A3.2 Classification Of Cladistics (HL)

Question 1

Why is classification of organisms needed? (4 reasons)

Answer 1

Immense diversity of organisms:

1. Better organise and understand
2. Better communication, common language
3. More efficient
4. Further research, pattern recognition

Question 2

What are the main taxa of Linnaeus’ hierarchy of taxonomy?

Answer 2

Hierarchy
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

[Domain King Philip Come Over For Great Spaghetti]

Question 3

What are some difficulties to classifying organisms according to the traditional hierarchy of taxa?

Answer 3

Does not reflect the complex evolution of organisms so does not always correspond to patterns of divergence.

A fixed ranking of taxa is arbitrary as it does not reflect gradation of organisms.

—>cladistics offer alternative approach to science using unranked clades**—>example of paradigm shift that sometimes occurs in scientific theories

Question 4

What are 4 advantages of classification corresponding to evolutionary relationships?

Answer 4

1. Reflects evolutionary relationships so all members of taxonomic groups have evolved form common ancestor
2. Reflects process of evolution, e.g. speciation
3. Make predictions about characteristics or organisms as shared between the same clade
4. Helps understand the diversity of life on earth

Question 5

What is a clade?

Answer 5

A group of species with a single common ancestor and a set of common traits or characteristics.

Question 6

How are species organised in clades?

Answer 6

Based on shared base sequences of genes, sequences of proteins, and shared traits. Morphological traits also used to assign clades.

Question 7

What is the molecular clock and when is it used?

Answer 7

Genetic and molecular differences between organisms slowly increase over time due to evolution.

Molecular clock is a technique that uses mutation rate of biomolecules to deduce the time since two species shared a common ancestor.

Question 8

Why can molecular clocks only provide estimates?

Answer 8

Mutation rates depend on:

Population size
Selection pressures
Genome size
Degree of randomness

Question 9

What are cladograms?

Answer 9

A visual representation of evolutionary relationships, common ancestors between groups of related organisms into clades.

Question 10

What is the root of a cladogram?

Answer 10

The most ancient common ancestor

Question 11

What is the node of a cladogram?

Answer 11

Hypothetical common ancestor

Question 12

What is the terminal branch of a cladogram?

Answer 12

Extant species (still in existence) at the ends of the branches of a cladogram

Question 13

What had the addition of molecular data in the creation of cladograms led to?

Answer 13

Reclassification of some organisms:

E.g. figwort family included more than 275 generations of with around 5000 species, based on shared morphological features. However, when scientists carries out genetic analysis, it was found that many species within this group were very different and should be re-classified. Now figwort family has 200 species and is 36th largest family of all angiosperms.

Question 14

Why was it proposed in 1977 to reclassify an extra taxonomic level above kingdoms that was proposed?

Answer 14

Finding that (ribosomal) rRNA sequences form 3 distinct groups.

This discovery fundamentally altered categorisation of creatures and that molecular traits accurately represent evolutionary characteristics.