Use process of elimination. From what you gave me to read, you can cross off competition. A drought killed the plants and not competition to live. Go down the list of words and look up the definition. Look at nudation and ecesis later because they are different words that may or may not be challenging to understand. You know what reaction and migration is without looking it up. Once you cross off all words answers that don't match up, ask yourself, which remaining answer goes? Nudation is basically new plants that have successfully started growing after a huge environmental change. Ecesis is sort of similar however, the establishment in a new habitat or environment is not from a big change. Therefore, nudation is the correct answer.
Metabolic pathways stimulate cell division.
I think its a density dependent limited factor
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.
