mak10

What do you mean by its electrode potential and chemical reaction's forte????

i dont know if i can explain electode potentials in a nutshell (you need to have fairly good idea about redox chemistry for which u can refer to any good advanced chemistry textbook) but let me give it a shot

any feasible set of reactions that take place, either involves loss (oxidation) or gain (reduction) of electrons. thus all reactions have an electrode potential value, which can be positive or negative, determined by electrolysis reactions (for details how its done, see here but be prepared for some agnozing moments!). if a reaction has a positive EP value, the forward part of the reaction, i.e - the product side, is more stable than the backward part, i.e - the reactant side, that is to say that the position of the equilibirum lies to the right. its the other way round if the EP is -ve. example:

1) Mg2+ + 2e- ===> Mg [EP = -2.37]

2) Cu2+ + 2e- ===> Cu [EP= +0.34]

the EP of the 1) reaction shows that the position of the equilibrium lies to the left, i.e - Mg2+ does not get easily reduced to Mg. the EP of 2) reaction shows that, compared to the EP of Mg2+, the position of equilibrium of copper lies to the right, i.e - the Cu2+ is almost fully reduced to Cu, since its easier, as the EP predicts.

Similarly, the EP of the reaction,

CH3COOH <==> CH3COO- + H+

is probably negative, hence the position of this equilibrium lies well to the left, as un-ionised ethanoic acid molecules, which is why its a weak acid. other factors such as the delocalisation of negative charge by oxygen lone electron pairs over the ethanoate ion "pushed" by the alky group attached (as they are an electron donating group), attracting the positive hydrogen ion and thus re-forming the un-ionised molecule most easily... are also important in determining the negative EP of the reaction.

here are some links u can go through to learn more, if u're interested in electrode potentials and the chemistry involved:

http://au.encarta.msn.com/encyclopedia_761569809/Electrochemistry.html

http://www.physchem.co.za/Redox/SEP.htm

http://www.pinkmonkey.com/studyguides/subjects/chem/chap9/c0909601.asp

How does it happen??? a positive ion should be bonded with a negative ion..... so there should be equaled amount of positive ion and negative ion....

well, there is 1 mole of ch3coo- and 1 mole of h+ in the ch3cooh molecule, by the reaction equation... but i am talking about how much of ch3coo- and h+ are ionised during the reaction... and out of the 1 mole, only 0.01 moles of H+ and 0.99 moles of ch3coo- are probably ionised at any one instant of time.

Why does H and coo has to be written together???

oxygen, in its un-ionised/neutral state, has to form two bonds.... so h is written in the cooh to indicate that one oxygen has formed double bonds with carbon and the other has formed a single bond with carbon and a single bond with hydrogen.

but the there are huge amount of partially positive and partially negative ends from water molecule, which could overcome the forces of CH3COO- and H+ to dissociate them, thus how could those ions asscociate with each other???

you are confusing the ionisation of an acid in an aqueous solution with their dissolution in dilute solutions. remember, the partially +ve end of the water is still H+.

-mak10

am doing my a-levels currently in bio/chem/phy and cant make up my mind whether to opt for pharmacy (concentrating on pharmacology) or getting an MD. as fas as i know, pharmacy with a concentration on pharmacology studies the effects of various types of drugs on the human body... in which case, i cant think of any difference between this and what a physician studies. someone told me that a major in pharmacology, as a premed, and then doing medicine is possible in states. is this a better option than doing MBBS directly and then MD?? thanks!

-mak10

In what condition, the reaction will be a dynamic equilibrium??? ie, there are are both back and forwards reaction taken place at the same time

the only conditions i can think of is that the system, where the reaction takes place, must be closed/isolated system and the influx of energy, if its there, must be constant.

For ethnoic acid, we know it is weak acid, because the reaction taken place in the solution is not completely forwards, it has both back and forward, so is a dynamic equilibrium, but why it does not fully be forwards reaction, like HCl???

the reaction is reversible but that doesn't mean all solutions of ch3cooh are in dynamic equilibrium. its a weak acid because it undergoes incomplete ionization, i.e - produces less H+ ions compared to ch3coo- ones.... the ratio is something like 1:99. and whether a reaction proceeds fuly forward or backward really depends on its electrode potential, whether oxidation or reduction is the chemical reaction's forte... i think. i can explain the latter in detail if u're interested...

