The cell is the smallest unit of life.All living cells contain the following elements:

• plasma membranes - a barrier that controls which substances can pass in and out of the cell, and allows the cell to maintain order
•  cytoplasm - the watery jelly in which all the cells reactions occur
• DNA - genetic material that determines which proteins are made and, through enzymes, controls the cells chemical reactions
• ribosomes  - organelles that are the site of protein synthesis
• Endoplasmic reticulum - a series of membranes forming a transport system within the cell.  Steroid are also synthesised by the ER. Ribosomes may be attached to the ER - this is Rough ER.  If no ribosomes are attached it is Smooth ER.
• Golgi apparatus - modified ER that envelopes the products of synthesis in a membrane vesicle to be released by the cell.  (eg hormones)