W_O_M_B_A_T t1_j6fqk67 wrote

>The key word is "can". In theory. It has never happened, because although certain humans have decided that swimming right next to the largest predator that ever lived is a rational thing to do, no human has ever been killed by it.

Blue whales are technically predators although they eat krill and very small fish. Also extraordinarily loud. It's not known how blue whales generate such loud sounds without injuring or ar least deafening themselves.


W_O_M_B_A_T t1_j6ff7py wrote

Coal synthesis gas /town gas contains significant amounts of carbon monoxide, hydrogen, water vapor along with minor amounts of a slew of other compounds. Methane content is typically only a few percent while the hydrogen content could be up you 55%.

The carbon monoxide made it highly poisonous. Looking back in hindsight, you'd be pretty foolish to cook with hydrogen cyanide gas which is also flammable, but has a similar toxicity level as carbon monoxide. There were many documented murders. All you needed to do was just turn the gas on in the victim's room while they were asleep, then go over to the pub and wait.

CO along with cyanide, ammonia, and certain nerve agents, is among the handful of toxic substances with the potential to kill in minutes, before rescuers are likely to arrive.

The hydrogen makes it uniquely explosive if it leaks into a confined, poorly ventilated space. Hydrogen has a much higher coefficient of thermal expansion than air, and has a wide range of mixture ratios with air in which it can burn. It can burn in as much as 90 H2 /10 air where most other fuel gases won't. Gas lamps were know to explode.

Hydrogen also has a unique tendency slowly to leak past o-rings, threaded pipe joints, gaskets, and packings that would contain other gases. It will also cause embrittlement of many materials like steels, cast iron, and many plastics. Stress induced cracks in threaded pipe fittings can be an issue, for example.


W_O_M_B_A_T t1_iujrftj wrote

>What is a Nightshade.

Nightshade is a colloquial name and not a technical one and is used to refer to many different plants.

Most of the plants with the colloquial english name "nightshade" are in the family Solanacea, However there are also several important food crops in that family.

Nightshade traditionally refers to plants in the genus Atropa, such as Atropa belladonna. This is the source of the useful drugs atropine and scopolamine. Atropa is a member of the family Solanacea. However large amounts of atropine are deadly and cause cardiac and respiratory arrest. All parts of plants in the genus Atropa are considered deadly poisonous.

Nightshade also refers to many plants in the genus Solanum, also of the Solanacea family.

This genus also includes the potato (Solanum tuberosa), the tomato (Solanum x lycopersicon), eggplant (S. melongena.). There are several wild relatives of tomatoes, native to south and central america that have edible and tasty fruits, but aren't widely grown.

However other members of the family Solanum have fruits that are toxic. For example, S. dulcamera, called bittersweet nightshade.

The word nightshade can be construed to mean plants in Solanum genus which have no edible parts.

For example, all aboveground parts of potatoes become quite toxic and the toxicity is triggered by light exposure. This includes the fruits and seeds of the potato, and cooking does not destroy the toxins. Only the underground tubers can be eaten. If potatoes are exposed to light for several days they may turn green. This is typically accompanied by modest toxicity, thus green-skinned potatoes are unfit for eating.

Europeans were originally quite skeptical of potatoes and eggplants due to their similarly to other members of the genus Solanum, native to europe which were themselves, very toxic including their fruits. They only became widely adopted in the late 1700s and early 1800's. Because potatoes are a very productive and nutritious crop even in relatively poor soils and are very tolerant of adverse weather conditions, they may be considered one of the unsung heroes of the industrial revolution.

Likewise, only the fruit of the tomato plants is fit for eating and other parts are generally mildly toxic.

Other members of the family Solanacea grown as crops include chile peppers (Capsicum fructescens), Physalis fruits such as tomatillo and lantern-fruit, Lycium barbatum also called wolfberry or goji. It also includes one of the most toxic plants in the family outside of the genus Atropa, Nicotiana tabaccum. This produces the highly toxic alkaloid nicotine.


W_O_M_B_A_T t1_iuiqreu wrote

Selenium biochemistry is also an interesting topic. Trace amounts of selenium are essential to the diet of, at least to my knowledge, vertebrate animals. I'm not aware whether or not other kinds of animals use it. In several of the enzymes that metabolize iodine-containing thyroid hormones, the amino acid cysteine which contains the R-SH (thiol group) is replaced with R-SeH. Thus creating the unique amino acid "selenocysteine" at the active site of the enzymes. The -SeH seems to be important in handling iodine in thyroid hormones.

Thus, selenium deficiency can mimic symptoms of iodine deficiency. Although the former is rare in humans. Grazing mammals can get selenium deficiency in areas with certain kinds of clay soils.


W_O_M_B_A_T t1_iuinxpj wrote

>A better way to phrase it might be...why oxygen instead of Sulfur or Selenium? Because those are both in the same column on the Periodic Table, they have the same number of valence electrons and therefore can form double-bonds easily.

Certain bacteria for example, purple sulfur bacteria, use thiosulfate or hydrogen sulfide as a final electron acceptor instead of water. These are reduced into small grains of elemental sulfur instead. Others use various organic compounds like amino acids. These types of organisms are either obligate anaerobes which live in air-free hot springs that are rich in H2S, or else are microaerophilic, meaning they can tolerate low levels of oxygen but do not generally utilize it themselves. The latter live in relatively shallow, nutrient rich, stagnant ponds where there's an excess of organic materials. That is, the water has become stratified with a layer of oxygen poor, H2S rich water below a shallow oxygen rich layer on the surface.

These types of bacteria may predate the first oxygen-generating Cyanobacteria by hundreds of millions of years. The first photosynthetic organisms were non-oxygenic.

Selenium is vastly rarer in most environments. It wouldn't make sense to use it as a primary electron acceptor because it's rarity would be an extreme limiting factor on growth. Excess amounts of selenium are also toxic to most organisms. This is probably related to it's chemical similarity to arsenic.

>However, the obvious answer comes to mind at the same time: they're both solid at room temperature.

There are a number of bacteria that derive energy by oxidizing sulfur and/or various metal sulfide minerals into thiosulfate and sulfur dioxide. (Lithochemotrophs)