1.1_water

CHAPTER 1

MOLECULES OF LIFE

1.1: Water

1.2: Carbohydrates

1.3: Lipids

1.4: proteins

1.5:Nucleic Acids 1

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

.

.

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

4

1.1 WATER

Learning Outcomes:

At the end of this topic, students should be

able to:

1.1 a) explain the structure of water

molecule.

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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.

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Structure of a water

molecule, H2O

Water molecule contains

one oxygen and

two hydrogen

atoms

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CHAPTER 1: MOLCULES 0F LIFE 1.1: Water

LEARNING OUTCOMES: 1.1 a) explain the structure of water molecule.


molecule, H2O

H2O is formed when

2 Hydrogen atoms form

polar covalent

bonds (by sharing of

electrons) with an oxygen atom

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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

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molecule, H2O


molecule, H2O

Water molecule is a

polar molecule,

due to the unequal

distribution of

electrical charge/

electron

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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 ( + )

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Structure of a water molecule, H2O

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 +

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Electrons are shared between H and O [forming polar covalent bond]


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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

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Hydrogen bonds

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H bonds are weaker than covalent bonds

but they are strong enough to hold H

2O

molecules

together

O H

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each H2O

molecule can form H bonds with up to

maximum 4

neighbours /

partners

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H H

H H

H H

H H

H H

O O

O O

+

O

+ +

+

+ +

+ +

+ +

- -

- -

- -

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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.

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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

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

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(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




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.

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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.

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Water molecule

Hydrogen bond

Polar compound

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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

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.

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Low viscosity because H bonds between H2O are being

continually broken & reformed

The H2O can slide easily over each other

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2. Low viscosity

a measure of liquid

resistance to flow.

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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)

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2. Low viscosity

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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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Definition of High specific heat capacity:

Amount of heat required to raise the temperature

of 1 gram of water by 1C.

34




~ 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

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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

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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

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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)

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..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

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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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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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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

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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

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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

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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

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eg: the water strider

48




H2O molecules can also cling to

the surface of

another substance

(adhesion)

helps in transport of water in plants

49




adhesive forces; that exist between H2O molecules &

walls of xylem

vessel elements

cohesive forces; exist between H2O

molecules

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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

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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

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Water expands

(ice less dense than liquid)


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.

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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


2. Low viscosity


4. High Latent heat of vaporization



6. 57



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PROPERTIES of a H2O molecule & its IMPORTANCE

RefresheR

59




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

+ )

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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

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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.

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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

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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

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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

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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.

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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.

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5. Water is a universal solvent due

to its

A. low viscosity.

B. polar molecules.

C. high specific heat.

D. high boiling point.

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