Plant Transport and Physiology

The cohesion-tension theory, which combines the cohesive properties of water molecules and the pull created by transpiration in the leaves, is the main mechanism for transporting water to the tops of tall trees.

The transpiration pull and cohesion theory (Cohesion-Tension theory) is the most widely accepted explanation for the ascent of sap because it accounts for the physical forces needed to move water over great heights.

Guttation is the process by which plants lose water in the form of liquid droplets through specialized pores called hydathodes, typically occurring under conditions of high humidity and low transpiration.

Plasmodesmata are microscopic channels that traverse the cell walls of plant cells enabling the transport and communication between the cells.

An increase in CO2 concentration in the leaf's micro-environment generally triggers the closure of stomata. This response helps the plant conserve water when CO2 levels are sufficient for photosynthesis.

The conversion of starch into organic acids like malate increases the solute concentration in guard cells. This lowers the water potential, causing water to enter the cells and the stomata to open.

If the anthocyanin pigments do not leak out of the beet root cells into the cold water, it demonstrates that the plasma membrane is impermeable to these molecules under those specific conditions.

Levitt (1974) postulate the theory of active potassium ion (K⁺) transport mechanism for opening and closing of stomata.

The synthesis of organic acids from starch in guard cells is a key step in stomatal opening. It leads to an influx of potassium ions and water, increasing the turgidity of the guard cells.

Transpiration causes evaporative cooling as water changes from liquid to vapor on the leaf surface. This process absorbs latent heat from the plant, effectively lowering its temperature.

Xylem & phloem are called vascular tissues and are present in every part of the plant. This special vessel called phloem, transports minerals from the leaf to different parts of the plant in the form of carbohydrates, sugars and proteins.

Plants excrete waste products through various methods, including storing them as resins and gums in the old xylem. These substances are eventually shed along with the bark or wood.

Phloem is the vascular tissue responsible for the transport of organic nutrients, particularly sucrose, from leaves to other parts of the plant. This process of moving food is known as translocation. Xylem, on the other hand, is primarily responsible for the transport of water and minerals.

Water transport in plants is driven by two main forces: transpiration pull from the leaves and root pressure from the bottom. Transpiration creates a suction effect that pulls water up the xylem, while root pressure helps push water upwards, especially when transpiration rates are low. Translocation refers to the movement of food, not water.