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 recognized.

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 labor between the specialized 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 hot 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, name the five groups of vertebrates, and give a key evolutionary novelty for each.

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...).

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).

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.

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.

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.

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 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.

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, lab 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.