Helper T cells <span>are required for almost all </span>adaptive immune responses<span>. They not only help activate B </span>cells to<span> secrete antibodies and macrophages </span>to<span> destroy ingested microbes, but they also help activate cytotoxic </span>T cells to<span> kill infected target </span>cells<span>.</span>
Organs of excretion make up the excretory system. They include the kidneys, large intestine, liver,and lungs. The kidneys filter blood and form urine. They are part of the urinary system, which also includes the ureters, bladder, and urethra.
Nonvascular plants require water for sexual reproduction.
