Root hair cells

A student uses this apparatus to investigate water loss from a plant.

This is the student’s method. step 1 measure the total mass of the flask, water, oil, cotton wool and plant step 2 leave the apparatus for 48 hours step 3 measure the new total mass of the flask, water, oil, cotton wool and plant step 4 calculate the rate of change of mass during the 48 hours Repeat steps 1–4 with the same conditions.

Name the piece of apparatus used in this investigation.

The total mass changes from 207.25 g to 204.50 g in the first 48 hours. Calculate, in grams per hour, the rate of change of mass. Give your answer to two significant figures.

rate of change of mass =_........ grams per hour

Explain why the student repeats the investigation with the same conditions.

The student then changes the conditions surrounding the plant.

Describe how the student could investigate the effect that moving air has on the change in mass.

Explain the effect that faster moving air has on the change in mass.

Describe how the student could modify the investigation to study the role of roots in the loss of water from a plant.

The diagram shows two cells from a plant root.

Which structure is the vacuole?

Which structure is the nucleus?

The actual length of the root cell from P to Q is 80 µ m.

Determine the magnification of the diagram.

[1000 µ m = 1 mm]

magnification =_........

Root hair cells are specialised cells adapted for their functions.

Explain how root hair cells are adapted for their functions in the plant.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Antitranspirants

Antitranspirants are substances applied to plants to reduce water loss. There are three types of antitranspirant, film‑forming compounds, stomatal regulators and reflective compounds.

The first type of antitranspirant contains film‑forming compounds. These compounds are oils or waxes that are mixed with water to form an emulsion. This emulsion is then sprayed onto the leaves of plants. The emulsion forms a physical barrier that covers the stomata. The film is designed to prevent water loss but allow gas exchange. Scientists have found that that the film‑forming antitranspirant is effective in increasing yield and increasing photosynthesis in drought conditions. The increased leaf turgor in plants sprayed with film, compared to control plants, shows that the film decreases water loss and maintains turgor in drought conditions.

Film‑forming antitranspirants are used in horticulture to reduce water stress. This can occur during storage, transport and planting of container grown plants. Application of the antitranspirant before transplanting, helps the plant survive until the root system is established. The film‑forming compounds are used to reduce drying out in rolled turf and in transporting flowering plants and trees with root balls.

The second type of antitranspirants are stomatal regulators that reduce the size of the stomatal pore. Stomatal pores affect diffusion as well as transpiration. Therefore, photosynthesis and growth may change when stomatal regulators are applied to leaf surfaces. If the stomatal pores close completely this will stop photosynthesis. However, if stomatal openings are only reduced in size, transpiration will be reduced but some photosynthesis will continue.

The third type of antitranspirants are reflective compounds. These work by adding a white coating to leaves. This changes the amount of light that is reflected by the leaf surface. The coating is only applied to the upper surface of leaves so does not block the stomatal pores. Coating a leaf with a reflective chemical can reduce leaf temperature, transpiration rate and also increase the efficiency of water use. Experiments show that transpiration rate can be reduced by up to 30% and leaf temperature reduced from 40C to 30C after a coating of reflective compound is applied to leaf surfaces.

Crops depend on photosynthesis for growth and final yield. Therefore, it is unlikely that currently available antitranspirants would increase the yield of a crop unless the crop suffers from a low water supply or very high rates of evaporation. Spraying film‑forming or stomata regulating antitranspirants on a field‑grown cereal crop under drought conditions, produced a grain yield increase of 17%. Experiments also show that any effect that antitranspirants have on the minerals supplied to the leaves has little effect on plant growth.

Explain why plants that have been dug up and transported are at most risk of drying out (Lines 13 to 18).

The photograph shows some stomata on a leaf surface.

Use the photograph to determine the number of stomata per mm² on this leaf surface.

[1 mm = 1000 µ m]

number of stomata per mm² =_........

Explain why stomatal regulators reduce photosynthesis (Lines 19 to 24).

Explain why reflective compounds should only be applied to the upper surface of a leaf (Lines 27 and 28).

Explain why reducing leaf temperature reduces transpiration rate (Lines 28 to 32).

Describe the role of one named mineral ion in plant growth.

Describe how water is transported from the soil to the leaves in plants.

The diagram shows a magnified image of a root hair cell from a young plant.

Give the names of structures labelled W, X, Y and Z.

The actual length of the cell, along the line between A and B, is 1000 µ m. Calculate the magnification of this drawing.

Explain the role of the root hair cell in absorption of water from the soil.

Sometimes gardeners give their plants too much water. The water fills up the air spaces in the soil around the plant roots. Explain how this can lead to plants failing to grow properly.

Plant roots absorb water from soil.

This water is transported to the leaves and then moves into the air.

Which of these processes is used to absorb water from the soil?

Name the tissue that transports water to the leaves.

Name the process that moves water vapour into the air.

Which of these reduces the movement of water from the leaves into the air?

Give two uses of water in a plant.

The diagram shows the path that the water takes when it is absorbed from the soil into the xylem of a plant.

Explain how root hair cells are adapted for efficient absorption of water.

Explain how water is transported from the soil to the leaves.

Describe how you could determine the rate of water loss from a leafy shoot.