TRANSPORT IN PLANTS | Uptake of the minerals |

TRANSPORT IN PLANTS

Following processes are involved in the transport of materials in the plants:

➤ Respiration

➤ Transportation

➤ Photosynthesis

➤ Absorption by roots

Uptake and transport of minerals and water

Role of root in absorption of minerals and water The roots of the plants anchor the plant body in the soil. The roots also absorb water and minerals form the soil. The plants need three types of nutrients.

These are:

Carbon dioxide

Water

Minerals

The plants also need light for photosynthesis. The roots have extensive branching system. So they have a large surface area for the absorption of light. The roots have dense clusters of tiny hair like structures called root hairs. The root hairs are extensions of the epidermal cells. Root hairs form 67% of the total root surface area. The root hairs absorb most of the water and minerals form the soil. Most of the material enters into the root hairs along with water in bulk flow. But some material is taken in by diffusion, facilitated diffusion or active transport.

The plants use minerals, water, CO₂ and light energy during photosynthesis and they synthesis all their required çompounds. A rye plant is less than one meter tall. It has 14 million branch roots. These roots have combined length of over 600 kilometres. Prospis trees (a  eguminoseae plant) have maximum depth of roots of 50 meters.

Uptake of the minerals

(Process involved in the absorption by roots)

The minerals are dissolved in the soil water. The concentration of the minerals depends on the fertility and acidity of the soil. Sometimes, the minerals are not in solution form. They are bounded by ionic bonds with the soil particles. So these minerals are not available to plants. The roots cells take in the minerals by passive or active uptake. The active uptake uses the energy in the form of ATP.

1. Simple diffusion

The movement of molecules form higher to lower concentration is called diffusion. The passive uptake takes place by diffusion. There are three pathways of diffusion:

(i) Symplast pathway: The movement of minerals through the plasmodesmata of the cells is called symplast pathway. There is a concentration gradient down the cells of cortex, endodermis, pericycle and sap of xylem cell. Water plus dissolved salt and sugar present in large vacuole of the plants cells is called sap. So the minerals move down through plasmodesmata into the cells of cortex, endodermis, pericycle and then te the sap of the xylem. The transpiration pull pulls these mineral to the different parts of plant from the sap of xylem.

(ii) Apoplast pathway: The m vement of the ions through the extracellula. pathway between the cell walls of the adjacent is cells is called apoplast. lon easily reaches the endodermis cells by apoplast

pathways. But the casparian strips of the endodermis prevent the 'urther movement. Thus these ions must enter into the endodermal cells by diffusion or active transport. They enter into cytoplasm or vacuole of the endodermal cells. The ions finally reach the xylem cells.

(iii) The vacuolar pathways: The ions can also move through vacuolar pathways. These ions move along concentration gradient. So ions move through cell me nbranes, cytoplasm and tonoplast. Tonoplast is the membrane of the vacuoles. These ions finally reach in the dead cells of the xylem.

2. Facilitated diffusion

The diffusion which takes place through the carrier molecules (protein molecules) of the cell membrane is called facilitated diffusion. Facilitated diffusion transports only some molecules of minerals through the epidermal cells of roots.

3. Active transport

The movement of molecules from lower to higher concentration by the expenditure of energy is called active transport. The roots take up most of the ions by active transport. Plant can absorb a mineral with higher concentration in the soil solution through active transport. So the molecule moves from area of lower concentration to the area of higher concentration against the concentration

gradient. Energy in the form of ATP is utilized in this process. Therefore, active transport depends on respiration.