Oh, yes, according to my knowledge, for the formula of ethonoic acid, something like CHCOOH, the positive ion is H, and the anion is CHCOO, my chemistry teacher told me that positive ion starts first in a chemical formula long time ago, how come it is not something like HCHCOO???

pardon me but i don't exactly understand what u're asking here. the formula is ch3cooh and yes, the positive ion is H+... so why doesn't the formula start off with the positive ion?? u can have ch3cooh as h3ccooh, but u certainly cannot have it as h4ccoo... the h of the coo which forms the positive ion must be with coo which must be written with, if not after, ch3. but u can write it as hoocch3... as long as the h+ is with the coo. and i don't recall any rule strictly stating that all formulae shud start off with the positive ion.... and even if there is, as per ur teacher, i highly doubt it being applicable to organic compunds like ethanoic acid.

Secondly, what is the difference between bases and alkalis??

anything which reacts with an acid is a base and bases that are soluble in water are alkalis.

-mak10

Is the double bond indicated on an alkene one sigma bond and one pi bond?

Alkyenes two pi bonds and one sigma bond?

correct...

Another q, how a hybrid orbitals named? like sp^3 or sp^2 what dinotes the 3 or two and what about s^2p^3?

it really depends on the bondings in the molecule. for example, methane CH4 is a sp3 hybridised molecule, i.e - the carbon in the methane molecule needs to hybridise 1 electron in the s orbital with 3 electrons in the next p-orbital (all of them being unpaired initially) in order to exchange electrons with 4 hyrogen atoms and form sigma bonds. the same goes for sp2... (work out the structure and electronic config of ethene to figure out why its an sp2 hybridised molecule ). i dont know abt s2p3 though... never heard of it, i dont know what the 2p stands... is it referring to electrons in the 2p orbital??

-mak10

You mentioned psychiatry and being a general practitioner, but keep in mind you'll have to go through medical school for those.

speaking of medical school... i am kinda confused of the chronology of degrees you need to undertake in order to be a GP, for example. it all starts with MCAT, as I've heard... but then, I've also heard that you dont need MCATs if you've done A-Levels.... is that true? And what exactly is after MCATs?? and how many years are required to finish each of the degree courses that follows after the MCATs?? at what point of time do you get to be an MD. ?? thanks guys!

-mak10

i find the subject of actually being able to synthesize drugs fascinating! you need a pharmacology degree for that, i think. but the market is too saturated with this, i reckon.

-mak10

Obviously we surpass them eventually, but for that time, they are more intelligent than us.

so if we can develop a drug that can increase the life-span of the average dog to that of the average man.. can it then surpass us by its 7x intelligence?? just a thought...

-mak10

finally, some responses! thx guys... i asked my school, whther I can do AS-Level math but i am not allowed to take more than 3 subs... which is very annoying!! and i dunno if we can do this privately either.. grrrr!! so many decisions.... i guess it pays to think about what you wanna do in the future when you're givin your GCSEs... but i didn;t. nonetheless.... can you guys advise me on a career, that is science application-based, that is more at demand these days.... i cant seem to get a decent figure on any of the science career options! all of them appear to be saturated throughout the world! my choices right now (after narrowing down among hundreds!) are allergy/immonology specialist, psychiatrist, dentist, or just a general practitioner. are my present a-level subjects (i.e - bio/chem/phy) adequate in doing a degree in any one of those career choices? thnx again!

-mak10

<bump> i really need some good advice... and its been a while i posted this and received no response yet. does anybody have trouble understanding my situation.. if so, plz inform me... thx!

-mak10

what qualifications must you possess (like a BSc or MSc) to be called a nanotek expert or something?

-mak10

thx skye and mokele... i just had my exams today anyways. one of the questions was similiar to 1) and it was like a polypeptide is made of 'n' number of amnio acids and there are 'r' number of different amino acids available. so what is the expression that gives the minimum number of different polypeptides possible with these variables? i think i chose r^n.... unless i remember the question incorrectly. is it right?

