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Phosphate-buffered saline (PBS) is a buffer solution (pH ~ 7.4) commonly used in biological research. It is a water-based salt solution containing disodium hydrogen phosphate, sodium chloride and, in some formulations, potassium chloride and potassium dihydrogen phosphate. The buffer helps to maintain a constant pH.
The three properties of water that are relevant to A-Level Biology are: Cohesion and surface tension: Water molecules are cohesive and tend to stick together due to hydrogen bonding. This gives water a high surface tension, which allows insects to walk on water and helps plants to transport water from roots to leaves.
The dew drops pictured to the left are another example of water molecules sticking together. Hydrogen bonds cause water to have a relatively high boiling point of 100°C (212°F). Extra energy is needed to break these bonds and separate water molecules so they can escape into the air as water vapor.
When the heat is raised as water is boiled, the higher kinetic energy of the water molecules causes the hydrogen bonds to break completely and allows water molecules to escape into the air as gas (steam or water vapor).
This process results in the release of individual water molecules at the surface of the liquid (such as a body of water, the leaves of a plant, or the skin of an organism) in a process called evaporation.
20 cze 2024 · Water regulates or even governs a wide range of biological processes. Despite its fundamental importance, surprisingly little is known about the structure of intracellular water.
Water, like carbon, has a special role in living things. It is needed by all known forms of life. Water is a simple molecule, containing just three atoms. Nonetheless, water’s structure gives it unique properties that help explain why it is vital to all living organisms.
