1.1 Water - Student
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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
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
• 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)
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