Primary succession is a process of forming ecosystems in an area that has never been inhabited before. Since living organisms are necessary for forming the soil, which is a foundation of every land ecosystem, at the point before the soil formation or pedogenesis has occurred the ecosystem provides very few habitats.
1. rise of angiosperms
2. rise of chemoautotrophs and photoautrophs
3. rise of multicellularity
4. rise of bryophytes
5. rise of gymnosperms
6. rise of eukaryotes
7. rise of cyanobacteria
The short answer is that cells respond to the chemical environment in which they find themselves. The cells around them, the specific conditions, and feedback from the environment all create specific chemical cues that inform the cells to which genes should be expressed, and in what amounts. Chemicals include hormones, cytokines, general signaling molecules, such as cAMP, etc.
i literally hopped on google for this, lol.
i hope this helps though. :)
