Nucleotides consist of a _________

A. Microvilli: Microvilli are tiny, finger-like projections on the apical surface of some cells, especially in the small intestine. They increase the surface area of the plasma membrane, allowing the cell to absorb more nutrients efficiently.

B. Stereocilia: Stereocilia are long, non-motile projections found in certain specialized cells, such as in the epididymis, and are primarily involved in mechanosensation and absorption, but they are less widespread than microvilli.

C. Primary cilia: Primary cilia are single, non-motile organelles present on many cells that function mainly as sensory structures to detect environmental signals rather than increase nutrient absorption.

D. Flagella: Flagella are long, whip-like structures used for cell motility, such as in sperm cells. They do not contribute significantly to nutrient absorption.

A. Organ systems operate independently of each other to maintain life: Organ systems work interdependently, with each system contributing to the overall homeostasis and function of the body rather than functioning in isolation.

B. The endocrine system is not a true structural organ system: The endocrine system is a recognized organ system consisting of glands that secrete hormones, which regulate various physiological processes, making it a true structural and functional system.

C. The immune system is closely associated with the lymphatic system: The lymphatic system provides structures such as lymph nodes, spleen, and lymph vessels that support immune responses. Lymphocytes and other immune cells travel through these pathways, linking immunity and lymphatic function.

D. Organ systems can be composed of cells or tissues, but not both: Organ systems are made up of multiple tissues, which in turn are composed of cells. Both levels are essential for the structure and function of organ systems.