The respiratory organ is the “gatekeeper” that determines the amount of oxygen available for distribution. Each system is adapted to deliver enough oxygen and eliminate enough carbon dioxide to allow the species to surmount specific environmental and predatory pressures while simultaneously limiting the energy cost of breathing and cumulative oxidative stress in cells and organelles within an acceptable range. Harnessing the energy from oxidative phosphorylation while minimizing cellular stress and damage is an eternal struggle transcending specific organ systems or species, a conflict that shaped an assortment of gas-exchange systems. While aerobic respiration is essential for efficient metabolic energy production, a prerequisite for complex organisms, cumulative cellular oxygen stress has also made senescence and death inevitable. Oxygen, a vital gas and a lethal toxin, represents a trade-off with which all organisms have had a conflicted relationship. Through the evolutionary directions and variety of gas exchangers, their shared features and individual compromises may be appreciated.
We, therefore, survey the comparative anatomy and physiology of respiratory systems from invertebrates to vertebrates, water to air breathers, and terrestrial to aerial inhabitants. In an evolutionary context, certain species also become adapted to environmental conditions or habitual organismic demands.
Within an organism's lifespan, the respiratory apparatus adapts in various ways to upregulate oxygen uptake in hypoxia and restrict uptake in hyperoxia. Here, we review the origin of oxygen homeostasis, a primal selection factor for all respiratory systems, which in turn function as gatekeepers of the cascade. Efficient respiratory gas exchange, coupled to downstream convective and diffusive resistances, comprise the “oxygen cascade”-step-down of PO 2 that balances supply against toxicity. Disparate systems exhibit similar directions of adaptation: toward larger diffusion interfaces, thinner barriers, finer dynamic regulation, and reduced cost of breathing. adult lungs) or simultaneous (e.g., skin, gills, and lungs in some salamanders).
Habitat expansion compels the use of different gas exchangers, for example, skin, gills, tracheae, lungs, and their intermediate stages, that may coexist within the same species coexistence may be temporally disjunct (e.g., larval gills vs. Ambient oxygen tension ( PO 2) fluctuated through the ages in correlation with biodiversity and body size, enabling organisms to migrate from water to land and air and sometimes in the opposite direction. As such, you might want to pick the weekly to speed things up.Life originated in anoxia, but many organisms came to depend upon oxygen for survival, independently evolving diverse respiratory systems for acquiring oxygen from the environment. If you’re doing the Magnum Opus quest for the Forerunner, there’s a step that requires you to finish 3x Starhorse bounties, but tougher bounties give more progress. Note: You’re only limited to one bounty at a time regardless of that being a daily or a weekly. Void, Arc, or Solar weapon kills that match your current subclass.Match Game – Weekly bounty that has to be done in Legend difficulty:.Elemental final blows (must disintegrate enemies upon death).Shotgun final blows rapid kills add more progress.Trace rifle final blows rapid kills add more progress.Pulse rifle final blows (rapid kills add more progress.Complete the 30th Anniversary Seal/Title – Class-specific universal ornament (i.e., Thy Fearful Symmetry for the Warlock looks like a tiger’s helm).The Richest Dead Man Alive – Hraesveglur (Gjallarhorn ornament).The Triumph can be completed by killing the special contestant mob if you can trigger the Lightning Round in Dares of Eternity.
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