Final answer:
Lymphocytes are a type of white blood cell that make up about 20-30% of all leukocytes in the blood. They include B cells and T cells, each with different functions.
Step-by-step explanation:
Lymphocytes are a type of white blood cell that play a crucial role in the immune response. They make up about 20-30 percent of all leukocytes in the blood. There are two major types of lymphocytes, called B cells and T cells, which mature in different organs and have different functions.