Question

Select the correct sequence of pathway of mineral absorption.

• A. Soil→ endodermis→ epidermis→ xylem
• B. Soil→ epidermis→ endodermis→ xylem
• C. Soil→ epidermis→ xylem→ endodermis
• D. Soil→ endodermis→ xylem→ epidermis

Answer 1

The correct option is B Soil→ epidermis→ endodermis→ xylem

In the 1st phase of mineral absorption by roots, the minerals need to travel from the environment to epidermal cells. It is a passive process and contributes to a very small percentage of mineral uptake. Since roots are constantly absorbing minerals, there is a higher concentration of minerals inside the roots. So, taking up more mineral ions against their concentration gradient, would require the use of more ATP. Majority of the mineral absorption takes place in an active manner.
The 2nd phase of mineral uptake is when the ions are taken into the cytoplasm of the cells, slowly. This is an active process where ATP is utilized. It takes place via special pumps.
After the active absorption of minerals into the epidermal cells, the 𝚿s further increases, which causes a decrease in 𝚿w. This decrease in 𝚿w further helps epidermal cells to absorb more water through osmosis. From root hair cells or epidermis, minerals have to move to xylem. Both water and minerals move from root hairs, epidermal cells through cortical cells towards xylem. Water and minerals through the apoplast are forced into the endodermal cells. The only way to pass through these cells is through the transport proteins in the membrane.

$\mathrm{Soil}\underset{\mathrm{passive}\mathrm{transport}}{\overset{\mathrm{active}\mathrm{transport}}{\to }}\mathrm{epidermis}\underset{\mathrm{symplast}}{\overset{\mathrm{apoplast}}{\to }}\mathrm{endodermis}\underset{\mathrm{passive}}{\overset{\mathrm{active}}{\to }}\mathrm{xylem}\to \mathrm{rest}\mathrm{of}\mathrm{the}\mathrm{plant}$