What is the scientific unit used to measure the radioactivity of a substance?

Correct Answer: A

Rationale: The correct answer is A: Becquerel (Bq). The Becquerel (Bq) is the scientific unit used to measure the radioactivity of a substance. It is named after Henri Becquerel, who discovered radioactivity. The Joule (J) is the unit of energy, Newton (N) is the unit of force, and Kelvin (K) is the unit of temperature. When measuring radioactivity, the Becquerel is used to quantify the rate of radioactive decay in a substance. Choices B, C, and D are incorrect as they represent units for energy, force, and temperature, respectively, not radioactivity.

Correct Answer: B

Rationale: The CRISPR-Cas9 system is a powerful tool used in gene editing to precisely target and cut DNA at specific locations within the genome. This system consists of a guide RNA that directs the Cas9 enzyme to the desired DNA sequence, where it creates a double-strand break. This break can then be repaired by the cell's natural DNA repair mechanisms, allowing for the introduction of specific genetic modifications. Options A, C, and D are incorrect as they do not accurately describe the primary function of the CRISPR-Cas9 system in gene editing. Amplifying DNA sequences, delivering genes into cells, and sequencing entire genomes are not the main functions of the CRISPR-Cas9 system, which is primarily focused on precise DNA cutting for targeted genetic modifications.

Correct Answer: C

Rationale: A genetic disorder caused by a mutation on the X chromosome is termed a sex-linked recessive disorder (Option C). This type of disorder is more commonly seen in males due to their single X chromosome, making them more vulnerable to X-linked mutations. Females have two X chromosomes, providing a protective effect against X-linked disorders.\n- Autosomal dominant disorders (Option A) result from a mutation in one copy of a gene on non-sex chromosomes (autosomes) and are not specifically related to the X chromosome.\n- Autosomal recessive disorders (Option B) occur due to mutations in both copies of a gene on autosomes, not on the X chromosome.\n- Sex-linked dominant disorders (Option D) are rare and lead to more severe symptoms in males as they only require one copy of the mutated gene on the X chromosome to express the disorder. However, this is not the term for a genetic disorder caused by an X chromosome mutation.

Correct Answer: D

Rationale: A) Carbohydrates: Carbohydrates require digestion by enzymes in the mouth, stomach, and small intestine before they can be broken down into simple sugars for absorption. B) Proteins: Proteins need to be broken down into amino acids by stomach acid and digestive enzymes in the stomach and small intestine before they can be absorbed. C) Fats: Fats require bile from the gallbladder to emulsify them into smaller droplets for enzymes to break them down into fatty acids and glycerol for absorption. D) Vitamins: Vitamins are organic compounds that are already in a form that can be readily absorbed by the body without extensive digestion. They are absorbed directly into the bloodstream from the small intestine and do not require significant breakdown before absorption.

Correct Answer: C

Rationale: A) Goblet cells: Goblet cells are specialized cells that secrete mucus to protect the lining of the digestive tract. While important for maintaining the health of the intestines, goblet cells do not increase the surface area for absorption in the small intestine. B) Paneth cells: Paneth cells are specialized cells found in the small intestine that secrete antimicrobial peptides. They play a role in protecting the intestinal stem cells and maintaining the gut microbiota balance, but they do not increase the surface area for absorption. C) Villi: Villi are microscopic finger-like projections found in the small intestine that increase the surface area available for absorption of nutrients. Each villus contains blood vessels and lacteals (lymphatic vessels) that help absorb nutrients from digested food. D) Crypts of Lieberk¼hn: Crypts of Lieberk¼hn are small pits located between the villi