Which examples are ways that models can help scientists solve problems? Select all that apply.

A. A model can represent something very large like the solar system.

B. A model can represent something very small like a single cell.

C. A model can represent something very complex like the flow of energy in an ecosystem.

D. A model can represent something that cannot be seen or touched.

E. A model can represent every aspect of a complex system.

1.A model can represent something very large like the solar system.

2.A model can represent something very small like a single cell.

3.A model can represent something very complex like the flow of energy in          an ecosystem.

4.A model can represent something that cannot be seen or touched.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.