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 ...
- 451
37
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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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 ...
- 431
32
votes
Accepted
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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27
votes
Accepted
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 ...
- 29.2k
24
votes
Accepted
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-...
- 6,152
22
votes
Accepted
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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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 ...
- 41.2k
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 ...
- 5,328
21
votes
Accepted
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)...
- 67.8k
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, ...
- 4,571
18
votes
Accepted
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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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,...
- 1,415
16
votes
Accepted
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 ...
- 2,878
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 ...
- 9,287
14
votes
Accepted
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, ...
- 52.2k
13
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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9
votes
Accepted
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 ...
- 3,050
9
votes
Accepted
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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9
votes
Accepted
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 ...
- 52.2k
8
votes
Accepted
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 ...
8
votes
Accepted
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 ...
- 2,603
8
votes
Can any organisms see non-electromagnetic radiation?
Some fungi have radiotropism; they grow toward radiation sources. Melanin-expressing (melanotic) fungi migrate toward radioactive sources, which enhance their growth. According to this paper.
These ...
- 478
8
votes
Accepted
Should there be separate Ramachandran plots for an amino acid in different contexts?
The phi and psi dihedrals describe the dihedral on both sides of the c-alpha of a single amino acid, and do not involve any angles of the neighboring amino acid.
The Ramachandran plot is something ...
- 1,463
7
votes
Which part of human body sustains most pressure when standing up straight?
It is logically clear that the ankle could only partly be analyzed in the group of joints that are below its height. There is no direct way to measure the pressure on ankle joint (on talus bone), but ...
- 5,670
7
votes
Accepted
What determines whether an action potential is inhibitory or excitatory?
Short answer
The physiological state of the postsynaptic cell ultimately determines the effect of an incoming action potential.
Background
An action potential occurring in a chemical synapse is ...
- 52.2k
7
votes
Why don't membrane proteins move?
No other answer has mentioned this so I created an account just to say this.
Some membrane proteins do not move. This is because they are fixed in that position in the membrane due to the ...
7
votes
Accepted
Is Einstein's mass energy equivalence ($E=mc^2$) relevant to biological systems?
Short answer
Any law of physics will of course be applicable to living beings. However, in the absence of mass gain and mass loss, the input = output equation for ...
- 67.8k
7
votes
Is the amount of the soil reduced when plants grow?
The soil is the source of a small quantity of vital elements like magnesium (component of the chlorophyll), phosphorus (DNA), sulphur (some proteins) and more. As the plant grows, these are removed ...
7
votes
Accepted
What is the biological potential for vision of wavelengths outside the human visual range?
There are some limits on what light can be detected biologically based on physics and chemistry. Although there are animals that can sense more UV or more infrared than humans, they are still subject ...
- 41.2k
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