Transport of water and minerals - class-XII

• Root hairs are the lateral epidermal extensions or tubular outgrowths in the roots (zone of maturation) of plants.
• The root hairs penetrate into the soil and prevent harmful microbes from entering the plant through the xylem vessels.
• They increase the surface area for absorption of water and nutrients from the soil.
  
• So, the correct answer is 'Epidermal extensions'.

Active absorption requires input of energy, which is obtained from cellular respiration. Respiration is an enzymatic process and is inhibited at extreme temperatures. Hence, the optimum temperature for active absorption is twenty to thirty five degree celsius.

At low temperature, there will be physical changes in water and also water absorption, both due to active and passive means will decrease. There will be an increase in viscosity of water and decrease in respiration in roots. The decreased respiration will lead to reduced supply of ATP. Hence, active absorption will decrease. Also, growth of roots will suffer due to decrease in rate of metabolism. The cell membrane will become less permeable and there will be lesser movement of solutes across them. As temperature rises, the lipids become more fluidic and permit movement of more solutes across the membrane.

Poorly aerated soil, particularly when it is deficient in oxygen, retards absorption of water from the soil. Accumulation of $CO _2$ in the soil also inhibits absorption.

Root hairs are unicellular extensions of root epidermis or epiblema. They increase the surface area for absorption and are involved with absorption of water. Root cap typically lacks root hairs and hence not involved in absorption process.

Water and salts travel upwards mainly in the xylem and food substance travel up and down in the phloem.

Root hairs are important for absorption of water and minerals. If root hairs are damaged during transplantation absorption of water and minerals will suffer. Hence, transplanted seedling may not survive.

In a typical dicot root; root hairs are present in the zone of cell maturation. Root hairs are unicellular extensions of root epidermis, called as epiblema, which absorb water due to increased surface area for absorption. Zone of cell division, zone of elongation and root cap generally lack root hairs.

When concentration of soil solutes is low then the soil solution is hypotonic as compared to cell sap. Water always flows from a hypotonic solution to a hypertonic solution. Hence, when the soil solution is hypotonic due to low concentration of solutes, the water flows into the cell due to the process of endosmosis and absorption of water is increased.

Water flows from higher water potential to lower water potential. Water potential of pure water is zero. As solutes are dissolved in it, the water potential decreases. More the dissolved solutes, lower will be the water potential. Water potential of all the solutions is always negative. Hence, water flows from higher water potential (i.e., less negative water potential) towards a lower water potential (i.e., more negative water potential). It is clear that absorption of water will occur if water potential of cell sap is lower than pure water and soil solution.

It is wrong to believe that water absorption and absorption of mineral salts are two unrelated processes. In fact the active uptake of ions is partly responsible for the water potential gradient in roots, and therefore for the uptake of water by osmosis. Some ions also move into the epidermal cells passively. Since soil has less concentration of minerals; most of the minerals are absorbed actively.

Roots absorp water from soil through diffusion process. Diffusion occurs in the presence of  concentration gradient. When amount of solute is less in soil solution then amount of water is more in soil solution. In this condition more amount of water will diffuse from soil to roots that's why water absorption is increased.

• The attraction between the molecules of dissimilar substances is termed as adhesion. 
• Walls of tracheid and vessels of xylem are made up of lignin and the cellulose. Hence due to the adhesive force, they have a close affinity for water.
• So, the correct answer is option A.

Water-logging indicates to the concentration of soil with water. When the soil is saturated with water over the course of time leads to blockage of air phases and anaerobic condition is succeeded, now the soil may be regarded as waterlogged. In the intense condition (physiologically dry) continued waterlogging leads to anaerobiosis (life sustaining by organism in the absence of oxygen), mostly occurs to mesophytes roots, denitrification and methanogenesis due to reduced atmosphere. 

Root hair absorbs water from soil through osmosis. Water will be absorbed by root hairs by osmosis as the environment in the soil is hypotonic. This kind of absorption takes place passively. The water can easily move from the region of higher concentration to the low concentration without expenditure of energy. The cell membrane of the root cells acts as a semipermeable membrane. It passes the epidermis, cortex, endodermis, casparian strip and pericycle and protoxylem and metaxylem.

