Smooth muscle, also called involuntary muscle, muscle that shows no cross stripes under microscopic magnification. It consists of narrow spindle-shaped cells with a single, centrally located nucleus. Smooth muscle tissue, unlike striated muscle, contracts slowly and automatically.
Negative feedback systems are responses in your body that happen in order to maintain homeostasis and balance within a system. One example of negative feedback system is thermoregulation. If we did`nt have that, the temperature of our organisms would change drastically and it could cause bad consequences for our health and body functioning. The correct answer is letter A: Negative feedback systems allow humans to regulate ans stabilize their systems.
In general, yes, the dorsal blood vessel of a worm be seen from the worm's exterior because a worm's "skin" is very thin. Although of course there are exceptions.
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Chromosomes females have xx and males are xy