<em>Answer:</em>
<em>A group of cells working together is defined as a tissue and several tissues working together comprise an organ. ... The heart is used as an example of an organ which is made up from muscle and valve tissue.</em>
<em>Explanation:</em>
Antibodies are immunoglobulins which are directed against specific antigens present on foreign substances or on pathogens.
<span>A parasite is an organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense. Hope I helped!</span>