Histamines are chemicals released by the body as an allergic response.They help the body by reacting when their are "intruders" so when enters, histamine acts as a messenger and sends out a signal for the body to create a reaction helping to get rid of teh intruder through some type of reaction.
The answer is C) selective breeding. This means that humans are deciding what to breed which means this is not a natural selection, but rather an artificial selection.
The scientists rely on the following cues to hypothesise and test for the presence of life on various extraterrestrial bodies:
1. Presence of water
2. Presence of hydrocarbons
3. Presence of carbon
4. Presence of salt pans
The presence of hydrocarbons may indicate that there's anaerobic life thriving beneath the surface of the meteorite. The presence of traces of carbon may indicate that there was life once thriving on its surface ( which however is not possible in case of a meteorite because of its size). The absence of any of the above listed items will indicate that the surface of the meteorite is devoid of any life.
If the stimulus reaches the threshold an action potential will be generated. If the stimulus doesn't reach it no action potential will be generated. If the stimulus will be stronger the action potential will have the same amplitude. The refractory period makes it harder to generate an action potential so they decrease the frequency of action potential production.
