Which cells engulf antigens and present fragments of them on their own surfaces where they can be recognized by cells that will deal with them? plasma cellst lymphocytesdendritic cellsnk cells

The correct option is DENDRITIC CELLS.

There are two types of immune system in vertebrates, these are  innate immune system and acquired immune system. The acquire immune system is also known as adaptive or specific immune system.  

The adaptive immune system is made up of antibody responses and cell mediated responses, which are brought about by different types of lymphocyte cells, B cells and T cells. Cell mediated immunity involves the activation of natural killer cells, antigen specific cytotoxic T lymphocytes, macrophages, dendritic cells, and various cytokines; these cells are highly specialized cells and they are always released in response to antigens,  they are responsible for the elimination or prevention of growth of  invading pathogens.  

Each of the adaptive immunity cells has its specific manner of operating. The dendritic cells and macrophages operate by engulfing invading pathogens and digesting them into thousands of antigens; these antigens are then detected and engulfed by antigens presenting cells.  

Acquired immunity system always creates immunological memory after an initial encounter with pathogens and this leads to an improved response in case they come in contact with the pathogen again in the future. This mechanism is the basis on which vaccination operates.  

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

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