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CHAPTER 1
MOLECULES OF LIFE
1.1: Water
1.2: Carbohydrates
1.3: Lipids
1.4: proteins
1.5:Nucleic Acids 1
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1.2 CARBOHYDRATES
MOLECULES OF
LIFE
1.1 WATER
1.3 LIPIDS
1.4 PROTEINS
1.5 NUCLEIC ACID
structure H2O
properties - H2O
structure
nucleotide
DNA, phosphodiester bond
RNA ( mRNA, tRNA & rRNA )
structure
amino acid,
polypeptide
peptide bond
structure triglycerides / fat/ triacylglycerol
phospholipids & steroids
structure
fat formation: 1 glycerol + 3 fatty acids
by condensation process, ester bonds
differences between DNA & RNA:
pentose sugar: deoxyribose , ribose
strands: double helix, single
bases: ATGC, AUGC
properties:
A & B soluble in water, sweet to
taste. C insoluble in water
polar molecules
covalent bonds
hydrogen bonds
1. universal solvent
2. low viscosity
3. high specific heat capacity
4. high latent of vaporization
5. high surface tension
6. Maximum density at 40C
protein classification:
1. level of organization & types of
bond ( 1 , 2 , 3 & 4 )
2. structure ( fibrous, globular &
conjugated proteins )
3. Functions: transport proteins,
defensive proteins,
enzymatic proteins..
A. monosaccharides:
1. triose ( 3C )
2. pentose ( 5C ) eg: ribose & deoxyribose
3. hexose ( 6C ) eg: glucose, galactose & fructose
B. disaccharides:
1. maltose -1,4 glycosidic bond
2. sucrose -1,2 glycosidic bond
3. lactose -1,4 glycosidic bond
C. polysaccharides:
1. starch ( amylose & amylopectin ) -1,4 & -1,6 glycosidic bond
2. glycogen -1,4 & -1,6 glycosidic bond
3. celluose -1,4 glycosidic bond
.
.
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5 MAJOR CLASSES OF MOLECULES
WHICH MAKE UP THE BODIES OF LIVING ORGANISM
MOLECULES OF LIFE
1. WATER
2. CARBOHYDRATE
3. LIPID
4. PROTEIN
5. NUCLEIC
ACID
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4
1.1 WATER
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Learning Outcomes:
At the end of this topic, students should be
able to:
1.1 a) explain the structure of water
molecule.
5
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WATER
a chemical substance with the chemical formula
H2O.
Made up of 70%
of human body
weight
a colourless, odourless and tasteless fluid with a neutral pH of 7.0 at room temperature (200C).
Water is the most
abundant compound in
the vast majority of
cells. It forms about 60 - 90% of the total chemical content of the cell.
6
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Structure of a water
molecule, H2O
Water molecule contains
one oxygen and
two hydrogen
atoms
7
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
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Structure of a water
molecule, H2O
H2O is formed when
2 Hydrogen atoms form
polar covalent
bonds (by sharing of
electrons) with an oxygen atom
8
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
polar
covalent
bonds
-
The angle between the 2 hydrogen atoms is 104.5
The 3 atoms form a
wide V-shape, not a straight line
9
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Structure of a water
molecule, H2O
-
Structure of a water
molecule, H2O
Water molecule is a
polar molecule,
due to the unequal
distribution of
electrical charge/
electron
10
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
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Water : polar molecule ~ coz oxygen is more
electronegative where
~ the region around oxygen
has a partial negative
charge ( - )
~ the region near 2 hydrogen
atoms has a partial positive
charge ( + )
11
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Structure of a water molecule, H2O
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Polarity of Water
Oxygen are more electronegative than hydrogen.
