(a) Name the parts indicated by guidelines 1 to 5. (b) Is the root hair cell unicellular or multicellular?
(c) Explain what would happen to the root hair cell if some fertilizer is added to the soil close to it. (d) Name the process responsible for the entry of water
molecules from the soil into A¹ and then into A².
(e) What pressure is responsible for the movement of water in the direction indicated by arrows?
(f) How is this pressure set up ?
Answers
A. 1. Vacuole (containing cell sap)
2. Soil particles
3. Xylem vessel
4. Cortex cells
5. Vacuole in cortical cells
B. In most dicotyledons and monocots, the root hairs are unicellular, thin walled and un-branched structures and are short lived. However, there are exceptions such as the ones found in the aerial adventitious roots of Kalanchoe where these are multicellular.
C. When fertilizers are added to the moist soil around it, it will form hypertonic solution, resulting the protoplasm to shrink and plasma membrane withdraw itself from the cell wall. Hence, the root hairs also become limp or flaccid.
D. In plants, the transpiration stream is the uninterrupted stream of water and solutes which is taken up by the roots and transported via the xylem to the leaves where it evaporates into the air/apoplast-interface of the substomatal cavity. It is driven by capillary action and in some plants by root pressure
E. Name the pressure responsible for the movement of water in thr direction indicated by the arrows. Define it. Root pressure is the pressure developed in the roots due to the inflow of water,because of the alternate turgidity and flaccidity of the cell.
F. Root pressure is caused by active distribution of mineral nutrient ions into the root xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. Water then diffuses from the soil into the root xylem due to osmosis