biology water

8/19/2019 Biology Water

1/22

MACROMOLECULES1.2 WATER


2/22

WATER:

The molecule that supports life

• Water is the biological medium on Earth

• All living organisms require water more than

any other substance

• Most cells are surrounded by water, and cellsthemselves are about 70 –95% water

• The abundance of water is the main reason the

Earth is habitable.


3/22

WATER:

The molecule that supports life

• Water is the only common substance to exist in

the natural environment in all 3 physical states

of matter:

•Solid ice•Liquid

•Gas vapour

• Molecules of water participate in many chemicalreactions necessary to sustain life.

e.g.: hydrolysis of ATP to release energy


4/22

The Polarity of Water

Water’s structure :

• Shape like a wide V

• 2 hydrogen atoms joined to the oxygen atom

by single covalent bonds.

• Water is a polar molecule.

• The 2 ends of water molecule have

opposite charges.•The oxygen region has a partial negative charge (2δ-)

•The hydrogens region have a partial positive charge (δ-)


5/22


Significances features:

• Polarity allows water molecules to

form hydrogen bonds with each

other.• Water is a versatile solvent due to

its polarity, which allows it to form

hydrogen bonds easily.

• When an ionic compound isdissolved in water, each ion is

surrounded by a sphere of water

molecules called a hydration

shell.


6/22



7/22

Properties of Water

• Four of water’s properties that facilitate

an environment for life are:

1. Cohesive behavior

2. Moderation of temperature

3. Floating of ice on liquid water

4. Solvent of life


8/22


• Water molecules form hydrogen bonds withother water molecules.

• This makes water molecules tend to stick or

stay close together.• This is called COHESION.

ADHESION:

• The attraction between different kind of

molecules.

• Example: between water and plant cell walls


9/22

• Cohesion helps:

a. The transport of water & dissolved

nutrients against gravity in plants.

• As water evaporates from leaves,

• the unbroken column of water held bycohesive forces within the xylem vessels

are drawn upwards to the top of trees.

• Adhesion of water to the xylemwall;

• will resists the downwards pull of gravity.



10/22

b. Surface tension,

• a measure of how difficult it is to break the surface of a

liquid. Water has a greater surface tension than other liquids.

• This is due to an ordered arrangement of water

molecules, hydrogen-bonded to one another and to thewater molecules below.



11/22

The high

surface tension

of water,

• allows the

water strider to

walk on the

surface of apond.



12/22

2. Moderation of Temperature

Water’s

properties:

Highspecific

heat

High heat of

vaporization


13/22


Water moderates air temperature by:

- absorbing heat from warmer air and

- releasing the stored heat to cooler air.


14/22

a. High specific heat:

• water can absorbed or release a relatively large

amount of heat with only a slight change in its own

temperature.


a. Water b. Ethyl alcohol


15/22

Large bodies of water (e.g. oceans, seas & lakes) have a

thermally stable environment for aquatic organisms.

– Water acts as thermal buffer & prevents large fluctuations in

body temperature of terrestrial organisms (enzymes to

function optimally ).



16/22


b. High heat of vaporization:

– Heat a liquid must absorb for 1 g to be converted

to gas

– As a liquid evaporates, its remaining surfacecools, a process called evaporative cooling

– Evaporative cooling of water helps stabilize

temperatures in organisms surface and bodies

of water.


17/22

• Water’s property:- Lower density of ice

• As water cools,

• the movement of water molecules slow down

• the molecules are farther apart.



18/22


• Water expands as it freezes

and the ice is less dense

than liquid water.

• Water reaches its greatestdensity at 4°C.

• If ice sank, all bodies of

water would eventually

freeze solid, making lifeimpossible on Earth


19/22


• At 0ºC & below,• ice is formed & floats on the surface of water forming a

insulating layer.

• This prevents water from freezing in lower depths.

• Therefore aquatic organisms in ponds & lakes can survive inliquid water during winter months.


20/22

4. Solvent of life

• Water’s property:

- Polar molecule

• Water can also dissolve

compounds made of nonionicpolar molecules;

e.g. sugar (water-soluble)

• Large polar molecules such as

proteins can dissolve in water if they have ionic and polar

regions on their surface.


21/22

4. Solvent of life

• Solution :

• a liquid that is a homogeneous mixture of 2 or

more substances.

• Solvent :

• the dissolving agent of a solution.

• Solute

• A substance that is dissolved in a solution.• Aqueous solution

• in which water is the solvent.


22/22

4. Solvent of life

• A hydrophilic substance is one that has an

affinity for water.

Example: alcohol

• A hydrophobic substance is one that does nothave an affinity for water.

Example: Oil molecules are hydrophobic

because they have relatively nonpolar

bonds.

• A colloid is a stable suspension of fine particles

in a liquid

biology water

Documents