CHAPTER 1:CHAPTER 1:

MOLECULES OF LIFEMOLECULES OF LIFE

1.1 WATER1.2 CARBOHYDRATES1.3 LIPIDS1.4 PROTEINS1.5 NUCLEIC ACIDS

LEARNING OUTCOMES:

1.1 WATER

• Explain the structure of water molecule• Describe the properties of water and its

importance

ROLES OF WATER

solvent for polar molecules medium for exchange of respiratory gases

medium for enzymatic reactions

external media for aquatic organisms (in locomotion,

secretion of waste products, for food resources, external

fertilization)

wide V-shaped structure : 1 oxygen atom 2 hydrogen atoms

bond angle: 104.5°

covalent bonds

STRUCTURE OF ONE WATER MOLECULE

STRUCTURE OF ONE WATER MOLECULE

Covalent bond

Schematic Diagram Showing Covalent Bond Within a Water Molecule

Polar molecule opposite ends of water molecule have opposite charges oxygen: partial negative charge; –

hydrogen: partial positive charge; +

STRUCTURE OF ONE WATER MOLECULE

Polarity allows water molecules to form hydrogen bonds between each other Hydrogen atoms (H) of one water molecule is attracted to oxygen atoms (O) of other water molecule by hydrogen bonds ONE water molecule will form hydrogen

bond to a maximum of FOUR water molecules

Formation of Hydrogen Bond

1

23

4

Schematic Diagram Showing Hydrogen Bonds

Between Water Molecules

Schematic Diagram Showing Hydrogen Bonds

Between Water Molecules

• Hydrogen bonds are weaker than covalent bonds but, strong enough to hold water molecules together

Hydrogen Bond

3. Has high specific heat capacity 2. Has low viscosity

4. Has high latent heat of vaporization

1. Is Polar molecule

5. Has high surface tension 6. Has maximum density at 4°C

PROPERTIES OF WATER

1. IS POLAR MOLECULE

oxygen atoms (O) are attracted to positively charged sodium ion (Na+) hydrogen atoms are attracted to negatively charged chloride ion (Cl-)

Due to its polarity, water act as universal solvent

It can dissolve ionic and polar molecules e.g. sodium chloride (NaCl)

Water molecule surround sodium and chloride ions,

separate and avoid them from each other.

BIOLOGICAL IMPORTANCE OF WATER IS POLAR MOLECULE

Universal solvent for most solutes

Provides an aqueous medium for biochemical reactions (i.e. enzymatic reactions)

Major transport medium in living organisms (e.g. in blood capillaries of human and in xylem of plants)

2. HAS LOW VISCOSITY

Hydrogen bonds between water molecules is continuously form, break and reform

Results in, water molecules can flow easily with less friction (for e.g. through narrow blood vessel)

As lubricant to lubricates movement of substances (e.g. peristaltic movement of food bolus in esophagus)

BIOLOGICAL IMPORTANCE OF WATER HAS LOW VISCOSITY

As lubricant to lubricates joints in vertebrates

3. HIGH SPECIFIC HEAT CAPACITYDefinition of high specific heat

capacity : Large @ high amount of heat energy that must be absorbed or released

for 1 gram of water molecules to change its temperature by 1ºC

Specific heat capacity for water = 1 cal/gºC @ 4.2 J/gºC-1

Biology Campbell 9th ed. (page 94)

Large amount of heat energy is absorbed to break ALL hydrogen bonds between water molecules in order to increase the temperature of water molecules

3. HIGH SPECIFIC HEAT CAPACITY

Large amount of heat energy is released to form hydrogen bonds between water molecules in order to decrease the temperature of water molecules

Can stabilize the ocean temperature thus, enable aquatic organisms to survive

Act as heat buffer thus, prevent large fluctuation in body temperature of terrestrial organisms

BIOLOGICAL IMPORTANCE OF WATER HAS HIGH SPECIFIC HEAT

CAPACITY

4. HIGH LATENT HEAT OF VAPORIZATION

Latent heat of vaporization for water = 580 cal/g

Definition of high latent heat of vaporization :

Large @ high amount of heat energy that must be absorbed for 1 gram of

water molecule to change from liquid water into water vapour

Biology Campbell 9th ed. (page 95)

4. HIGH LATENT HEAT OF VAPORIZATION

Large amount of heat energy is absorbed to break ALL hydrogen bonds between water molecules in order to change liquid water into water vapour

evaporation of sweat on skin of human

transpiration from leaves of plants

or panting in animals e.g. dog

Give the cooling effects during :

BIOLOGICAL IMPORTANCE OF WATER HAS HIGH LATENT HEAT OF

VAPORIZATION

Definition of cohesive force: Force of attraction between the same molecules

e.g. between water molecules Definition of adhesive force: Force of attraction between different molecules

e.g. between water molecules and wall of xylem vessels

COHESIVE AND ADHESIVE FORCE

5. HIGH SURFACE TENSION

Surface tension is related to cohesive forces between water molecules

Is a measure of how hard it is to break the surface of a liquid

Definition of high surface tension :

5. HIGH SURFACE TENSIONWater molecules on the surface is bonded by hydrogen bonds with water molecules at the below to form a ‘skin like’ layer at the surface

of water

Allows insects to walk on the water surface. e.g. water skater

HIGH SURFACE TENSION: BIOLOGICAL IMPORTANCE

6. MAXIMUM DENSITY AT 4°C at 0°C, liquid water transforms into ice (solid) ice is less dense than liquid water at 4°C

Ice floats in liquid water because hydrogen in ice are more “ordered”, making ice less dense

As ice floats, it acts as insulator to prevent ponds, lakes, oceans from freezing thus, allow aquatic organisms to survive under the floating ice.

6. HAS MAXIMUM DENSITY AT 4°CBIOLOGICAL IMPORTANCE

Test your knowledge….

How does aquatic life survive in extremely cold conditions ?

REFERENCE BOOK :

Campbell et. al. (2011). Biology (9th Ed.), Pearson Benjamin Cummings. Page 92-97 (Unit 1: The Chemistry of Life; Chapter 3: Water and Life)