Nokea
Bone is primarily composed of which of the following inorganic materials?
- A. calcium
- B. magnesium
- C. collagen
- D. potassium
Correct Answer: A
Rationale: Bone is primarily composed of calcium, making up about 70% of its inorganic content. Calcium is essential for bone strength and structure, playing a key role in maintaining bone health. Choice B, magnesium, while important for bone health, is found in smaller amounts in bones compared to calcium. Choice C, collagen, is a protein and is a major organic component of bone, not an inorganic material. Choice D, potassium, is an essential mineral for various bodily functions but is not a primary inorganic material found in bones.
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What is the primary function of the pyloric sphincter?
- A. to regulate the movement of food material from the stomach to the duodenum
- B. to neutralize stomach acid
- C. to prevent digested food materials and stomach acid from entering the esophagus
- D. to begin the process of chemical digestion
Correct Answer: A
Rationale: The primary function of the pyloric sphincter is to regulate the flow of partially digested food material (chyme) from the stomach into the small intestine, specifically the duodenum. This control is essential for proper digestion and absorption of nutrients in the small intestine. Choices B, C, and D are incorrect. Choice B is incorrect because neutralizing stomach acid is primarily the function of the stomach lining and antacid mechanisms. Choice C is incorrect because preventing the backflow of digested food materials and stomach acid into the esophagus is mainly the role of the lower esophageal sphincter. Choice D is incorrect because the chemical digestion process primarily starts in the stomach through the action of gastric juices, not the pyloric sphincter.
Which of the following is the primary physical barrier the body uses to prevent infection?
- A. mucus membranes
- B. stomach acid
- C. skin
- D. urine
Correct Answer: C
Rationale: The correct answer is 'C: skin.' The skin is the primary physical barrier the body uses to prevent infection. It acts as a protective shield that prevents harmful microorganisms from entering the body. The outer layer of the skin, known as the epidermis, acts as a tough physical barrier that blocks the entry of pathogens. Additionally, the skin has special immune cells that can help fight off invaders that manage to breach the physical barrier. Choices A, B, and D are incorrect. While mucous membranes, stomach acid, and urine play important roles in the body's defense against pathogens, the primary physical barrier is the skin, which covers the entire body and provides a robust protective barrier.
Which of the following is specialized tissue in the right atrium that acts as the heart's natural pacemaker by generating the electrical signal for the heartbeat?
- A. sinus venosus
- B. sinoatrial node
- C. atrioventricular node
- D. tricuspid valve
Correct Answer: B
Rationale: The sinoatrial node, often referred to as the SA node, is specialized tissue located in the right atrium of the heart. It functions as the heart's natural pacemaker by generating the electrical signal that initiates each heartbeat. This electrical signal spreads to the atrial muscles and then to the atrioventricular node, causing the heart to contract rhythmically and efficiently. The other options listed do not serve as the heart's natural pacemaker responsible for generating the electrical signal for the heartbeat. Sinus venosus is a developmental structure in fetal hearts, the atrioventricular node delays the electrical signal, and the tricuspid valve is a heart valve that prevents backflow of blood from the right ventricle to the right atrium.
Which of the following biological macromolecules is non-soluble, composed of hydrocarbons, and acts as an important source of energy storage for the body?
- A. carbohydrates
- B. nucleic acids
- C. lipids
- D. proteins
Correct Answer: C
Rationale: Lipids are non-soluble biological macromolecules composed mostly of hydrocarbons such as fatty acids. They act as an essential source of energy storage for the body, providing efficient storage of energy in the form of fats. Carbohydrates are also an energy source for the body, but lipids excel in long-term energy storage. Nucleic acids are not known for energy storage; instead, they are involved in genetic information transmission and protein synthesis. Proteins play diverse roles in the body, such as enzymatic functions, structural support, and immune response, but they are not primarily known as a source of energy storage.
Which of the following distinguishes the isotopes of an element?
- A. Isotopes are atoms of the same element that have different ionic charges.
- B. Isotopes are atoms of elements within the same group on the periodic table.
- C. Isotopes are atoms of the same element that have different numbers of neutrons.
- D. Isotopes are atoms of the same element with different electron configurations.
Correct Answer: C
Rationale: Isotopes are defined as atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. This leads to variations in atomic mass for isotopes of an element. The different number of neutrons in isotopes results in differences in their atomic mass and properties while still belonging to the same element. Choice A is incorrect because isotopes do not have different ionic charges, they have the same chemical properties. Choice B is incorrect because isotopes are not atoms of elements within the same group on the periodic table; they are variants of the same element. Choice D is incorrect because isotopes of an element have the same electron configuration, differing only in the number of neutrons in the nucleus.