l09 - 2. chemistry of life - water

8/8/2019 L09 - 2. Chemistry of Life - Water

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NATS 1610 - 2. Chemistry of Life - Water 1

2. Chemistry of Life Water


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References

Visualizing Human Biology, Ireland, 2/ed

Chapter 3

Theses notes

Links: http://www.physicalgeography.net/fundamentals/8a.html

http://www.pbs.org/wgbh/nova/mars/essential.html

http://www.youtube.com/watch?v=CT4pURpXkbY&feature=related


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All organisms contain water ~ 70% total body weight

Life originated in liquid water

The biochemical reactions that sustain life need liquid waterin order to operate

To dissolve molecules dissolve

So chemical reactions can occur

When organisms moved to land Carried water with them inside their cells

The physical & chemical properties of liquid water make lifepossible

1. The capacity to dissolve or repel substances

2. Cohesiveness

3. Temperature-stabilizing effects4. Always in flux transports materials

5. In a liquid form over range of temperature from 0-100C

This range allows water molecules to exist as aliquid in most places on our planet


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NONPOLARCovalent Bonds

Usuallyreferred to onlyas covalent bonds

When atoms share electrons equally

i.e., Hydrogen gas (H - H), Methane (CH4)


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POLARCovalent Bonds

Atoms dont share electrons equally

Electrons spend more time near nucleus with most protons

i.e., water and its electrons

oxygen end is slightly negative in charge (electronegative)

hydrogen end is slightly positive in charge


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The HYDROGENBOND is a weak chemical bond

Formed when the slightly positive hydrogen atom of a polar covalent bond

is attracted to

the slightlynegative atom of a polar covalent bond in another molecule (usually)

Water molecule Ammonia molecule

Hydrogen bond

H

HH

H

HO N

http://bcs.whfreeman.com/thelifewire/content/chp02/02020.html


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hydrogen bond

ammonia

molecule

one

large

molecule

another

large

molecule

a large

molecule

twisted

back

on

itself

H-Bonds

can occur between

different molecules

or within the same

molecule

water

molecule


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Hydrogen Bonding in LiquidWater-molecules held loosely

flows (no spaces)

Hydrogen Bonding in Ice-molecules held tightly

solid (with spaces)


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2.Water is a solvent for other polar

molecules

due to its polarnature

permits chemical reactions

spheres of hydration

hydrophilic

water loving

binds with water

hydrophobic

water hating

repels waterNaCl (sodium chloride)

dissolves in water

1.Water is liquid at room and bodytemperature

other materials are gaseous at these temperatures

can be utilized in world and in body can travel & carry materials


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3.Water is cohesive and adhesive

Due to hydrogen bonds

Water molecules cling to

each other

Water flows and fills things

CapillaryMovement Adhesion to other materials

Excellent transport medium

Surface tension

Water molecules stick tightly toeach other at air interface


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4.Water temperature rises and falls slowly

Highheat capacity i.e., a great deal of heat is required to raise its

temperature because

H-bonds can absorb a lot of energy before they break apart

Takes one calorie of energy to raise the temperature of one gram of

water one degree Celsius

Thus - water holds heat, causing its temperature to drop or rise slowly

Water protects organisms from rapid temp changes

High % of body water in organisms

e.g., 150 lb human is 100 lbs water (~67% body weight)

Resistchanges in body temperature

Keeps relativelystable internal environment

Water in bloodhelps to distribute heat throughout body

heat is picked up from muscles where its generated

Large bodies of water maintain relatively constant temperatures marine life


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5.Waterhas a highheat of vaporization

This is a measure of the amount of heat neededto vaporize the liquid.

a large amount of heat energy, 540calories, is needed to convert 1 gram ofwater to vapor

H-bonds absorb a lot of energy before theybreak apart

Water evaporating from a surface carriesaway heat, cooling the surface

Heat is released from the high energy

stored in the H-bonds of water molecules at

the surface

Body heat is used to evaporate sweat

As sweat evaporates, body is cooled

Prevents body from overheating


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6.Frozen water is less dense than liquid

water

At low temperature water molecules

Move slower Are further apart - frozen water

expands

H-bonding becomes rigid

Spaces between molecules

Less dense ice floats

1 litre of ice weighs less than 1litre of water

A fixed volume of ice has fewer

water molecules than does the

same fixed volume of liquid

water (because the water

molecules are further apart in the

ice and so fewer water

molecules fill that fixed volume of

ice)

Frozen bodies of water

surface ice insulates water below it


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Water, Acids, Bases, pH, & Buffers

Water molecules can dissociate (breaks down) to form hydrogen ions (H+)

andhydroxyl ions (OH-) these in turn can then re-bind to form water

H O H H+ + OH-

The amount ofH+ in the body is preciselyregulated

Slight changes in H+ can cause severe illness bydisrupting chemical

reactions in the body


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Acids & bases defined bywhathappens when each is added to water

Acids

Anything that dissociates in water & releases hydrogen ions (H+)

In water, HCl -- > H+ + Cl-

Acids increase H+ concentration in solution

Bases

Anything that takes up hydrogen ions (H+) & releases hydroxide ions (OH-)when in water

In water, NaOH -- > Na+ + OH- OH- will bind withH+ in water

Bases decrease H+ concentration in solution

pHscale

Measures concentration of H+ & indicates how acidic something is

Buffers

Biological systems function within a verynarrowrange of pH

Help keep the pH within normal limits by

1. Taking up excess H+ when concentrations increase

2. Adding H+ when concentrations decrease

Various buffering systems in body maintain correct body pH levels


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The carbonic acid bicarbonate buffering system

in human blood keep the pH of blood at about 7.4

CO2 + H20 H2CO3 H+ + HCO3

-

Carbon Water CarbonicAcid Hydrogen Bicarbonate

Dioxide Ion Ion

IfH+ levels in blood decrease, carbonic acid will dissociate to release H+ into

the blood

Thus increasing blood H+ levels

IfH+ levels increase, theycombine with the bicarbonate ions to form carbonic

acid which in turn will dissociate into carbon dioxide and water the carbon

dioxide will be exhaled

Thus removing H+ from the blood


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l09 - 2. chemistry of life - water

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