Pain caused by innocuous touch

The four parts of a cell

  1. Nucleus – this is where the chromosomes are, containing the genes. It is surrounded by cytoplasm and contained within an inner and outer membrane
  2. Nucleoplasm – the stuff inside the nucleus
  3. Cytoplasm – the part of the cell outside the nucleus. This is where metabolic reactions happen. The fluid part of the cytoplasm is called cytosol, and within the cytosol and nucleoplasm are organelles which each have a function determined by their structure
  4. Plasma membrane.


The more hydrogen atoms a solution has, the more acidic it is; the more hydroxyl it has, indicates how alkaline the solution is. If the solution has an equal number of hydrogen and hydroxyl, it is neutral.


Isomers are compounds having a different molecular structure to substances with the same molecular formula.


A water molecule interacts with another molecule to break that molecule’s bonds. This is then arranged into different bonds. Smaller molecules result.


This is the opposite to hydrolysis; small molecules are joined to form larger molecules and a few water molecules are eliminated.

Oxidation-Reduction reactions

Oxidation occurs when an atom or molecule loses electrons or hydrogen atoms producing a positive charge.

Reduction occurs when an atom or molecule gains an electron or hydrogen atom producing a negative charge. They occur together.

Ionic bonding

This occurs when an atom develops an electrical charge and is attracted to an atom with an opposite charge.

Replacement reactions

When atoms, ions or molecules change places with other atoms, ions or molecules. The breaking and forming of bonds results in new substances.

Decomposition reactions

This is the opposite of a combination reaction, it occurs when chemical bonds are broken to form two or more products.

Combination reaction

When two or more atoms, ions or molecules combine to form another more complex substance.

Hydrogen bonding

This is where a hydrogen electron is drawn to another atom, leaving a proton behind which leaves the hydrogen atom with a positive charge. The proton is then attracted to negatively charged atoms of oxygen or nitrogen in nearby molecules.

Covalent bonding

Atoms share pairs of electrons (rather than donating as in ionic bonding). A single pair bonding atoms is a single bond, and obviously, a double bond is formed when a double pair is involved.

A nonpolar covalent bond involves the even distribution of electrons; when the bond is polar, the electrons are shared unevenly between two atoms which creates a slight charge at the ends of the molecule. The charge is positive where the electrons spend the least time and negative where they spend the most time.


An atom with an electrical charge through either losing or gaining electrons. A positive ion is known as a ‘cation’ and a negative ion is known as an ‘anion’.


An isotope is an element in another form – it has the required nnumber of protons and electrons, but it has a different number of neutrons, which means its atomic weight differs from the regular form of the element.

Energy-level shells

There are seven of these known to exist, they are formed concentrically around the nucleus of an atom and contain electrons. There are never more than two electrons in the shell nearest the nucleus. More electrons are in the outer shells. Only the electrons in the outer shell can participate in chemical reactions. The shell is stable when it has the maximum number of electrons possible. If the shell is unstable, it will gain, lose, or share electorns with other atoms.

Bits and bobs in atoms

  • Protons – positive charge
  • Neutrons – no charge
  • Electrons – negative charge

Atomic Weight

The weight of an atom compared with an atom of carbon. The atomic weight is equal to the number of protons plus neutrons.

Atomic Number

This is the number of protons in the nucleus of a particular atom.

Carbohydrates used in the Body

Name Type Description
Cellulose Polysaccharide Undigestible by the body, but provides bulk for moving food through the intestines
Deoxyribose Monosaccharide Constituent of DNA
Fructose Monosaccharide The sweetest sugar, found in fruits and used in cellular metabolism of carbohydrates
Galactose Monosaccharide Found in brain and nerve tissue
Glucose(dextrose) Monosaccharide Main energy source for the body. Breakdown produces ATP, used by cells. Brain requires a constant supply
Glycogen Polysaccharide Main form of carbohydrate storage, stored in the liver and muscles until required, when converted to glucose
Heparin Polysaccharide Prevents excessive blood clotting
Lactose Disaccharide Milk sugar, aids the absorption of calcium
Ribose Monosaccharide Constituent of RNA
Starch Polysaccharide Main food carbohydrate
Sucrose (saccharose) Disaccharide Cane or beet sugar. Yields fructose and glucose on hydrolysis

Adapted from Human Anatomy and Physiology by R, Carola et al, with thanks.