The structures of nutrition

List the four processes of animal nutrition and explain in one sentence the function of each, indicating what would happen to a cell if any of them failed.

Explain the function of the kidney in the formation of urine and which substances it eliminates, and distinguish excretion (urea, salts, water) from egestion (faeces), discussing why faeces are not a product of cellular metabolism.

Observe the image of the human digestive system. a) Describe what happens to food in structures 1, 4, and 8. b) Indicate which numbered structures are accessory glands, that is, those that are not part of the digestive tract, and what each secretes into the tract. c) Order structures 1, 3, 4, 8, 9, and 11 according to the path of the bolus.

A paleontology team analyzes the remains of two extinct mammals of similar size (~50 kg). Species A possesses worn molars with pronounced enamel ridges (lophodont) and an abdominal cavity volume that suggests a large-capacity digestive system; species B presents molars with sharp cutting cusps (secodont) and a remarkably reduced abdominal cavity.

1. a) Predict and justify in a comparative manner the relative length of the digestive tract and the food retention time in both species based on the chemical constraints of degrading cellulose versus proteins.
2. b) If a live animal with a digestive anatomy analogous to species A is given prolonged treatment with broad-spectrum antibiotics, it suffers drastic loss of body mass despite continuing to consume abundant forage. Justify this phenomenon at the biochemical and physiological levels.
3. c) Why has natural selection not favored a hypertrophied digestive tract with microbial fermentation in obligate carnivores if this would allow them to extract nutrients from plant material when prey is scarce?

Analyze the following two physiological scenarios regarding nitrogen excretion:

• Case 1: Amphibian tadpoles are obligate ammonotelic organisms, but during metamorphosis into terrestrial adults they activate the genes for the enzymes of the ornithine cycle and become ureotelic.

• Case 2: The placental mammal embryo eliminates urea across the placenta, whereas the embryo of birds and reptiles encloses its nitrogenous wastes inside the shelled (cleidoic) egg.

1. a) Justify the switch in excretion during amphibian metamorphosis by evaluating the trade-off among cellular toxicity, environmental water availability, and energy cost in ATP molecules.
2. b) Predict the physiological and osmotic consequences for the development of a bird embryo if it were to carry a mutation preventing it from synthesizing uric acid and causing it to excrete only urea inside the egg. Compare its viability with that of a mammal embryo.
3. c) A student states: "Uric acid is the best evolutionary strategy for any animal because it allows water conservation at no biological cost." Refute this statement using thermodynamic and metabolic arguments.

Order the path of a mouthful of food through the human digestive tract, from the mouth to the anus, naming all the organs it passes through.

Name the accessory glands of the human digestive system (salivary glands, liver and pancreas) and indicate which substance each one pours into the digestive tract and what it is for.

Compare branchial (gill), tracheal, and pulmonary respiration: in which animal group each occurs, what exchange surface it uses, and to which environment (aquatic or terrestrial) it is adapted.

Inhaled air contains $21\ \%$ $\text{O}_2$ and $0{,}04\ \%$ $\text{CO}_2$; exhaled air, $16\ \%$ $\text{O}_2$ and $4\ \%$ $\text{CO}_2$. Interpret these figures: what they demonstrate about the efficiency of the exchange, why not all the oxygen is extracted, and why mouth-to-mouth ventilation can oxygenate another person.

Compare the structure of arteries, veins and capillaries (thickness and composition of the wall, diameter, presence of valves) and relate it to their function and to the pressure of the blood they carry.

The cardiorespiratory function of two 60-year-old individuals with the same body mass is evaluated:

• Subject A (non-smoker): Normal total lung capacity, forced expiratory volume in one second ($\text{FEV}_1$) of 3.4 L, and hematocrit of 44%.

• Subject B (smoker of 25 cigarettes/day for 35 years): Hyperinflated lungs, $\text{FEV}_1$ of 1.1 L, carbon monoxide diffusing capacity of the lung ($\text{DLCO}$) reduced to 45% of the predicted value, and hematocrit of 55%.

1. a) Apply Fick's law of gas diffusion across biological membranes to justify why the breakdown of interalveolar septa (emphysema) and the loss of lung elasticity cause the collapse of $\text{DLCO}$ and severe dyspnea during moderate exertion.
2. b) Justify at a physiological level why Subject B presents with polycythemia (hematocrit of 55%), relating the impairment in gas exchange to the renal endocrine response.
3. c) A commercial product claims to "regenerate alveolar walls and clean up destroyed elastin in smokers in just three months." Refute this claim using histological arguments regarding the mitotic and regenerative capacity of the alveolar parenchyma.