A person who has AIDS contracts rare and often life-threatening infections because their helper T cell count is so low. Which of the following components of the immune response still respond to antigen despite the low helper T cell count?
Clonal selection of B cellsActivation of cytotoxic T cells by helper T cellsagglutination

CLONAL SELECTION OF B CELLS.

Explanation: B cells are also known as B lymphocytes( a type of white blood cell),when antigens binds to receptors in the cell,B lymphocytes in the body recognizes this antigen and selection is made from the pre-existing pool of different antigens,each with it's unique specification,this B lymphocytes undergo reproduction and from there a clonal population of cells are formed which kills/get rid of the antigen.

These antigens are eliminated by either the plasma cells that form immediately from the B lymphocytes secreting antibodies that fight the antigen,but in AIDS (people living with AIDS),the B lymphocytes that fight the antigen are known as memory B cells which are long lived from the stage of proliferation and are left to fight antigens in later life by forming plasma cells.so even if the helper T cells in AIDS patients are low,the memory B cells are stimulated to form plasma cells,activate antibodies to fight off life threatening infections.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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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.