Nokea
T cells in the immune system can be categorized into different types. What type of T cell directly kills infected body cells?
- A. Helper T cells
- B. Cytotoxic T cells
- C. Regulatory T cells
- D. Memory T cells
Correct Answer: B
Rationale: Cytotoxic T cells directly kill infected body cells by recognizing specific antigens on the surface of infected cells and releasing cytotoxic substances to induce cell death, eliminating the infected cells. Helper T cells assist in coordinating the immune response, regulatory T cells help maintain immune tolerance, and memory T cells mount a faster and stronger response upon re-exposure to a previously encountered antigen. Therefore, the correct answer is cytotoxic T cells as they play a crucial role in directly targeting and destroying infected cells.
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Which statement is TRUE about valence electrons?
- A. They are located in the innermost electron shell.
- B. They have the highest binding energy to the nucleus.
- C. They are most likely to participate in chemical bonding.
- D. They have no influence on the element's chemical properties.
Correct Answer: C
Rationale: Valence electrons are the outermost electrons in an atom's electron cloud and are crucial in forming chemical bonds with other atoms. These electrons determine the reactivity and chemical properties of an element, making option C the correct statement. Option A is incorrect as valence electrons are found in the outer shell, not the innermost shell. Option B is incorrect because valence electrons have lower binding energy compared to inner electrons. Option D is incorrect since valence electrons play a significant role in an element's chemical behavior.
What is the process of converting lactic acid back into pyruvate called?
- A. Glycolysis
- B. Gluconeogenesis
- C. Cori cycle
- D. Oxidative phosphorylation
Correct Answer: C
Rationale: A) Glycolysis is the process of breaking down glucose into pyruvate.
B) Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources.
C) The Cori cycle is the process by which lactic acid produced by anaerobic metabolism in muscles is transported to the liver and converted back into glucose or pyruvate.
D) Oxidative phosphorylation is the process by which ATP is synthesized using energy derived from the transfer of electrons in the electron transport chain.
During embryonic development, all tissues originate from
- A. Epithelial tissue only
- B. Muscle tissue only
- C. Connective tissue only
- D. Embryonic germ layers
Correct Answer: D
Rationale: During embryonic development, all tissues originate from the three primary germ layers: ectoderm, mesoderm, and endoderm. These germ layers give rise to various tissues and organs in the developing embryo through a process called gastrulation. Epithelial, muscle, and connective tissues are derived from these germ layers during development. Therefore, choices A, B, and C are incorrect as tissues do not originate from a single type of tissue but rather from the embryonic germ layers which differentiate into various tissues and organs.
A car skids on a wet road. What is the main force preventing the car from stopping?
- A. Friction
- B. Gravitational force
- C. Normal force from the road
- D. Air resistance
Correct Answer: A
Rationale: The correct answer is A: Friction. Friction is the force that opposes the motion of the car on the wet road surface, making it harder for the car to stop. When the car skids, the friction between the tires and the wet road surface is reduced, leading to a loss of traction and making it challenging for the car to come to a halt. Gravitational force (choice B) is the force that pulls objects toward each other due to gravity and does not directly impact the car's ability to stop on a wet road. The normal force from the road (choice C) is the force exerted by the road surface perpendicular to the car's tires and does not play a significant role in stopping the car. Air resistance (choice D) is the force that opposes the motion of an object through the air, but it is not the main force preventing the car from stopping on a wet road.
Which group of elements is known for their reactivity and ability to form strong bonds with other elements?
- A. Noble gases
- B. Halogens
- C. Alkali metals
- D. Transition metals
Correct Answer: B
Rationale: Halogens are a group of elements in the periodic table known for their high reactivity and ability to form strong bonds with other elements. They possess seven valence electrons, requiring only one more electron to achieve a stable electron configuration, making them highly reactive. Halogens readily form compounds with other elements by gaining an electron to achieve a full outer shell, resulting in the formation of strong covalent bonds. Noble gases (option A), on the other hand, are known for their inertness and stable electron configurations, making them unlikely to form bonds. Alkali metals (option C) are highly reactive but do not form bonds as strong as halogens. Transition metals (option D) are recognized for their variable oxidation states and ability to create complex ions but are not as reactive as halogens when it comes to bond formation.