- 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
Properties of water molecules
The solvent properties of water
- 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
High heat capacity
- 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.
High heat of evaporation
- 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
High heat of fusion
- 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.
Density and freezing properties
-
- 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.
High surface tension and cohesion
- 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 as a reagent
- 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.
Functions of water
- Turgidity of exoskeletons
- Preventing friction of joints /lubricant
- Fertilization of swimming gametes
- Component of blood
- Raw material for photosynthesis
- Part of fluid produced e.g. mucus and tears to clean the body
| 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
Explain the functions of water to living organisms.
Describe the biological significance of the following properties of water:
1. high heat capacity
2. high surface tension and cohesion
3. universal solvent