-mak10

ok, i need some help.. some serious help! i recently undertook AS-level bio/chem/phy having done my GCSEs and i've had some pretty good grades in the latter. My former just ended today.. its all over and I think my results are gonna be published sometime in Jan. I've done rather good in physics, ok in chem and very good in bio. now... the major reason i took these subjects is because i thought there was a good life to be lived as a scientist, a biomedical engineer, perhaps... with good wage and interesting work (since i love science). and everyone advised me so. but realizing now and seeing all the entry requirements in order for a degree for the universities that I've come across.... you need a basic A-level in math too. is this true for all science application-based subjects like biomedical science, biotek, medical physicist, and almost all general engineering based fields that are closely related with bio/chem/phy ?? if so... now that I have my AS-Levels on all the above three (and I don't wanna spend another year for doing separately one subject!!)... assuming that i do very good in bio (which i really think i will), will it be wise for me to drop it for A2 and take the AS math instead?? i dont know... i am very confused... will they only accept me for their degree based on AS math (i can assure that i can do very good there, since i have a strong GCSE record) and i dont want to waste another year in unis doing foundations either. any good advise from people who've 'been-thru-and-done-that' will be greatly appreciated!!

-mak10

could you explain the reasoning in q.1 ?? is there some kid of formula for these things?

-mak10

I have come across certain simple questions in my MCQ past papers whose answers I am not really very sure of... so here it goes:

1) if there were 34 amino acids and DNA only contained two types of nitrogenous bases, what would be the minimum number of bases per codon that could code for proteins?

2) what single feature is correct for all enzymes?

3) A capillary tube is inserted into the phloem. what force/pressure causes the sap to flow out of the tube?

4) what proportion (in %) of the stored chemical energy in grass is converted into new tissue by a growing cow?

ask me for the options if you need'em.

-mak10

Now how does the two cells continue diving if the Chromosomes are not double stranded? Do they regenerate a new strand for the next dividing, or what?

yes, the DNA replicates and the chromosomes again divide into two chromatids, marking the onset of interphase. this can go on an on, depending on the instructions encoded in your genes. if this instruction is disrupted (like in cancer), then the cell may start dividing uncontrollably and can form unspecialized masses canlled tumors. i don't want wanna into more detail on this but thats basically it.

-mak10

what is the scientific career, that is one of the highest paid in the industry, could one pursue, should he have a keen interest in 'making stuff' (from facial creams to weight loss inducer to any sort of complex useful gadgetry) using principles of biology, physics and chemistry ??

-mak10

Had our retina been non-inverted, like the cephalopod, we'd've developed an entirely different, but similarly effective, set of adaptions.

maybe... possible. but to say that the non-inverted retina would work much better in humans than the present inverted retina that we have.... is not exactly very agreeable, taking in account all the functional features of the present arrangement.

Evidently it is, since it happened. From what I've read, in vertebrates, the eyes develop as outgrowths from the brain, while in cephalopods, they develop as invaginations from the skin. This probably means that they have similar photoreceptor genes, but that the expression of those genes was altered so they were expressed in the skin rather than the embryonic brain tissue.

from what i understand, natural selection, even though it isn't perfect, couldn't be going though all those developmental constraints, that you mentioned, to change the inverted invertebrate eye to the non-inverted arrangement that we see in cephalopods, had that not been an advantage. on the other hand, the inverted eye remained unchanged throughout the millenia in chordates.. and that wouldn't have been possible, if it weren't advantageous for us. since, as we have seen, it could have been wholly possible to change the arrangment as it did in cephalopods.

i don't know what to attribute this inconsistency to. i guess we still have a lot to learn but at the present state, i can think of two possible reasons: 1) either natural selection is conscious and dont like chordates, so stuck them with a supposedly disadvatageous eye arrangement or 2) the inverted eye is actually advantageous for chordates, in the context of their habitual environment and the non-inverted system is advantageous for the cephalopods, in context of theirs. take yr pick!

-mak10

Had our retina been non-inverted, like the cephalopod, we'd've developed an entirely different, but similarly effective, set of adaptions.

maybe... possible. but to say that the non-inverted retina would work much better in humans than the present inverted retina that we have.... is not exactly very agreeable, taking in account all the functional features of the present arrangement.

