Absorption of Solutes in Plants

Absorption of Solutes

• Plants absorb nutrients from the soil via passive and active absorption methods.
• Passive Absorption utilizes mechanisms like mass flow, ion exchange, and Donnan equilibrium.
  • Mass Flow: Movement of solutes along with water flow from high to low concentration areas.
  • Ion Exchange: The process where cations in the soil solution are exchanged for cations held by the soil particles.
  • Donnan Equilibrium: Movement of ions across a semipermeable membrane driven by concentration gradients.
• Active Absorption: Requires metabolic energy to move solutes against their concentration gradient.
  • Carrier Concept: Proteins or other molecules bind to specific solutes and facilitate transport.
  • Protein-Lecithin Carrier: This theory suggests that proteins and phospholipids act as carriers for solutes.
  • Goldacre's Theory: Involves the movement of ions across a membrane using a potential difference.
  • Cytochrome Pump Theory: Electrons released from oxidation reactions drive the movement of ions across the membrane.

Translocation of Food

• Direction of Phloem Transport: Primarily from the leaf (source) to the root (sink), but can also occur upwards towards the shoot meristem.
• Components Transported: Primarily sugars (mainly sucrose), amino acids, and other organic molecules.
• Phloem Loading: Sugars are actively transported from mesophyll cells into sieve tubes of the phloem.
  • Pressure Flow Hypothesis: The widely accepted theory explaining the movement of sap within the phloem.
  • Mechanism: Sugars are loaded into sieve tubes using active transport, which increases the solute concentration and draws water in via osmosis, creating a pressure gradient responsible for the movement of sap.
  • Source-Sink Dynamics: The leaf is the source of sugar due to photosynthesis, while the root is a major sink, but sinks can also include growing stems, fruits, and flowers.