1.1 water

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TOPIC 1 :

BIOLOGICAL MOLECULES1.1 Water1.2 Carbohydrates1.3 Lipids1.4 Proteins1.5 Nucleic Acids 1.6 Analytical techniques

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Water / H2O Chemical Properties of Water Physical Properties of Water

1.1WATER

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Chemical Properties of Water1. Water molecule (H2O ) is composed of 2 hydrogen

atoms & 1 oxygen atom.

2. Two H atoms attached to an O2 atom at an angle of

104.5o. Each H atom shares a pair of

electrons with the O2 atom to 2 covalent bonds.

O-H covalent bond (within molecule)

hydrogen bond (between molecule)

3. Water molecule is a polar compound (due to anunevencharge distribution within the molecule) .

Hydrogen atoms : slightly +ve

Oxygen atom : slightly

veO2 atom draws the electrons in the bond towardsitself, giving itself a partialve charge relative to theH atom.

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4

Water Molecule

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Hydrogen bonds

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Structure of water molecule, a polar molecule

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4. A universal solventto dissolveionic

substanceslike salts, which contain

charged ions & some non-ionicsubstances such as sugars that contain

polar groups. This substances have OH,

-COOH, -NH2, -CO- and PO4 groups. Water molecules can surround polar

groups after weakening & separating

inter-molecular or inter-ionic bondswithin a substance such as in sodium

chloride .

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Ionic compounds dissociate in water

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5. Sucrose, an organic substance is soluble in

water as water molecules interact & surround

the sugar molecules breaking down theirinter-molecular bonds. Water molecules are

linked through hydrogen bonds.

6. Water is a liquid at room temperature. Each

molecule of water can form a maximum offoursuch bonds with different molecules of

water. Under room temperature, about 20%

hydrogen bonds exist in water. The lower the

temperature, the more hydrogen bonds are

formed.

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11

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6. At0 oC, itfreezeswhere all the molecules are

involved in forming the three-dimensional

structure of ice. This explains why iceexpands when it is formed and has a lower

density. Example : ice floats on water.

7. Because of the chemical properties, the

physiological roles of water :(a) Provides a medium for reactions to take

place.

(b) Acts as a solventto transportsubstances in

the blood of animals, or in xylem and phloem

of plants.

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(c) Water ionises and acts as substrates for

photolysis during photosynthesis and

hydrolysis reactions during digestion of food.

(d) Water interacts with macromolecules such as

proteins, nucleic acids and molecules in the

lipoprotein membrane structure. Water

molecules surround these macromoleculesmaking their structures more stable and

maintaining their three dimensional

structures to perform their functions.

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Physical Properties of Water1. Water has a high specific heat capacity of

4.2kJ/K/kg, which means 4.2 kJ of heat isrequired to raise the temperature by 1 K for 1kg of water.

A large amount of heat is required to cause a

slight increase in temperature as much of theenergy is used in breaking the hydrogen bondswhich restrict the movement of the molecules.

Physiological roles :

Enable water temperature in cells or in thesurrounding of the aquatic organisms toremain relatively constant. Water is a goodtemperature buffer.

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Physical Properties of Water2. Water has a high latent heat of vaporisation

of 2260 kJ/kg, that is 2260 kJ of heat isrequired to vaporise 1 kg of water.


a) Enable many land invertebrates to survive.b) Lower our body temperature when we sweat.

c) Panting helps to rid the body of excessive heat

in dogs and birds. Effective to cool body

temperature.

d) Lower temperature of leaves .

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16

Evaporative Cooling of Animals

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Physical Properties of Water3. Density or specific gravity of water is

highest at 4o

C. E.g. Ice floats on water andinsulates the water below.


a) Enable aquatic organisms to survive during

winter or in the tundra ocean.b) Nutrients circulate in the lake,helping

colonisation of organisms into greater depth.When the atmospheric temperature decreases,

the surface water sinks at 4oC. When thetemperature of the water at the bottomincreases after winter, water moves upbringing soluble salts along.

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18

Density of Water at Various Temperatures

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20

A Pond in Winter

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Physical Properties of Water4. Water has a high cohesive force.

A high attractive force that exists among watermolecules due to the hydrogen bonds.


a) Creates atranspirational pull in the xylem

vessels when evaporation occurs in the leaves. Ithelps to transportwater & mineral ions up intothe leaves for photosynthesis.

b) Cohesion & adhesion of water molecules enable

water to stay in the upper layer of soil calledtopsoil. Good quality soil of fine grain sizestogether with humus retain the right amount ofwater so that plants and other soil organisms can

live well in it.

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Physical Properties of WaterCohesion

Cohesion

Hydrogen bonds hold water

molecules tightly together

Adhesion

Adhesion Hydrogen bonds for between

water and other polar materials

Allow water be drawn many meters up a

tree in a tubular vessel

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Water as a

Transport

Medium

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Physical Properties of Water5. Water has a high surface tension.

There is a strong inward pull of water forming askin-like layer at the surface of water. It is caused

by the high cohesive forces of water molecules as

a result of hydrogen bonding.


a) Create a habitaton the water surface. Allow insects

to stay on the surface where they can gather food

or catch their preys like water-skaters.

b) Allow female mosquitoes to stand on water to lay

eggs. Allow the tiny eggs to float & larvae to attach

to the surface for their syphons to breathe air.

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Water skater
http://www.google.com.my/url?sa=i&source=images&cd=&cad=rja&docid=SvPg3ibOsQI84M&tbnid=t0kF_GNBpdR1IM:&ved=0CAgQjRwwAA&url=http://www.kmph.matrik.edu.my/wbl/Web%20Base%20Learning%20Biology/Main/SB017/C3%20Molecules%20of%20life/Diagram/&ei=cYCTUbj-EMi8rAeQj4CwDw&psig=AFQjCNFc9keop0-b1tc9ph1dp3SSTI0DuQ&ust=1368707569371270

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http://www.google.com.my/url?sa=i&source=images&cd=&cad=rja&docid=dJ5MWHsVzXaPpM&tbnid=bNWShgLk8M4NeM:&ved=0CAgQjRwwAA&url=http://fmel.ifas.ufl.edu/key/anatomy/larval.shtml&ei=1X2TUfrAEYeLrQeh6YAw&psig=AFQjCNF6-5MBxfiuPf1sejLXt1L4hPIc3A&ust=1368706901351387

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THE IMPORTANT PROPERTIES OF WATER

Water as universal solventand lubricantin joints

Water dissolves many substances by surroundingcharged particles and pulling them into solution

Viscosity of water (low; movement)

Specific heat capacity (temperature)

Latent heat of evaporation of water (cooling effect)

Surface tension (transportation)

Density (freezing-free)

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Questions

1. Which of the following properties of water are

notimportant or the functions of humanplasma?

I Good solvent

II High heat capacity

III Highest density at 4oC

IV Low viscosity

V High surface tension

A. I and II B. II and IV

C. III and V D. I, II and V

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Questions

2. Which of the following contributes the most to

the polar nature of the water molecule? [2008]A. Polar substances are able to dissolve in water.

B. Oxygen is more electronegative than hydrogen.

C. The angle between hydrogen atoms is 104.3o

.D. Hydrogen is bonded by covalent bonds with

oxygen.

3. What are other properties of water that are

important to organisms?

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1.2 Carbohydrates

Monosaccharide

Disaccharides

Polysaccharides

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Take 5

1.1 water

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