Water | GCE A-level Biology

Table of Contents

The molecule consists of one oxygen atom covalently bonded to two hydrogen atoms.
the oxygen atom is capable of pulling them towards itself and further away from the hydrogen atoms.
the oxygen part becomes slightly negatively charged, and the hydrogen atoms slightly positively charged.
it forms hydrogen bonds

To dissolve chemicals inside the cells/ metabolic reaction takes place in aqueous solutions
Uptake of mineral salts from soil
Excretion of waste products dissolved in water e.g urine
Water has high solvent of polar molecules e.g. ionic compounds like NaCl
On contact with water the ions and the polar group are surrounded by water molecules which separate the molecules from each other.
Biochemical reaction takes place in aqueous conditions.
Water as a solvent act as transport medium e.g. in blood

Water has high heat capacity
A large amount of heat energy results in a small rise in temperature.
Temperature changes within water or aqueous unitary therefore minimized.
Biochemical processes consequently operate over a small temperature range and are less likely to be affected extremities of temperatures.
Water also provides a very constant external environment for many cells and organisms.

Latent of evaporation is the measure of vaporization is a measure of heat energy required to vaporize a liquid.
A large amount of water is required to make water vapour.
This is due to hydrogen bonding of water molecules.
Therefore, water have usually high boiling point.
Evaporating water as a result takes a lot of heat energy with them from the surrounding thus cooling takes place.
This is made use of in the transpiration, sweating and panting of mammals.
High heat of evaporation also means that a large amount of heat can be lost with minimal loss the body, plant etc

Latent heat of fusion is the measure of the heat energy required to melt a solid i.e. (ice)
Ice requires a relatively large amount of heat energy to thaw it.
Conversely, liquid must loss a relatively large amount of heat to freeze.
Content of a cell and their environment are less likely to freeze.

- Water has highest density at 4 degrees
- Its density increases as the temperature decreases

Ice therefore tends to float.

Ice insulates the water below it thus increasing survival chance of organisms below it.
Since water below 4 degrees tend to rise, this also tends to maintain circulation in lentx ecosystem.
This may result in nutrient cycling and colonization of water to greater depth. Iced therefore tends to float.
Ice insulates the water below it thus increasing survival chance of organisms below it.
Since water below 4 degrees tend to rise, this also tends to maintain circulation in lentx ecosystem.
This may result in nutrient cycling and colonization of water to greater depth.

Cohesion is the force where individual molecules stick together at the surface, a force called surface tension between the molecules as they try to occupy the least possible space (ideally a sphere).
Water has a higher surface tension which makes it possible for small organism to skate over its surface.
The high cohesion of water is important in cell and in the translocation of water in the xylem vessel.
Movement of water in the xylem
Habitat for less dense aquatic organism

Water is biological significant as an essential metabolite that is, it takes part in chemical reaction of metabolism.
For example, it is used as a source of hydrogen and electron.

Property	importance	role in living organisms
solvent	Allows cells to maintain concentration gradients Any polar molecule will dissolve in water	70-95% of cytoplasm is water
cohesion	Water molecules stick to each other, creating surface tension	Transport of water in xylem relies in cohesion of water
habitat	Water is a common habitat Water contains oxygen that is essential to life	Fish and marine creatures
metabolic	Water is a reactant in important chemical processes	Used in hydrolysis and photosynthesis
freezing	ice is less dense than water and foats	organism to survive the water beneath

Practice questions

1. high heat capacity

2. high surface tension and cohesion

3. universal solvent