The major groups of living things

List the major groups (kingdoms) of living organisms and write a distinctive characteristic for each that allows it to be recognised.

Classify each of these organisms into its major group (monerans, protoctists, fungi, plants or animals) and justify your choice: an amoeba, a mushroom, an oak, a cyanobacterium and a sponge.

What is a protoctist (protist)? Explain why it is said to be a "catch-all" group, what its members have in common, and give two examples that show its enormous diversity (a unicellular alga and a protozoan).

Distinguish between a unicellular and a multicellular organism with two examples of each, and explain what advantage the division of labour between the specialised cells of a multicellular organism brings.

Identify which major group each organism belongs to based on these descriptions, justifying your answer: a) a unicellular organism without a distinct nucleus, with ether-linked membrane lipids, living in thermal springs; b) a multicellular eukaryotic organism with heterotrophic nutrition by absorption; c) a photosynthetic unicellular eukaryotic organism from plankton.

Differentiate bryophytes, pteridophytes, gymnosperms, and angiosperms based on the presence of vascular tissue, seeds, and flowers, and give an example of each group.

Order the appearance of these innovations in the history of plants and explain what independence from the aquatic environment each one provided: conducting vessels, the seed and the flower.

Explain the criterion separating vertebrates from invertebrates, cite the five groups of vertebrates, and give a key evolutionary novelty for each.

Name three major groups of invertebrates (for example cnidarians, annelids, arthropods, molluscs or echinoderms) and one evolutionary innovation that characterises each (radial symmetry, segmentation, jointed exoskeleton...).

Explain what anatomical and physiological adaptations allowed the first vertebrates to transition from aquatic to terrestrial environments, and what problems they had to solve (support, respiration, desiccation, and reproduction).

Based on the simplified phylogenetic tree in the diagram: a) state which present-day group shares the most recent common ancestor with animals; b) explain what the node marked with "?" represents and what type of cellular organisation is shared by all groups descending from it; c) explain whether it is correct to claim that bacteria are "less evolved" than animals.

Explain what a synapomorphy (a shared derived character) is using the hair and mammary glands of mammals, and discuss why shared derived characters, and not general similarities, are used to build evolutionary trees.

Distinguish between divergent and convergent evolution using these examples: the human arm and the wing of a bat (homologous organs) versus the wing of a butterfly and the wing of a bird (analogous organs). Explain what each case indicates about relatedness.

Explain two traits that distinguish fungi from plants (composition of the cell wall, form of nutrition, reserve substance) and discuss why fungi are more closely related to animals than to plants.

In a sample of Arctic permafrost, a microorganism ("A-24") has been isolated with the following properties: it possesses a 400 nm icosahedral capsid, a double-stranded DNA genome of 1,2 Mb (larger than that of bacteria such as Mycoplasma genitalium), encodes DNA repair enzymes and several aminoacyl-tRNA synthetases, but lacks its own ribosomes, ATP synthases, and membrane potential. It only multiplies upon entering a free-living amoeba.

1. a) Critically assess whether "A-24" should be considered a living organism or a viral particle according to cell theory and traditional metabolic postulates.
2. b) Contrast how the "reduction hypothesis" (degenerate parasitic cells) and the "gene escape hypothesis" would explain the evolutionary origin of "A-24". What specific genomic signatures would you expect to find in "A-24" to support the reduction hypothesis over the escape hypothesis?
3. c) A group of biologists proposes creating a "fourth domain of life" to place these giant viruses alongside Bacteria, Archaea, and Eukarya. Using the foundations of Carl Woese's molecular phylogeny based on ribosomal RNA (16S/18S), refute the technical viability of this proposal and propose a coherent taxonomic alternative.

In a biological sampling, a sessile, terrestrial multicellular organism provided with cell walls and with heterotrophic nutrition by absorption is collected. Traditional Linnaean classification would place it close to plants due to its morphological appearance. However, laboratory analyses reveal:

1. Presence of N-acetylglucosamine polymer chains in its cell wall.

2. Storage of energy reserves in the form of glycogen and lipids, with a complete absence of starch.

3. In phylogenetic trees based on ribosomal RNA sequences and contractile proteins, this organism forms a monophyletic clade with animals and choanoflagellates (Opisthokonta).

1. a) Justify why the morphological similarities to plants (sessile, presence of a cell wall) are homoplasies (adaptive convergences) and not evolutionary homologies.
2. b) Argue, using the concepts of molecular homology and synapomorphy, why data 1, 2, and 3 demonstrate that this fungus shares a more recent common ancestor with a snail than with a fern.
3. c) A student remarks: "If fungi used to be plants and now they say they are related to animals, biological classifications are mere arbitrary inventions." Refute their comment by reasoning out the methodological difference between a phenomenological classification and a phylogenetic systematics based on testable hypotheses.