Plant Transport and Physiology

High humidity restricts the transpiration because humid air is almost saturated with water vapour and cannot absorb much more by transpiration.

By utilizing capillary action and the inherent surface tension of water, transpiration pull and cohesion force transport the water by xylem in tall trees.

Sir J.C. Bose (1923) advocated pulsation theory to explain ascent of sap. He proved that the living cells of innermost layer of cortex lying just outside the endodermis were in a state of rhythmic pulsations.

Guttation is the secretion of water, during conditions of high humidity, on to the surface of leaves through specialized pores, or hydathodes. 

Transpiration primarily occurs through the stomata, which are located in the epidermis of the leaves. The epidermis is a type of dermal tissue, making it the site of maximum water loss.

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.