Which statement best describes a kay stone species? a. it has little genetic variation. b. it has an extremely high population. c. it remains unaffected by all environmental changes. d. it has a strong influence on the ecosystem. e. it’s the first species to populate a new ecosystem.

The correct answer is D.

A keystone specie refers to a plant or animal which play very important roles in the way a particular ecosystem functions. Without the keystone specie the ecosystem will be totally different or even cease to exist, thus keystone species have strong influence on the ecosystems in which they exist. Most of the time a keystone specie is a dominant predator whose removal allow a prey population to increase dramatically in size and thus reduce the overall diversity in that particular ecosystem.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation: