What does it mean to be a “successful” organism? Bacteria are certainly the most numerous organisms on Earth, they live in nearly all environments, and they are the least susceptible to being eliminated through environmental catastrophe. Are they Earth’s most successful organisms?

Microbes:

a. produce most of the world’s atmospheric oxygen.

b. make nitrogen available to plants.

c. recycle dead organic matter.

d. account for most of the world’s biomass.

e. All of the above.

Viruses:

a. are the smallest living things.

b. have only one organelle.

c. are beneficial to most organisms.

d. replicate only by invading living cells.

e. have circular chromosomes.

All viruses possess ______, which they

a. toxins; kill cells with

b. cell walls; protect themselves with

c. DNA or RNA; copy inside themselves

d. many cells; insert inside a host cell

e. DNA or RNA; transfer into a host cell

Bacteria:

a. are single-celled eukaryotes.

b. live outside cells.

c. reproduce sexually or asexually.

d. are multicelled prokaryotes.

e. are single-celled prokaryotes.

Within the human body, bacteria exist in greatest numbers in the _____, with most of these bacteria having a ______ relationship with their human host.

a. lungs; commensal

b. feet; antagonistic

c. digestive tract; mutualistic

d. digestive tract; pathogenic

e. kidneys; mutualistic

Archaea (select all that apply):

a. are single-celled prokaryotes.

b. are restricted to marine environments.

c. are superficially similar to bacteria.

d. are restricted to extreme environments.

e. constitute one of the three domains of life.

Protists were the first life-forms to (select all that apply);

a. appear on Earth.

b. reproduce through binary fission.

c. reproduce sexually.

d. evolve following bacteria and archaea.

e. exhibit true multicellularity.

Phytoplankton are important because they (select all that apply):

a. produce antibiotics.

b. produce oxygen.

c. sit at the base of terrestrial food chains.

d. sit at the base of aquatic food chains.

e. fight viruses.

Human beings appear to have evolved into their present anatomical form in _______.

Were modern human beings the first hominin species to reach Europe and Asia?