What is the term for a hydrocarbon chain with no double or triple bonds between carbon atoms?

Correct Answer: A

Rationale: A saturated hydrocarbon chain contains only single bonds between carbon atoms, making it 'saturated' with hydrogen atoms. Therefore, the correct answer is choice A, 'Saturated.' Choice B, 'Unsaturated,' is incorrect because it refers to hydrocarbon chains with double or triple bonds. Choice C, 'Aromatic,' is not the correct term for a hydrocarbon chain without double or triple bonds; it describes a specific type of cyclic and conjugated hydrocarbon structure. Choice D, 'Alkene,' is also incorrect as it specifically indicates a hydrocarbon chain with at least one double bond between carbon atoms.

Correct Answer: B

Rationale: The primary function of the cell membrane, also known as the plasma membrane, is to regulate the movement of substances in and out of the cell. It acts as a selectively permeable barrier, allowing specific molecules to pass through while blocking others. This role is crucial for maintaining the internal environment of the cell by enabling essential nutrients to enter and waste products to exit. While the cell membrane provides some structural support for the cell, its main function is substance transport. Protein and lipid synthesis predominantly occur in organelles like the endoplasmic reticulum and Golgi apparatus, and storing genetic material is the nucleus's responsibility. Therefore, choices C (To synthesize proteins and lipids) and D (To store genetic material) are incorrect as these functions are carried out by other cell organelles, not the cell membrane.

Correct Answer: B

Rationale: Aseptic meningitis is typically caused by viral infections, such as enteroviruses (e.g., coxsackievirus, echovirus), herpes simplex virus, varicella-zoster virus, and others. These viruses can infect the meninges, leading to inflammation and symptoms of meningitis without the presence of bacteria. While bacterial meningitis is a serious and life-threatening condition, aseptic meningitis caused by viruses is usually less severe and has a better prognosis. Fungi and parasites are less common causes of meningitis compared to bacteria and viruses.

Correct Answer: B

Rationale: Transcription is the correct answer. Transcription is the process of making copies of RNA from DNA. During transcription, the enzyme RNA polymerase binds to a specific region of DNA and synthesizes a complementary RNA strand based on the DNA template. This process is essential for gene expression and protein synthesis in cells. Replication (option A) refers to the process of making copies of DNA, not RNA. Translation (option C) is the process of synthesizing proteins from mRNA, not making copies of RNA from DNA. DNA repair (option D) involves mechanisms that cells use to repair damaged DNA, not the process of making RNA copies from DNA.

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.

Correct Answer: A

Rationale: A) Mouth: The mouth is involved in the mechanical breakdown of food through chewing and the initiation of carbohydrate digestion by the enzyme amylase in saliva, but it does not produce digestive enzymes. The salivary amylase in the mouth helps in breaking down carbohydrates. However, it is not an organ that produces digestive enzymes. B) Stomach: The stomach produces gastric juices containing enzymes like pepsin that help break down proteins. C) Pancreas: The pancreas produces various digestive enzymes such as amylase, lipase, and proteases that aid in the digestion of carbohydrates, fats, and proteins. D) Small intestine: The small intestine produces enzymes such as peptidases, sucrase, lactase, and maltase that further break down proteins, carbohydrates, and fats for absorption. Therefore, the mouth is the organ that is NOT involved in the production of digestive enzymes.

Correct Answer: B

Rationale: Elasticity is the correct term that describes the ability of a muscle to return to its original length and shape after being stretched or contracted. Contractility refers to the ability of a muscle to contract or shorten. Extensibility is the ability of a muscle to be stretched. Excitability is the ability of a muscle to receive and respond to stimuli. Therefore, the correct answer is 'Elasticity' as it specifically relates to the muscle's ability to regain its original form.

Correct Answer: A

Rationale: Collagen fibers are the main component that gives connective tissue its strength. Collagen is a fibrous protein that provides structural support and tensile strength to connective tissues, allowing them to withstand stretching and tension. Epithelial cells, nerve cells, and blood cells are not the main components responsible for the strength of connective tissue. Epithelial cells are specialized for covering and lining surfaces, nerve cells transmit signals, and blood cells are involved in various functions like oxygen transport and immune response, but they do not provide the structural strength typical of collagen fibers in connective tissue.

Correct Answer: B

Rationale: The correct answer is B, Urethra. The urethra is not directly involved in urine production. It is a tube that carries urine from the bladder to the outside of the body. The kidneys are responsible for filtering waste and excess substances from the blood to produce urine. The bladder stores urine until it is expelled from the body. The lungs are not involved in urine production; they are responsible for gas exchange during respiration. Choice A, Kidneys, is directly involved in urine production by filtering the blood to form urine. Choice C, Lungs, plays a role in respiration and oxygen exchange but is not directly involved in urine production. Choice D, Bladder, stores urine before it is excreted from the body and is directly involved in the final stages of urine elimination, unlike the urethra.