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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 from the ground is water which, of course, is constantly being replaced when it rains (or by Charlie with her watering can).


32

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-state. This gel state allows phase behaviour which means that the protein is able to move around on the surface. This results in an effect that is often referred ...


32

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 reasonable level of sterilization. Let's bring some examples with a few (hastily found) references. Pressure My guess is that most examples the OP mentions (hit ...


24

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 signal (i.e., Action Potential) propagation. If you want to see a really wonderfully simplified explanation, see this Quora post by Edward Claro Mader. Four ...


23

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 to support the statement that modern humans are "wimps" is a study of ancient fossilized footprints from Australia, which claim that the individuals making the ...


23

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-A was (and still is) used in tanning beds due to its perceived safety over UV-B. However, a lot of research has been done since. UV-A is well understood now ...


22

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 also full of proteins and often coated with carbohydrates, which serve to keep membranes from interacting too strongly. See this diagram of a membrane bilayer: ...


21

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 masked lapwing clearly shows its nicitating membrane in action, where it covers the eye in a horizontal motion. This is analogous to blinking in humans, and the ...


20

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) of the different parts of the leg. A Plantigrade walks on the sole of the foot. 'Sole' translates to 'planta' in Latin hence the name. Examples: Human, ...


20

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, beer distributers might snake a brush through a keg line to disrupt any bacterial biofilms before flushing them out with disinfectant. Similar logic applies to ...


18

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 approximation. Measuring the drag coefficient is going to be very challenging, because it will vary with the orientation of the oncoming airflow. A feather falling with ...


17

There are two factors that need to be taken into account here: 1. Myelination decreases membrance capacitance. The rate at which sodium influx through a node can depolarize the axon at the next node is related to both the current and capacitance across the membrane (in addition to a few other factors). So while adding a new node to the axon would indeed ...


17

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" around the hydrophobic molecule. When two hydrophobic molecules come into contact, they force the water between them out. This increases the entropy because ...


17

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,G or C belonging to two classes. A & G are guanines while T & C are pyrimidines. When you have pyrimidine bases next to each other on a DNA strand, they ...


16

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 of 100 dB using cicadas in various stages of deconstruction. The cicada uses a resonant organ-system called the tymbal which buckles and unbuckles rapidly to ...


16

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 proteins, that is a dimer, is known by crystallography (see Kull et al. (1996) for the structure publication). Even before that, the movement of single kinesin ...


15

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 photolyase reactivation or nucleotide excision repair. (That's just DNA, excluding O2 and other cell constituents) chemist ref and wiki ref Molecules that absorb ...


14

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, closed and inactivated (Fig. 1). Fig. 1. Gating of a voltage-activated sodium channel. Source: Balseiro Institute. Basically, ion channels are protein pores in ...


12

While Luke's answer is perfectly correct, the answer can be given in a more intuitive manner. First, the main point is that it is increased positive voltage (inside the axon) that opens the sodium ion channels to propagate the action potential. The question is: how fast can this voltage get to the sodium channels? In an unmyelinated axon, the movement of ...


12

It isn't about heat but ultraviolet light. Melanin is the pigment that makes our skin colour whatever it is and in darker skin there's more melanin. Melanin dissipates UV, which otherwise would cause skin cancer as it introduces mutations into DNA. Melanin production is stimulated by UV so that's why tanning beds work, our body senses the danger and responds ...


12

Disclaimer: This is not my field of research. First, this is not a complete answer to our question. A nice explanation of the current hypothesis of water transport in trees (Dixon-Joly cohesion-tension theory, originally proposed 1894) can be found at The Amazing Physics of Water in Trees but also in Tyree (1997). The key points are that the stoma (leaf ...


11

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 than the strength of interaction among the solute molecules then the solute dissolves. (Also have a look at this post). Phospholipid is an amphipathic ...


10

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. The medium itself can also affect light absorption by electronically interacting with the chromophore. Frequency is proportional to the energy (given by the ...


9

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 transport phenomenons is that there will always be a flux of quantitative properties (e.g. charges, particle number, entropy, volume, etc...) where the qualitative ...


9

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 cell while expelling the Na+ ions. Finally only the Na+/K+ ion pumps can restore the ionic equilibrium. The full scene: Once the threshold is reached the Na+ ...


9

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 Mitochondrial membrane: 150mV-180mV with negativity on the matrix side. Seth et al 2011 Endoplasmic reticulum membrane: 75-95mV with negativity in the ER. Qin et al 2011, ...


8

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 equal. But if it is finite, then there can be a difference due to the structure of the material. In bone, I believe porosity will provide most of the dissymetry ...


8

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 signals are being processed via a monosynaptic route. There are short reflex arcs between the spinal cord and the limb (meaning that you can react before you ...


8

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 Melanotic fungi inhabit some of the most extreme habitats on earth such as the damaged nuclear reactor at Chernobyl and the highlands of Antarctica, both of ...


8

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 directly correlated to the number of cells, which is linearly correlated to their body mass. They checked their model with experimental data from Chown et al. (...


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