14 WJEC Biology AS Level - Marianne Izen - 2nd Edition Flashcards
Dipole (Key Term)
A polar molecule, with a positive and a negative charge, separated by a very small distance.
Hydrogen bond (Key Term)
The weak attractive force between the partial positive charge of a hydrogen atom of one molecule and the partial negative charge on another atom, usually oxygen or nitrogen.
Condensation reaction (Key Term)
Chemical process in which two molecules combine to form a more complex molecule, with the elimination of a molecule of water.
Hydrolysis (Key Term)
The breaking down of large molecules into smaller molecules by the addition of a molecule of water.
Latent heat of vaporisation (Key Term)
The energy required to convert 1 g of a liquid into vapour at the same temperature.
Specific heat capacity (Key Term)
The energy required to raise the temperature of 1 g of a substance through 1 degree centigrade.
Draw water molecules showing hydrogen bonding.
How do water molecules arrange themselves in solution?
Water molecules arrange themselves around ions in solution
Why is water important for living beings?
Water is a medium for metabolic reactions.
It is an important constituent of cells, being 65-95% of the mass of many plants and animals.
About 70% of each individual human is water.
Describe the dipole nature of water and its importance
The water molecule is a dipole, which means it has a positively charged end (hydrogen) and a negatively charged end (oxygen), but no overall charge.
A molecule with separated charges is ‘polar’.
The charges are very small and they are written as a+ and a, to distinguish them from full charges, written as + and -.
Hydrogen bonds can form between the a+ on a hydrogen atom of one molecule and the on an oxygen atom of another molecule.
Hydrogen bonds are weak, but the very large number of them present in water makes the molecules difficult to separate and gives water a wide range of physical properties vital to life.
Water’s properties make it essential for life, as we understand it.
Describe the property of water: As a solvent
Living organisms obtain their key elements from aqueous solution.
Water is an excellent solvent.
Because water molecules are dipoles, they attract charged particles, such as ions, and other polar molecules, such as glucose.
These then dissolve in water, so chemical reactions take place in solution.
Water acts a transport medium:
in animals, plasma transports dissolved substances
in plants, water transports minerals in the xylem, and sucrose and amino acids in the phloem.
Non-polar molecules, such as lipids, do not dissolve in water.
Describe the property of water: water is a metabolite
Water is used in many biochemical reactions as a reactant, e.g. with carbon dioxide to produce glucose in photosynthesis.
Many reactions in the body involve hydrolysis, where water splits a molecule, e.g. maltose + water→glucose + glucose.
In condensation reactions, water is a product, e.g. glucose + fructose->sucrose + water
Describe the property of water: high specific heat capacity
This means a large amount of heat energy is needed to raise its temperature.
This is because the hydrogen bonds between water molecules restrict their movement, resisting an increase in kinetic energy and therefore resisting an increase in temperature.
This prevents large fluctuations in water temperature, which is important in keeping aquatic habitats stable, so that organisms do not have to adapt to extremes of temperature.
It also allows enzymes within cells to work efficiently.
Describe the property of water: high latent heat of vapourisation
This means a lot of heat energy is needed to change it from a liquid to a vapour.
This is important, for example, in temperature control, where heat is used to vaporise water from sweat on the skin or from a leaf’s surface.
As the water evaporates, the body cools.
What is the importance of high latent heat of vaporisation of water for aquatic organisms?
The high latent heat of vaporisation of water provides a benefit for aquatic organisms.
So much energy would be needed to vaporise all the water that aquatic habitats rarely evaporate away.
