biochemistry - What makes a wet dog so stinky?

From this source,

We answered this question on the show...

We posed this question to Dr David williams from the Veterinary School
at the University of Cambridge... David - First of all, what actually
makes something smell? Molecules have to leave the smelly objects
and get to your nose through the air and that means that these
molecules must be very small and volatile. That's to say they must be
easily evaporated. The chemicals that make dogs smell are mostly what
we call volatile organic acids and they are produced by bacteria from
the fats that are breaking down from sweat; and that's maybe why we
find these body odours unpleasant. They signal a presence of bacteria
and decay and death to us.

Their [dogs] skins mostly have
Staphylococcal bacteria, which don't produce much in the way of a
smell at all, but they've also got some yeasts too which are really
pongy. But why does the smell seem worse when the dog is wet? Here,
I think we have to go into some physics. The amount of evaporation of
a substance is related to the concentration of the compound on a
surface it’s evaporating from and the amount of compound that's in the
air, just above the surface.

So how might that change when it’s wet?

Well, if the organic acids are dissolved in water on the fur of the
wet dog, as the water evaporates, the concentration of those smelly
acids increases, so they'll evaporate more, so there are more
molecules in the air for us to smell. Diana - A bit of evaporation
can effectively amplify the amount of volatile chemicals that emanate
from a dog’s skin, and Dr. Williams thinks it’s the same effect that
causes that damp earth smell when it rains. It may also alter how
dogs interact with each other when they're wet. So, if you have a
dog, watch to see if it sniffs differently at other dogs on a dry day
versus a wet one...

There's a start, sounds legitimate to me...

physiology - To which distinctions does the term "hymenoptera" refer?

I don't have a definitive answer, but I suspect Hymenoptera is "just a name," albeit a name that has lasted through the phylogenetic nomenclature revolution.

Hymenoptera was erected by Linnaeus in the 10th edition of Systema Naturae (1758). The description of Hymenoptera (membrane wing; p. 553 [hope your Latin is better than mine]) follows that of Lepidoptera (scale wing) and Neuroptera (net wing) and precedes Diptera (two wing).

Classical taxonomy, which Linnaeus was more or less inventing at the time, was based on shared similarities. Those insects which Linnaeus thought more similar to each other than to other insects (e.g., ants, wasps, bees) all shared the characteristic of having a membrane based wing. The scaly wings of moths and butterflies made them more similar to each other.

He needed names for these groups, so he chose logical ones based on outward appearance of the wings: scaly, netted, membranous, or paired. That fact that these major groupings have more or less stood the test of time suggests that Linnaeus picked a good characteristic on which to name his classification of the major groups of insects.

human biology - Understanding Membrane / Resting Potential from the perspective of ions?

Ah, what a classic biophysics problem.

One first needs to understand how a membrane gets a potential. The lipid bilayer is a large sea of hydrophobic interactions that essentially prevents any ion from crossing. As a result, Na⁺ and K⁺ concentrations remain constant and different on the cytoplasmic side and the extracellular side. However, ions can pass through ion channels like the K⁺ channel. It is important to understand that in K⁺ channels, only K⁺ can pass and these channels are actually selective against Na⁺ (answer to question 1).

There are two potentials at work here. First is a chemical potential created by the flux of K⁺ from high K⁺ to low K⁺. The second is a counteracting membrane potential created by a charge imbalance. Note, that the swapping of a few ions will a) result in a negligible change in the concentration ie. the chemical potential, b) result in a large change in the membrane potential. At some point, the flux out due to the chemical potential and the flux in due to the membrane potential will be equilvant and the cell will reach a resting potential otherwise known at the Nernst potential or equilibrium potential (technically a steady state).

When a cell depolarizes by closing these channels, the local charge will quickly go back to an equilibrium or a non-charged state.

So why K⁺ rather than Na⁺? For typical cells, the extracellular concentration of Na⁺ is 145 mM and cytoplasmic is 12 mM. For K⁺, it is 4 mM and 155 mM respectively. Doing the appropriate calculations of the Nerst potential, for Na⁺ it is +67 mV and for K⁺ it is -98 mV. Qualitatively we can see that this would result in vastly different things.

Most of this information can be found from Pollard and Earnshaw's Cell Biology

evolution - How and when did a dedicated immune system evolve?

I have recently been doing a lot of research into the interplay between the innate and adaptive immune systems in humans, and mammalian laboratory models. This has led to my reading some interesting information on the immune response in insects;

Insects have a highly efficient immune system. In response to a bacterial attack, their fat body (the equivalent of the liver in mammals) synthesizes a whole range of peptides with an antibacterial and antifungal effect.

This fascinated me, as the clear inference is that there are no ‘dedicated’ immune cells, but that adipose tissue has far more diverse functions that I had realized.

I have done a little more reading, and also looked at plant immune systems, which seems far more analogous to those in insects than mammals;

Plants, unlike mammals, lack mobile defender cells and a somatic adaptive immune system. Instead, they rely on the innate immunity of each cell and on systemic signals emanating from infection sites.
(Jones, 2006)

My questions relates to the need of an adaptive immune response in mammals. The immune systems in insects and plants - a more 'systemic' immunity due to the lack of dedicated/mobile immune cells - seems much simpler.

Given that evolution works incrementally (there are no 'jumps' - for instance, going from a non-dedicated immune system, to a dedicated immune system), I would hypothesise that organisms less distantly related to insects and plants may have tissues with duel functions (similar to insects?), but that specialize further as immune cells until gradually (down the evolutionary tree) a complex and specific immune system emerges. (This is complicated by the fact that our immune systems do have multiple roles - e.g. tissue remodelling, but I wasn't going to go into that here. Feel free in your answers if it is necessary!).

My overall curiosity can be summarized as 2 questions;

1. What are the possible reasons why a dedicated and immensely complex immune system evolved in some lineages of organism?


2. Is there any evidence of 'half-way' organisms, and about what ecological time-frame might the dedicated immune system have developed?