Water 🟡 Flashcards
Why is water important?
Water is a major component in cells
Water is of great biological importance. It is the medium in which all metabolic reactions take place in cells.
Between 70% to 95% of the mass of a cell is water
As 71% of the Earth’s surface is covered in water it is a major habitat for organisms
What is water composed of?
Water is composed of atoms of hydrogen and oxygen. One atom of oxygen combines with two atoms of hydrogen by sharing electrons (covalent bonding)
Why is water considered dipolar?
Although water as a whole is electrically neutral the sharing of the electrons is uneven between the oxygen and hydrogen atoms
The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms(δ+), this also results in the asymmetrical shape
This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole.
When a molecule has one end that is negatively charged and one end that is positively charged it is also a polar molecule
Water is a polar molecule
What are hydrogen bonds (+diagram of water)?
Hydrogen bonds form between water molecules as a result of the polarity of water hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules
Different poles attract, this attractive force between these opposite charges is called a hydrogen bond.
Why are hydrogen bonds important in water?
Although each bond is fairly weak, (about one-tenth as strong as a covalent bond) together they form important forces that cause the water molecules to stick together, giving water it’s unusual properties.
For example, water is very cohesive. This means that it flows well and makes it great at transporting substances.
Why is water so important in living organisms?
-used in metabolism
-used as a solvent
-used for cooling
-provides support
-its transparent (organisms can live in water and still get the energy they need from the sunlight).
Why is water a good solvent?
As water is a polar molecule many ions (e.g. sodium chloride) and covalently bonded polar substances (e.g. glucose) will dissolve in it
This allows chemical reactions to occur within cells (as the dissolved solutes are more chemically reactive when they are free to move about)
Metabolites can be transported efficiently (except non-polar molecules which are hydrophobic)
Which substances does water readily dissolve?
-gases such as oxygen and carbon dioxide
-wastes such as ammonia and urea
-Inorganic ions and small hydrophilic molecules such as amino acids, monosaccharides and ATP.
-enzymes, whose reactions take place in solution.
What is specific heat capacity?
The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of that substance by 1°C.
What is the specific heat capacity of water?
Water’s specific heat capacity is 4200 J/kg°C
Why does water have a high specific heat capacity?
Water has a high specific heat capacity of 4200 J / Kg oC meaning a relatively large amount of energy is required to raise its temperature
The high specific heat capacity is due to the many hydrogen bonds present in water. It takes a lot of thermal energy to break these bonds and a lot of energy to build them, thus the temperature of water does not fluctuate greatly
Why is it an advantage for living organisms that water acts as a buffering agent?
The advantage for living organisms is that it:
-Provides suitable habitats
-Is able to maintain a constant temperature as water is able to absorb a lot of heat without big temperature fluctuations
-This is vital in maintaining temperatures that are optimal for enzyme activity
-Water in blood plasma is also vital in transferring heat around the body, helping to maintain a fairly constant temperature
-As blood passes through more active (‘warmer’) regions of the body, heat energy is absorbed but the temperature remains fairly constant
-Water in tissue fluid also plays an important regulatory role in maintaining a constant body temperature
How is water’s latent heat of vaporisation an advantage for living organisms?
In order to change state (from liquid to gas) a large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate
This is an advantage for living organisms as only a little water is required to evaporate for the organism to lose a great amount of heat
This provides a cooling effect for living organisms, for example the transpiration from leaves or evaporation of water in sweat on the skin
How is there cohesion in water and what is the benefit of this?
Hydrogen bonds between water molecules allows for strong cohesion between water molecules
Water has large cohesive forces which allows columns of water to move through the xylem of plants and through blood vessels in animals
This also enables surface tension where a body of water meets the air, these hydrogen bonds occur between the top layer of water molecules to create a sort of film on the body of water (this is what allows insects such as pond skaters to float)
What is cohesion?
The tendency off molecules to stick together
