Answer:
a) hypothalamus
Explanation:
Within the hypothalamus are nerve cells that, when activated, produce the sensation of hunger.
Answer: Immune system
Explanation:
Lymphocytes are a class of white blood cells (leukocytes) involved in immune response when activated by the a foreign molecule (an antigen). B lymphocytes develop in the bone marrow of mammals and are responsible for the production of circulating antibodies.
Thus, lymphocytes are associated with the immune system.
There is obviously not a definite number because there are so many kinds of insects that we are not familiar with yet. However, approximate numbers mention as low as 2 million up to as high as 30 million. Scientists cannot still determine the correct number, but it is somewhere between 2 and 30 million species.
