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Biology Dictionary for GCSE Biology and A Level Biology




TAQ polymerase: DNA polymerase enzyme from the bacterium Thermus aquaticus (hence the TAQ); a thermostable enzyme widely used in PCR, optimum temp about 72 degrees C


Taxonomy: The very exciting science of classification.

Test cross: Cross with a homozygous recessive (aa) to find out if an individual is AA or Aa


Thermostable enzyme: Active across a range of temperatures, not denatured at the usual 50/60oC. From thermophilic (heat loving) bacteria in hot springs e.g. TAQ polymerase. 


Tissue Fluid: Fluid which surrounds all cells and is similar to plasma without the plasma proteins. Cells obtain nutrients from the tissue fluid and deposit cellular waste (urea and CO2).


Tracheids: the main conducting cell of the xylem, characterized by an elongated shape and lignified secondary cell wall. See also vessel element. 


Transcription: First step in protein synthesis, basically ‘gene copying’. Involves transferring the genetic code from DNA to mRNA. Happens in the nucleus.


Transfer RNA [tRNA]: a molecule that brings specific amino acids to ribosomes. Clover leaf shaped, has an anticodon on one end & carries an amino acid at the other.


Transgenic organism: An organisms whose DNA has been altered, such as the bacteria with human genes inserted


Translation: Second step in protein synthesis. Using the code on the mRNA to build a protein. Takes place on ribosomes


Translocation: The movement of the products of photosynthesis (sucrose, amino acids etc) throughout a plant in phloem tissue. The driving force behind translocation is called the mass flow hypothesis, or Munch’s theorem. 


Transpiration stream: the passage of water through the plant from roots to leaves and out into the atmosphere.


Transpiration: Loss of water vapour from the plant’s upper surfaces, mainly leaves.


True breeding: Homozygous individuals which always produce offspring on the same type

As I write the biology dictionary and make the videos to help you learn the definitions by listening in addition to reading them, you'll get the added benefit of hearing and learning the correct pronunciation of biological terminology - but there's more! I'm also making some interactive revision flashcards too! So you can revisit the key words when revising and really embed those a level biology definitions in your head! - The flashcards will be like this (See image below and click to download).

A-Level Biology is a whole lot easier when you know the definitions of commonly used words. This biology dictionary is here to help you learn those A level biology definitions. Remember, a good command of biological terminology (at GCSE but especially at A level) can mean the difference between a poor grade and an excellent one! Since of course you get marks awarded for using the correct biological definitions in the right context when answering exam questions and writing up lab work, coursework and assignments.

The biology dictionary is mainly aimed at a level biology students since at a level, the amount of new technical language expect is quite a lot!


Make learning biology definitions a regular part of your studies and keep checking in as more keywords and gcse biology definitions and a level biology definitions are added.

Thanks for using
Helping you to Learn, Revise, Practice and Succeed in your GCSE and A-Level Biology.

*Note this A-Level biology Dictionary / Glossary of key terms is not comprehensive and will be updated and added to regularly, so keep checking in and make learning and revising a level biology definitions a consistent part of your biology studies

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