Chapter 25

Question 1

a collection of abiotically produced molecules surrounded by a membrane or membrane-like structure.

Answer 1

protobiont

Question 2

an RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing.

Answer 2

ribozymes

Question 3

a method for determining the absolute ages of rocks and fossils, based on the half-life of radioactive isotopes.

Answer 3

radiometric dating

Question 4

the amount of time it takes for 50% of a sample of a radioactive isotope to decay.

Answer 4

half-life

Question 5

the division of Earth’s history into time periods, grouped into three eons–Archaean, Proterozoic, and Phanerozoic–and further subdivided into eras, periods, and epochs.

Answer 5

geologic record

Question 6

layered rock that results from the activities of prokaryotes that bind thin films of sediment together.

Answer 6

stromatolites

Question 7

a process in which a unicellular organism (the “host”) engulfs another cell, which lives within the host cell and ultimately becomes an organelle in the host cell; also refers to the hypothesis that mitochondria and plastids were formerly small prokaryotes that began living within larger cells.

Answer 7

endosymbiosis

Question 8

a hypothesis for the origin of eukaryotes consisting of a sequence of endosymbiotic events in which mitochondria, chloroplasts, and perhaps other cellular structures were derived from small prokaryotes that had been engulfed by larger cells.

Answer 8

serial endosymbiosis

Question 9

a relatively brief time in geologic history when large, hard-bodied forms of animals with most of the major body plans known today appeared in the fossil record. This burst of evolutionary change occurred about 535-525 million years ago.

Answer 9

Cambrian explosion

Question 10

period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill vacant ecological roles in their communities.

Answer 10

adaptive radiations

Question 11

evolutionary change in the timing or rate of an organism’s development.

Answer 11

heterochrony

Question 12

the retention in an adult organism of the juvenile features of its evolutionary ancestors.

Answer 12

paedomorphosis

Question 13

any of the master regulatory genes that control placement and spatial organization of body parts in animals, plants, and fungi by controlling the developmental fate of groups of cells.

Answer 13

homeotic genes