242

Apparently you're not the first person to notice this; in 1895, a German nose specialist called Richard Kayser found that we have tissue called erectile tissue in our noses (yes, it is very similar to the tissue found in a penis). This tissue swells in one nostril and shrinks in the other, creating an open airway via only one nostril. What's more, he found ...


138

This is a natural phenomenon called the nasal cycle. It is discussed in this paper by Telles et al. (1994), among many others. The nostrils are used on an alternating cycle of about 2-3 hours, controlled by the autonomic nervous system. If you notice alternating congestion, that also seems to be coupled to the nasal cycle (Hasegawa and Kern 1977, 1978). ...


99

Blood is not a good source of water. 1 liter of blood contains about 800 mL of water, 170 grams of protein and 2 grams of sodium (calculated from the composition of lamb blood). When metabolized, 170 grams of protein yields the amount of urea that requires 1,360 mL of water to be excreted in urine (calculated from here); 2 grams of sodium requires about 140 ...


98

Short answer The concept of species is poorly defined and is often misleading. The concepts of lineage and clade / monophyletic group are much more helpful. IMO, the only usefulness of this poorly defined concept that is the "species" is to have a common vocabulary for naming lineages. Note that Homo neanderthalis is sometimes (although it is rare) ...


81

I'm extremely skeptical of @leonardo's answer. I suspect that what would happen if you drank only distilled water is nothing perceptible. The only place where concentrations of distilled water would ever be high enough to conceivably matter is in the tissues of the mouth and throat, and even there, the effect would be temporary. Compare drinking 8 glasses ...


75

Good observation! Gene coding for the lactase Gene LCT Mammals have a gene (called LCT C/T-13910) coding for the lactase enzyme, a protein able to digest lactose. Lactose is a disaccharide sugar found in milk. Expression of LCT In mammals, the gene LCT is normally expressed (see gene expression) only early in development, when the baby feeds on his/her ...


70

You must tell facts from fiction; viruses need living cells to replicate because they do not have the molecular machinery at hand to generate energy and construct building blocks essential to life. So no, viruses cannot bring back the dead or revitalize dead cells. One thing that comes close to it are the so-called zombie ants. These ants have been ...


54

Sometimes men wake up with an erection in the morning. Why does this happen? Shortly speaking: REM (Rapid Eye Movement) is one phase of sleep. During this phase, we dream and some of our neurotransmitters are shut off. This include norepinephrine, which is involved in controlling erections. Norepinephrine prevents blood from entering the penis (preventing ...


52

There are two relatively common contagious cancers: Tasmanian Devil Facial Tumor, and Canine Transmissible Venereal Tumor. Both are truly contagious cancers, in that the cancer cells themselves are transmitted from one host to the next, and expand and cause disease in each successive host. (There was also a contagious cancer of hamsters, which has long ...


50

Short answer: There is no benefit for their use in households. Long answer: These soaps (see here for the complete list) contain the so called quaternary ammonium compounds Benzalkonium chloride and Cetrimonium chloride which indeed have antimicrobial properties. While they do not promote resistance to these compounds (see reference 1), their use is still ...


44

For the same reason that when you urinate or use the toilet, you have to exert pressure and urine or faeces just does not simply leak out when you stand up. The urethra seals shut when the urethral sphincter muscles relax. Similarly Sphincter ani externus muscle seals shut in the anal canal when there is no antagonistic force. So water can't just simply ...


42

It's an interesting question and one that has been asked before. NPR did a story in 2013 on this topic, but their question was a bit more focused than just "why are so many black people good runners?" The observation that led to their story wasn't just that black people in general were over-represented among long-distance running medalists, but that ...


42

Thiomersal is broken down into two compounds, thiosalicylate and ethylmercury (Ensink 2015). The thiosalicylate it is relatively non-toxic, and there is even some evidence that this compound could counteract some of the effects of mercury poisoining (Asadi et al 2010), though the mechanism of this inhibition has yet to be elucidated. Although they have ...


40

This information is all strictly for Entonox - a brand of analgesic gas comprising 50% Oxygen (O2) and 50% Nitrous Oxide (N2O), Laughing Gas. This mixture is known as 'Gas and Air' and is in very common use. The active ingredient in Entonox is of course the nitrous oxide, so the discussion of the mechanism below refers solely to the N2O as you asked for. ...