Evidently it is, since it happened. From what I've read, in vertebrates, the eyes develop as outgrowths from the brain, while in cephalopods, they develop as invaginations from the skin. This probably means that they have similar photoreceptor genes, but that the expression of those genes was altered so they were expressed in the skin rather than the embryonic brain tissue.

from what i understand, natural selection, even though it isn't perfect, couldn't be going though all those developmental constraints, that you mentioned, to change the inverted invertebrate eye to the non-inverted arrangement that we see in cephalopods, had that not been an advantage. on the other hand, the inverted eye remained unchanged throughout the millenia in chordates.. and that wouldn't have been possible, if it weren't advantageous for us. since, as we have seen, it could have been wholly possible to change the arrangment as it did in cephalopods.

i don't know what to attribute this inconsistency to. i guess we still have a lot to learn but at the present state, i can think of two possible reasons: 1) either natural selection is conscious and dont like chordates, so stuck them with a supposedly disadvatageous eye arrangement or 2) the inverted eye is actually advantageous for chordates, in the context of their habitual environment and the non-inverted system is advantageous for the cephalopods, in context of theirs. take yr pick!

-mak10

1.Which newton's law describes inertia is proportional to mass? 1st or 2nd?

i think its the first law since it describes how objects continue with their state of rest or motion unless compelled otherwise by an external force. the bigger the mass, the more inertia requied to affect its state. the second law highlights only the rate of change of momentum of a body in the direction of the force.

2.An object is on a slope, the graph of v-t shows that there is negative acceleration, how do you explain it ?

the object is decelerating.

-mak10

1.Which newton's law describes inertia is proportional to mass? 1st or 2nd?

i think its the first law since it describes how objects continue with their state of rest or motion unless compelled otherwise by an external force. the bigger the mass, the more inertia requied to affect its state. the second law highlights only the rate of change of momentum of a body in the direction of the force.

2.An object is on a slope, the graph of v-t shows that there is negative acceleration, how do you explain it ?

the object is decelerating.

-mak10

thanks for the info mokele... i'll look into this cephalopods thing when I've the time. but it would have been more appealing if i could find some real experiment being carried out on this... as to whther the non-inverted arrangement would work better in human eyes, but i understand that this might raise some ethical issues, so i'll stay quiet

but i will make some comments on your post,

Think of it as if the retinal epithelium in our eyes, photoreceptors and all, were taken out, flipped over, and placed back against the back wall of the eye (in terms of geometry, not that such an operation could work). They'd still be the same distance from the retinal epithelium, but facing the other way around.

but then, where would you place the choroidal capillaries, that suppy blood to the retinal epithelium?? also, i learned that the bipolar and ganglion cells present are actually very important in being where they are, i.e - in between the incoming light and the photoreceptors. I finally found a link to the American Scientist article I was talking about:

How the Retina Works

Its by Dr. Helga Kolb who is considered an authority in the human retina. The article is a bit long and heavily detailed, so i'll just quote a few passages from her paper to highlight my point:

First off, she starts off explaining the very thing we are discussing about (all emphasis in italics are mine):

Intuitively, one might expect that the surface of the retina (the layer exposed to the liquid in the eyeball's vitreous chamber) would contain the sensory cells, the photoreceptors, but actually these cells lie at the very back of the retina; light rays must pass through the entire retina before reaching pigment molecules to excite. This is because the pigment-bearing membranes of the photoreceptors have to be in contact with the eye's pigment epithelial layer, which provides a steady stream of the vital molecule, retinal or vitamin A. Retinal becomes fixed in the photoreceptors' opsin proteins, where this small molecule changes its conformation in response to photons, or packets of light.

Also unknown to me was the presence of horizontal cells, let alone their vital function. These are also present between the photoreceptors and the incoming light. About them she writes:

Horizontal cells respond to more than the photoreceptors that link to them. Feedback signals from the inner plexiform layer influence horizontal-cell activity as well. These feedback signals are transmitted via substances such as dopamine, nitric oxide and retinoic acid. The result is that horizontal cells modulate the photoreceptor signal under different lighting conditions—allowing signaling to become less sensitive in bright light and more sensitive in dim light—as well as shaping the receptive field of the bipolar cells, as we have seen.

