Question

Describe the path of a molecule of water would take from the soil until it exits one of the leaves through transpiration.

Answer 1

Answer and Explanation:

The soil-plant-atmosphere continuum, SPAC, describes the movement of water molecules from the soil, through the transportation system of a vascular plant, and then into the surrounding air in the plant's environment or atmosphere. Within plants, specialized tissue, called the xylem and phloem, form a plant-wide network of tubes to facilitate the movement of molecules to different tissues. Water molecules typically move through the plant in the order:

                         

                         soil→roots→stems→leaves

This occurs as follows:

• As part of the vascular system, the xylem is responsible for the transportation of minerals and water firstly from the roots, where it enters from the surrounding soil into the root hairs.  
• The water moves up the xylem vessel via transpiration pull. The dead cells in mature xylem vessels, are devoid of cytoplasms and arranged end-to-end, forming an empty tube within the plant's stem.
• Transpiration pull, exerts tension on the xylem vessel, as water is lost continuously through evaporation from the surface of the leaves, through pores or stomata; this is called transpiration.

• Guard cells control the transpiration rate by changing their shape to allow for more or less evaporation dependent upon the amount of water available in the surrounding tissue.

1. open stomata= turgid guard cells= high water availability
2. closed stomata= flaccid guard cells= low water availability

• The cohesion of water molecules, where the molecules are thought to readily cling to each other, forms a continuous column. Along with osmosis, the movement of water molecules from regions of high concentration to regions of low concentration, cohesion is responsible for the movement of the water molecules into the atmosphere.