Where does the phosphorus cycle begin

The phosphorus cycle starts in the earth's crust. The phosphate salts are broken down from the rocks. These salts are washed away into the ground where they mix in the soil.

the first step of the phosphorus cycle involves the extraction of phosphorus from the rocks by weathering.

Explanation:

Weather events, such as rain and other sources of erosion, result in phosphorus being washed into the soil.

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Step 1: DNA replication takes place in the nucleus of the cell. the DNA double helix seperates after that an enzyme named DNA helicase attatches to the DNA molecule and moves along the molecule and 'unzips' the two strands of DNA. now it does this by breaking the hydrogen bonds between the bas pairs.
Step 2: since nucleotides are floating in the nucleus that means there are A, G, T and C's floating around also. these are bases that form hydrogen bonds with the bases of DNA strands.
Step 3: the enzyme they call DNA polymerase catalyzes the formation of the sugar phosphate unts at the sides of the helix. then they connect one base pair to the next one. two new DNA molecules. each one from the old DNA stand and from the new DNA strand.
I hopd this helped :)