The properties of water

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  1. List the properties of water in relation to living organisms and describe the significance of its hydrophilic nature

 Water is a molecular compound, with the formula H2O. The atoms in a water molecule are held together by strong covalent hydrogen bonds.

The hydrogens have a small positive charge, whereas the oxygen possesses a small negative charge.

The fact that water is a polar molecule helps dissolve other substances, making it a great solvent.

Water has a very high heat capacity, which makes it a temperature buffer. It requires a lot of heat energy in order to convert a liquid to a gas or a solid to a liquid.

Huge bodies of water such as oceans help regulate the temperature and climate of the earth.

Water is important for several biological functions within the living organism. All the chemical and physical processes within a cell compose the metabolism. The chemicals involved are called metabolites. Water is a metabolite in many reactions, either as a reactant or as a product of reaction. It plays a vital part in photosynthesis, digestion and aerobic respiration.

Water is also a crucial living environment for many organisms, such as fish, who have adapted to living in it and cannot survive out of it. Due to extensive hydrogen bonding, water molecules have the capacity to absorb significant amounts of heat before changing state. In freezing weather, ice forms on the surface of ponds and lakes forming an insulating layer above the water below. This provides a living environment for some organisms until the ice melts.

  1. Summarise how glucose, amino acids, cholesterol, fats, oxygen and sodium chloride are transported in blood in relation to their solubility in water.

 

Blood plasma mainly consists of water (95%) and the substances it transports.  The blood plasma carries Glucose as it is a polar molecule and hence freely soluble.

Amino acids possess both positive and negative charges and are therefore soluble. Their R group varies which determines whether they are polar, non-polar or charged. The R group also determines the degree of solubility.

Oxygen is a non-polar molecule and is mainly carried in hemoglobin which could be found in the red blood cells. Due to its small size, it is barely soluble. Water becomes saturated with oxygen at relatively low concentrations. As temperature increases the solubility of oxygen decreases. At body temperature, very little oxygen can be carried by the plasma, which isn’t enough to support aerobic respiration.

Cholesterol is carried in the blood by lipoprotein complexes, located in the plasma. It is mainly a hydrophobic molecule, apart from a small hydrophilic region at one end. This is not enough to make it dissolvable in water.

Fats are large, non-polar molecules that are insoluble in water. They share the same location with cholesterol.

Sodium chloride is an ionic compound which is freely soluble in water. It is carried in the blood plasma and often dissolves to form sodium or chloride ions.

  1. Relate, using specific examples the uses of water in plants and animals to water’s properties.

Cohesive and adhesive forces are important for the transport of water from the roots to the leaves in plants. These forces create a “pull” on the water column. Plants use this natural phenomenon to help transport water from their roots to their leaves. Without these properties of water, plants would be unable to receive the water and the dissolved minerals they require.

 In another example, insects such as the water strider use the surface tension of water to stay afloat on the surface layer of water and even mate there.

4: Explain the importance of the properties of water named organisms including adhesion, cohesion, surface tension, thermal properties, as a metabolite and compared to the properties of methane

Cohesion can be described as the various intermolecular forces that hold solids and liquids together. It is the attraction between molecules with the same structure.

Adhesion is the ability of a substance to stick to an unlike substance. It is the attraction between unlike molecules.

Cohesion is very important as it holds hydrogen bonds together to create surface tension on water.

Since water is attracted to other molecules, adhesive forces pull the water toward other molecules. Photosynthesis and respiration occur with the help of cohesive and adhesive forces.

 

Methane provides a good basis for comparison with water due to the many similarities between their structures: similar in size and weight. However, water is polar and can form intermolecular hydrogen bonds, whereas methane is non-polar and can only form weak dispersion forces between its molecules. This means water absorbs more heat before changing state. Water also has a significantly higher melting and boiling point.

 

Sources:

http://www.rsc.org/Education/Teachers/Resources/cfb/water.htm

http://www.slideshare.net/diverzippy/bioknowledgy-22-water

https://www.boundless.com/biology/textbooks/boundless-biology-textbook/the-chemical-foundation-of-life-2/water-51/water-s-cohesive-and-adhesive-properties-286-11419/

http://ib.bioninja.com.au/standard-level/topic-2-molecular-biology/22-water/thermal-properties.html

 

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