Match the given terms with the immune defense mechanisms.

antibodies
tissues lining hollow organs
phagocytosis
skin
antigen
leukocytes

cellular
structural
chemical

The immune system is the body's natural defense mechanism against organisms that can cause infection.There are three types of mechanisms:
1. Cellular : refers to the recognition and/or killing of virus and virus-infected cells by leukocytes and  the production of different soluble factors (cytokines) by these cells when stimulated by virus or virus-infected cells

2. Structural: barriers and the immune system defend the body against organisms that can cause infection. Natural barriers include the skin, mucous membranes, tears, earwax, mucus, and stomach acid.

3. Chemical: Some of these include the low pH of the stomach, which inhibits the growth of pathogens; blood proteins that bind and disrupt bacterial cell membranes; and the process of urination, which flushes pathogens from the urinary tract. 

antibodies - chemical
tissues lining hollow organs - cellular
phagocytes - cellular
skin - structural
antigen - chemical
leukocytes - cellular

He used pea plants to study the patterns of heredity.