Which of the test tubes shown below was most likely produced by a sprig of elodea and a snail in the dark after 12 hours of incubation?
test tube 1
test tube 2
test tube 3
test tube 4

the test tube will be most likely the one with yellowish color.

This happen because of the respiration process between the snail and Elodea. Actually, this will heavily affected by the control factors. The more elodea that exist in the incubation, the lower the amount of CO2 would be,

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).