Edexcel Biology B is very scarce when it comes to finding information on it online. I've taken it upon my self to publish my own notes to help fellow students that have a hard time understanding the subject. The information in the text book is very large and can be hard to narrow down to a particu...
i Know that the classification system consists of a hierarchy of domain, kingdom, phylum,
class, order, family, genus and species.
Classification is the process by which we name and organise organisms into specific groups
based on their characteristics. We classify them using 8 levels of grouping which are domain
,kingdom,phylum class order family genus and species
The three different domains are Archaea, Bacteria and Eukaryota.
ii Understand the limitations of the definition of a species as a group of organisms with
similar characteristics that interbreed to produce fertile offspring.
Species are often defined as a group of organisms with similar characteristics which
interbreed to produce fertile offspring. However there are many limitation of this definition
which include:
● Plants of different but closely related species frequently interbreed to produce a
fertile hybrid. So its not known if the hybrid is a different species
● Many species have not been observed mating so finding the evidence to say an
organism is part of the same species could be difficult especially if a new species is
found which is similar to an existing species.
● Doesn’t account for asexual reproduction
, iii Understand why it is often difficult to assign organisms to any one species or to identify
new species
● Organisms of the same species can change their morphology due to external
conditions
● Scientist do not know where to classify hybrids as new species or not
iv Understand how gel electrophoresis can be used to distinguish between species and
determine evolutionary relationships.
We use a process called gel electrophoresis to distinguish between species. This allows us
to compare amino acid sequences of similar proteins of species,which we can then use to
classify them or trace their evolutionary pathway.
This is a variation of chromatography which can be used to separate DNA and RNA
fragments,proteins or amino acids according to their size and charge.
E.g DNA:
● DNA molecules are cut into small fragments by an enzyme called restriction
endonuclease which cut the fragments at specific sites
● The fragments are then added to a gel which contains a dye. The dye binds to the
fragments (this will later fluoresce under UV Light)
● An electric current is passed through in which anad DNA fragments move towards
anode due to negative phosphate group
● Fragments move at different rate accordion to their size charge
● The plate is then placed under U.V light where the DNA fluoresces and different band
patterns can be identified
● The resulting pattern of bands represent amino acids which and is unique to every
individual
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