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.