What structure surrounds the cell and regulates materials that enter and leave the cell?

Which term refers to the total dollar value of the goods and services produced in a country in a year?

Apopulation of black bears depends on salmon from a stream for food. if a drought causes the stream to run dry one year, how will this likely impact the black bear population?

Which of the following statements about protists are true? a.they are typically found in moist environments. b.they are all unicellular. c.they have a nucleus. d.they are all multicellular.