Question 1 - Reasoning Through Language Arts Practice Test for the GED Test

This is an article published in World Science News (http://www.world-science.net/) that cites evidence for the theory that some bacteria may have a sense of sight. It was written with the support of eLife.

How Slime Sees

(1) “The idea that bac­te­ria can see their world in bas­ic­ally the same way that we do is pret­ty ex­cit­ing,” said lead re­searcher Con­rad Mul­l­i­neaux, a bi­ol­o­gist at Queen Mary Un­ivers­ity of Lon­don. “The fact that bac­te­ria re­spond to light is one of the old­est sci­en­tif­ic ob­serva­t­ions of their be­hav­ior,” he added. But the fact that they use their bo­dies as eye­balls, he said, though, is “pret­ty ob­vi­ous with hind­sight… we nev­er thought of it un­til we saw it. And no one else no­ticed it be­fore ei­ther, de­spite the fact that sci­en­tists have been look­ing at bac­te­ria un­der mi­cro­scopes for the last 340 years.”

(2) His team of Brit­ish and Ger­man re­search­ers de­scribes in the jour­nal eLife how bac­te­ri­al cells act as the equiv­a­lent of a mi­cro­scop­ic eye­ball or the world’s old­est, small­est cam­era eye.

(3) Cya­no­bac­te­ria live in huge num­bers in wa­ter bod­ies or can form a slip­pery green film on rocks. The spe­cies used in the stu­dy, Sy­ne­cho­cys­tis, lives in freshwa­ter lakes and riv­ers. Cyanobac­te­ria evolved an es­ti­mat­ed 2.7 bil­lion years ago. The fact that they can pro­duce ox­y­gen and con­vert car­bon di­ox­ide to or­gan­ic ma­te­ri­al us­ing en­er­gy from the sun—the pro­cess of pho­to­syn­the­sis—is thought to have caused mass ex­tinc­tions and the old­est known ice age.

(4) As pho­to­syn­the­sis is cru­cial to these bac­te­ri­a’s sur­viv­al, sci­en­tists have sought to un­der­stand how they sense light. Pre­vi­ous stud­ies have shown that they con­tain light-sens­ing mo­le­cules and that they can per­ceive and ap­proach a light source, a pro­cess called pho­to­tax­is.

(5) The new study found they can do this be­cause the cell body acts like a lens. As light hits the round sur­face, it re­fracts, or bends in­to a point on the oth­er side of the cell. This trig­gers move­ment by the cell away from the fo­cused spot. With­in min­utes, the mi­crobe grows ti­ny tentacle-like things called pi­li that reach out to­wards the light. As they at­tach to the sur­face that they’re on, they re­tract and pull the bac­te­ria along.

(6) Sy­ne­cho­cys­tis serves as a spher­i­cal lens but the team thinks that rod-shaped bac­te­ria can al­so trap light and sense the di­rec­tion it is com­ing from us­ing re­frac­tion, act­ing like an op­ti­cal fi­ber.

(7) The sci­en­tists called the find­ings a likely ex­am­ple of con­ver­gent evo­lu­tion—where two or more or­gan­isms evolve si­m­i­lar struc­tures, but us­ing dif­fer­ent ge­net­ic means.

(8) “The phys­i­cal prin­ci­ples for the sens­ing of light by bac­te­ria and the far more com­plex vi­sion in an­i­mals are sim­i­lar, but the bi­o­log­i­cal struc­tures are dif­fer­ent,” said co-author An­negret Wilde from the Un­ivers­ity of Frei­burg in Ger­many.

(9) A Sy­ne­cho­cys­tis cell is about half a bil­lion times smaller than the hu­man eye. As with the ret­i­na in the hu­man eye, the im­age on the rear of the cell will be up­side down. But its res­o­lu­tion will be much low­er, so only a blurred out­line of any ob­ject can be per­ceived. The abil­ity of op­ti­cal ob­jects to dis­tin­guish fi­ne de­tail is de­ter­mined by “an­gu­lar res­o­lu­tion.” In the hu­man eye this is an im­pres­sive 0.02 de­grees; in Sy­ne­cho­cys­tis, an esti­mated 21 de­grees.