What does the phrase 'survival of the fittest' refer to?

Correct Answer: B

Rationale: The phrase 'survival of the fittest' is often associated with the concept of natural selection, proposed by Charles Darwin. Natural selection is the process by which organisms best adapted to their environment are more likely to survive and reproduce, passing on their advantageous traits to the next generation. This process does not necessarily favor the most complex anatomical structures (option A) or the strongest and most aggressive individuals (option D). Instead, it emphasizes the importance of adaptations that enhance an organism's ability to survive and reproduce in a specific environment. Option C is incorrect because natural selection results in differential reproductive success based on an organism's traits, meaning that not all organisms have an equal probability of survival and reproductive success.

Correct Answer: C

Rationale: Phagocytes are a type of white blood cell that is crucial in the initial attack on pathogens. These cells have the ability to engulf and digest foreign particles such as bacteria and viruses, thereby preventing infections. Red blood cells primarily function in oxygen transport, platelets are vital for blood clotting, and lymphocytes are involved in the immune response. However, phagocytes are specifically designed to provide the initial defense against pathogens by directly attacking and eliminating them.

Correct Answer: B

Rationale: The correct answer is B, cytoplasm. Cytoplasm is the fluid-filled, jelly-like substance within the cell that suspends the organelles. The nucleus, not the correct answer, is the organelle that contains the cell's genetic material. The plasma membrane, another incorrect choice, is the outer boundary of the cell that regulates what enters and exits the cell. The Golgi apparatus, also an incorrect choice, is an organelle involved in processing and packaging proteins.

Correct Answer: B

Rationale: Simple epithelium consists of a single layer of cells. This type of epithelium is found in areas where absorption, secretion, and filtration occur, as it allows for efficient exchange of substances across the epithelial barrier. Simple epithelium is well-suited for diffusion and filtration processes due to its thin nature, enabling substances to pass through easily. Choice A, 'No layers,' is incorrect as epithelial tissue always consists of at least one cell layer. Choice C, 'Two to several layers,' describes stratified epithelium, not simple epithelium, which has only one layer. Choice D, 'Many tightly packed layers,' is more characteristic of stratified epithelium, where multiple layers of cells are present. Therefore, the correct answer is B: 'One layer.'

Correct Answer: C

Rationale: The myelin sheath, a fatty substance that insulates nerve fibers, is derived from nervous tissue, specifically glial cells. Glial cells, including oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system, are responsible for producing the myelin sheath that surrounds and insulates nerve fibers, aiding in the conduction of nerve impulses. Epithelial tissue (Choice A), Muscle tissue (Choice B), and Connective tissue (Choice D) are not responsible for producing the myelin sheath; instead, nervous tissue (glial cells) plays this crucial role.