Questions tagged [biology]

Questions about biology are OFF TOPIC and should be asked on the Biology Stack Exchange. However, questions about biology in the context of physics (e.g., biophysics) can be on topic here if the primary concern is physics.

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306 views

Insect Eyes Vs Human Eyes?

Humans have frontal eyes. Less field of view. But better resolving power. Insects have lateral eyes. This means they have a large field of view. In some female insects the lateral eyes have much more ...
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162 views

What biology knowledge can be applied in physics? [closed]

After asking a commensurate question in Biology.SE (What physics knowledge can be applied to biology of organisms and ecosystems?), I wonder about the reverse direction: What biology knowledge can be ...
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1answer
361 views

Would a six-inch person face certain death when falling from a great height?

In Mary Norton's The Borrowers Aloft, the borrowers are like humans in every way except size - normal adult height is six inches. One family of three is captured by a human couple and housed in an ...
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1answer
128 views

What is the physical clock ticking inside a living cell? [closed]

What is the physical process which determines the timescale of the aging of a living cell? It might be that on the macroscopic scale, i.e., aging of the human, the gravitational force is one factor ...
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3answers
3k views

Death by entropy [closed]

An idea struck me as I was walking to class today. According to Wikipedia, entropy is defined as the number of specific ways in which a thermodynamic system may be arranged, commonly understood as a ...
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1answer
55 views

How big are soluted salts in drinking water?

I have just seen the TED talk Michael Pritchard: How to make filthy water drinkable where a device called LifeSaver bottle that filters particles that are bigger than 15nm out of water. I have heard ...
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9answers
5k views

Why can we cycle faster than we can run? [duplicate]

This seems obvious: faster long-distance runners hit ~20 km/h (marathon records) while fastest cyclists can do ~40 km/h (Tour de France stats). But on the physical/biological level this doesn't seem ...
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4answers
2k views

Breathing Air Underwater From A Car Tyre

I've seen in many movies and programs the event where a car plummets off the road and in to a body of water, sinking rapidly. The car slowly fills with water as it sinks and the occupant(s) don't ...
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2answers
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Can life exist in intergalactic space? [closed]

A terrifying idea I think, to be so utterly alone. Do you reckon life could exist in intergalactic space? A lot of cosmic radiation is shielded from us by the Milky Way's magnetic field, but the ...
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1answer
97 views

What are some publications which continue Schrödinger's “What is life?” discussion?

I'm looking for modern publications on the physical nature of life in which the primary reference is to the discussion started by Schrödinger in 1944 in his book "What is life". For example, ...
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3answers
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Is it possible to kill a human with a powerful magnet?

I'm asking in terms of physics. Can powerful magnetic induction rearrange spins of my body in such way I will die? How? Or maybe it can rip all iron from me, which would make my blood cells useless? ...
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590 views

How does cryptochrome produce quantum entanglement?

I found this video on the net, which explains how a bird called "European robin" uses a trick based on quantum entanglement to see the earth's magnetic field. I am just asking if some of you know any ...
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Audio anomaly identification

I left an audio recorder in the forest in many different locations for fauna identification. I am collecting subjects on my audio recorder that are clearly not in the frequency range of any animal ...
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1answer
3k views

Why do the trees` trunk assumes a circular/curvy shape but not rectangle or square? [closed]

Why does the trees grow circular? What are the forces that force a plant to grow with a circular trunk? If the stability of the tree were the reason then why does the trees bend in their natural ...
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Medical/Physics Question - Cut Off Finger Preservation

This question might require some knowledge of medical/tissue, but physicists seem to know everything, so figured I've give it a shot here ;) When people put cut off fingers they are told to put the ...
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1answer
119 views

Is there any other solar system in the universe?

