A circular molecule of DNA contains 1 million base pairs. If the DNA synthesis at a replication fork occurs at a rate of 100,000 nucleotides per minute, how much time will theta replication require to completely replicate the molecule, assuming that theta replication is bidirectional?

Explanation:

1. In bidirectional replication;  there are two replication forks, and each proceeding at a rate of 100,000 (as given in the question) nucleotides per minute.  

2. So, by  the given rate of replication, we can calculate that, it would require 5 minutes for the circular DNA molecule to be replicated by bidirectional replication because each fork synthesize  500,000 nucleotides in 5 minutes ( 100,000 per minute) ( as given, in 5 minutes × 100,000 nucleotides per minute= 500,000 and by 2 forks= 1,000,000) within the time period.  

a- all cells come from pre-existing cells

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.