Water

• Cohesion


  A water molecule consists of two hydrogen atoms and one oxygen atom. Due to their covalent bonds, the electrons from the hydrogen atoms are pulled closer to the oxygen atom, meaning that due to less shielding of the nucleus, the hydrogens are (delta) slightly positive. Because the electrons from the hydrogens are pulled closer to the oxygen, the oxygen is (delta) slightly negative. This makes the water molecule dipolar. Because unlike charges attract, when many water molecules are together, the negative oxygens of one molecule are electrostatically attracted to the oxygens of another molecule, forming weak hydrogen bonds. Although the hydrogen bonds between molecules are individually weak, because there are so many of them in water, overall, they are strong and difficult to break. Cohesion is the ability for the water molecules to stick to one another, which is possible due to the molecules dipolarity and the hydrogen bonds between molecules
• Examples of Cohesion


  Surface tension is caused by cohesion. This is when the layer of water molecules on top of a body of water form hydrogen bonds with the water molecules beneath them, rather than with the air above. This causes an elastic- like membrane on top of the body of water, also known as surface tension. The surface tension allows organisms such as the pondskater to glide on top of bodies of water. Cohesion also allows a long column of water to be transported in plant xylem, during capillary action
• Adhesion


  Due to its polarity, water molecules are attracted to other polar molecules. Polar molecules that exert adhesive forces on water are known as hydrophilic, and non-polar molecules that do not exert adhesive forces on water are known as hydrophobic. Hydrophobic substances repel water. Materials with large surface areas, such as porous ones, often exert strong adhesive forces. Lipids, oils, steroids and organic compounds are hydrophobic. Glucose is hydrophilic.
• Examples of Adhesion


  Water is attracted to the chemical substances in soil, which is why water may rise upwards (against gravity). Water adheres to cellulose molecules in cell walls to keep them moist. If water is evaporated and lost, adhesive forces can draw out the water so that the cell walls can stay moist. They must stay moist to allow photosynthesis. The adhesion of water from the lignin in the xylem to the cell walls means that the water pressure inside the xylem is lower, allowing movement, known as a transpiration stream. If a xylem vessel is filled with air, water will adhere to the lignin, refilling the vessels. This is known as Capillary action, which is where adhesive forces pull the water molecules up against gravity, and cohesive forces mean that the water is a long column. Tension is created through a transpiration stream, which is when water evaporates through the stomata. Therefore capillary action is a result of surface tension, cohesion and Adhesion. It is most common in plant xylem, when the lignin exerts adhesive forces on the water.
• Latent heat of vaporisation


  The amount of energy needed to turn a liquid into a gas. For water this is extremely high, as a lot of energy is needed to break the hydrogen bonds. This does not change the temperature of the water.
• Examples of latent heat of vaporisation


  The evaporation of water in sweat in the skin causes marked cooling, due to the release of energy that is needed to change the liquid water into a gas, as does evaporation during transpiration from leaves in plants. The temperature does not change
• Specific heat capacity


  The amount of heat energy needed to raise one gram of water by one degree Celsius. This is due to the energy needed to break the hydrogen bonds holding them together. Water has an extremely high SHC.
• Examples of specific heat capacity


  Because the specific heat capacity of water is extremely high, it means that bodies of water are relatively stable in temperature (as it takes a large amount of energy to raise the temperature). It also means that Large organisms have a stable temperature.
• Solvent properties


  As water molecules are polar, water stays as a solution and does not clump together. Hydrophilic substances can act as solutes, as the water molecules form hydrogen bonds with one another, surrounding the hydrophilic molecules, that are attracted to the water molecules. This causes the hydrophilic substances to dissolve in water, forming a solution.
• Examples of solvent properties

  Salt is an essential mineral that must be transported around organisms. Because it is charged, and therefore hydrophilic, it is able to dissolve in water, and be transported. Once dissolved, the solute is free to move around and is therefore more reactive than it would be in an undissolved solid. All ions (either anions or cations) are able to dissolve in water, as their charges are attracted to the charges of the water molecules. Sugars and alcohols also dissolve in water, due their ionisation. Catabolic and Anabolic reactions take place with a water medium. A catabolic reaction is whereas substance breaks down, and an anabolic reaction is where larger substances are built up.
• Thermal conductivity

  The rate at which heat travels through a material. Water has a high thermal conductivity.
• Examples of thermal conductivity

  Water has high levels of thermal conductivity. Warm-blooded animals are at a risk of loosing high amounts of body heat. Because water is a good conductor, this means that in animals, the high water content of blood means that heat can be transferred from areas where it is generated, to other areas
• Buoyancy


  The upward force exerted on an object fully submerged in a liquid. If the density of the object is lower than water, then the buoyancy will be higher than gravity, and the object will float, and vice versa.
• Examples of buoyancy


  Living organisms have a density similar to that of water. This means that It acts as a good habitat for many organisms, as they do not have to expend much energy to stay afloat. Air is much less dense than water, so airborne animals will have to generate more lift to stay in the air. Most birds are adapted to live in and on water as their bones are hollow, making them less dense. Bony fish can control their densities by filling a swim bladder with gases as they please.
• Latent heat of fusion


  The amount of energy needed to turn water to ice. In water, this is extremely high.
• Examples of latent heat of fusion


  This means that in extreme temperatures, water in cells are slow to freeze. so are large bodies of water (due to more hydrogen bonds).
• Viscocity


  The 'stickiness' of a fluid that determines how easily it can flow. Viscosity is a result of internal friction. The more friction, the more viscous a fluid, and the greater resistance to flow. water has a higher viscosity than organic solvents.
• Examples of viscocity


  If a solute is dissolved in water, it becomes more viscous, such as saltwater, or blood. Organisms that move through water would experience drag, so would need to adapt to be streamlined. Air is much less viscous than water.
• Metabolism

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  Water is the medium for metabolism, as it allows many different chemical reactions to take place. Both anabolic and catabolic reactions can take place in water, due to its cohesive, adhesive and solvent properties.
• Examples of metabolism


  In the water base of the cytoplasm, many solvents perform chemical reactions known collectively as metabolism. Without water these reactions would not take place.
• High boiling point


  The temperature at which a liquid becomes a gas. For water this is relatively high (100 degrees Celsius)
• Examples of high boiling point


  Because of water's relatively high boiling point, water is a liquid state on earth. Liquid water is needed by all living organisms due to all of its other properties. So, it's high boiling point means that liquid water is abundant and available to all organisms.