Electrons are more attracted to oxygen than to hydrogen
Therefore, oxygen is slightly negative - and hydrogen slightly positive +
12
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Electrons are shared between H and O [forming polar covalent bond]
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Structure of a water molecule, H2O
13
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Hydrogen bonds
formed when a hydrogen atom is attracted to another strongly electronegative
atom ( e.g. F, O & N )
-
A partial positive H ( + ) of one H2O is attracted to the partial negative O ( - ) of nearby H2O molecule
The molecules are held
together by a hydrogen bond (H bond)
Areas with opposite charges are attracted
14
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Hydrogen bonds
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15
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Structure of a water molecule, H2O
H bonds are weaker than covalent bonds
but they are strong enough to hold H
2O
molecules
together
O H
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16
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Structure of a water molecule, H2O
each H2O
molecule can form H bonds with up to
maximum 4
neighbours /
partners
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17
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
Structure of a water molecule, H2O
H H
H H
H H
H H
H H
O O
O O
+
O
+ +
+
+ +
+ +
+ +
- -
- -
- -
-
18
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.
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Learning Outcomes:
At the end of this topic, students should be
able to:
1.1 b) describe the properties of water &
its importance: universal solvent, low
viscosity, high specific heat capacity, high
latent heat of vaporization, high surface
tension and maximum density at 40 C.
19
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20
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
unique properties of H2O are due mostly to its;
i. polarity
H2O are attracted to charged particles or charged
surfaces
ii. ability to form H bonds
iii. small size
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Properties Of Water And Its Importance
1. Universal solvent
2. Low viscosity
3. High specific heat capacity
4. High Latent heat of vaporization
5. High surface tension
6. Maximum density at 4oC
6. 21
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
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22
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
1. Universal solvent
(Water as universal solvent)
because of its polarity and its ability to form H bond;
dissolves other polar compound easily
& acts as medium for transportation of H
2O
soluble substances
-
Powerful solvent for;
i. polar substances:-
~ eg: sugars which have slightly charged
hydroxyl (- OH) groups
ii. ionic compounds:-
~ eg: sodium chloride, NaCl
iii. organic molecules with ionized groups:-
~ such as the carboxyl group (COO-)& amino group (NH3
+) 23
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
1. Universal solvent
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Eg : powerful solvent for ionic compounds
(NaCl), when a crystal of salt
( NaCl ) is placed in water:-
1. Negative oxygen regions of polar H2O are attracted to sodium cations (Na+) ~ positively charge ion.
2. Positive hydrogen regions of polar H2O cling to chloride anions (Cl-) ~ negatively charge ion.
24
oxygen
hydrogen
-
Salt
The NaCl crystal dissociates &
dissolves when added to water
-
Eg: Organic compound: glucose dissolved in water
- Soluble organic molecules like sugars dissolve in water due to: formation of hydrogen bonds between water molecules &
hydroxyl (-OH) groups in these organic molecules.
26
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
1. Universal solvent
Water molecule
Hydrogen bond
Polar compound
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27
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
1. Universal solvent
Hydrophilic:
polar substances that can dissolve in water
eg: biological fluids such as blood & plant sap
Hydrophobic:
non-polar substances (lipids & hydrocarbons) that do not interact
with water eg: oil on the surface of water
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Importance of water as Universal
solvent
Most cell component dissolve in water
Metabolic reactions normally takes place in solution
Able to dissolve salts, acids, sugar, nutrients & gases which make it able to transport within
and between the cell.
28
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
1. Universal solvent
-
Low viscosity because H bonds between H2O are being
continually broken & reformed
The H2O can slide easily over each other
29
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
2. Low viscosity
a measure of liquid
resistance to flow.
-
30
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
The lower the viscosity, the easier the water flow.
a measure of liquid
resistance to flow.
2. Low viscosity
-
Makes it suitable as medium of
transportation in living organisms.
Eg: blood easily flow with less friction
through the narrow vessels in the
circulatory system.
Water is a good lubricant due to its low
viscosity (enables it to move in & out of cells)
31
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
2. Low viscosity
-
32
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
Also suitable for lubrication;
1. mucus ( eg saliva ) : helps in the movement of food
2. pericardial fluid:
lubricates movement of the heart
3. synovial fluid: lubricates joints in vertebrates
2. Low viscosity
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33
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
3. High specific heat capacity
Definition of High specific heat capacity:
Amount of heat required to raise the temperature
of 1 gram of water by 1C.
