Pathway of Water Through a Plant:

Root Hair Cells:

• Water enters the plant through the root hairs via osmosis.
• Root hairs are specialized structures in the epidermis of the root that increase the surface area for water absorption.

Root Cortex Cells:

• Water moves from the root hairs into the root cortex cells through the process of osmosis and diffusion.
• The root cortex is the region of the root located between the epidermis and the vascular cylinder.

Xylem Vessels:

• Water is transported upwards through the xylem vessels.
• The xylem is a specialized tissue responsible for conducting water and mineral ions from the roots to the rest of the plant.
• Water moves through the xylem vessels via cohesion and adhesion forces, as well as transpiration pull.

Stem:

• In the stem, water moves through the xylem tissue towards the leaves.
• The stem provides structural support and serves as a conduit for water and nutrients between the roots and leaves.

Mesophyll Cells in Leaves:

• Water reaches the mesophyll cells in the leaves, primarily in the spongy mesophyll and palisade mesophyll layers.
• Mesophyll cells are where photosynthesis occurs and where exchange of gases takes place.
• Water is used in photosynthesis and transpiration, and excess water vapor exits the leaf through stomata.

The large surface area of root hairs plays a critical role in enhancing the rate of water absorption by osmosis and the uptake of ions by active transport. 

Water Absorption by Osmosis:

• Root hairs are elongated, slender structures protruding from the surface of the root.
• Their elongated shape and numerous extensions significantly increase the surface area available for water absorption.
• With a larger surface area, root hairs can come into contact with a greater volume of soil particles and water.
• This increased surface area provides more opportunities for water molecules to diffuse into the root hairs through osmosis.
• Osmosis is the passive movement of water molecules from an area of higher water potential (in the soil) to an area of lower water potential (inside the root hairs).
• The extensive surface area of root hairs allows for a higher rate of osmotic water uptake, facilitating efficient hydration of the plant.

Uptake of Ions by Active Transport:

• In addition to water, root hairs are also responsible for the uptake of essential mineral ions from the soil.
• Mineral ions, such as nitrates, phosphates, potassium, and magnesium, are crucial nutrients required for plant growth and development.
• Unlike water, the uptake of mineral ions often requires active transport mechanisms, as these ions may need to move against their concentration gradient.
• Active transport is an energy-requiring process that utilizes ATP to pump ions across the cell membrane.
• The large surface area of root hairs increases the number of transport proteins and ion channels available for active transport.
• This allows root hairs to efficiently absorb and transport a higher quantity of mineral ions from the soil into the root cells.
• By maximizing the surface area for ion absorption, root hairs ensure that the plant receives an adequate supply of essential nutrients necessary for various metabolic processes.