40

Yes. Far-red vision (>700nm) The ability for retinal-binding proteins to absorb far-red (between 700nm-850nm) light has been experimentally confirmed in this paper. While the authors did not attempt this in vivo in an animal model, they managed to use directed mutagenesis to induce a significant shift in the absorption peak of the chromophore of the ...


40

The phrase "Breast is best" is a hotly debated one (source: The Guardian and personal communications with many folks). The reason why we don't want to feed infants cow's milk is, however, anything but debated, because Cow's milk does not provide enough: Vitamin E Iron Essential fatty acids And because it contains too much: Protein Sodium Potassium (...


38

As others have said, this phenomena is called the nasal cycle, a process controlled by the autonomic nervous system that alternants congestion between your nostrils. Mentalfloss of all places has an article about this that explains: ...it makes our sense of smell more complete. Different scent molecules degrade at different rates, and our scent ...


38

This is called a phosphene — the experience of perceiving light in the visual cortex without light actually entering the eye. This commonly happens due to stimulation of the retinal ganglion cells by something else. The most frequent source in normal individuals is pressure to the retina (e.g. rubbing a closed eye.) It is also possible for phosphenes ...


38

A single molecule of rhodopsin (actually the cis-retinal bound to it) can and actually does react to one photon (Purves et al. Chapter: Phototransduction in Neuroscience). It has been estimated that a single light-activated rhodopsin molecule can activate 800 transducin molecules, roughly eight percent of the molecules on the disk surface. Although ...


37

First of all, it is corrosive. People which are bulimic often get problems with their teeth getting damaged by the permanent exposure to the acidic stomach fluids. See the paper for more information: Bulimia and tooth erosion Then it is a matter of concentration. According to Wikipedia, the concentration of the acid in the stomach is around 0.5% which is a ...


37

There are both biological and social factor for that: Biological Females have two X chromosomes. When mutations in genes of the X chromosome occur, females have a second X to compensate. Males, on the other hand gave just one chromosome X and all genes its genes express themselves, even those lethal or deleterious. Females have better resistance to ...


36

but I get lost on the 'border' cases. Not surprisingly, since there are no borders, and this is probably the greatest misunderstanding: Evolution is gradual. It’s not generally possible to say where a complex feature (or a species) starts and another one ends. We could in theory say, for individual mutations on the genetic level, in which generation they ...


36

Do physicians/biologists not know all the different types of viruses out there? No, Biologists don't know all the viruses that exist out there. There's a lot! We do know many of the ones infecting humans, though, especially the ones leading to the most common diseases. The fact that the doctor didn't know what type of virus she has bothers me. ...


36

When differences between prokaryotes and eukaryotes are taught in an introductory biology course, a generic prokaryotic cell and a generic eukaryotic cell are typically compared. Cells in a complex multicellular organism, like a human, are quite diverse. Human red blood cells are one example of a highly specialized cell with a mature form that is quite ...


36

Can a cancer cells from someone else's body cause cancer in a healthy person? No. Cancer cells from another person cannot cause cancer in a healthy person. The rare cases of transmissible tumors all involve unhealthy or not yet developed persons. Transmission of tumor cells from one individual to another happens, but is quite rare, and in all cases ...


35

While others have addressed the big picture aspects of your question, I think it would be useful to look at the specifics. Have a look at the heart (or more accurately, the hearts) of the earthworm: They're nothing more than veins with some pumping muscles wrapped around them. It seems almost a stretch to call them hearts, they are shaped so different ...


35

The problem with this question is 1) wording and 2) access. "Drink" and "digest thoroughly" are two different things. The latter does not prohibit the former. It is only lactose that is not tolerated; Calcium and other minerals, proteins, fats, etc. are also present in milk and are beneficial to the consumers if the lactose intolerance is not incapacitating....


35

Percent of basal metabolic rate by organ (BC Campus Open Education): Liver and spleen : 27% Brain: 19% Skeletal muscle: 18% Kidneys: 10% Heart: 7% Other tissues (lungs, intestine, skin, bone, fat tissue, glands...): 19% Basal metabolic rate by 1 kg of specific organ tissue (kcal/kg of organ/day) (Table 5 from American Journal of Clinical Nutrition, 2010): ...


33

I believe that MattDMo's hypothesis is incorrect. Only one group of ants, the Attini tribe, cultivates fungus as a food source. This group is exclusively a New World group, thought to have originated in the Amazon rainforest and spread out from there. I see from your profile that you are located in India, which is outside the range of the fungus-...


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