Final answer:
Diabetes mellitus is caused by low or ineffective insulin. Type 1 diabetes is caused by a deficiency of insulin, while type 2 diabetes is caused by target cell resistance to insulin.
Step-by-step explanation:
Diabetes mellitus is a disorder characterized by high blood glucose levels. In cases of diabetes mellitus, the hormone insulin is either low or ineffective. Insulin is produced by the pancreas and allows cells to utilize blood glucose and store excess glucose for later use. When insulin is low or ineffective, cells do not take up glucose, leading to high blood glucose levels. Type 1 diabetes is caused by a deficiency of insulin, while type 2 diabetes is caused by target cell resistance to the effects of insulin.