Transpiration

Xylem vessels maintain the transpiration stream by transporting water up plant stems.

The sentences describe the role of meristems in producing xylem vessels.

Complete the sentences using the most appropriate words or phrases.

Meristem cells are located between xylem and........ tissues in

plants. Cells of either of these vascular tissues can be produced when meristem cells divide and

A pair of students dissect the vascular tissue of the primrose plant, Primula vulgaris.

State and explain one safety precaution that the students should take when dissecting the vascular tissue.

This is a light micrograph of a transverse section through the stem of P. vulgaris.

The diameter of one of the vascular bundles is shown by the line labelled V.

Calculate the actual diameter of the vascular bundle labelled V.

Give your answer in mm and to 2 significant figures.

A scientist plans to investigate the effect of temperature on the rate of transpiration in P. vulgaris.

The scientist uses a potometer in their investigation, as shown in the diagram below.

The scientist plans to calculate the rate of transpiration by measuring the distance moved by the air bubble.

The scientist carries out a preliminary trial by measuring the distance moved by the air bubble in 30 minutes at 20 C.

The bubble moves 18 mm in 30 minutes. The diameter of the capillary tubing in the potometer is 1 mm.

Calculate the rate of transpiration, in mm³ h^–1, during this preliminary trial.

Use the formula: Volume of cylinder = r²l

Rate of transpiration =........ mm³ h^–1

* Describe how the scientist could use the potometer to collect the data needed to assess the effect of temperature on the rate of transpiration in P. vulgaris.

Details of how to set up and use a potometer are not needed.

In your answer you should name an appropriate statistical test that could be used to analyse the data.

Extra answer space if required.

Many plants, such as Erica cinerea (bell heather), have evolved adaptations to limit water loss by transpiration.

This is a drawing of a leaf of E. cinerea.

State and explain how the leaf of E. cinerea is adapted to limit water loss by transpiration.

In 1933 two scientists published a study in which they investigated the movement of coloured dyes in the transpiration stream of the stems of sycamore trees growing in a wood.

They bored holes in the stems and poured dye solution into the borehole. Then they sealed the hole with impermeable tape.

Describe what is meant by the term transpiration stream.

Suggest why the scientists sealed the borehole with tape.

The scientists found that the dye moved both up and down the stems.

A student wanted to investigate this in the laboratory. They devised an experiment using water-soluble food dyes injected into the stems of sunflower plants growing in pots.

Suggest how they could observe the route taken by the dyes.

Plants are often watered with a solution containing minerals to help them grow.

While preparing a class practical a technician accidentally watered some sunflower plants with a mineral concentration that was 1000 times higher than normal.

Explain why the plants wilted, even though they were given a lot of water.

The teacher suggested that the same effect would be seen if the plants had been watered with a solution containing cyanide ions that inhibit ATP synthesis.

Explain whether the teacher was correct.

Explain why plants growing in high light intensity require more water than plants growing in shade, even when the temperatures are the same.

The figure shows a potometer used to measure the rate of transpiration in a leafy shoot.

Besides safety precautions, explain one practical precaution that should be taken when using a potometer.

A student carried out an investigation to measure the effect of air movement on the rate of transpiration.

The student used the apparatus shown in the figure, adding an electric fan to create air movement. They measured the distance travelled by the air-water meniscus in 5 minutes.

This was replicated five times with the fan switched off and then five times with the fan switched on.

The results are shown in the table.

Calculate the standard deviation for the distance travelled when the fan was switched

Give your answer to 2 significant figures.

What can you conclude from comparing the standard deviations of the two means?

The student carried out another investigation.

The student wanted to estimate the total leaf surface area of the shoot.

At the end of the investigation they removed all the leaves from the shoot.

They placed the leaves on graph paper and then counted squares to obtain an estimate of leaf area.

State two things the student would have to do to ensure that the estimate of leaf area was accurate.

In this investigation, the student calculated the rate of transpiration to be 30 mm³ min (ii)

They estimated the total leaf surface area of the shoot to be 37 cm².

Calculate the rate of transpiration in cm³ hr^–1 cm^–2.

Give your answer in standard form to 2 significant figures.

Rate =........ cm³ hr^–1 cm^–2

Plant growth requires the production of new xylem cells.

Describe how new xylem cells are produced.

* Explain how glucose produced in photosynthesis is translocated to parts of the plant where glucose is metabolised or stored.

Additional answer space if required.

Which of the following statements about water transport in plants is/are correct?

1 Transpiration happens as a consequence of the need for gas exchange. 2 There are cohesive forces between water molecules because they form hydrogen bonds with one another. 3 Water is drawn up the stem due to adhesive forces between water molecules.

A 1, 2 and 3

B only 1 and 2

C only 2 and 3

D only 1

Your answer

Which of the statements, A to D, applies to transpiration and evaporation?

A It occurs at a faster rate at higher humidity.

B It occurs at a slower rate at greater wind speed.

C It occurs at a slower rate at higher temperature.

D It occurs at the surface of leaves.

Your answer

* Plants lose water by transpiration.

The rate of transpiration varies between different species of plant.

The rate of transpiration can be measured using a potometer.

Plan an investigation into the rate of transpiration in two species of plant that would allow valid data to be collected.

Details of how to set up a potometer are not required.

Plant cell walls are made of cellulose. Cellulose is a polymer of -glucose.

Give three properties of cellulose that make it suitable as the basis of plant cell walls.

Cellulose cannot be digested by animals. Some mammals have bacteria in their stomachs that produce enzymes that can digest cellulose.

Explain whether the action of these enzymes is intracellular or extracellular.