Describe the path of a molecule...?

Question

could you describe the path of a molecule of water in detail as it is absorbed from the ground through the leaves of a tree into the atmosphere?

Answer 1

Water and mineral enter through root epidermis, cross the cortex, pass into the stele, and are carried upward in the xylem. Active accumulation of Mineral Ions. The cells cannot get enough mineral ions from the soil by diffusion alone. The soils solution is too dilute. Active transport of these ions must occur. Specific carrier proteins in the plasma membrane attract and carry their specific mineral into the cell. A Proton Pump: H+ is pumped out of the cell causing a change in pH and a voltage across the membrane. This helps drive the anions and cations into the cell. Water and minerals cross the cortex in one of 2 ways: Via SYMPLAST which is the living continuum of cytoplasm connected by PLASMODESMATA. Via APOPLAST which is nonliving matrix of cell walls. At the endodermis the apoplastic route is blocked by the CASPARIAN STRIP. this is a ring of suberin around each endodermal cell. Here water and minerals MUST enter the stele through the cells of the endodermis. Water and minerals enter the stele via symplast, but xylem is part of the apoplast. Transfer cells selectively pump ions out of the symplast into the apoplast so they may enter the xylem. This action requires energy.

ASCENT of XYLEM SAP:
Water transported up from the roots must replace water lost by transpiration.

WATER POTENTIAL: Xylem sap rises against gravity, driven by a gradient of water potential. Water flows from an area of high potential to an area of low potential. Water Potential is expressed in units of pressure: 1 bar is the pressure needed to push up a column of water 10 meters. 1 megapascal = 10 bars. Pure water has a potential of 0. Addition of pressure increases water potential. Addition of solutes decreases it.
ROOT PRESSURE: When transpiration is low, ions pumped into the stele decrease water potential and cause water uptake by the stele. This uptake force is called root pressure. It Cannot keep pace with transpiration, and can only force water up a few meters.

TRANSPIRATION-COHESION-ADHESION THEORY:

a). water exits leaf through stomata.
b). this water loss is replaced by evaporation from mesophyll cells, lowering their water potential, causing them to take water from neighboring cells.
c). the process connects back to the tracheids causing water to be taken from the xylem.
d).Water travels from the tracheids to the air following a water potential gradient.
e). Waters cohesive and adhesive properties and the small diameter of xylem aid in its movement of up the tube.
f). This pull decreases water pressure in the xylem causing the roots to take water from the soil.

Answer 2

From the nose it follows the respiratory track (pharynx, trachea, bronchi) to the lungs where in the alveoli it passively diffuses into the blood enters the red blood cells and gets attached to an iron atom in haemoglobin. It is then transported to the body where it gets released and passively diffuses into a cell to be used in cellular respiration to accept electrons that originated in fuel molecules.

Answer 3

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