Nokea
What is a lysosome?
- A. A sac-like structure that contains enzymes that break down cellular components
- B. A network of tubules that transport proteins and lipids throughout the cell
- C. The site of protein synthesis
- D. The site of cellular respiration
Correct Answer: A
Rationale: A lysosome is a membrane-bound organelle found in animal cells that contains digestive enzymes. These enzymes are responsible for breaking down various cellular components, such as proteins, lipids, carbohydrates, and even foreign particles like bacteria. This breakdown process is crucial for maintaining cell health and function by recycling and disposing of cellular waste. Options B, C, and D are incorrect because lysosomes are not involved in transporting proteins and lipids throughout the cell (option B), protein synthesis (option C), or cellular respiration (option D). Lysosomes primarily function as the cell's 'recycling center' by breaking down and processing cellular materials.
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The Gram stain is a differential staining technique used to classify bacteria based on their cell wall composition. Gram-positive bacteria appear
- A. Pink
- B. Blue
- C. Red
- D. Purple
Correct Answer: D
Rationale: The Gram stain is a differential staining technique that categorizes bacteria into two groups based on their cell wall composition: Gram-positive and Gram-negative. Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, which retains the crystal violet stain used in the Gram staining procedure. Consequently, Gram-positive bacteria appear purple under the microscope after staining. On the other hand, Gram-negative bacteria possess a thinner peptidoglycan layer and an outer membrane that can be penetrated by the counterstain safranin, leading them to appear pink or red. Blue is not typically used to describe the color of bacteria in a Gram stain, making it an incorrect choice.
When ethanol (Câ‚‚Hâ‚…OH) reacts with sodium metal (Na), what is the product?
- A. Ethene (Câ‚‚Hâ‚„)
- B. Sodium ethoxide (Câ‚‚Hâ‚…ONa)
- C. Ethane (C₂H₆)
- D. Sodium acetate (CH₃COONa)
Correct Answer: B
Rationale: When ethanol (C₂H₅OH) reacts with sodium metal (Na), the product formed is Sodium ethoxide (C₂H₅ONa). This reaction is a classic example of a metal displacing hydrogen in an alcohol to form an alkoxide. In this specific case, sodium replaces the hydrogen in ethanol, resulting in the formation of sodium ethoxide. Choice A, Ethene (C₂H₄), is incorrect as it is a different compound formed from the dehydration of ethanol, not its reaction with sodium. Choice C, Ethane (C₂H₆), is incorrect as it is a saturated hydrocarbon, not the product of the reaction of ethanol with sodium metal. Choice D, Sodium acetate (CH₃COONa), is incorrect as it involves acetic acid, not ethanol, reacting with sodium to form the salt sodium acetate.
During embryonic development, most vertebrates exhibit structures called pharyngeal pouches. These pouches eventually develop into different structures in various vertebrate groups, such as the human jaw and inner ear. Pharyngeal pouches are an example of:
- A. Analogous structures with different evolutionary origins but similar functions
- B. Homologous structures with a common evolutionary origin but diverse functions
- C. Vestigial structures that no longer serve a vital function in some organisms
- D. Atavisms, the reappearance of a trait absent in recent generations
Correct Answer: B
Rationale: Pharyngeal pouches in vertebrates are an example of homologous structures because they share a common evolutionary origin. Despite developing into different structures in various vertebrate groups, such as the jaw and inner ear in humans, these structures originated from the same ancestral feature. This concept of homology highlights the evolutionary relationship between different species and how structures can be modified over time to serve different functions while retaining a common origin. Choice A is incorrect because analogous structures have similar functions but different evolutionary origins, which does not apply to pharyngeal pouches. Choice C is incorrect as vestigial structures are remnants of features that were functional in ancestors but have reduced or lost their original function, which is not the case for pharyngeal pouches. Choice D is incorrect because atavisms refer to the reappearance of traits absent in recent generations, which is not the characteristic of pharyngeal pouches.
Identify the opposing muscle pair.
- A. Bicep and tricep (Arm flexion and extension)
- B. Hamstring and quadriceps (Knee extension and flexion)
- C. Pectoralis major and pectoralis minor (Chest muscles)
- D. Trapezius and deltoid (Shoulder movement)
Correct Answer: A
Rationale: The correct answer is A. The bicep and tricep muscles form an antagonistic muscle pair, where one muscle contracts while the other relaxes. The bicep, located on the front of the upper arm, is responsible for arm flexion (bending the elbow), while the tricep, situated on the back of the upper arm, is responsible for arm extension (straightening the elbow). This opposing action allows for controlled movement at the elbow joint. Choice B, hamstring and quadriceps, are not opposing muscles in the context of the knee joint; the hamstring group flexes the knee, while the quadriceps group extends it. Choices C and D do not represent an opposing muscle pair related to joint movement.
Which of the following organs is responsible for the mechanical breakdown of food into smaller pieces?
- A. Esophagus
- B. Stomach
- C. Small intestine
- D. Mouth
Correct Answer: D
Rationale: The correct answer is D: Mouth. The mouth is responsible for the mechanical breakdown of food through chewing and mixing with saliva. This process is essential for breaking down food into smaller, more digestible pieces before swallowing. The esophagus (choice A) is a muscular tube that transports food from the mouth to the stomach and does not participate in the mechanical breakdown of food. The stomach (choice B) primarily functions to further break down food using acids and enzymes, rather than mechanical means. The small intestine (choice C) is responsible for absorbing nutrients from the digested food, not for the mechanical breakdown of food.