Sodium and potassium ion channels have several negatively charged residues at the entry to the channel. on what basis do k+ channels specifically select for k+ ions? (in other words, why dont k+ channels enable na+ ions to cross the membrane? )
a. ionic radius, na+ is to smallb. energy cost, it is to energetically costly to dehydrate na+c. charge, na is slightly more electronegative than k and does not interact with the channel carbonyl groupsd. charge, na is slightly less electronegative than k and does not interact with the channel carbonyl groupse. ionic radius, na+ is too big

A. Ionic radius, Na⁺ is to small.

Explanation:

The channel pore contains a narrow selective filter that is delimited by carbonyl oxygens (C = O) of the polypeptide skeleton. When a K⁺ ion enters the selection filter it interacts with these carbonyl oxygens, and the water molecules to which the K⁺ was attached move, allowing the dehydrated K⁺ to pass through the pore. However, a dehydrated Na⁺ is too small to interact with these carbonyl oxygens in the selective filter, which is kept open. As a consequence, this hydrated sodium ion is too large to pass through the canal.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

he is very short, and he can only reach halfway up on the elevator buttons. but on a rainy day, he has his umbrella with him, and he uses it to poke the button at the top.