Is there any other solar system far away from ours in the universe? Why don't we expect another solar system based on another star similar to sun in the universe? If so, Why probably there wouldn't ...
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1answer
2k views

The effect of high frequency AC current in a fresh corpse [closed]

Given two AC currents of the same intensity, eg 20 mA, but different frequency, 60 Hz and 20MHz, which one would be more likely to reach the heart ? I've read about the skin effect and how current ...
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1answer
201 views

phospholipid bilayer [closed]

I'm a high school student. The head is hydrophilic, the tail is fatty acid,in other words hydrophobic. Here is the thing I don't understand, all textbooks state that water is repelled by hydrophobic ...
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3answers
24k views

Could submarine SONAR kill a diver?

Could a diver swimming next to a submarine be killed or seriously injured by its SONAR? What physical aspect of SONAR affects the human body in a potential harmful way?
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1answer
425 views

Can there be some non-electromagnetic radiation which would be perceived by human eye as light?

Can there be some non-electromagnetic radiation which would be perceived by human eye as light? I mean, say ultra-sound or some particle rays etc.
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1answer
315 views

physically modelling the Saltatory nerve impulse transmission?

The nerve impulse transmission is specifically a biophysical process. Under a resting stage, the membrane is already polarised (presence of charge on either side leading to a potential difference ...
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3answers
1k views

What is the relationship between the second law of thermodynamics and evolution?

On one hand evolution seems to drive against the second law in that it creates a state of (locally) higher order. On the other hand the second law seems to drives evolution - in the sense that it ...
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3answers
180 views

How much energy does it take to simply run forward?

I'm interested in tracking as much data about my runs as I can in an effort to get faster, and while I can easily estimate energy expenditure during an uphill run due to the change in elevation, I can'...
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1answer
333 views

Quantum randomness and brownian motion in biological systems, e.g., fertilization

I am looking for examples of physical indeterminacy impacting the macroscopic world. By physical indeterminacy, I mean physical sources of randomness such as quantum indeterminacy or brownian motion. ...
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2answers
369 views

Background radiation: radon vs potassium 40

In doing a little research into natural background radiation, I came upon a table from the National Council on Radiation Protection and Measurement (NCRP). It shows that inhaled radon gas is by far ...
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2answers
292 views

Does physics address the topic of consciousness? [closed]

Does physics address the topic of consciousness? For instance, does physics say anything about how it might arise or what might be its qualitative properties? I'm wondering because it's interesting ...
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Why is there a size limitation on animals?

Why is there a size limitation on human/animal growth? Assuming the technology exists for man to grow to 200 feet high, it's pretty much a given that the stress on the skeletal structure and joints ...
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0answers
128 views

Biological Themodynamics - What does an endpoint saturated signal mean. How does it relate to equillibrium constant

I have had a question that has been bugging me for a couple of years in my graduate school career, and I was wondering if perhaps some physicist could help explain it to me. Given an endpoint assay ...
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4answers
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Why do whips hurt so much?

What exactly is the mechanism that makes a whip deliver such a strong impact? Elasticity, torque, or pressure? Just hitting something with a plank doesn't deal nearly as much damage. What's the ...
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6answers
21k views

Google interview riddle and scaling arguments

I am puzzled by a riddle to which I have been told the answer and I have loads of difficulties to believe in the result. The riddle goes as follows: "imagine you are shrunk to the size of a coin (...
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3answers
720 views

Harmlessness of a pure alpha decay particle

From my high school physics class I remember that there are some particles which exhibit pure alpha decay (i.e. alpha decay to there stable isotope), like Po-210, Po-211 and Bi-209. What I also know ...
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1answer
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What is the minimum pressure difference for your ears to pop?

I'm assuming the answer to this largely varies from person to person. Assuming you could instantly change the pressure around your head by amount $\Delta p$, what is the minimum $\Delta p$ for your ...
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2answers
2k views

Why is it hard to breathe when cycling against the wind?

