Leaving Certificate Biology: Classification and Taxonomy

Comprehensive review flashcards covering biological classification, history of taxonomy, binomial nomenclature, five-kingdom and three-domain models, phylogenetic trees, and domain characteristics.

How is biodiversity defined?

Biodiversity describes the variety of life on Earth.

What is the biological definition of a species?

A group of living things that can reproduce and produce offspring, which can go on to reproduce themselves.

What is taxonomy?

The science of placing living things into ordered groups (also known as classification).

What early hierarchical classification concept, developed by Aristotle in the $4\text{th}$ century BCE, arranged matter from 'lower order' (such as rocks) to 'higher order' (such as humans)?

Scala naturae

What three criteria did Aristotle use to distinguish between plants and animals?

1. Their ability to move
2. Whether or not they had blood
3. Whether they lived in water or on land

What was a major limitation of Aristotle's classification system, which persisted for nearly $2{,}000$ years?

Not all organisms were included, such as micro-organisms.

What significant contribution did Gaspard Bauhin make to classification in the $1600\text{s}$?

He was the first to use a two-name system (binomial nomenclature) for naming organisms, giving each a Latin name composed of a genus and a species.

What book did Carl Linnaeus publish in $1735$, and what three kingdoms did he originally propose?

He published Systema Naturae, proposing three kingdoms: Animalia (animals), Plantae (plants), and Minerae (minerals).

What hierarchy of smaller groups did Carl Linnaeus introduce within each kingdom?

Kingdoms contained smaller groups called classes, followed by orders, genus, and finally species.

What did Charles Darwin propose in the $1800\text{s}$ regarding populations and new species?

He proposed that populations contain variation (differences) which can give advantages in their environment and result in new species forming from older ones over a long period of time.

How did Gregor Mendel's experiments on pea plants contribute to modern classification?

He showed that organisms pass on genetic information (genome) to the next generation, establishing that closely related species share similar genetic makeup and sequences.

Why was the kingdom Protista introduced into classification?

To classify all single-celled organisms.

What discovery led to the creation of the kingdom Prokaryotae (Monera)?

The discovery that some single-celled organisms lacked a nucleus (prokaryotes), unlike those with a nucleus (eukaryotes).

Why were ancient bacteria (archaea) reclassified out of the kingdom Prokaryotae?

They possessed different structures, genes, and biochemistry compared to true bacteria.

What are the three domains of life in the current classification system?

Bacteria, Archaea, and Eukaryota.

Which kingdoms belong to each of the three domains in the current six-kingdom model?

• Domain Bacteria: Kingdom Bacteria (Eubacteria)
• Domain Archaea: Kingdom Archaebacteria
• Domain Eukaryota: Kingdoms Protista, Fungi, Plantae, and Animalia

What is the complete order of taxonomic ranks from broadest to most specific?

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

What is the key difference between phenetic (trait-based) classification and phylogenetic classification?

Phenetic classification groups organisms solely according to structural similarities (e.g., bone structure), whereas phylogenetic classification also accounts for similarities in DNA, behaviors, and biochemistry to reflect evolutionary relationships.

What is the Most Recent Common Ancestor (MRCA)?

The most recent individual from which all the individuals in a given group are directly descended.

What is a clade in phylogenetic classification?

A grouping on a phylogenetic tree that shares a common ancestor.

Based on the provided phylogenetic tree, at which numbered point is the common ancestor between mammals and reptiles located?

Point $3$.

Based on phylogenetic classification, are birds more closely related to reptiles or mammals, and why?

Reptiles, because birds share a more recent common ancestor with reptiles (such as crocodiles at point $4$ and $5$) than with mammals (point $3$).

What are the key structural features of a bacterial cell?

Single-celled and prokaryotic (no nucleus), containing a large circular DNA strand called a nucleoid, smaller circular DNA pieces called plasmids, ribosomes, a cell wall made of murein, a phospholipid membrane, and potentially a flagellum or capsule.

How do members of domain Archaea differ biochemically and structurally from domain Bacteria?

• Archaea cell walls lack murein and are made from complex sugars.
• Archaea have slightly different cell membranes.
• Archaea have different protein-building ribosomes.
• Archaea possess genes that are more similar to Eukaryota.

What are the three main groups of Archaea and their characteristic environments?

1. Halophiles: thrive in high-salt environments (e.g., the Dead Sea)
2. Thermophiles: thrive in extreme heat (e.g., geysers or hydrothermal vents)
3. Methanogens: anaerobic organisms living in sewage, pond bottoms, and animal intestines

What are four defining cellular characteristics of all organisms in the domain Eukaryota?

1. Membrane-bound nucleus containing DNA
2. Membrane-bound organelles (e.g., mitochondria)
3. Complex division via mitosis
4. Ability to reproduce sexually via gametes

What are the cellular organization, mode of nutrition, and representative examples of Kingdom Protista?

• Organization: Complex single cell, some multicellular
• Nutrition: Absorb, photosynthesise, or ingest food
• Examples: Paramecium, Euglenoid, Slime mould, Dinoflagellate

What are the cellular organization, mode of nutrition, and representative examples of Kingdom Fungi?

• Organization: Some unicellular, most multicellular filamentous forms with specialised complex cells
• Nutrition: Absorb food
• Examples: Black bread mould, Yeast, Mushroom, Bracket fungus

What are the cellular organization, mode of nutrition, and representative examples of Kingdom Plantae?

• Organization: Multicellular forms with specialised complex cells
• Nutrition: Photosynthesise food
• Examples: Moss, Fern, Pine tree, Non-woody flowering plant

What are the cellular organization, mode of nutrition, and representative examples of Kingdom Animalia?

• Organization: Multicellular forms with specialised complex cells
• Nutrition: Ingest food
• Examples: Coral, Earthworm, Crow, Squirrel

In the phylogenetic diagram showing the three domains of life, what does the root point marked by the red circle represent?

LUCA (the Last Universal Common Ancestor).

What was LUCA, approximately when did it live, and in what habitat?

LUCA (Last Universal Common Ancestor) was a single-celled autotrophic organism thought to have existed $4\text{ billion}$ years ago, likely living around hydrothermal vents at the bottom of the ocean.