Water

What percentage of the fresh mass of a human is made up of water?

About 60–70%

Why is water essential for biochemical reactions?

All biochemical reactions take place in aqueous solution (dissolved in water)

What type of molecule is water?

A polar molecule

What charges do the hydrogen and oxygen atoms in water carry?

Hydrogen atoms: partial positive (δ+), Oxygen atom: partial negative (δ−)

How are bonds within a water molecule usually represented?

Solid lines between hydrogen and oxygen atoms

How are partial charges shown in water molecules?

As δ+ (delta positive) and δ− (delta negative)

Why do water molecules attract each other?

Because of their polarity, they form hydrogen bonds

How are hydrogen bonds between water molecules represented?

By a series of vertical lines

Why can water dissolve charged particles?

Because its polarity allows it to be attracted to charged particles

Why is water called the 'universal solvent'?

Because a large number of substances can dissolve in it

What is a condensation reaction?

A reaction where small molecules combine with the loss of a water molecule

What is hydrolysis?

The breakdown of large molecules by the addition of a water molecule

Why is water important in condensation and hydrolysis reactions?

It is lost in condensation and required in hydrolysis

Why is ice less dense than water?

Hydrogen bonds hold water molecules further apart in ice

What is the significance of ice being less dense than water?

Ice forms an insulating layer over aquatic habitats, preventing them from freezing solid

Why is water liquid at most temperatures on Earth?

Due to hydrogen bonding holding molecules together

What is the significance of water being liquid at Earth temperatures?

It acts as a transport medium (e.g., blood in mammals, xylem transport in plants)

Why is water colourless and transparent?

Because it does not absorb visible light significantly

What is the significance of water being colourless/transparent?

Light can pass through for aquatic photosynthesis and within plant cells to chloroplasts

Why does water have a high surface tension?

Due to strong hydrogen bonding at the surface

What is the significance of water’s high surface tension?

It supports small organisms (e.g., pond skaters)

Why does water have a high specific heat capacity?

It can absorb a lot of energy with only a small rise in temperature

What is the significance of water’s high specific heat capacity?

Aquatic habitats and cytoplasm remain thermally stable; enzymes don’t denature

Why does water have a high latent heat of vaporisation?

A lot of energy is needed to evaporate water

What is the significance of water’s high latent heat of vaporisation?

Organisms cool by evaporation (sweating, transpiration); aquatic habitats don’t evaporate easily

Why does water have cohesive properties?

Hydrogen bonds make water molecules stick to each other

What is the significance of water’s cohesion?

Water can be pulled under tension through plants during transpiration

Why does water have adhesive properties?

It sticks to other polar or charged substances

What is the significance of water’s adhesion?

Helps water move through plant xylem during transpiration