AS Biology Unit 1 Edexcel - Key words

These are some useful key words that you may have to define. These are based on past exam questions and textbooks. I obviously can't include all the key words because there are so many but I hope these help!

Cohesion: hydrogen bonds occurring between water molecules

Adehesion: hydrogen bonds occur between water and other molecules, e.g. the xylem vessel

Diffusion: the movement of single molecules from a high concentration gradient to a low concentration gradient. (NB - no energy from ATP required)

Osmosis: the net diffusion of water molecules through a semi-permeable membrane from a high concentration to a low concentration. 

Active transport: the movement of molecules across a cell membrane from low concentration to high concentration, assisted by enzymes and requiring energy.

Carrier proteins: these move large molecules into or out of a cell, down a concentration gradient.

Channel proteins: these form pores in the membrane for charged particles to diffuse through, down a concentration gradient. 

Glycosidic bond: the bond that is made between two glucose molecules, formed in a condensation reaction.

Triglyceride: a kind of lipid with one molecule of glycerol and 3 fatty acids.

Primary structure (of a protein): the sequence of amino acids in the polypeptide chain. Held together by peptide bonds.

Secondary structure (of a protein): H-bonds form between amino acids in the chain, making the structure coil into an alpha…