39 votes

Is the amount of the soil reduced when plants grow?

The vast majority of the mass of a plant is carbon-based which is obtained directly from the air via photosynthesis. So trees are, in a loose sense, solidified air! And most of the mass that comes ...
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  • 451
36 votes

Why don't viruses reach broad concentration outdoors in a city like allergens?

2, 4, 5, and 6. 6 being that the UV light (from the sun), fluctuations in temperature, humidity, wind etc mean that the virions are decayed relatively rapidly for most virus species. To address (1): ...
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  • 6,278
33 votes

Can bacteria be killed by purely physical trauma?

My (limited) understanding is that it is quite hard to avoid killing some bacteria even with very gentle physical manipulation. On the other hand, it is quite hard to use physical force to achieve ...
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32 votes
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Why don't membrane proteins move?

Proteins can move around the membrane. Most proteins do move within the membrane. The membrane is a liquid crystal and has fluid behaviour. Specifically, this is due to the membrane being in a gel-...
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25 votes
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Why is saltatory conduction in myelinated axons faster than continuous conduction in unmyelinated axons?

Short Answer Myelination acts as an electrical insulator and allows saltatory propagation. By reducing membrane capacitance and increasing membrane resistance, myelination increases the velocity of ...
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24 votes
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Can UV radiation be safe for the skin?

You're talking about long-wave UV, or UV-A radiation. In the 80s, experts claimed that this was a safe wavelength. Protection against UV-A was not part of sunscreen in the early days. Consequently, UV-...
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  • 5,582
23 votes
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How fast can a human run?

An older answer that referred to the physiological feats of ancient humans, and why modern humans are wimps made me look up a couple of papers on running speeds a while ago. One of the examples used ...
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22 votes

Why don't viruses reach broad concentration outdoors in a city like allergens?

In another answer elsewhere on StackExchange, a poster estimated that there might be something like 100 g to 1 kg of SARS-CoV-2 virus worldwide, and that's an estimate of all the virus, including what ...
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  • 34.9k
21 votes
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How do birds deal with their eyes drying out at high speeds?

Birds have a body part known as the nicitating membrane otherwise known as the "third eyelid". This part has become vestigial in humans, where it remains as the plica semilunaris. This image of a ...
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  • 9,304
21 votes

Why don't our cells merge when their phospholipid membranes touch each other?

Phospholipid bilayers found in cells are usually negatively charged. The phosphate groups repel each other by like charges and prevent two membranes from coming too close to each other. Membranes are ...
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  • 5,288
21 votes

Can bacteria be killed by purely physical trauma?

There are plenty of physical or mechanical methods of killing bacteria, but most are used in conjunction with other agents and probably don't qualify as "blunt force trauma". For example, ...
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  • 4,496
20 votes
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What is the anatomical term for a two jointed leg?

Welcome to Biology.SE! I think you are talking about plantigrade, digitigrade and unguligrade. Please note that the number of joints in mammals does NOT vary, but only the relative length (and shape)...
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18 votes
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What is the mass of a pigeon tail feather?

I just weighed a pigeon tail feather (~10 cm) long. The mass was 0.05 g. Although all tail feathers are not equal in length (and all pigeons are not equal in size), this is probably a good ...
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  • 12.1k
17 votes
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Why doesn't the cell membrane just...break apart?

The membrane bilayer is held together by hydrophobic forces. This is an entropy driven process. When a greasy or hydrophobic molecule is suspended in water, the water molecules form an organized "cage"...
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  • 5,288
17 votes

Why does UV radiation from the Sun cause skin cancer?

Rather than 'breaks' caused by high energy radiation, UV radiation causes chemical modifications of the bases ('letters') that make up DNA. There are four bases in the DNA alphabet abbreviated to A,T,...
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  • 1,405
16 votes
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How do small animals make loud sounds?

The Cicada A careful study of the noise-making apparatus of the cicada can be found in a 1994 paper by Young and Bennet-Clark.$^1$ The authors generated sounds at about 0-16 kHz at peaks on the order ...
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  • 2,759
16 votes
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What physical evidence exists that shows motor proteins "walking" within a cell?

Since you chose kinesins as an example class of motor proteins, I will also stick to them. In general, the movement mechanisms of kinesins are well studied and the general structure of kinesin ...
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  • 2,867
15 votes

Why does UV radiation from the Sun cause skin cancer?

There are very many photochemical reactions: Up to 50–100 mutagenic reactions on DNA per second might occur in a skin cell during exposure to sunlight, but are usually corrected within seconds by ...
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14 votes
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Why are potassium channels slower than sodium channels?

Short answer The activation kinetics of Na+ channels are faster than K+ channels. Background Voltage-dependent channel gating basically occurs through three possible states of the channel: open, ...
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  • 51k
11 votes

Why don't phospholipid bilayers dissolve?

We should first understand what happens when a substance dissolves. During dissolution water interacts with the solute molecule; if the strength of interaction between the molecule and water is higher ...
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10 votes

How does spermaceti make a whale float?

Buoyancy is controlled by "Archimedes' principle", as described in Britannica: ... any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, ...
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9 votes

Is human vision sensitive to frequency or wavelength?

It is not the wavelength or frequency that determines light absorption- it is the energy of the photon that matters. The energy of incident light should match the excitation energy of the chromophore. ...
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9 votes
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Problems understanding membrane potential

I think this question has more to do with kinetics / transport phenomenons than biology, but that's okay, everything is connected especially my computer to the internet. ;-) The basic idea behind ...
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  • 4,450
9 votes
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Why does the membrane of a neuron not stay at its depolarized state?

Three facts: The K+ ions are heavily concentrated on the inside while the Na+ ions are heavily concentrated on the outside The Na+/K+ ion pump is unidirectional. It can only pump K+ ions inside the ...
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  • 3,010
9 votes
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How does membrane potential vary between intraceullar membranes and the cellular membrane?

Yes, various intracellular membranes do have potential differences, but as you can imagine they are more difficult to measure experimentally, so in general data on this is scarce. Summary ...
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  • 5,595
9 votes
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How much energy does a small spider expend per day just waiting for its web to vibrate?

Short answer Approximately 240 J on a daily basis. Background Ballesteros et al. (2018) modeled basal metabolic rates of insects. They reckoned that endotherms, like insects, basically use energy ...
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  • 51k
8 votes
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What physics knowledge can be applied to biology of organisms and ecosystems?

This question is really asking for examples, and the list of ways that knowledge of physics can be used in biology could be very long. However, here are a couple of examples: Systems ecology, ...
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8 votes
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Stretching and compressing bones

Citing your source would help to answer. In order to test an elastic modulus, you need to apply some non-zero strain. If the strain is infinitesimal, then compression and stretch modulus will be ...
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8 votes

How does spermaceti make a whale float?

The buoyancy theory of the function of the spermaceti organ has essentially no empirical support. On the contrary, there is overwhelming support for the idea that the spermaceti organ, together with ...
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8 votes
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Would the human body react faster to touch or sight

A "touch" or "haptic" sensation will be much faster due to several reasons: Haptic feedback can be processed without the presence of any higher-order cognitive processing, therefore meaning that the ...
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