How do populations, and communities respond to external factors such as pollution?

How do chloroplasts set plants apart from other living things

The table below shows the number of foot bones in some horse fossils.horse fossil recordhorse fossil number of foot bonesp 19q 17r 24s 13ancient horses had more bones in their foot then present-day horses. the present-day horse has 11 foot bones. what is the correct order of evolution of the horse starting from the youngest fossil? a. q p r s b. s r p q c. s q p r d. r p q s

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important