Briefly describe the extracellular pathway of water and nutrient absorption in roots.

The extracellular pathway of water and nutrient absorption in roots involves the following steps:

1. Absorption: The process begins with the absorption of water and nutrients from the soil by the root hairs. These root hairs increase the surface area of the roots, allowing for more efficient absorption.

2. Apoplast Pathway: Once absorbed, the water and nutrients move through the cell walls and intercellular spaces of the root cells. This is known as the apoplast pathway. This pathway allows for the rapid movement of water and nutrients, but it is blocked by a waxy substance called suberin in the Casparian strip of the endodermis.

3. Symplast Pathway: The water and nutrients then enter the cytoplasm of the root cells and move from cell to cell through plasmodesmata, small channels connecting the cells. This is known as the symplast pathway.

4. Xylem Loading: Finally, the water and nutrients are loaded into the xylem, the water-conducting tissue in plants. From here, they can be transported to other parts of the plant where they are needed.

This process is driven by the transpiration stream, a flow of water and nutrients from the roots to the leaves caused by the evaporation of water from the leaves. This creates a suction force that pulls water and nutrients up from the roots.