Transport of Food and Minerals in Plants

The roots have thin layered, unicellular outgrowths of the epidermis; which are called root hairs. They increase the surface area for absorption of water from the soil. Following are the steps of absorption of water:

• Water is absorbed by the root hairs by the process of Osmosis. The concentration of water molecules is more in soil as compared to the cell. This causes osmosis to occur, and so water is absorbed by the root hair cells from outside as shown in the given diagram.
• Water molecules move through osmosis from root hair cells to adjacent cells of the inner tissue.
• This process continues until water reaches the xylem tissue in the root. Thus, water moves from root hair cells through the root cortex to the xylem in the root.
• Inside the xylem, water travels upwards from one cell to another against the force of gravity.

Below diagrams shows the absorption and movement of water in root cells:

Mineral molecules are more concentrated inside the root hair cells than in the soil outside. Still, root hair cells absorb them. For this, they use the process of active transport. The movement of minerals ions from a region of their lower concentration to a region of their higher concentration is called active transport. This process involves the use of energy in the form of ATP.

There is a direct relationship between absorption and transpiration. As water is lost through transpiration, more water is absorbed as more water is required. This creates a suction pressure which pulls up water from the xylem of the roots to the stem and then to the leaves. It is called transpiration pull. Thus, the amount of water in the roots gets reduced. In turn, water from the surrounding soil passes on to the root hair cells by the process of osmosis. Thus, the cycle of absorption and transpiration continues.

The sugar molecules manufactured by the leaves by photosynthesis are transported throughout the plant by phloem. The transport of soluble products of photosynthesis is called translocation. Phloem has cells called sieve tubes which are placed one above the other to form long tubes through which food is transported.

Two points of importance of transpiration in plants are:

1. Cooling effect — Transpiration from the aerial parts of the plant, cools down the plant surface.
2. Ascent of sap and distribution of minerals — Transpiration results in the development of low water potential in the leaf tissues. Thus, water moves from the xylem tissue to the leaf cells and helps in the ascent of sap. Mineral ions also move up along with water due to the transpiration pull.

Root hairs cells are unicellular thin-walled outgrowths of the epidermis, which is the outermost layer of a root. They increase the surface area for absorption of water and nutrients from soil.

The pressure developed in roots due to the continuous inflow of water which pushes the plant sap upwards is called root pressure.

The loss of water in the form of water vapour through the stomata of the leaves and other aerial parts of a plant is called transpiration.

If water is lost through transpiration more quickly than it is absorbed by the root hair cells, the plant cells tend to lose water. As a result, the leaves, stem and flowers droop. This is called wilting.

The transport of soluble products of photosynthesis, that is the sugar molecules is called translocation.

Boron and manganese are examples of two micro-nutrients.

Chlorosis is a disease in plants caused by the deficiency of zinc.

1. False
   Correct Statement — Xylem carries water from the roots to the leaves in plants.

2. False
   Correct Statement — Phloem parenchyma performs the function of storage (food).

3. False
   Correct Statement — Water is absorbed by the root hair cells by a process called Osmosis.

4. True

Osmosis — The movement of water through a semi-permeable membrane from an area of its higher concentration to an area of its lower concentration is called Osmosis.

Diffusion — The movement of salt or mineral molecules from a region of their higher concentration to a region of their lower concentration is called diffusion.

Active transport — The movement of minerals ions from a region of their lower concentration to a region of their higher concentration by using energy (ATP) is called Active transport.

Transpiration — The loss of water in the form of water vapour through the stomata of the leaves and other aerial parts of a plant is called transpiration.

Transpiration pull — The process by which water is sucked up through the xylem as a result of water loss by transpiration is called transpiration pull.

Water in xylem moves only in one direction.

Xylem is a plant tissue which conducts water and minerals from roots to upper parts of the plant.

Phloem is the food-conducting tissue in plants.

Root hairs are unicellular, thin-walled outgrowths of roots.

Roots absorb minerals by diffusion and active transport.

The upward movement of sap through the xylem is called ascent of sap.

There is a direct relationship between absorption and transpiration.

Nitrogen is an example of a macro-nutrient.

The figure shows a root hair. The parts labelled a, b, c are:

a → Nucleus

b → Cell Membrane

c → Cytoplasm

The shrivelled vegetables start looking fresh again when kept in water because the concentration of water is more outside the vegetable and the semipermeable cell membrane allows osmosis to take place. By the process of osmosis, slowly the vegetable absorbs water, in absence of any opening.

In xylem, tracheids and xylem vessels are placed end to end like tubes. These cells are dead that means they don't have protoplasm. Thus it makes a clear straw-like passage for the easy movement of water and minerals in the plant. Also, these cells have lignified walls, which make their walls stiff, provide structural support and prevent the walls from collapsing during water transport.

epidermis

Reason — Root hair cells are unicellular thin-walled outgrowths of the epidermis which is the outermost layer of a root.

both upwards and downwards

Reason — Food material moves through the phloem in both directions, upwards as well as downwards.

osmosis

Reason — The concentration of water in the root is lower than that of soil, thus water flows from soil to cell by Osmosis.

diffusion

Reason — Diffusion is the movement of salt or mineral molecules from a region of their higher concentration to a region of their lower concentration.

cell sap

Reason — Cell Sap is the fluid containing mineral salts and water enclosed in the vacuole of a cell.

root pressure

Reason — The pressure developed in roots due to the continuous inflow of water which pushes the sap upwards is called Root Pressure.

transpiration

Reason — The loss of water in the form of water vapour through the stomata of leaves and other aerial parts of a plant is called transpiration.

stomata

Reason — Stomata are the openings present on lower side of leaves, through which transpiration as well as gaseous exchange occurs.