the stems.

State the features of xylem vessels that enable them to conduct water.

Complete the sentences by placing appropriate words in the spaces to give a definition of transpiration.

In transpiration water is lost from the .............................................. of a plant.

The water .............................................. from the surface of the ..............................................  cells and water vapour is produced.

The water vapour moves by .............................................. out of the plant through pores called ..............................................

Complete Table 1 by

• stating two environmental conditions that affect the rate of transpiration
• stating how a decrease in each environmental condition affects the rate of transpiration

Table 1

When water is in short supply, plants can wilt as shown in Fig. 1

Fig. 1

State two conditions that are likely to increase the chances of wilting.

Explain what happens to the cells of a leaf to cause wilting.

Wilting may look harmful, but it is often a strategy for survival.

Suggest the advantages to a plant of wilting.

Compare the plant processes of transpiration and translocation.

Name the two main products of a plant's metabolism that are carried in the phloem. 

Define the term 'source' when used in the context of plant biology. 

The image shows a wild banana, cut lengthways. Inside the banana, its seeds are clearly visible. Seeds are usually regarded as sinks. 

Give an example of when seeds such as these act as a source. 

Plant leaves have many adaptations to maximise the rate at which they can photosynthesise. A group of students wanted to investigate the behaviour of stomata in different plants.

Fig. 1 is a drawing of the underside of a leaf of one of the plants as visualised under a light microscope.

Fig. 1

Name cell X in Fig. 1 and outline its role in the leaf.

[3]

Calculate the number of stomata per mm² of this leaf surface.

Another plant species has 200 stomata per mm² of its leaf surface.

An increased number of stomata is not always advantageous.

Explain why.

The students then measured the mean widths of the stomata from three different species of plant which had been growing under different light conditions.

Table 1 shows their results.

Table 1

Species A is unlikely to be found growing in a hot, dry desert.

Explain why, using data from Table 1.

Scientists wanted to determine the flow-rate of water in roots.

They measured the flow-rate in three zones of onion roots as shown in Fig. 1 

Fig. 1

They measured the flow-rate in healthy roots and roots that had been treated with a toxic solution.

Their results are shown in Table 1.

Table 1

Calculate the percentage increase in the average flow-rate between zone 1 and 3 for healthy roots.

Give your answer to two significant figures.

Show your working.

The scientists observed that the xylem vessels nearer the root tip were narrower than the xylem vessels higher up the root.

Describe how the width of xylem vessels in different zones of a root affects the average flow-rate of water.

Use the information in Table 1 in your answer.

Suggest why there was little difference in the flow-rate in healthy roots and in roots treated with the toxic solution.

Fig 1

(i)

Identify the position of the xylem tissue by drawing a label line and the letter X on Fig. 1

[1]

(ii)

State why the xylem is a tissue.

[2]

Water absorbed by the roots moves through the stem and enters the leaves. Most of this water is lost in transpiration.

Explain how the internal structure of leaves results in the loss of large quantities of water in transpiration.

Describe and explain how a reduced concentration of water vapour in the air would increase the movement of water through crop plants.

Aphids are insects that feed on the phloem sap in plants.

Fig. 1 shows a diagram of an aphid with its mouth parts inserted into the stem of a plant.

Fig. 1

The mouth parts of the aphid reach the phloem tissue of the stem. 

State the name of the foods the aphid could suck out of the phloem tissue.

[2]

Explain the role of phloem in plant transport. Use the words source and sink in your answer

Fig. 1 shows some of the features of xylem.

Describe how xylem is adapted for its functions.

Fig.1 is a photomicrograph of some xylem vessels.

Fig. 1

State one structural feature of xylem vessels and explain how this is related to the function of water transport.

Explain the mechanism that is responsible for the movement of water in xylem vessels.

State one role of xylem vessels other than transport.

The rate of transpiration is affected by several factors including the temperature and the humidity of the air.

State and explain the effect of an increase in temperature on the rate of transpiration.

Fig. 1 shows a potometer set up to measure the rate of transpiration in a piece of cut plant. 

Fig. 1

Identify labels W, X, Y and Z.

In the experiment shown in Fig. 1, the bubble moved a distance of 23 mm in 47 minutes of experiment time. 

The bore (internal diameter) of the capillary tube that the bubble is in is 1 mm.

Calculate the volume of water taken up by the plant in the time of the experiment.

[2]

Calculate the rate of transpiration of the piece of plant.

State your answer in mm³hr^-1.

[2]

For the experiment described in part (b), a subsequent experiment used an electric fan to blow air across the leaves of the plant throughout the experiment. 

Predict the rate of transpiration that would be measured. State your answer as a number with units. 

Explain your reasoning. 

A different piece of the plant (from a species of tree) was measured and its transpiration rate was found to be 350 mm³hr^-1.

The piece of the tree being studied contained 8 leaves whereas a mature tree of the same species would consist of an average of 65 000 leaves.

Estimate the rate of transpiration of a mature tree of this species.

Express your answer in litres per day (dm³day^-1)

1dm³ = 1 000 000 mm³

[3]

Give three reasons to suggest why the estimate in part (d) (i) is likely to be inaccurate.

[3]