2.4 Water Flashcards
Why is water a polar molecule?
- O is more electronegative than H —> so
attracts the electrons in the
covalent bond more strongly. - Forms O 𝛿- (slight negative charge) &
H 𝛿+ (slight positive charge).
State 5 biologically important properties
of water
- An important solvent in reactions
● Metabolite
● High specific heat capacity; buffers temperature
● High latent heat of vapourisation; provides a cooling effect with loss of water through evaporation
● Strong cohesion between water molecules; supports water columns and provides surface tension
How much of your body is made up of water
60-70%
Why does water have a high specific heat capacity
Latent heat is the heat energy that’s needed to change a substance from one state to another, e.g. from a liquid to a gas.
Water evaporates (vaporises) when the hydrogen bonds holding water molecules together are broken. This allows the water molecules on the surface of the water to escape into the air as a gas. It takes a lot of energy (heat) to break the hydrogen bonds between water molecules, so a lot of energy is used up when water evaporates. This means water has a high latent heat of vaporisation — lots of heat is used to change it from a liquid to a gas.
This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water. When water evaporates it carries away heat energy from a surface, which cools the surface and helps to lower the temperature (e.g. when humans sweat to cool down).
What is the effect of the high specific latent heat of water
Water acts as a buffer to any sudden temperature changes
Why is sweat an effective means of reducing body temperature
Because body heat is used to evaporate the water that heat energy needs to break the H bonds in water
How is water important in metabolism
Many metabolic reactions involve a condensation or hydrolysis reaction.
A hydrolysis reaction requires a molecule of water to break a bond. A
condensation reaction releases a molecule of water as a new bond is formed.
Energy from ATP is released through a hydrolysis reaction.
A metabolic reaction is a chemical reaction that happens in a living organism to keep the organism alive. A metabolite is a substance involved in a metabolic reaction.
What is the structure of Water
- Dipolar molecule
- Unevenly distributed charges -oxygen is slightly negative hydrigen is slightly positive-
How is water a metabolite
What are the reactions water is used in
Water is involved in many reactions such as:
* Photosynthesis
* Hydrolysis
* Condensation reactions
Due to this plasma is made up of approximaiately 90% water
What is a solvent
A solvent is something that many substances dissolve in
Why is water a good solvent? (3)
- It is a dipolar molecule and polar molecules dissolve readily in water
- The slight positive charge on hydrogen atoms will attract any negative ions solutes and the slight negative charge on oxygen atoms of water will attract any positive ions in solutes
- Many essential substances are polar which allow them to dissolve in water —> enables them to be transported easily around animals and plants, either in blood or xylem to cells they are needed in inside of the organism
Explain how water has a High specific heat capacity and why is this important
Buffers changes in temperature.
This is the energy needed to raise the temperature of 1kg of a substance by 1 °C.
Hydrogen bonds give water a high specific heat capacity. When water is heated, a lot of the heat energy is used to break the hydrogen bonds between the water molecules. This means there is less heat energy available to actually increase the temperature of the water. So water has a high specific heat capacity as it takes a lot of energy to heat it up.
This is useful for living organisms because it means that water doesn’t experience rapid temperature changes. This makes water a good habitat because the temperature under water is likely to be more stable than on land. The water inside organisms also remains at a fairly stable temperature which helps them to maintain a constant internal body temperature.
Enzyme activity is affected by temperature. Some important biological processes need enzymes to work (e.g. digestion and respiration). These may not work properly if the organism’s temperature is not kept fairly stable.
What is a benefit of large proportions of organisms being made up of mainly water
- The internal temp of plants and animals remain relatively constant despite the outside temperature.
- This is important so enzymes do not denature or reduce in activity with temperature fluctuations as it provides a stable environment
How does water have a high latent heat of vapourisation?
- A lot of energy is required to convert water in its liquid state to a gaseous state due to hydrogen bonds needing to be broken and provide water with a significant cooling effect.
What does Cohesion mean
Term used to describe water mooecules sticking together by hydrogen bonds