-
34
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
3. High specific heat capacity
~ By definition,
Specific heat capacity of a water:
1 cal / g / oC
@
4.184 J / g / oC
( 4.184 J g-1 oC-1 )
-
Water has a high specific heat (1 cal/g/ oC)
A lot of heat energy is required to raise / lower the temperature of water
High energy is needed to break / form the H bonds
35
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
3. High specific heat capacity
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36
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
Importance of High specific heat capacity of
water
1. Terrestrial
organisms
2. Aquatic environments
2.~ stabilize ocean
temperatures, creating a
favourable environment for
marine life
1.~ water act as a thermal buffer & prevents
large fluctuations in body temperature
-
37
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
Definition of High latent heat of vaporization :
Amount of heat that a
liquid must absorb for 1 g of it to be converted
from the liquid to the
gaseous state
4. High latent heat of vaporization
-
38
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
water has a high latent heat of vaporization;
relatively requiring about 580 calories of heat to evaporate 1g of water at
room temperature ( 25 oC )
much energy required to break its many hydrogen bonds
-
580 cal/g of heat needed to turn
liquid water into
water vapor (gas)
39
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
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40
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
..much energy required to break its many
hydrogen bonds
H bonds between H2O make it difficult for them to be separated & vaporized;
for a H2O to evaporate, it must vibrate & move quickly
enough to break all the H bonds
holding it to the other H2O molecules
-
41
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
much energy required to break its many hydrogen bonds
only the fastest moving H2O, carrying the most energy,
can break their H bonds &
escape as water vapour ( gas )
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42
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
Importance high latent heat of
vaporization of water
evaporation of water from a surface as heat is removed;
causes cooling effect
cooling mechanism in; animals ( sweating & panting )
plants ( transpiration )
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43
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
Importance high latent heat of vaporization of
water
Eg: When a persons body temperature begins to rise,
he sweats.
Evaporation of sweat uses a lot of heat energy.
This energy has a cooling
effect to the skin and
helps prevent overheating
-
44
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
Importance high latent heat of
vaporization of water
Eg: a plant can keep cool in the bright sunlight as water evaporates
from its surface
~ transpiration from green leaves, gives cooling effect because the
escaping molecules absorb a lot of
heat energy
-
45
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
4. High latent heat of vaporization
Importance high latent heat of vaporization of
water
Eg: animals that do not sweat will bathe
or wet themselves with water to prevent
their bodies
from
overheating
during
hot days
-
46
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
5. High surface tension
High Surface tension
- measure of how
difficult to break the
surface of liquid.
- they stick to one another supporting relatively dense
objects
eg: the water strider
-
47
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
5. High surface tension
eg: the water strider
-
48
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
5. High surface tension
H2O molecules can also cling to
the surface of
another substance
(adhesion)
helps in transport of water in plants
-
49
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
5. High surface tension
adhesive forces; that exist between H2O molecules &
walls of xylem
vessel elements
cohesive forces; exist between H2O
molecules
-
50
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
5. High surface tension
in land plants, the interplay of adhesive & cohesive forces & also
transpiration pull from the leaves,
maintains a continuous flow of water up the stem
Importance High surface tension
-
Transpiration pull from the leaves maintains a continuous flow of water up the stem.
Water can move up in a fine capillary tube coz the upwards adhesive force can support the weight of the
water column & resists the downward pull of gravity.
Cohesive forces
Adhesive forces
Water molecules
Hydrogen bonds
Wall of Xylem
51
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
5. High surface tension
-
52
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
6. Maximum density at 4oC
Most liquids reach their maximum density
at their freezing point;
water reaches its maximum density at
4C
water expands when they solidify/become ice at 0C ( as H
bonds become stable & keep the
molecules far apart )
-
As water solidifies /become ice at 00C, water molecules expand
Causing ice to become less dense & floats above water surface
53
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
6. Maximum density at 4oC
-
54
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
6. Maximum density at 4oC
Water expands
(ice less dense than liquid)
-
5. Maximum density at 4oC
When the temperature is more than 4C, the ice will expand more and melting.
The ice floats on top.
the floating layer of ice insulates will the water below.
This is why the ponds, lakes or sea rarely freeze solid. (only the surface is frozen)
Aquatic life can generally survive a freeze-up.
