What system is responsible for defending the body against harmful substances? a. circulatory system b. musclar system c. endocrine system d. immune system

The right option is; d. Immune system

The immune system is responsible for defending the body against harmful substances.

The immune system is the body’s defense system that protects the body against infectious pathogens and other invaders. The immune system is composed of many biological structures (special cells, proteins, tissues, and organs) and processes that functions together to protect the body. White blood cells are one of the important cells of the immune system that destroy harmful substances or disease-causing organisms that invade body systems.

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.

the answer is z.

the human body has five levels of organization. level 1: cells. cells are the basic units of life and form the first level of organization. cells in the human body have specific functions. examples include nerve cells, blood cells, liver cells, and so on.