Fleming discover a mold as Penicillin<span>, isolated an extract of the unknown agent, and named it penicillin. Then later Florey tested the penicillin on mice and realized it would be as effectively on humans as well.
hope this helps (:
</span><span>
</span>
Explanation:
The lac operon
When lactose is present, bacteria need the enzymes to break it down. But if no lactose is present, bacteria do not need to waste resources making enzymes to break down a sugar that isn't there. Like a switch, the operon is turned on when the enzymes are needed.
Arteries like veins, are tube-shaped vessels that carry blood in the body.
But the difference is that the artery carries oxygenated blood away from the heart to the body. But the veins carry poor-oxygen blood back from the body to the heart!
I hope this helps! :)
<span>Sense organs, such as the ear, and sensory receptors, such as those in the skin, are sensitive to external stimuli such as sound and touch.</span>