Your teacher likes to copy. Found this at https://examples.yourdictionary.com/examples-of-keystone-species.html
Grizzly bears: As predators, bears keep down the numbers of several species, like moose and elk. They also carry and deposit seeds throughout the ecosystem. Bears that eat salmon will leave their dropping and the partially eaten remains that provide nutrients such as sulfur, nitrogen and carbon to the soil.
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. :)
Well, the food is in the environment. I would like to compare it with how bacteriae feed (however my biology is quite rusty), that is, they engulf their food and they "digest" -- not the proper term, since there are no organs to do real digestion -- it.
