Xylem and phloem

The roots of plants contain a variety of cells and tissues.

The photomicrograph shows a transverse section through the root of a herbaceous dicotyledonous plant.

Name the cells labelled A and B in the photomicrograph.

The outer surface of a root is made up of root epidermal cells.

A root hair cell is a type of root epidermal cell that has a hair‑like extension called a root hair.

A typical root epidermal cell has a surface area to volume ratio (SA: V) of 0.3: 1.

A root hair cell has a higher SA: V than a typical root epidermal cell.

The diagram shows a root hair cell. The diagram is not to scale.

The root hair has:

• a diameter of 10 m

• a length of 800 m.

Calculate the SA: V of the root hair.

Assume the root hair is cylindrical.

Use the equations:

Surface area of cylinder = 2r(r + l)

Volume of cylinder = r²l

State how a high SA: V helps a root hair cell perform its function.

Carbohydrates produced in palisade cells are transported in phloem to sinks, such as roots.

Describe how carbohydrates move from palisade cells into companion cells in phloem.

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.

Dicotyledons are a large and diverse group of multicellular plants that includes oak trees and dandelions.

Explain, using examples of transported substances, why multicellular plants need transport systems.

Fig. 16.1 is a light micrograph of a transverse section through the leaf of a dicotyledon.

Identify the tissue labelled B in Fig. 16.1.

State two functions of structure A.

Fig. 16.2 on the insert is a coloured scanning electron micrograph (SEM) of a longitudinal section through vascular tissue in the stem of a dicotyledon.

Explain how two features, visible in Fig. 16.2, show that this tissue is adapted to its function.

A mycorrhiza is mutualistic association between a fungus and a plant. The fungus penetrates root cells and assists with uptake of water and nutrients.

A group of scientists investigated the role of mycorrhiza in the uptake of phosphates by plants.

Wild type barley plants produce root hairs. Mutant (brb) barley plants do not produce root hairs.

brb mutant and wild type plants were grown in pots and half of each group had mycorrhiza fungus added. After 28 days, the dry mass and phosphate content of the plants was measured.

The results are shown in the table.

The scientists concluded that the mycorrhiza compensated for the absence of root hairs in the mutant (brb) barley plants.

Evaluate this conclusion.

The figure below shows a drawing of a light microscope image. The image is a cross-section taken from the stem of a dicotyledonous plant.

Which of the rows, A to D, correctly identifies the name of the tissue labelled E and the functions of tissue F and tissue G ?

Your answer

Which of the following statements, A to D, does not correctly describe the structure or formation of plant vascular tissues?

A Companion cells are linked to xylem vessels by plasmodesmata.

B Mature sieve tube elements do not contain nuclei.

C Phloem and xylem are formed by differentiation of vascular meristems.

D Xylem vessels have non-lignified pits to allow movement in and out.

Your answer

The onion plant, Allium cepa, is grown as a food crop around the world.

The table below contains statements about the root cells of an onion.

Place ticks (✓) in the boxes in the table to indicate whether the statements are true or false.

Fig. 1 shows a cross section of the root of an onion plant.

Identify the tissues shown at M and N.

The colour of onion bulbs is determined by two genes, A/a and B/b.

• A is a dominant allele and codes for the production of a red pigment.

• Onion bulbs that are homozygous for the recessive allele, a, produce no pigment and are white.

• B is a dominant allele that inhibits the expression of allele A.

• The recessive allele, b, allows the production of the red pigment.

A white onion plant was cross-pollinated with a red onion plant. All 15 offspring had the genotype AaBb.

Identify the following:

The genotype of the white onion plant........

The genotype of the red onion plant........

The phenotype of the offspring........

State the type of gene interaction shown by the genes A/a and B/b.

Suggest how allele B inhibits the expression of allele A.