A3.2 Classification and Cladistics (HL Only)

Today, we'll start by discussing taxonomy, which is the system used to classify all living organisms. Can anyone tell me what the highest categories in biological classification are?

Exactly! We have three domains: Bacteria, Archaea, and Eukarya. Can anyone explain what distinguishes Archaea from Bacteria?

Correct! Instead, their membranes contain ether-linked lipids. Now, let’s remember these three domains with the acronym 'BAD' – Bacteria, Archaea, Eukarya. Let’s move on—what’s the significance of the kingdoms in classification?

Exactly! For instance, the traditional five-kingdom model includes Monera, Protista, Fungi, Animalia, and Plantae. But it's often simplified in modern systems to focus mainly on the three domains. Great! Let’s recap key points: what are the three domains?

Now, let’s discuss binomial nomenclature. Why do we need a specific naming system for species?

Exactly! This system gives each species a unique two-part name, consisting of the genus name and species epithet. Can you remember how they are formatted?

Perfect! For example, how would we write the scientific name for humans?

Great! Remember, you can use 'WHEELS' to recall: 'Write' (format), 'Use' (two-part), 'Genus' (capitalized), 'Lowercase' for species, 'Italicized', and 'Species' (unique). Let’s sum up the ways we name organisms: why is it important?

History of taxonomy has evolved into cladistics, which helps us infer evolutionary relationships. What does cladistics focus on?

Correct! These shared derived characters help us define clades, which are groups of organisms that share a common ancestor. What term do we use for a trait that is present in all descendants of an ancestor?

Spot on! Remember: Synapomorphy = Shared Derived Characters. And what about traits that are shared from an ancestor but may not be unique to a particular group?

Yes! Great job connecting those terms. Now, let's wrap up this session by highlighting how shared derived characters help classify organisms?

Now that we understand what cladistics is, let’s discuss how we construct a cladogram. What’s the first step?

Yes! Then what's next?

Exactly! Ensuring those characters are homologous is crucial. After that we create a data matrix—what does that involve?

That’s right! Then we can use methods like parsimony. What does parsimony mean?

Exactly! This ensures we are not making assumptions about evolution's path. Lastly, what is an outgroup used for in this context?

Great recap! Let’s summarize the key steps involved in cladogram construction.

To understand modern classifications, molecular data play a big role. What types of data do we compare?

Exactly! Molecular comparisons provide characters for constructing cladograms. Do molecular clocks help us with timing?

Absolutely! This is significant for tracking how species have evolved. Lastly, which genes are particularly useful for these comparisons?

That's correct! Thus, they are great for deeper phylogenetic studies. Now, let's summarize the importance of molecular data in our classification efforts.