Guest Author - Sarah Meadmore

This glossary is here to help you if there is a word that you don’t understand. I will add words in here as I add articles. When I feel it is important to know the meaning of a word - but adding an explanation will either make an article too long/boring or would require taking a tangent - I will make the word in the article bold, and you will know that I have added an explanation here in the glossary.


Cilia Hair-like growths on many eukaryotic cells. Cilia beat in a bull-whip movement. This either propels free-living cells or it forces movement of fluid over the surface of static cells.

Cytoplasm All the living part of a cell, within the cell membrane, but excluding the nucleus.

Cytosol The fluid within the cell membrane that is outside the organelles.

Flagella Long whip-like or feathery “hairs” much like cilia.

mRNA Messenger RNA

Nucleoplasm The substance within the nuclear membrane, but excluding the nucleolus and chromatin.

Phospholipid Bilayer Phospholipids are derived from fatty acids. Within the molecule, a phosphorylated alcohol “head” replaces one of the fatty acids. The remaining fatty acid portion makes the “tail” and the backbone of the molecule, which joins the head and tail, is either glycerol or sphingosine-derived.

Phosphoplipids are amphipathic, which means part of the molecule is hydrophobic (water-hating) and part of the molecule is hydrophilic (water-loving). In phospholipids the alcohol head is hydrophilic and the fatty acid tail is hydrophobic.

As a result of the amphipathic nature of phospholipids, chains of them naturally double to form bilayers. The hydrophobic tails are next to each other at the center of the bilayer, and the hydrophilic heads are on the outside of the bilayer. The phospholipid bilayer is the basis of all biological membranes.

Protoplasm Everything found within a living cell.

rRNA Ribosomal RNA.