Water and Transport

Properties and Functions of Water

Water is a polar molecule due to the uneven distribution of electrons, leading to partial positive and negative charges at different ends.
The polarity of water allows it to form hydrogen bonds with other water molecules, creating a cohesion that aids in water transport. This is critical for the transpiration stream in plants.
The polarity of water also contributes in its use as a solvent. It can dissolve a variety of solutes, which facilitates transport of nutrients and waste in organisms.
Water’s high heat capacity speaks for its ability to absorb significant amounts of heat before increasing in temperature. This helps organisms maintain stable internal body temperature.
The evaporation of water causes a cooling effect. In animals, this helps with thermoregulation, such as sweating in humans.

Transport Systems in a Human Body

The human body has a dual circulatory system, encompassing the systemic circulation and the pulmonary circulation.
Blood vessels, including arteries, veins, and capillaries, play a central role in the transport of water, nutrients, gases, and wastes.
The heart fuels the circulatory system through its regular contractions and relaxations, constituting the cardiac cycle.
The systemic circulation transports oxygen and nutrients to cells around the body, while the pulmonary circulation offloads carbon dioxide and picks up oxygen from the lungs.
Water forms a significant part of the plasma in blood, allowing the smooth transport of cells and molecules in the bloodstream.

Water and Transport in Plants

Xylem vessels conduct water and dissolved minerals from roots to stems and leaves.
Transpiration, the loss of water from plant surfaces, mainly through stomata in the leaves, drives water up the plant due to the resulting transpiration pull.
Unlike in animals, plant cells are connected by plasmodesmata—small channels in the cell walls that allow the flow of water via osmosis.
Root hair cells in plants absorb water from the soil. The high surface area to volume ratio of these cells allows efficient water absorption.
Transpiration also aids in the cooling of the plant and creates a concentration gradient that facilitates absorption of nutrients from the soil.