13) according to theories concerning the origin of life, the atom shown is a likely choice for the basic element of all livings things because it a) is small and unstable. b) is relatively stable and can form four covalent bonds. c) forms four ionic bonds with other elements and itself. d) is large and takes up enough space to fill the structure of a cell.

Which best explains why viruses do not have special structures or enzymes that allow them to make their own food? viruses can use energy in living cells that they infect. viruses can replicate inside a host that they infect. viruses can cause contagious illnesses in host cells. viruses integrate their rna or dna into infected cells.

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

Anne, an intern in a microbiology lab, was observing the characteristics of various specimens of protists. match each specimen to the category of protist to which it belongs.