She also gives us some good amount of very detailed information regarding the ganglion and amacrine cells that are also involved in the processing. I wouldn't wanna quote all that here since this can really lengthen the post and I don't like long posts myself ! Nonetheless, anyone interested can go ahead and read it up... its very high stuff but very interesting.

You also write:

so the ancestral invertebrates (from which the chordates had evolved) also had the inverted arrangement??

 

 

Yep. Photoreceptor cells are delicate, so exposing them to the external environment wouldn't be good. And, when you're small and pretty much transparent, inverting them solves the problem nicely.

but cephalopods are also invertebrates, arent they? i dont know if they're small or transparent, but they do appear to have the non-inverted arrangement, as you've said. that would mean that the ancestral invertebrates changed from the advantageous inverted retina to the not-so-advantageous non-inverted retina and it bloomed in cephalopods. is that evolutionarily possible?? i've got some more questions since this is all very interesting and stuff and i am no expert, (which is why i've to rely on authorities ). besides, i've to sleep... so later!

-mak10

thanks for the info mokele... i'll look into this cephalopods thing when I've the time. but it would have been more appealing if i could find some real experiment being carried out on this... as to whther the non-inverted arrangement would work better in human eyes, but i understand that this might raise some ethical issues, so i'll stay quiet

but i will make some comments on your post,

Think of it as if the retinal epithelium in our eyes, photoreceptors and all, were taken out, flipped over, and placed back against the back wall of the eye (in terms of geometry, not that such an operation could work). They'd still be the same distance from the retinal epithelium, but facing the other way around.

but then, where would you place the choroidal capillaries, that suppy blood to the retinal epithelium?? also, i learned that the bipolar and ganglion cells present are actually very important in being where they are, i.e - in between the incoming light and the photoreceptors. I finally found a link to the American Scientist article I was talking about:

How the Retina Works

Its by Dr. Helga Kolb who is considered an authority in the human retina. The article is a bit long and heavily detailed, so i'll just quote a few passages from her paper to highlight my point:

First off, she starts off explaining the very thing we are discussing about (all emphasis in italics are mine):

Intuitively, one might expect that the surface of the retina (the layer exposed to the liquid in the eyeball's vitreous chamber) would contain the sensory cells, the photoreceptors, but actually these cells lie at the very back of the retina; light rays must pass through the entire retina before reaching pigment molecules to excite. This is because the pigment-bearing membranes of the photoreceptors have to be in contact with the eye's pigment epithelial layer, which provides a steady stream of the vital molecule, retinal or vitamin A. Retinal becomes fixed in the photoreceptors' opsin proteins, where this small molecule changes its conformation in response to photons, or packets of light.

Also unknown to me was the presence of horizontal cells, let alone their vital function. These are also present between the photoreceptors and the incoming light. About them she writes:

Horizontal cells respond to more than the photoreceptors that link to them. Feedback signals from the inner plexiform layer influence horizontal-cell activity as well. These feedback signals are transmitted via substances such as dopamine, nitric oxide and retinoic acid. The result is that horizontal cells modulate the photoreceptor signal under different lighting conditions—allowing signaling to become less sensitive in bright light and more sensitive in dim light—as well as shaping the receptive field of the bipolar cells, as we have seen.

She also gives us some good amount of very detailed information regarding the ganglion and amacrine cells that are also involved in the processing. I wouldn't wanna quote all that here since this can really lengthen the post and I don't like long posts myself ! Nonetheless, anyone interested can go ahead and read it up... its very high stuff but very interesting.

You also write:

so the ancestral invertebrates (from which the chordates had evolved) also had the inverted arrangement??

 

 

Yep. Photoreceptor cells are delicate, so exposing them to the external environment wouldn't be good. And, when you're small and pretty much transparent, inverting them solves the problem nicely.

but cephalopods are also invertebrates, arent they? i dont know if they're small or transparent, but they do appear to have the non-inverted arrangement, as you've said. that would mean that the ancestral invertebrates changed from the advantageous inverted retina to the not-so-advantageous non-inverted retina and it bloomed in cephalopods. is that evolutionarily possible?? i've got some more questions since this is all very interesting and stuff and i am no expert, (which is why i've to rely on authorities ). besides, i've to sleep... so later!