Sometimes when I bicycle against hard wind, I find it difficult to breathe. Others I have discussed it with have also noticed this effect. A possible related phenomenon that I heard from an ...
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2answers
64k views

Effects of a very large magnetic field on the human body

Ever since reading about the NHMFL I have always wondered about this and asked several people without getting a good satisfactory answer. My question is, considering the simplest case let's say a ...
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3answers
4k views

What is the minimum optical power detectable by human eye?

If one is in complete darkness, what is the minimum optical power that the eye can "see" (let's say in 500-600 nm range). I found that for 510 nm, 90 photons can be detected (http://en.wikipedia.org/...
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1answer
100 views

What is the $Q_y$ transition in a bacteriochlorophyll?

Bacteriochlorophyll (BChl) are pigments that occur in the photosynthetic mechanisms of bacteria. I am studying some papers on the excitonic properties of BChl's, and the term $Q_y$ transition comes up ...
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1answer
2k views

Will a plant grow faster or slower when affected with less/more gravitational forces

Will a plant grow faster when you would apply more upward gravitational force? and/or Will a plant grow slower when you would apply more downward gravitational force?
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1answer
248 views

Relation between Casimir and hydrophobic effects

Background Some years ago I was studying "Fundamentos de biología" (Biology fundamentals) and learned how the lipids create a bilayer due to the water repulsion. Some time later I learned that this ...
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1answer
3k views

Would travelling at relativistic speeds have any impact on human biology?

If a person was sitting on a craft that has accelerated to near light speed speed from Earth (e.g. 99.999% of light speed) would there be any impact on his or her human biology due to relativistic ...
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3answers
875 views

Can endergonic reactions occur outside of living organisms?

If the Gibbs free energy equation is defined as: ∆G = ∆H - T∆S And the amount of energy/work released from a reaction is: ...
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4answers
1k views

How does the introduction of living things into a closed system affect the rate of change of entropy?

Does the introduction of living things into a closed system increase or decrease the overall rate of change of entropy of a system?
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1answer
295 views

Validity Of the Drake Equation [closed]

The Drake Equation is designed to estimate the number of Planets possibly having intelligent life forms existing in our Galaxy. But I don't see how it's justified. As far as we know, Earth is the only ...
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1answer
1k views

Physical Explanation of Being Able to “Think” [closed]

This may look like a philosophical question, but I'm looking for physical explanations (if there's any), that's is why I'm asking it here. What is the ability of thinking? We are all creatures ...
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2answers
2k views

Are cosmic muons causing mutations or even influence evolutionary rate?

As there are experiments studying influence of cosmic rays on organisms, http://www.ncbi.nlm.nih.gov/pubmed/11541768 I ask my self, if there any influence to DNA from atmospheric muons on the Earth ...
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1answer
228 views

Is a low-current electrical arc harmful to humans?

I've heard that electrical flux non-destructive particle testing machines are considered safe because they use less than 2 amps. I have seen an arc created between two objects do considerable damage, ...
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2answers
857 views

Human perception of distance

When we see things around us, distant objects look smaller to our eyes than nearby objects do. Is there any physics-related reason why our eyes or brain perceive things like this? Or if this is ...
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2answers
10k views

How can an an ant lift 50 times its own weight and pull 30 times its weight?

According to many sites like this one, an ant can apparently lift 50 times its own weight and pull 30 times its weight. Is it true? Can it be proved using physics? Though most sites agree that an ...
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7answers
17k views

How can a human eye focus on a screen directly in front of it? [closed]

I am asking this question here because I think the answer has something to do with the way light is bent as it's captured through the eye. I saw a show a while ago about tiny screens on contact ...
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2answers
177 views

Why (infra-)red light is not used in diagnostics?

I noticed that human body conducts red visible light quite well. A hand placed over a powerful red lamp seems to be semi-transparent while over any other color it does not. Possibly the light ...
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1answer
9k views

How much sky do we see at any one moment?

When we look at any particular point the sky, what percentage of the celestial sphere do we see? This question arises from the notion that on average there passes one meteor per hour overhead. So ...