Transport in Plants
107 questions· page 1 of 11
Suggest why only a small proportion of the absorbed phosphate ions are transported to the growing points.
Gossypium hirsutum is the most common species of plant grown for the production of cotton across the world.
Scientists carried out an investigation to trace the pathway taken by phosphate ions from the leaves of cotton plants into the stems. The scientists used a radioactive isotope of phosphorus () to trace the pathway of phosphate ions.
Some cotton plants were divided into two groups: A and B.
In group A, the scientists:
- inserted impermeable waxed paper between the xylem and phloem in the stem below a leaf of each plant
- injected a solution containing phosphate ions labelled with (labelled phosphate ions) into a vein of each leaf, as shown in Fig. 5.1.
The procedure was repeated on the plants in group B but without inserting the waxed paper.
After one hour, the scientists determined the percentage of labelled phosphate ions in the four sections of the stem, S1 to S4, shown in Fig. 5.1. The results are shown in Table 5.1.
Table 5.1
| region of stem sampled | percentage of injected labelled phosphate ions in stem tissues | |||
|---|---|---|---|---|
| group A – stems with waxed paper | group B – stems with no waxed paper | |||
| phloem | xylem | phloem | xylem | |
| S1 | 12 | 1 | 15 | 5 |
| S2 | 7 | <1 | 10 | 6 |
| S3 | 13 | 0 | 5 | 2 |
| S4 | 5 | <1 | 3 | 1 |
Use Fig. 5.1 and the data in Table 5.1 to discuss the pathway taken by the solution containing phosphate ions labelled with in cotton plants.
The procambium tissue shown in Fig. 1.1 consists of stem cells.
Suggest a role of the procambium tissue in the roots of this plant.
Some species in the Ranunculus genus are xerophytes.
State and explain two adaptations of the leaves of xerophytic plants that reduce water loss.
adaptation ______
explanation ______
adaptation ______
explanation ______
Fig. 5.1 is a diagram of a cross section through the leaf of a herbaceous dicotyledonous mesophyte.
Complete Fig. 5.1 by naming structure A and tissue layer B.
In xerophytes, some of the structural features shown in Fig. 5.1 are modified as adaptations for surviving conditions of water stress.
Complete Table 5.1 to show how the structural feature listed may be modified in the leaf of a xerophyte.
Each feature should have a different example of a modification.
Table 5.1
| structural feature in Fig. 5.1 | one example of a xerophytic adaptation |
|---|---|
| structure A | |
| upper epidermis | |
| lower epidermis |
State and explain why the same leaf of a plant can be described as a source or as a sink, depending on the stage of maturity (age) of the leaf.
Fig. 6.1 lists seven types of plant cell found in leaves.
Match the correct type of cell from the list in Fig. 6.1 with each statement, A to E.
Each cell type can be used once, more than once, or not at all.
The first match has been done for you.
A This is a thick-walled cell that provides support. ______ 5
B This cell is one of a pair of cells that form a stoma. ______
C This cell receives water to build up hydrostatic pressure for mass flow. ______
D This cell needs water for photosynthesis and is columnar-shaped. ______
E This cell secretes a waxy substance to help prevent water loss. ______
Fig. 5.2 shows part of a plant of N. oleander.
Fig. 5.3 shows a cross-section of part of an oleander leaf.
Fig. 5.4 is a drawing of a high-power view of region N on Fig. 5.3.
State and explain two adaptations shown by the leaves of N. oleander that are visible in Fig. 5.3 and Fig. 5.4.
one adaptation visible in Fig. 5.3 ..............................................................................................
explanation ...............................................................................................................................
one adaptation visible in Fig. 5.4 ..............................................................................................
explanation ...............................................................................................................................
The structure labelled Y in the cell wall is a barrier to the apoplast pathway. State the name of structure Y.
With reference to Fig. 6.1, complete the statements about the movement of water in the flowering plant.
Water moves from the soil solution to the cytoplasm of root hair cells by ______
Water moves from the xylem in the root to the leaf by ______
Water moves from mesophyll cell walls to intercellular air spaces by ______
Water vapour moves from intercellular air spaces to the atmosphere outside the leaf by ______
A photomicrograph of a transverse section of a dicotyledonous stem is shown in Fig. 5.1.
Use label lines and labels to identify the phloem tissue and xylem tissue in Fig. 5.1.
Describe how sucrose is transported in phloem sieve tubes from photosynthesising leaves to other parts of the plant.
Cyanide ions () inhibit the activity of an enzyme involved in respiration.
Suggest why the treatment of photosynthesising leaves with results in less sucrose being transported into phloem sieve tubes.
A student was asked to carry out semi-quantitative Benedict’s tests on two solutions.
• Solution A was extracted from the cytoplasm of cells in the mesophyll tissue of photosynthesising leaves.
• Solution B was extracted from the phloem sap in phloem sieve tubes.
The solutions were taken from the same plant, and other variables were standardised.
For each solution, the student measured the time taken for the first colour change to appear.
Suggest which of the two solutions, A or B, would change colour in the shortest time.
Explain your answer.
The walls of the cells forming the xylem vessel walls become lignified during development.
Explain how this feature is important for the efficient transport of water.
During the development of xylem vessels, the end walls of the cells forming the vessels break down. This contributes to minimising resistance to the flow of water.
Describe one other main change that needs to occur to these cells so that their structure becomes suited to their function.
Describe and explain the mechanism that is responsible for the movement of phloem sap in sieve tubes.
Tobacco mosaic virus (TMV) infects many crop plants. The virus passes between cells in the leaves and can travel throughout plants in the phloem.
The enzyme pectin methylesterase (PME) is involved with the production of cell walls. The enzyme is also known to influence the movement of TMV through plants. Scientists investigated the effect of PME on the transport of TMV through plants.
The scientists used three varieties of tobacco plants. Two varieties, V1 and V2, have small quantities of PME. A third variety, C, has the normal quantity of PME and was used as the control in this investigation.
The plants in each group were infected with TMV at the same time. The accumulation of the virus particles transported to the leaves at the top of the plants was determined over 36 days.
The results are shown in Fig. 5.1. The arrow indicates when all the plants were infected with TMV.
Compare the results for varieties V1 and V2 with the control group of plants, C.
The source of mineral ions for the plant is the soil solution. These mineral ions are transported from the roots in the xylem. Mineral ions are also found in the phloem sap within phloem sieve tubes.
Suggest why mineral ions are found within phloem sieve tubes and state how they are transported within phloem sieve tubes.
Phloem tissue consists of different cell types.
Complete the passage using the most appropriate terms to summarise some of the features of phloem tissue.
The end walls of sieve tube elements are modified to allow efficient flow of phloem sap by the formation of ______ . These structures also prevent the cells from bursting under pressure. The cytoplasm of sieve tube elements is very much reduced and is found at the ______ of the cells. Most of the organelles in the cell are absent. Adjacent to sieve tube elements are ______ cells that carry out the metabolic processes of the missing organelles, allowing the sieve tube elements to function.