Nutrient Uptake into the root and plant cells

Before both water and nutrients are incorporated into plants, both must first be absorbed by plant roots.

UPTAKE OF WATER AND NUTRIENTS BY ROOTS

• Root hairs, along with the rest of the root surface, are the major sites of water and nutrient uptake.
• Water moves into the root through osmosis and capillary action.
• Soil water contains dissolved particles, such as plant nutrients. These dissolved particles within soil water are referred to as solute. Osmosis is the movement of soil water from areas of low solute concentration to areas of high solute concentration. Osmosis is essentially the diffusion of soil water.
• Capillary action results from water’s adhesive (attraction to solid surfaces) and cohesion (attraction to other water molecules). Capillary action enables water to move upwards, against the force of gravity, into the plant water from the surrounding soil.
• Nutrient ions move into the plant root by diffusion and cation exchange.
• Diffusion is the movement of ions along a high to low concentration gradient.
• Cation ion exchange occurs when nutrient cations are attracted to charged surface of cells within the root, called cortex cells. When cation exchange occurs, the plant root releases a hydrogen ion. Thus, cation exchange in the root causes the pH of the immediately surrounding soil to decrease.
• Once water and nutrient ions enter the plant root, they move though spaces that exist within the root tissue between neighboring cells.
• Water and nutrients are then transported into the xylem, which conducts water and nutrients to all parts of the plant.

Once water and nutrients enter the xylem, both can be transported to other parts in the plant where the water and nutrients are needed. The basic outline of how nutrient ions are absorbed by plant cells follows.

ABSORPTION OF NUTRIENTS INTO PLANT CELLS

• Plant cells contain barriers (plasma membrane and tonoplast) that selectively regulate the movement of water and nutrients into and out of the cell. These cell barriers are:
• permeable to oxygen, carbon dioxide, as well as certain compounds.
• semi-permeable to water.
• selectively permeable to inorganic ions and organic compounds, such as amino acids and sugars.
• Nutrient ions may move across these barriers actively or passively
• Passive transport is the diffusion of an ion along a concentration gradient. When the interior of the cell has a lower concentration of a specific nutrient than the outside of the cell, the nutrient can diffuse into the cell. This type of transport requires no energy.
• Active transport is the movement of a nutrient ion into the cell that occurs against a concentration gradient. Unlike passive transport, this type of movement requires energy.