6.6. Classification

Question 1

Traditionally, how were organisms classified?

Answer 1

Traditionally, organisms were classified according to similarities and differences in their observable characteristics, i.e. things you can see (like how many legs something has).

Question 2

What did Carl Linnaeus propose?

Answer 2

A new type of classification to do with characteristics and bone structure (linnaean system). These were used to classify organisms in the five kingdom classification system. In this system, living things are first divided into five group called kingdoms (e.g. the plant kingdom, the animal kingdom). The kingdoms are then subdivided into smaller and smaller groups that have common features - phylum, class, order, family, genus, species.

Question 3

How did developments in biology lead to improvements in classification?

Answer 3

• Scientists can use DNA sequencing to compare particular genes or entire genomes of different organisms, using only small samples of tissue. They look for similarities, e.g. if the different species share the same number of genes, or a similar number of genetic variants for a particular gene. If different organisms share the same number of genes or genetic variants for a gene, then they are likely to have inherited these similarities from a common ancestor. The more similar the DNA sequences between species are, the more closely related they are and the more likely it is that they’ll be classified in the same group. E.g. the base sequence for human and chimpanzee DNA is about 94% the same, so humans and chimpanzees are closely related to each other.
• Scientists can also use DNA sequences to estimate how long ago two species separated from each other. This is because genetic variants arise by mutations and scientists have estimates for how frequently these mutations can happen. By finding the number of different genetic variants between two species, scientists can estimate when speciation occurred.

Question 4

Evolutionary trees

Answer 4

In an evolutionary tree, species are connected to each other by lines via their most recent common ancestor. This helps to show their relationship with each other. The more closely related two species are to each other, the fewer the number of steps between them on the tree.

Question 5

What is a mnemonic to remember the Linnaean system?

Answer 5

Dear - Domain
Kate - Kingdom
Please - Phylum
Come - Class
Over - Order
For - Family
Great - Genus
Sex - Species

Question 6

What did Carl Woese propose?

Answer 6

That some species were less related than we thought. He introduced 3 new categories called ‘domains’ that were placed above kingdoms. The domains were eukaryota, bacteria, and archaea.

Question 7

What is the advantage of using a binomial system to name species?

Answer 7

• Each species has a unique name
• It lets scientists discuss individual species

Question 8

Which 18th Century scientist developed the traditional classification system for classifying living things?

Answer 8

Carl Linnaeus

Question 9

Which international system is commonly used to classify organisms?

Answer 9

The Linnaean classification system

Question 10

What is the binomial name for humans?

Answer 10

Homo sapiens

Question 11

How do we write the binomial name of a species? (2)

Answer 11

• All in italics
• All lower case except the first letter of the genus

Question 12

Which 20th century scientist used microscopes and modern technology to develop the three domain system to classify organisms?

Answer 12

Carl Woese