2.4 Plant Tissues, Organs & Systems

Which statement from A to D would indicate that transport of materials in the phloem involves metabolic processes rather than just a physical process?.

Figure 1 shows an aphid feeding on a plant stem.

Figure 1

Explain why they target structure X.

Describe how the xylem is adapted for the transport of water.

Compare the transport systems in plants and animals.

Figure 2 shows a cross section of a leaf.

Figure 2

State what is unusual about the underside of the leaf.

Explain which kind of environment the leaf shown in Figure 2 is adapted for.

Many plants that grow in hot arid environments like the desert, take in CO₂ during the night and store it.

Explain how this is advantageous to the plant.

During an exam a student wrote the following statement:

"Transpiration and photosynthesis in plants is a compromise".

Suggest what evidence they could use to support this statement.

The development of root hair cells is complicated and under the control of many genes.

Scientists have created mutants where particular genes are deleted ('knocked out'), these result in different phenotypes (observable characteristics). Table 1 shows the effect of knocking out various genes on the growth of root hair cells.

Table 1

Suggest why it is important for a plant to have such developmental control over the growth of root hair cells.

Explain why a tree loses more water during the day compared to night time.

Xerophytes are plants that are specially adapted to live in the desert.

Explain why Xerophytes need to be adapted to their environment.

Describe the special features that allow guard cells to open and close stomata.

Explain how a potometer can be used to estimate transpiration rates. 

A student set up a potometer and stated that:

"the potometer can tell me exactly how much water has been lost through transpiration".

Suggest what is inaccurate about the student's statement.

A student investigated the effect of light intensity on transpiration in a plant using a mass potometer as shown in Figure 3.

Figure 3

Six plants were used, three in each of two different conditions: in a room or in the same room next to a bright lamp. Table 2 shows the results.

The student then set up an investigation to study the effect of increasing humidity levels on transpiration.

Explain why the results of the two investigations may differ.

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.

Figure 2 is a drawing of the underside of a leaf of one of the plants as visualised under a light microscope.

Name cell X in Figure 2 and outline its role in the leaf.

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.

Figure 3 shows a drawing of the cross-section of a plant root.

The transport tissues are labelled.

Figure 3

What tissue is labelled X?

Name two substances transported by the xylem.

Compare the structure of the xylem with that of tissue X.

A process called translocation occurs in tissue X.

What is translocation and why is it important for plants?

Figure 4 shows two guard cells surrounding an open stoma and two guard cells surrounding a closed stoma.

Figure 4

When light intensity is low, the stoma closes.

Describe how the stoma close.

Guard cells have cell walls with unevenly distributed cellulose.

Suggest why this is important.

A student investigated the effect of varying concentrations of salt solution on the opening of stomata on the lower epidermis of a leaf.

Her results are shown in Table 2.

Table 2

The student calculated one of the percentages for open stomata in the field of view incorrectly.

Identify for which solution the result was incorrect and give the correct value.

Write a conclusion for the results of the experiment as shown in Table 2.

The student measured the real diameter for the field of view to be 0.475 mm.

Calculate the total number of stomata per mm² of the leaf epidermis placed in 0.8 mol / dm³ salt solution if the value of π (pi) is 3.14.

Show your working.

A potometer can be used to measure the uptake of water by a leafy shoot.

Figure 5 shows a potometer.

Figure 5

A group of students measured the uptake of water by the shoot under normal conditions.

As water was taken up by the shoot, the level of water in the capillary tube decreased.

Explain why.

The water level of the shoot was recorded at 2 minute intervals over a 12 minute period.

The results are shown in Table 3.

Table 3

The area of the cross section of the capillary tube was 0.6 mm².

Calculate the volume of water taken up by the shoot in mm³ per minute.

Show your working.

The students decided to repeat the investigation but this time placed a humidifier in the room next to the potometer.

A humidifier adds water vapour to the air.

Suggest and explain how the results would be different to those obtained in Table 3.

The students considered repeating the investigation again by measuring the uptake of water at different temperatures.

They were conscious of not leaving the leaves for too long at temperatures above 30 °C.

Explain why.