Water loss in plants occurs through transpiration (stomata), cuticular transpiration, and guttation (hydathodes). The cell wall of mesophyll cells is the site where evaporation starts, making option A the most comprehensive.

For water to move into the root hair via osmosis, the water potential inside the root hair (specifically the vacuolar sap) must be lower than that of the soil solution.

Matching the phenomena: (a) Degree of hydration relates to Turgor pressure (3), (b) Stretches cell walls relates to Wall pressure (1), (c) Increases free energy relates to Water potential (2), (d) Direction of diffusion relates to Osmotic potential (4).

Pistia is a hydrophyte where absorption of water by root is insignificant   It floats on the surface of the water, its roots hanging submersed beneath floating leaves. 

There is a continuous column of water from root through the stem and into the leaves. The water column is present in tracheary elements. The column of water does not fall down under the impact of gravity because forces of transpiration provide both energy and necessary pull. Cohesion, adhesion and surface tension-keep the water in place.

Cohesion tension theory(Cohesion-tension and transpiration pull theory) explains the ascent of sap best. It was put forward by Dixon and Jolly in 18941894. It was further improved by Dixon in 19141914. Therefore, the theory is also named after him as Dixon's theory of ascent of sap. Today most of the workers believe in this theory.

Plants obtain Carbon from CO2 in the air, Oxygen from air and water, Hydrogen from water, and Nitrogen from the soil. Therefore, H and N are the elements procured mainly through roots.

When a plant cell is placed in the hypotonic solution, it causes endosmosis i.e. movement of surrounding water into the cell. This creates a turgor pressure against the rigid walls due to the entry of water.

During the day time, plants lose a lot of water in the form of water vapour due to the process of transpiration. Whereas it takes up carbon dioxide through stomata to carry out photosynthesis.

While living cells and imbibition play roles, the force of capillarity (and the cohesive-adhesive properties of water) is the primary driver for the movement of water through the xylem in plants.

Plant absorb water from the soil by osmosis. Root hair cells are adapted for this by having a large surface area to speed up osmosis. The absorbed water is transported through the roots to the rest of the plant where it's used for different purposes. It's a reactant used in photosynthesis.

Plants can absorb minerals that are dissolved in solution.The minerals present in the soil can be absorbed through
their root hair cells. However, the concentration of minerals in the soil is very low. While water is absorbed by the plants through osmosis,  minerals are absorbed as ions by
active transport (transport against the law of diffusion, by spending
cellular energy). The cell membrane has transport proteins that allow
the ions to cross the membrane. The ions then move upward through the
xylem, to the leaves and other aerial parts of the plant. The absorption of minerals using respiratory energy is called active absorption and is influenced by temperature, oxygen concetration and respiratory poisons

Absorption of water occurs via root hairs of roots through diffusion of water from high concentration to lower concentration.

Osmosis occurs when there is a concentration gradient and water flows out from the region of high water potential to lower water potential. So for absorption of water roots act as an osmotic system because there is high er solute concentration (water) in the soil as compared to the roots due to which water is absorbed by the roots by osmosis.

So the correct answer is 'Osmotic system'.

Temperature about 30°C favours water absorption. At higher tem­peratures water absorption is decreased. Also, low temperature decreases the permeability of the cell membrane. Metabolic activities of the root cells are decreased below the optimum temperature. 

So the correct answer is '25°C - 35°C'.

• Osmosis occurs only through the semi-permeable membrane. Osmosis is a gradient dependent process, osmosis is different from diffusion as it is characterized by a semi-permeable membrane.
  
• Net direction and rate of osmosis depend on both pressure gradient and concentration gradient.

The force of water absorption is created at the leaf end i.e transpiration pull. The water will enter the plant via the root cells that can be found in the roots.

The leaves prepare food for the plant, using water and carbon dioxide during photosynthesis. The roots have root hair. The roots hair increase the surface area of the root for the absorption of water and mineral nutrients dissolved in the water.