AS/A-level Biology - Classification and Evolution (1)

• A system that uses the genus name and the species name to avoid confusion when naming organisms.

Reasons for the binomial naming system:

• The same organism may have a completely different common name in different parts of a country.
• Different common names are used in different countries.
• Translation of languages and dialects may give different names.
• The same common name may be used for a different species in a different part of the world.

• The process of placing living things into groups.

Reasons for classification:

• For convenience
• To make the study of living things easier
• For easier identification
• To show the relationships between species

• As you descend the taxonomic ranks from Domain to Species, it becomes harder to distinguish and separate closely related organisms from each other and to place them accurately.

• Species – a group of organisms that can freely interbreed to produce fertile offspring.
• This definition does not work for organisms that reproduce asexually and is very hard to apply to organisms known only from fossil records and the like.
• Phylogenetic definition of species – a group of individual organisms that are very similar in appearance, anatomy, physiology, biochemistry and genetics.

Early classification systems by Linnaeus and Aristotle were based solely on appearance and features which limited the classification to observable features only.

When it comes to AS/A-level Biology, do you know what evidences are used in classification?

(1) Biological Molecules

• Some biological molecules, such as those for DNA replication and respiration are essential for life and therefore all living things have a variant that can be compared to show how closely related they are.
• If we assume that the earliest living common ancestors to living things had the same version of these molecules then any changes are a direct result of evolution.

(i) Cytochrome C

• The protein cytochrome C is essential in respiration but is not identical in all species due to evolution.
• The sequences of amino acids in the protein can help draw conclusions about how closely related they are.
• If the sequences are the same then the two species must be closely related and if they are different they are not so closely related.
• The more differences found between the sequences, the less closely related the two species.

(ii) RNA Polymerase

• RNA Polymerase is also used as an indicator of evolution because of its essential role in protein synthesis

(2) DNA

(i) Genome Sequencing

• Advances in genome sequencing have meant that the entire base sequence of an organism’s DNA can be determined.
• The DNA sequence of one organism can then be compared to the DNA sequence of another organism. This will show you how closely related they are to each other.

(ii) Comparing amino acid sequences

• Proteins are made of amino acids.
• The sequence of amino acids in a protein is coded for by a base sequence in the DNA.
• Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.

(3) Immunological Comparisons

• Similar proteins will bind to the same antibodies.
• If antibodies to a human version of a protein were added to isolated samples from other species, then any protein similar to the human version will be recognised and bind to the antibody.

• Classification for convenience, for example, in plant identification books, sorting by flower colour.

• Biological classification involves a detailed study of the individuals in a species, it uses many characteristics, reflects evolutionary relationships and may change with advancing knowledge.

• The study of the evolutionary relationships between organisms.

• It is where another species has evolved from the original common ancestor and the two species get progressively less similar.

• It is where two species, who may share the same environment and therefore the same factors that affect survival, evolve similar characteristics.

• The term is used to explain how features of the environment apply a selective force on the reproduction of individuals in a population.
• Charles Darwin did not invent the theory of evolution but he proposed natural selection as a mechanism towards the theory.
• It was controversial at the time as it countered the popular religious beliefs.
• Darwin developed his ideas from the expedition he sailed with the HMS Beagle around the Galapagos Islands.
• Wallace was another naturalist who came to the same conclusion as Darwin.
• Offspring generally appear similar to their parents.
• No two individuals are identical.
• Organisms have the ability to produce large numbers of offspring.
• Populations in nature tend to remain fairly stable in size.
• There is a struggle to survive.
• Better adapted individuals survive and pass on their characteristics.
• Over time a number of changes may give rise to a new species.

• In the past, the world was inhabited by species that were different from those present today.
• Old species have died out and new species have arisen.
• The new species that have appeared are often similar to the older ones found in the same place.
• One of the most complete fossil records is that of the horse.

In part 2, you will know more about variation.

 CLICK HERE TO LEARN MORE ABOUT OUR AS/A-LEVEL BIOLOGY COURSES

Drafted by Bonnie (Biology)