Which type of cell secretes antibodies?

Correct Answer: D

Rationale: The correct answer is D: Plasma cells. Plasma cells are a type of white blood cell that secretes antibodies. Antibodies are essential components of the immune system, as they help in identifying and neutralizing pathogens. Choice A, B, and C are incorrect as bacterial cells and viral cells do not secrete antibodies, and lymph cells are involved in the immune response but do not secrete antibodies like plasma cells.

Correct Answer: D

Rationale: Long bones are characterized by their elongated shape and include bones like the ulna, fibula, and humerus. These bones are crucial for providing support, structure, and facilitating movement in the human body. The sacrum, clavicle, and patella are not classified as long bones. The sacrum is a triangular bone at the base of the spine, the clavicle is a collarbone, and the patella is the kneecap. While these bones have important functions, they do not fit the definition of long bones due to their shape and structure.

Correct Answer: C

Rationale: The correct answer is C - 'An inference'. An inference is a conclusion drawn based on evidence and reasoning, not directly observed facts. In this statement, the conclusion that someone must have forgotten to water the flower is inferred from the observed fact that the flower is dead. Choice A - 'A classification' is incorrect because the statement does not categorize or classify the flower in any way. Choice B - 'An observation' is incorrect because it does not involve interpreting or drawing a conclusion from the observed fact. Choice D - 'A collection' is incorrect as it does not relate to the process of drawing a conclusion based on evidence.

Correct Answer: B

Rationale: The correct answer is B. If an organism is AB, it indicates that it carries two different alleles. During gamete formation, each gamete receives only one allele from the pair present in the organism. Therefore, in this case, the possible gametes would be 'A' and 'B,' making 'AA' impossible. Choice A, 'AB,' is possible as each gamete can carry one of the alleles from the genotype. Similarly, 'BB' is also possible if one of the alleles separates into a gamete. Choice D, 'AB,' is essentially the same genotype as the organism and is a possible combination in the gametes.

Correct Answer: B

Rationale: The liver is the primary organ responsible for detoxifying chemicals and metabolizing drugs in the body. It plays a crucial role in breaking down toxins, filtering blood, and producing bile, making it essential for overall detoxification processes. The kidney primarily filters waste and excess substances from the blood to form urine. Lungs are responsible for gas exchange, not detoxification. The heart is responsible for pumping blood and does not play a direct role in detoxification processes.

Correct Answer: A

Rationale: Medical advances, higher standards of cleanliness, and the creation of vaccines have all significantly contributed to the increase in life expectancy over time. While human evolution plays a role in adaptation to the environment over millennia, it is not a primary factor that has led to the substantial increase in life expectancy within a few centuries. The human body's evolution is a slow process that occurs over generations, while the advancements in medical technology, cleanliness, and vaccines have had a more immediate and direct impact on improving life expectancy.

Correct Answer: B

Rationale: The correct answer is B - a gene. Genes are the smallest units that can encode for a trait as they contain the specific instructions for producing a particular characteristic or protein. While codons are sequences of nucleotides that code for specific amino acids in a protein, they are not the smallest unit that encodes for a trait. Nucleotides are the building blocks of DNA and RNA, and chromosomes are made up of DNA and proteins, containing many genes.

Correct Answer: D

Rationale: The correct answer is 'D: Ionic bond.' An ionic bond is formed when electrons are transferred between atoms. In an ionic bond, one atom donates electrons to another atom, resulting in the formation of positively and negatively charged ions that are attracted to each other, creating a strong bond. Choice A, 'Transfer bond,' is incorrect because there is no common term known as a 'Transfer bond' in chemistry. Choice B, 'Static bond,' is incorrect as it does not describe the process of electron transfer between atoms. Choice C, 'Covalent bond,' is incorrect because in a covalent bond, electrons are shared between atoms rather than transferred outright, making it different from an ionic bond.

Correct Answer: A

Rationale: The correct answer is the sinoatrial node. This node, also referred to as the pacemaker of the heart, is responsible for initiating the electrical impulses that stimulate cardiac muscle contractions. It plays a crucial role in setting the pace and rhythm of the heart's contractions. Choices B, C, and D (the left ventricle, the aorta, and the tricuspid valve, respectively) do not serve as the primary electrical stimulator of the cardiac muscle. While the left ventricle is a chamber of the heart that pumps oxygenated blood to the body, the aorta is the main artery that carries blood away from the heart, and the tricuspid valve is a one-way valve that ensures blood flows properly through the heart, none of these structures initiate the electrical impulses that cause the cardiac muscle to contract.