55
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
-
56
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
6. Maximum density at 4oC
Importance Maximum density at 4oC
~ As water freezes, ice formed is
less dense than cold water around it.
The ice floats on top.
the floating layer of ice will insulates the water below.
aquatic organisms are able to live below the ice in winter
-
Properties Of Water And Its Importance
1. Universal solvent
2. Low viscosity
3. High specific heat capacity
4. High Latent heat of vaporization
5. High surface tension
6. Maximum density at 4oC
6. 57
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
-
58
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
RefresheR
-
59
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
Properties of
water
Importance
1. Universal
solvent because of its
polarity and its
ability to form H
bond
Dissolves other polar substances (eg: easily & acts as medium for transportation of water soluble substances
Powerful solvent for;
polar substances (eg: sugar has slightly charged hydroxyl OH group)
ionic substance (eg: NaCl)
organic molecules with ionised groups (eg: carboxyl group COO-, & amino group NH3
+ )
-
60
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
Properties of water Importance
2. Low viscosity (Def: viscosity is a measure of
liquid resistance to flow.
Low viscosity of water allows
it to flow easily & quickly).
because H bonds between H2O
molecules are constantly formed,
broken & reformed;
allows water molecules to slide
past each other
Suitable as medium of transportation in
living organisms
Blood easily flows with less friction through the
narrow blood vessels in
the circulatory system
-
61
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
Properties of water Importance
3. Water has high
specific heat
capacity Def: Amount of heat
required to raise the
temperature of 1 gram of
water by 1C.
1 cal / g / oC @ 4.184 J / g / oC
( 4.184 J g-1 oC-1 )
Minimises fluctuations in temperature.
Allows body cells to have
stable temperature for physiological activities.
Allows aquatic
environments to have
stable temperature when the surrounding air
temperature changes.
-
62
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
Properties of water Importance
4. Water has high latent
heat of vaporisation Def: Much energy (580
calories of heat) is needed
/ absorbed to turn 1 g of
liquid (water) into water
vapour (gaseous) at room
temperature ( 25 oC ) this is to break H bonds to
separate water molecules
Evaporation of water in sweat
on a skin and
transpiration
from leaves as
heat is removed
will give a
cooling effect
-
63
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
Properties of water Importance
5. Water has high
surface tension ( hard to break the
surface of water ). H bonds make H2O
molecules stick to each other cohesion
H2O molecules can also attach to the surface of
another substance adhesion
Allows small organisms (eg: water strider) to
move on the surface of
water
transpiration pull from the leaves, maintains a
continuous flow of
water up the stem
-
64
CHAPTER 1: MOLCULES 0F LIFE 1.1: Water
LEARNING OUTCOMES: 1.1 b) describe the properties of water & its importance.
PROPERTIES of a H2O molecule & its IMPORTANCE
Properties of water Importance
6. Water has the highest
density at 4 0C Water expands when
temperature drops below
4 0C until becoming ice at 0 0C
(H bonds become stable
and keep the molecules far
apart).
Ice is less dense than the cold water around it
Allows aquatic organisms to live
below the floating
ice layer of lake
during winter (ice floats on top
and insulating the
water below
-
65
References:
Subtopic: WATER
-
1. The slight negative charge at one end of
one water molecule is attracted to the
slight positive charge of another water
molecule. What is this attraction called?
A. a covalent bond.
B. a hydrogen bond.
C. an ionic bond.
D. a hydrophilic bond.
66
-
2. Water carries out all the following
functions of life, except that it
does not act as a
A. lubricant.
B. cooling agent.
C. source of carbon.
D. chemical reagent. 67
-
3. At what temperature is water
at its densest?
A. 0C
B. 4C
C. 32C
D. 100C 68
-
4. What gives rise to the
cohesiveness of water molecules?
A.hydrophobic interactions.
B.nonpolar covalent bonds.
C.ionic bonds.
D.hydrogen bonds.
69
-
5. Water is a universal solvent due
to its
A. low viscosity.
B. polar molecules.
C. high specific heat.
D. high boiling point.
70