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.

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.

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

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).

Amphibians are the most threatened group of vertebrates on the planet, including in Mexico. Analyze what traits of their biology make them especially vulnerable and propose two justified conservation measures.

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.

A 1st-year Bachillerato student states in class: "Crocodiles and lizards belong to the same class (Reptiles) because they share characters such as keratinized scales and ectothermy, whereas birds are a completely different group because they have feathers and homeothermy. Grouping crocodiles and birds in the same clade contradicts morphology." Based on the principles of phylogenetic systematics:

1. a) Refute the student's statement by explaining why basing classification on keratinized scales or ectothermy creates a paraphyletic group. Distinguish in your answer between plesiomorphies (ancestral characters) and synapomorphies (shared derived characters).
2. b) Draw or sketch a cladogram showing the common ancestor of amniotes, lepidosaurs (lizards), crocodiles, and birds. Place on the corresponding branches at least two synapomorphies exclusive to the clade Archosauria (which encompasses birds and crocodiles).
3. c) Predict what would happen if in a fossil stratum you discovered an organism with an antorbital fenestra in the skull and a muscular gizzard, but covered in scales and without a trace of feathers: where would you place it on your cladogram, and what implication would this have for the traditional definition of a "reptile"?

In an experimental plot of a deciduous forest, a broad-spectrum systemic fungicide was applied to the soil for three years, keeping solar radiation, rainfall, and atmospheric CO₂ concentration unchanged. After that period, three empirical observations were recorded:

1. The thickness of the undecomposed leaf litter layer increased by 180%.

2. Oak seedlings (Quercus robur) experienced a 45% reduction in their growth and a marked foliar deficiency of phosphorus and nitrogen.

3. The soil respiration rate dropped drastically.

1. a) Justify observations 1 and 3 based on the metabolic strategy and the mode of external digestion characteristic of saprophytic fungi compared to plant autotrophic nutrition.
2. b) Explain the biological mechanism underlying observation 2: which specific symbiotic interaction has been destroyed in the soil, and what net nutrient flow between fungus and plant has been interrupted?
3. c) Predict, with reasoning, how the continued absence of fungi will affect the forest's net primary productivity and the biogeochemical carbon cycle in the medium term.