Yeast cells, plant cells, and mammal cells all share many similarities in cell signaling. This provides evidence that: a. cell-signaling mechanisms are only found in organisms that use methods of sexual reproduction
b. intercellular communication evolved as a way for multicellular organisms to coordinate cell functions
c. eukaryotic cells use signal transduction pathways while prokaryotic cells use a more primitive form of signaling
d. signal transduction pathways appeared in cells before the evolution of multicellular organisms

What are some things that limit population growth?

Suggest why placing wheels under a heavy box reduces the neccessary force required to push it along at a constant speed.

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area