Common examples of this would be if you place your hand in extremely warm or cold water, and an immediate response of pulling out of the water or any fluid, is an example of this extreme response, other responses are what is done in everyday, like being thirsty or hungry etc.
These behaviours are shared by all organisms even the most simple ones.
The substance that would be added in order to reverse the reaction would be any substance that is found in the product side. Adding a substance that tends to be a product will shift the equilibrium of the system and will allow the reaction to produce the substances that is found in the reactant side.
Natural selection means that the organisms better adapted to their environment, that is, they have developed the right characteristics/skills/response to the external ambient, have higher chance to survive, making the next generations genetically inherit such acquired surviving characteristics.
These generations will thus have a higher chance of survival, making these species being "naturally selected" as survivors, while those who haven't or are slower in this process, have a higher risk of elimination.
Clearly your only giving 5 points but ok.
Answer: Humans impact the physical environment in many ways: overpopulation, pollution, burning fossil fuels, and deforestation. Changes like these have triggered climate change, soil erosion, poor air quality, and undrinkable water.
Buy less plastic and bring a reusable shopping bag. Use long-lasting light bulbs. Energy efficient light bulbs reduce greenhouse gas emissions. Also flip the light switch off when you leave the room!