Exercises: The major groups of living organisms

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

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

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

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

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.

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.

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

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).

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 hot springs; b) a multicellular eukaryotic organism with heterotrophic nutrition by absorption; c) a photosynthetic unicellular eukaryotic organism from plankton.

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 organization is shared by all groups descending from it; c) explain whether it is correct to claim that bacteria are "less evolved" than animals.

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.

Order the appearance of these evolutionary novelties of the vertebrates and assign each one to the group in which it arose: jaws, lungs and limbs with digits, the amniotic egg, and the feather.

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.

Sponges are the living animals with the simplest organization. Describe their body plan (no true tissues, choanocytes that filter the water) and discuss what they suggest about how animals could have arisen from colonial protists.

When analyzing the fossil record of continental deposits before and after the biological crisis at the Permian-Triassic boundary (~252 Ma), it is observed that therapsids (synapsids known as "mammal-like reptiles"), which dominated more than 70 % of the herbivore and carnivore faunal communities, suffered a mass extinction exceeding 85 % of their families. During the Triassic, basal archosaurs—previously scarce and marginal—underwent rapid diversification, occupying the vast majority of terrestrial ecological niches.

1. a) Interpret this faunal turnover by applying the concepts of ecological bottleneck, niche vacancy, and adaptive radiation. Was the diversification of archosaurs a consequence of a prior "competitive biological superiority" or of historical contingency?
2. b) Apply the same reasoning to the Cretaceous-Paleogene (K-Pg) boundary extinction event: justify whether the ecological rise of placental mammals following the meteorite impact supports the idea of cumulative evolutionary progress or that of contingency.
3. c) In the face of the current biodiversity loss crisis caused by human action, a report states: "The species that are dominant today (humans, poultry, rodents) guarantee the stability of future ecosystems because their abundance demonstrates their adaptive success." Critically assess this statement based on the survival patterns observed in the major extinctions of the fossil record.

Unit Challenge. Imagine you are working as a scientific advisor for a natural science museum. Your mission is to analyze how the major milestones in the history of life explain the biodiversity that inhabits your region today.

Follow these phases:

1. Gathering real data: Access the official GBIF platform (gbif.org) and consult the biodiversity data for your county or state. Extract the number of recorded species for four lineages: bacteria, plants, fungi, and animals.

2. Evolutionary reconstruction: Design a chronological table placing the appearance of each group on the geologic time scale (from the earliest evidence of cellular life $\approx 3.8$ Ga ago to the Cambrian explosion $\approx 0.54$ Ga ago). Include a key adaptive innovation for each (such as oxygenic photosynthesis, symbiogenesis, or multicellularity).

3. Synthesis report: Create a comparative graph of current species richness versus their antiquity, and write a reasoned proposal ($1$ page) arguing how extinctions and adaptive radiations have shaped the local biosphere you observe.

Assessment criteria:

• Rigor in extracting and tabulating real biological data from the official database.

• Scientific accuracy in dating evolutionary milestones and linking them to their biological innovations.

• Quality of the critical analysis connecting geologic history with current biodiversity patterns.