Nokea
What is the primary function of tight junctions, specialized regions between animal cells?
- A. Communication between cells
- B. Anchorage between cells
- C. Selective passage of materials
- D. All of the above
Correct Answer: C
Rationale: The correct answer is C: Selective passage of materials. Tight junctions act as specialized structures between animal cells that create a barrier to the passage of materials. Their primary function is to prevent the leakage of extracellular fluid and control the selective passage of molecules between cells. This selective control is crucial in regulating the movement of substances across cell layers. Tight junctions do not directly facilitate communication between cells or provide anchorage between cells, as their main role is to regulate the passage of materials. Choices A and B are incorrect as tight junctions do not primarily serve for communication or anchorage between cells.
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Which statement accurately describes the electron cloud model of the atom?
- A. Electrons precisely orbit the nucleus in defined paths.
- B. Electrons occupy specific energy levels around the nucleus with varying probabilities.
- C. Electrons are clustered tightly within the nucleus.
- D. Electrons move randomly throughout the entire atom.
Correct Answer: B
Rationale: The electron cloud model of the atom describes electrons as occupying specific energy levels around the nucleus with varying probabilities. This model does not suggest that electrons precisely orbit in defined paths as stated in option A. It acknowledges the wave-like behavior of electrons and their uncertainty in position, which is not accounted for in options C and D. Option C is incorrect as electrons are not clustered tightly within the nucleus but exist in the space surrounding the nucleus. Option D is incorrect as electrons do not move randomly throughout the entire atom but have specific probabilities of being found in different regions based on their energy levels. Therefore, option B is the most accurate description of the electron cloud model of the atom.
What is the 'lock-and-key' model?
- A. Protein folding
- B. Enzyme-substrate interaction
- C. Muscle contraction
- D. Blood clotting
Correct Answer: B
Rationale: The 'lock-and-key' model describes the specificity of the interaction between enzymes and their substrates. In this model, the enzyme's active site acts like a lock that can only be opened by the specific substrate molecule, which serves as the key. This specific binding ensures that enzymes catalyze particular reactions and do not interact with other molecules indiscriminately. Protein folding (option A) is the process by which a protein attains its functional three-dimensional structure but is not directly related to the lock-and-key model. Muscle contraction (option C) and blood clotting (option D) are complex biological processes but are not directly associated with the lock-and-key model of enzyme-substrate interaction.
Calcitonin, a hormone that helps regulate calcium levels, is produced by the:
- A. Thyroid gland
- B. Parathyroid gland
- C. Thymus gland
- D. Adrenal gland
Correct Answer: A
Rationale: Calcitonin is a hormone produced by the thyroid gland. It helps regulate calcium levels in the body by inhibiting the breakdown of bone and promoting calcium excretion by the kidneys. The parathyroid gland produces parathyroid hormone (PTH), which works in opposition to calcitonin to regulate calcium levels. The thymus gland is involved in the development of the immune system, and the adrenal gland produces hormones such as cortisol and adrenaline. Therefore, the correct answer is the thyroid gland as it specifically secretes calcitonin for calcium regulation.
What is the general formula for an alcohol?
- A. Câ‚™Hâ‚‚â‚™
- B. CₙH₂ₙ₊₂
- C. Câ‚™H₂ₙ₋â‚
- D. Câ‚™Hâ‚‚â‚™O
Correct Answer: D
Rationale: The correct general formula for an alcohol is CnH2n+1OH, which can be simplified to CnH2nO. In this formula, 'n' represents the number of carbon atoms, '2n' represents the number of hydrogen atoms, and 'O' represents the oxygen atom present in the hydroxyl group of the alcohol. Therefore, the correct general formula for an alcohol is CnH2nO. Choice A, Câ‚™Hâ‚‚â‚™, does not account for the oxygen atom, which is essential in alcohols. Choice B, Câ‚™H₂ₙ₊₂, does not include the oxygen atom or the necessary hydrogen atoms for the hydroxyl group. Choice C, Câ‚™H₂ₙ₋â‚, lacks the oxygen atom and also does not fulfill the requirements of the hydroxyl group. Thus, the most accurate representation of the general formula for an alcohol is CnH2nO.
How are genetic markers utilized in paternity testing?
- A. They identify unique sequences in the father's DNA present in the child.
- B. They analyze the presence or absence of specific alleles for certain genes.
- C. They compare the child's blood type to the parents' blood types.
- D. They measure the child's physical resemblance to the father.
Correct Answer: B
Rationale: Genetic markers are specific DNA sequences that can vary among individuals. In paternity testing, genetic markers are used to compare the DNA of the child with that of the alleged father. By analyzing the presence or absence of specific alleles (different forms of a gene) at these genetic markers, scientists can determine the likelihood of paternity. This method is more accurate and reliable than comparing blood types (choice C) or physical resemblance (choice D) as genetic markers provide a direct comparison of DNA sequences between individuals. Therefore, option B is the correct choice as it accurately describes the use of genetic markers in paternity testing.