Which is the most accurate description of an ecosystem?
a. an ecosystem consists of a biological community-the physical and chemical factors-that make up its abiotic environment
b. an ecosystem consists of the biological community that occurs in some locale
c. an ecosystem consists of the biological community that occurs in some locale and the chemical factors that make up its biotic or abiotic enviorment

All phases of matter may have a fixed mass

You will create a molecular clock model for an arthropod gene. follow these guidelines to make your model: . your timeline will span from 90 million years ago to the present. the common ancestor in your model is an arthropod that lived 90 million years ago. the gene that you'll track codes for a protein in the species venom . the dna sequence youll track contains 10 nitrogen bases. you can choose the order of the bases and where the mutations occur. this gene mutates at a rate of approximately 0.76 base pairs every 17.1 million years. to build your model,/ calculate the estimated time period it takes for 1 base pair to mutate. the first time period will only show the common ancestor. at the beginning of the second time period, three lineages will diverge from the common ancestor, each with a different mutation in their gene sequences. the first and third descendant species will survive for the rest of the timeline. the second descendant species was extinct 50 million years ago. calculate how long it will take for one full base pair mutation to occur. explain your reasoning by constructing a mathematical equation

Which part of the spine is likely to cause a nerve signal to travel faster? a. backbones b. white matter c. nuclei d. gray matter