-mak10

Reduced sensitivity to light, and the whole problem of "detatched retinas".

I am not an expert in this, which is why I need to ask my superiors. but can you give me any experimental evidence for this... that a non-inverted eye would increase resolution and acuity of the eye than the inverted arrangement?? no doubt, its going to be more sensitive to light, i agree.... but the question is more of its maintenance. can it maintain that sensitivity for an appreciable period of time, taking in account of the fact of the increased distance of the retinal epithelium (that is actually very important for the proper functioning of the photoreceptor cells!) from the photoreceptors in a non-inverted arrangement? Also, how would the non-inverted eye solve the problem of alleviating the risk of a detached retina??

On top of that, her logic about warm-blooded animals needing it is similarly off, for two reasons: 1) I cannot think of why a human eye needs more energy than, say, a lizard eye, since both are similarly acute

do lizard eyes possess a similar density of photoreceptor cells as the human eye? if yes, then I would agree with you.

2) the vertebrate eye is present in this form in *all* vertebrates, including cold-bloods (which are the vast majority of species anyway).

agreed, but the density of the the photoreceptors in different species are different and I think that determines the energy considerations.

It evolved from an inverted eye, that or the original chordates.

so the ancestral invertebrates (from which the chordates had evolved) also had the inverted arrangement??

Furthermore, there was a very good article on the American Scientist entitled How the Retina works and it had something at the end about certain ganglions (which, BTW, are facing towards the incoming light) working as a photoreceptor itself... along with the fact that they are necessary to sharpen the vision. But nonetheless, the bottom line would depend on any experimental evidence provided (otherwise this entire theory of the non-inverted being better than an inverted eye is nothing more than a mere conjecture!).

its been also said that the inverted arrangement we have is so sensitive as it will produce an electrical signal even from a single photon (!!)... that it really defeats the purpose of having a non-inverted eye.... don't you think?? just my thoughts....

-mak10

Reduced sensitivity to light, and the whole problem of "detatched retinas".

I am not an expert in this, which is why I need to ask my superiors. but can you give me any experimental evidence for this... that a non-inverted eye would increase resolution and acuity of the eye than the inverted arrangement?? no doubt, its going to be more sensitive to light, i agree.... but the question is more of its maintenance. can it maintain that sensitivity for an appreciable period of time, taking in account of the fact of the increased distance of the retinal epithelium (that is actually very important for the proper functioning of the photoreceptor cells!) from the photoreceptors in a non-inverted arrangement? Also, how would the non-inverted eye solve the problem of alleviating the risk of a detached retina??

On top of that, her logic about warm-blooded animals needing it is similarly off, for two reasons: 1) I cannot think of why a human eye needs more energy than, say, a lizard eye, since both are similarly acute

do lizard eyes possess a similar density of photoreceptor cells as the human eye? if yes, then I would agree with you.

2) the vertebrate eye is present in this form in *all* vertebrates, including cold-bloods (which are the vast majority of species anyway).

agreed, but the density of the the photoreceptors in different species are different and I think that determines the energy considerations.

It evolved from an inverted eye, that or the original chordates.

so the ancestral invertebrates (from which the chordates had evolved) also had the inverted arrangement??

Furthermore, there was a very good article on the American Scientist entitled How the Retina works and it had something at the end about certain ganglions (which, BTW, are facing towards the incoming light) working as a photoreceptor itself... along with the fact that they are necessary to sharpen the vision. But nonetheless, the bottom line would depend on any experimental evidence provided (otherwise this entire theory of the non-inverted being better than an inverted eye is nothing more than a mere conjecture!).

its been also said that the inverted arrangement we have is so sensitive as it will produce an electrical signal even from a single photon (!!)... that it really defeats the purpose of having a non-inverted eye.... don't you think?? just my thoughts....

-mak10

I know that 'vitamin' comes from 'vital amine', because they thought, early on, that all vitamins were amines, but what's the etymology of 'hormone'?

According to Merriam-Webster, its derived from the Greek word hormOn, present participle of horman to stir up, from hormE impulse, assault; akin to Greek ornynai to rouse.

-mak10