Population density is defined as a. an approximation of a number, based on reasonable assumptions. b. the number of individuals of a population in a specific area. c. the number of individuals moving into a population. d. the smallest level of ecological organization.

Plz plz plz quick! 49 points for whoever which of the following statements about greenhouse effect is true? *life on earth is suffering because of greenhouse effect *the greenhouse effect is caused by human activity *all greenhouse gases are harmful *life on earth would not exist without the greenhouse effect

How does pregnancy begin? a) a placenta forms in the uterus b) a sperm reaches an egg in the fallopian tubec) the blastocyst differentiates into two cell types d) contractions begin in the uterine wallapex

Environmental differences within ecosystems are generally caused by