water as a medium of life

a1.1-a4.2

water as the medium of life

hardly ever changes chemcially, without it most chemcial reactions within organisims would not take place- remains liquid at a wide range of temperatures allowing it to keep constat and dissolve and transport substances

water is made up of

two hydrogen atoms covalently bonded to an oxygen atom (h2O)

Polarity

describes the slight difference in charge that occurs at the different poles of water molecule

• oxygen(due to having higher electronegativity) attracys the aelectron more strongly, forming a slightly negative charge

• the hydrogen atoms have a weaker attraction towards the electrons resulting in a slightly positive charge

polarity of water

allows it to form weak associations with other polar molecules or charged ions

slightly negative poles will attract slightly positive poles of other molecules and vice versa

Hydrogen bonds

intermolecular associations fromed as a consequences of the polar covalent bonds within a water molecules

hydrogen bonds part two

these bonds forms when a hydrogen atom is attracted to a fluorine, oxygen or nitrogen atom of another molecule

hydrogen bonds are stronger than standard polar associations due to the particularly high electronegativity

hydrogen bonding

responsible for several unique properties of water including thermal cohesive and solvent properties

cohesion in water

water molecule is able to stick to other water molecules allows the liquid to resist low levels of external force(it creates surface tension)

Surface tension in water

high surface tension o water makes it sufficiently dense for certain smaller organisims to move along its surface

water strides

small insects that can move along the surface of water due to its high surface tension

• they distribute their weight via long legs that contain thousands of microscopic hairs to trap air and increase buoyancy

• high surface tension of water makes it sufficiently dense for certain smaller organisims to move along its surface

Adhesion in water

water molecule is able to stick to other polar or charged molecules via the formation of polar associations

attraction to charged polar surfaces (such as cellulose cell walls) allows water to flow in opposition to gravitational forces (capillary action)

Capillary action in water

necessary to allow water to be transported up plant stems via transpiration stream

the loss of water vapour from the leaves (via ecaporation) and the absorption of water into the roots (via osmosis) creates a pressure gradient

water will move along the gradient by using capillary action and cohesion to be transported up the stem of the plant via narrow xylem vessels

Capillary action

responsible for the movement of water through the soil from the deeper water table

• the type of soil will influence the strentgh of the capillary action dependant on how porous it is affection the efficact of aricultural practices

Solvation

process by which solvent molecules sorround and interact with solute molecules

• a solute is any substance (usually a solid) that is dissolved by a solvent molecule to from a solution

• solute that are able to be dissolved by a solvent are considered to be soluble (insoluble substances will not form a solution)

Water as a universal solvent

due to its capactiy to dissolve a large number of substances

• water can dissolve any substance that contains charged particles (ions) or electronegative atoms (polarity)

• The polar regions of the water molecule associate with molecular surfaces that have an opposing charge, forming dispersive hydration shells

Metabolic medium

The capacity of water to dissolve a large varity of substances makes it an important medium for metabolic reactions

• solutes dissolved into aqueous solutions are more likely to colled with enzymes and undergo necessary chemical reactions

• water can also promote enzyme activity b absorbing heat from exothermic reactions and maintain acid-base neutrality

Hydrophilic and hydrophobic

substances that are involved in metbolic reactions can be described as being either hydrophilic or hydrophobic

hydrophilic-substances that freely associate and readily dissolve in water and includes polar molecules and ions

hydrophobic0 do not freely associate of dissolve in water and inclues all large non polar molecules (lipis ie fats and oils)

Transport medium

the movement of water soluble substances in plants and animals involves different transport systems

in aniamls the blood plasma transports, amina acids simple sugars , urea and small amounts of gases

in vascular plants, mineral ions are transported bia xylem vessels while dissolved nutrients are transported via the phloem

non soluble substances that are transported in aqueous enviroments

animals-lipids are packages with proteins to form a water soludle lipoprotein that can be transported via the blood

the mechanisims of lipid transport is not well understood in plants but may involved conjugation of amino acids and transport via the phloem

Buoyancy

the upward force applied to an object in a medium and is determined by the density of the medium

• as water is more dense than air it applied a great upward force which allows objects to float in water- the capacity of an object in water will be determined by its relative weight

viscosity

a measure of a fluids tendancy to flow (more viscous- more resistance)

• water is more viscous than air as it can form hydrogen bonds which increase the friction fo flowing molecules

Thermal conductivity

a measure of a mediums ability to move heat across a temperature gradient

water absorbs and transfers heat more readily than air because water particles are packed more tightly together

specific heat capacity

the amound of energy require to raise the temperatur of 1g of substance by 1c

the high specific ehat capacity of water makes it an effective coolant in sweat (sweat absorbs a lot fo thermal energy resulting in a high latent heat of vaporisations)

remember loon and seal