Which of the following statements is true?
a. arteries carry only oxygenated blood.
b. the systemic circuit leaves the heart from the left ventricle.
c. blood never passes through more than one capillary bed on its trip through the systemic circuit.
d. platelets survive a longer time than erythrocytes.
e. blood from the pulmonary system returns to the heart at the right atrium.

The true statement is option B.

Explanation:

The systemic circuit is the component of the circulatory system, which carries the blood from the heart, and supply it to the majority of the organs and tissues, and returns it back to the heart. The oxygenated blood from the lungs goes into the left atrium and is mediated towards the left ventricle in order to supply the blood to the organs of the body.  

The systemic circuit is different from the pulmonary circuit that only mediates blood between the heart and lungs.  

a few examples of ethical concerns involving genetically engineering of humans include

-privacy of genetically tested people

- potential side effects

-long term effects

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.