2.1.1 AS BIOLOGY OCR

• A water molecule occurs when one O atom is joined to 2 H atoms - H20 through sharing of electrons.
• The shared H atoms are pulled towards the Oxygen atom and the other side of the H atoms are left with a slight + charge.
• The oxygen atom has unpaired electrons so it has a slight negative charge.
• These charges make water polar:
• The - on the O and the + on the H

How this forms the structure:

The  - charged O atoms attract other water molecules through the + charged H atoms: this is called Hydrogen Bonding.

How this forms the structure:

The  - charged O atoms attract other water molecules through the + charged H atoms: this is called Hydrogen Bonding.

• Reactant:
• Reactant in lots of important chemical reactions e.g. photosynthesis and hydrolysis reactions
• Universal solvent:
• Its a solvent to many substances and this is important because most reactions take place in solutions
• Transport substances:
• Its a liquid and a solvent so can transport many different things e.g. glucose and oxygen around animals
• Temp control
• Helps water maintain a certain temperature by evaportating the surface of the water when it gets too high , this cools it down. Useful for living organisms who live in the sea

High specific heat capacity:

• The H bonds between water molecules can absorb a lot of heat energy
• So it takes a lot of energy to break water molecules
• Useful for living organisms because it maintains a certain temperature by stopping rapid temp changes

Hig latent heat of evaporation

• Evaporation of water cools surfaces by providing the heat neccesary for evaporation.
•  takes a lot of heat energy to break H bonds in the first place
• Useful for liiving organisms because they can resist body temp changes ( as their bodies contains lots of water)

Cohesion:

• A water molecule will attract neighbouring water molecules so they tend to stick together
• This happens because they are polar
• helps water to flow- good for transporting substances e.g. in xylem via the transpiration stream

Surface tension:

• Caused by cohesion
• Water molecules at the surface are attracted to those below and adjacent
• Reduces the surface to the smallest possible area
• acts like a extremely think membrane