What are the malleus, incus, and stapes?

The marked structure is the mandible, which is the largest and strongest facial bone forming the lower jaw. It is the only movable bone of the skull, articulating with the temporal bone at the temporomandibular joint (TMJ). The mandible supports the lower teeth and plays a critical role in mastication, speech, and facial structure. It is shaped like a horseshoe and consists of the body and two rami.

A. Maxilla: The maxilla forms the upper jaw and is a fixed bone of the facial skeleton. It contributes to the hard palate, the floor of the orbit, and the upper dental arch. Unlike the mandible, it is immovable and does not form a joint for chewing motion.

B. Zygomatic bone: The zygomatic bone forms the prominence of the cheek and part of the lateral wall of the orbit. It contributes to facial contour and protection of the eye. Compared to the mandible, it is a non-movable facial bone and does not participate in jaw movement or mastication.

C. Mandible: The mandible is the lower jawbone and the only movable bone of the skull. It articulates with the temporal bone at the TMJ, allowing chewing, speaking, and mouth opening. It supports the lower teeth and provides attachment for muscles of mastication such as the masseter and temporalis. Since the marked structure is the movable lower jaw, it corresponds to the mandible.

D. Temporal bone: The temporal bone forms part of the lateral skull and houses structures of the ear. It contributes to the cranial base and forms the socket for the mandibular articulation (TMJ). However, it is not the jawbone itself but rather the bone that articulates with the mandible.

Metabolism refers to the totality of biochemical processes that occur within living organisms to maintain life. These processes include both anabolic reactions, which build complex molecules from simpler ones, and catabolic reactions, which break down molecules to release energy. Metabolism is essential for growth, repair, reproduction, and the maintenance of cellular functions. It is a continuous and highly regulated process that ensures cells and tissues receive the energy and substrates required for survival.

A. The removal of wastes produced by chemical reactions: This describes excretion rather than metabolism. Excretion involves eliminating metabolic waste products such as carbon dioxide, urea, and ammonia from the body. While waste removal is a consequence of metabolic activity, it is not the definition of metabolism itself. Therefore, this option represents only a small component of physiological function rather than the full concept of metabolism.

B. The chemical reactions occurring in an organism that support life: metabolism includes all chemical reactions within a living organism that sustain life. These reactions involve energy production (catabolism) and biosynthesis (anabolism), both of which are essential for maintaining cellular structure and function. Metabolism encompasses processes such as respiration, protein synthesis, and nutrient breakdown. Together, these reactions ensure survival, growth, and homeostasis.

C. The breakdown of food only during digestion: This limits metabolism to digestion alone. While digestion is part of catabolic metabolism, metabolism also includes cellular respiration, biosynthesis, and energy storage processes. Additionally, metabolic reactions occur at the cellular level, not just within the digestive tract. Therefore, this definition is too narrow and does not represent the full scope of metabolism.

D. The transport of oxygen throughout the body: This option describes a function of the circulatory and respiratory systems rather than metabolism. Oxygen transport is carried out by red blood cells and the cardiovascular system to support cellular respiration. While oxygen is essential for metabolic reactions, its transport is not itself metabolism.