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 of the following is NOT a type of asexual reproduction in bacteria?
- A. Binary fission
- B. Conjugation
- C. Budding
- D. Transduction
Correct Answer: D
Rationale: A) Binary fission: This is a common method of asexual reproduction in bacteria where a single cell divides into two identical daughter cells.
B) Conjugation: This is a process in which genetic material is transferred between bacterial cells through direct cell-to-cell contact, leading to genetic recombination.
C) Budding: Budding is a form of asexual reproduction where a new organism develops from an outgrowth or bud on the parent organism.
D) Transduction: Transduction is a method of horizontal gene transfer in bacteria where genetic material is transferred from one bacterium to another by a bacteriophage (a virus that infects bacteria). It is not a form of asexual reproduction in bacteria.
Therefore, the correct answer is D) Transduction, as it is not a type of asexual reproduction in bacteria but a mechanism of genetic exchange.
What happens to the frequency of a wave if its wavelength decreases while the speed remains constant?
- A. Frequency decreases
- B. Frequency increases
- C. Frequency remains constant
- D. Frequency becomes zero
Correct Answer: B
Rationale: The correct answer is B: Frequency increases. Frequency and wavelength are inversely proportional in a wave with a constant speed. When the wavelength decreases while the speed remains constant, the frequency must increase to maintain the constant speed of the wave. This relationship is governed by the equation: speed = frequency x wavelength. Choice A is incorrect as frequency increases when wavelength decreases. Choice C is incorrect as the frequency changes in this scenario. Choice D is incorrect as the frequency does not become zero but increases when the wavelength decreases.
What is the function of ribosomes?
- A. Packaging and transporting proteins
- B. Storing genetic material
- C. Controlling cell division
- D. Synthesizing proteins
Correct Answer: D
Rationale: The correct answer is D: Synthesizing proteins. Ribosomes are cellular organelles responsible for protein synthesis. They read the messenger RNA (mRNA) and utilize the information to assemble amino acids into proteins through a process known as translation. Choice A, packaging and transporting proteins, is incorrect as this function is typically performed by the Golgi apparatus and vesicles. Choice B, storing genetic material, is incorrect as genetic material is usually stored in the nucleus in the form of DNA. Choice C, controlling cell division, is incorrect as this function is primarily regulated by the cell cycle checkpoints and specific proteins involved in cell cycle regulation.
How does the Pauli exclusion principle relate to the structure of the atom?
- A. It defines the maximum number of electrons allowed in each energy level.
- B. It explains why oppositely charged particles attract each other.
- C. It describes the wave-particle duality of electrons.
- D. It determines the arrangement of protons and neutrons in the nucleus.
Correct Answer: A
Rationale: The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers. This principle directly influences the structure of the atom by defining the maximum number of electrons allowed in each energy level. As a result, it helps determine the electron configuration and the arrangement of electrons in different orbitals within an atom. Choices B, C, and D are incorrect as they do not directly relate to the Pauli exclusion principle's specific impact on the electron distribution within an atom.
Salts are formed by the reaction between:
- A. Two acids
- B. An acid and a base
- C. Two bases
- D. A metal and a nonmetal only
Correct Answer: B
Rationale: Salts are formed by the reaction between an acid and a base. This reaction is known as a neutralization reaction. In this reaction, the acid donates a proton (H+) to the base, resulting in the formation of water and a salt as the products. Choice A is incorrect because salts are not formed by the reaction of two acids. Choice C is incorrect as salts are not produced by the reaction of two bases. Choice D is incorrect because while salts can be formed from the reaction between a metal and a nonmetal, it is not the only way salts are produced.