2. How has scientific understanding about the composition of the universe changed over time? Select the two correct answers. The percentage of dark matter has shrunk in scientists' estimates since the 1980s
The percentage of unknown material has grown in scientists' estimates since the 1970%
The percentage of ordinary matter has grown in scientists' estimates.
The percentage of dark energy has shrunk in scientists estimates

Which of the following statements is true of enzymes? a)they dont provide an active site for substrates to bind in a reaction b)they act on a specific type of substrate in a reaction c)they unusable after a reaction d)they change shape after a reaction

Autotrophs a.consume their food to get energy b.may use photosynthesis to gain energy c.are also called consumers d.cannot use solar energy

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.