IB 2.2 Water

2.2 Water

Plan

1 Introduction:

2 Properties of Water:

2.1 Solvent

2.2 Specific Heat Capacity

2.3 Latent heat of Vaporisation

2.4 Density

2.5 Cohesion

2

3 1 3 Water in Organisms:

3.1 Solvent

3.2 Way of Transport

3.3 Reactant

3.4 Way of Support

3.5 Lubricant

3.7 Constant temperature

4 Water as an Habitat:

4

Xavier DANIEL, Ph.D. AS IB

.

Life on earth evolved in water,

and all life still depends on water

Almost all chemical reactions of life take place in

aqueous solution

Introduction 1


Water In Organisms

• Organisms usually contain

60% to 90% water

• Lowest- Plant Seed (20%)

• Highest- Jellyfish (99%) 99%

Water

20%

Water

Introduction 1


.

Around 70% of the mass of living organisms is water

Introduction 1


.

Around 70% of the mass of living organisms is water

Introduction 1


.

Introduction 1

Hydrogen bonds

Water molecules are charged

Oxygen atom

slightly negative

Hydrogen atoms

slightly positive


.

Introduction 1

Hydrogen bonds

Water molecules are polar

“Negative pole”

“Positive pole”


.

Introduction 1

Hydrogen bonds

The negative pole and the positive poles attract each other

Formation of hydrogen bonds

Weak, long distance bonds that are very common and very

important in biology.


.

Introduction 1

Hydrogen bonds

Between molecules of water only


.

Introduction 1

Hydrogen bonds

Between molecules of water

and other molecules ?

NO YES

Hydrophobic

Cannot dissolve in water

Hydrophilic

Can dissolve in water


Plan

1 Introduction:


2.1 Solvent



2.4 Density

2.5 Cohesion

2


3.1 Solvent


3.3 Reactant

3.4 Way of Support

3.5 Lubricant



4

Xavier DANIEL, Ph.D. AS

2.2 Water

IB

.

Properties of Water 2

Solvent

Water is a very good solvent

Molecules such as salts, sugars, amino acids dissolve readily in water

Once dissolved they can be transported

e.g. glucose in the bloodstream


.

Introduction 1

Hydrogen bonds

Between molecules of water

and other molecules ?


.


Specific heat capacity

Water has a high specific heat capacity (4.2 joules of energy to heat 1g water by 1oC)

Water does not change temperature easily

Minimises fluctuations in temperature inside cells and means that organisms’ temperature is quite constant


Methane : 52.93 J/(mol K)

.


Latent heat of vaporisation

Water requires a lot of energy to change state from a liquid to a gas

Provides a cooling mechanism

in animals (sweating) and plants (transpiration)

As water evaporates it extracts heat from the surrounding

area, cooling the organism


.


Density

Water in its solid state (ice) is less dense than in its the liquid state

As the air temperature cools, bodies of water freeze on the

surface

Formation of a layer of ice on top of the liquid beneath

Allowing aquatic ecosystem to exist in low temperatures


17 .


Cohesion

Water molecules stick together (hydrogen bonds)

Water has a high cohesion

Long columns of water can be suck up tall trees by transpiration without breaking

Surface tension: small animals can walk on water


Plan

1 Introduction:


2.1 Solvent



2.4 Density

2.5 Cohesion

2


3.1 Solvent


3.3 Reactant

3.4 Way of Support

3.5 Lubricant



4


2.2 Water

IB

3 Water in Organisms

Solvent

Water is a very good solvent

Molecules such as salts, sugars, amino acids dissolve readily in water

Almost all chemical reactions of life take place in

aqueous solution


Dissolving table sugar (Sucrose = Saccharose)


Solvent


Dissolving table salt (Sodium Chloride)


Solvent


Dissolving table salt (Sodium Chloride)


Solvent



Way of Transport

Many different life solutions, such as blood and sap, are mainly made of water

Sap and blood contain high amounts of water making them good solvents

Being good solvents allows them to dissolve the substances they are transporting



Way of Transport



Reactant

Water is a source of OH- and H+

Allows many reactions to occur

Depolymerisation…

Photosynthesis to make sugar = source of energy for plants

Photosynthesis releases O2, which organisms breathe

Without water in photosynthesis, life as we know it would be impossible



Way of Support in Plants When water enters the cell by osmosis,

the water fills up the cell so much that the cell prevents other water intake

This makes the cell turgid, or stiff

The cell must be turgid to support the plant’s leaves



Way as a Lubricant When bones meet at a joint, they need a fluid between the bones to prevent scraping against each other Synovial fluid, which is mainly made of water Many internal organs have fluid around them to keep them protected Examples: Brain: Cerebro-spinal fluid Lungs: Pleural Fluid

Eyes: Mix of fluids.

Synovial

Fluid



For constant internal Temperature

Organisms need constant internal temperature

Fluctuations: not healthy !

Too hot ………… Sweating

Sweat = mostly water

Cooling effect


Plan

1 Introduction:


2.1 Solvent



2.4 Density

2.5 Cohesion

2


3.1 Solvent


3.3 Reactant

3.4 Way of Support

3.5 Lubricant



4


2.2 Water

IB

Water as an Habitat 4

Water Is Lighter as Solid than as a Liquid

Ice forms an

insulating blanket

over water.

For constant external Temperature


Water as an Habitat 4

Water can provide a good protective layer for organisms

Water provides buoyancy for organisms in the water

Dissolved oxygen can be plentiful in water,

for use in respiration

Water helps maintain a constant temperature

Water keeps out UV rays from the sun


Documents

IB 2.2 Water