Chemistry for Biologists: Photosynthesis

Glossary of Terms: P - Physical Geography

Lab: Exploring the Rate of Photosynthesis - The Biology …

Many reasons were proffered to explain the Minoan decline and collapse, including the . What is increasingly cited as the reason for the Minoan decline (and was probably the ultimate reason for its collapse), was that Minoans , primarily via deforestation. Minoans, just as with many other collapsed civilizations, exceeded their land's carrying capacity. For organisms, carrying capacity always meant food and the ability to reproduce, but for civilizations, it also meant the energy needed to run the civilization’s moving parts, including transportation and the energy used to build structures and goods. If we revisit the “” that life faces, whether to use energy to fuel biological processes or build biological structures, civilizations faced the same choice. Humans commandeered the energy that a tree invested in its growth, and there were two basic ways to use it: liberate the energy in the structure by burning it, or use that structure for building human-usable tools or structures, which included buildings and ships. , as did pottery-making and fireplaces and furnaces to heat buildings. Minoans also built a tremendous fleet of ships for trade and military dominance. When rebuilding Minoan palaces, Crete’s inhabitants used wood exuberantly, but by 1500 BCE, the use of wood in palaces declined precipitously, and when Mycenaean Greece annexed Crete, the forests were gone and Greeks used Crete for pasturing their sheep.

Remove several leaves from around the cut end of the stem

Polar forests reappeared in the Eocene after the , and the Eocene’s was the Cenozoic’s warmest time and . Not only did alligators live near the North Pole, but the continents and oceans hosted an abundance and diversity of life that Earth may have not seen before or since. That ten million year period ended as Earth began cooling off and headed toward the current ice age, and it has been called the original Paradise Lost. One way that methane has been implicated in those hot times is that leaves have , which regulate the air they take in to obtain carbon dioxide and oxygen, needed for photosynthesis and respiration. Plants also lose water vapor through their stomata, so balancing gas input needs against water losses are key stomata functions, and it is thought that in periods of high carbon dioxide concentration, . Scientists can count stomata density in fossil leaves, which led some scientists to conclude that carbon dioxide levels were not high enough to produce the PETM, so that produced the PETM and , and the controversy and research continues.

Most plants produce seeds, which would have largely survived the catastrophe and began growing when conditions improved. Ferns came back first, in what is called a , as ferns are a . Crocodiles, modern birds (which included ), mammals, and amphibians also survived, and all could have found refuge in burrows, swamps, and shoreline havens, lived in tree holes and other crevices that they were small enough to hide in, and all could have eaten the catastrophe’s detritus. In general, freshwater species fared fairly well, especially those that could eat detritus. Also, the low-energy requirements of ectothermic crocodiles would have seen them survive when the mesothermic/ dinosaurs starved. The primary determinants seem to have been what could survive on detritus or energy reserves and what could not, and what could find refuge from the initial conflagration. While there may have been some evidence of dinosaur decline before the end-Cretaceous extinction (it was gradually growing colder), and the may have caused at least some local devastation, the complete extinction of non-avian dinosaurs, ammonites, marine reptiles, and others that would have been particularly vulnerable to the bolide event’s aftermath has convinced most dinosaur specialists that the bolide impact alone was sufficient to explain the extinction and no other hypothesis explains the pattern of extinction and survival that the bolide hypothesis does. In general, the key to surviving the end-Cretaceous extinction was being a marginal species, and all of those on center-stage paid the ultimate price. The end-Cretaceous extinction's toll was nearly 20% of all families, half of all genera, and about 75% of all species, and marked the end of an era; the Mesozoic ended and made way for the Age of Mammals, also called the , which used to have the .


Difference Between Aerobic and Anaerobic Cellular Respiration

There is also evidence that life itself can contribute to mass extinctions. When the eventually , organisms that could not survive or thrive around oxygen (called ) . When anoxic conditions appeared, particularly when existed, the anaerobes could abound once again, and when thrived, usually arising from ocean sediments, they . Since the ocean floor had already become anoxic, the seafloor was already a dead zone, so little harm was done there. The hydrogen sulfide became lethal when it rose in the and killed off surface life and then wafted into the air and near shore. But the greatest harm to life may have been inflicted when hydrogen sulfide eventually , which could have been the final blow to an already stressed ecosphere. That may seem a fanciful scenario, but there is evidence for it. There is fossil evidence of during the Permian extinction, as well as photosynthesizing anaerobic bacteria ( and ), which could have only thrived in sulfide-rich anoxic surface waters. Peter Ward made this key evidence for his , and he has implicated hydrogen sulfide events in most major mass extinctions. An important aspect of Ward’s Medea hypothesis work is that about 1,000 PPM of carbon dioxide in the atmosphere, which might be reached in this century if we keep burning fossil fuels, may artificially induce Canfield Oceans and result in . Those are not wild-eyed doomsday speculations, but logical outcomes of current trends and , proposed by leading scientists. Hundreds of already exist on Earth, which are primarily manmade. Even if those events are “only” 10% likely to happen in the next century, that we are flirting with them at all should make us shudder, for a few reasons, one of which is the awesome damage that it would inflict on the biosphere, including humanity, and another is that it is entirely preventable with the use of technologies .

Solar-to-Fuel System Recycles CO2 to Make Ethanol …

Biologists consider extinctions to be due to failure to adapt to environmental changes, and the “environment” includes other organisms. Exactly how species go extinct is still poorly understood, but the idea that the battle for survival is a common understanding among biologists, and ecosystems . makes the relationship explicit. There are many interacting variables, including those environmental nutrients, both inorganic and those provided by life forms. The ability of an organism or species to adapt is partly dependent on how specialized it is and how unique its habitat is. Absolute numbers, geographic distribution, position in the food chain (higher in the food chain is riskier), mobility, and reproductive rates all impact extinction risk. During the , about 80% of all animals were immobile. Today, 80% of all animals are mobile. The immobile animals were at higher extinction risk, for obvious reasons.