Q.Which cells stimulate B-cells to form antibodies?

(c) 900 molecules per second.

A single mature plasma cell can secrete antibodies at the remarkably high rate of about 900 molecules per second.

Plasma cells are terminally differentiated B-lymphocytes specialized for large-scale antibody (immunoglobulin) secretion as part of the humoral immune response. A single, fully mature plasma cell has an extensively developed rough endoplasmic reticulum and Golgi apparatus dedicated to antibody synthesis and secretion, enabling it to produce and release antibody molecules at the remarkably high rate of roughly 900 molecules per second — illustrating just how prolific plasma cells are in mounting an effective immune defence.

Plasma cells are antibody 'factories' -- the effector form that activated B cells become.

When a B lymphocyte encounters its specific antigen (often with helper T-cell assistance), it proliferates and differentiates mainly into plasma cells, which are packed with extensive rough endoplasmic reticulum specialised for synthesising and secreting large quantities of antibody (immunoglobulin) molecules matching that antigen. Killer (cytotoxic T) cells directly destroy infected/abnormal cells rather than secreting antibody; memory cells persist long-term to enable a faster response on re-exposure but do not themselves mass-produce antibody; and basophils are innate immune granulocytes involved in inflammatory/allergic responses, not antibody-secreting B-cell derivatives.

Basophils are the blood cells that contain heparin.

Basophils are granulocytic white blood cells whose cytoplasmic granules store heparin (an anticoagulant that inhibits blood clotting) and histamine (involved in inflammatory/allergic responses); tissue-resident mast cells, which are related to basophils, perform a similar role. Lymphocytes, neutrophils and monocytes are other leukocyte types with different primary functions (antibody production/cell-mediated immunity, phagocytosis of bacteria, and phagocytosis/antigen presentation respectively) and do not store heparin.