Water as Level

8/2/2019 Water as Level

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MOLECULES THAT ARE USUALLY FOUNDCOMMONLY IN LIVING ORGANISMS


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COMMON BIOLOGICAL

COMPOUNDS Two types:

Inorganic water and mineral ions

Organic : produced by living things :-carbohydrates

-lipids

-proteins

-nucleic acid


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Water Small molecules; 2 hydrogen and one oxygen

Liquid at room temperature unlike similar small

molecules such as ammonia or methane which are gasat room temperature.


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Structure of a water moleculeWhen water molecule is formed, two pairs of electrons

are shared and two pairs are not shared.

The oxygen is linked to the hydrogen by two covalentbonds


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Shape of water molecules The unshared electrons of the oxygen molecule tend to

repel the shared electrons , causing the hydrogenatoms to be pushed towards each other giving the

water molecule a V-shape structure.


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Nature of water moleculeWater is a polar molecule; A polar molecule is a

molecule with an uneven distribution of charges.

The unshared electrons of oxygen tends to pull theshared electrons towards the oxygen side causing theformation of a small negative charge at the oxygen end(2-) and slight positive charges at the Hydrogen end

(+

)


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Formation of Hydrogen bonds Hydrogen bond: is a force of attraction between the

small negative charge on an electronegative atom, suchas oxygen and the small positive charge on a hydrogenatom which is bonded to another electronegativeatom.


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Formation of Hydrogen bondsWater is dipolar; its electronegative oxygen tends to

form Hydrogen bonds with hydrogen atoms of otherwater molecules; its own hydrogen atoms getsattracted to oxygen atom from other water molecules.


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Water molecules are sticky Water molecules are polar molecules therefore they

form ? Bonds with other water molecules. They tendto stick / cling to each thus giving them uniqueproperties which are important to life


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High specific heat capacity The amount of heat energy required to increase the

temperature of 1 g of substance by 1 degree celsius.

Relevance: It takes a lot of heat energy to raise thetemperature of water ( ???) . So water temperature isfairly stable even if the air temperature changes rapidly: application???


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High latent heat of vaporisation Much heat is needed to change liquid water into

vapour (?)

so much heat energy is absorbed as water evaporatesfrom body surfaces

Application??


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High densityWater is a dense liquid (???) it is able to support

organisms by the up thrust it exerts; animals like whaleare able to support its body weight in water

can a whale supports its body weight in air?

Ice is less dense than liquid water. Relevance?

Ice floats on water and during winter lakes freezes at

the top first , protecting organisms below. In a way, itinsulated the water below.


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High density Max density is at 4 degrees; therefore as the ice melts

the water sinks, which produces water currents thatmix the nutrients (?) in the water

Extra info: water expands upon freezing (more H-bonds form a lattice in ice crystals)


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COHESION Cohesion is a tendency of molecules of a substance to

attract one another

Hydrogen bonding increases the cohesive forcesbetween water molecules.

Water molecules are pulled inwards towards eachother.


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EFFECTS OF COHESIONWater molecules form spherical drops rather than

spreading out in a layer.

Water molecules on the surface are attracted to thosebelow forming a skin-like surface .

The force that causes this skin like surface is known assurface tension- this allow small organisms to support

themselves on the surface of water without sinking in


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Cohesion and movement of water

in columnsWater rises in a column because of cohesion

Example : water travels up the xylem vessels when the

water are pulled from above by transpiration.


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Adhesion and CapillarityAttraction between two unlike moleculesWater in a column is attracted to one another -? And

also water molecules that are in contact with the wallof the xylem tends to be attracted to the walls of

xylem. This cause the water to travels up the xylem.This is capillarity

Capillarity also occurs in small glass tubes or evendrinking straws.


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Good solventWater is a ? Substance

Many molecules have polar groups or molecules thatcan dissociate to give polar ions. These chargedparticles are attracted to the polar water molecules andbecome dispersed among water molecules.

Relevance of this property?

1) water as a transport medium2) most metabolic reactions takes place in solution


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ReactivityWater can take part in chemical reactions in body

metabolism. It is an important reactant inHYDROLYSIS reaction and also inPHOTOSYNTHESIS


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transparencyWater is transparent allowing light to pass through

Light is important in photosynthesis


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Summary of water function METABOLIC ROLE

Hydrolysis

Medium for chemical reaction Diffusion and osmosis

photosynthetic substrate


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WATER AS A SOLVENT

Transport

Removal of waste secretions


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WATER AS A LUBRICANT

Mucus

Synovial f luid Pleural fluid

Pericardial fluid


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WATER FOR SUPPORT

Hydrostatic skeleton

Turgor pressure Humours of the eye

Amniotic fluid

Habitat


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OTHER FUNCTIONS

Temperature control

Medium for dispersal Hearing and balance

Water as Level

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