In a Punnett square, a capital letter represents what type of allele?

Simple diffusion is the passive movement of molecules or ions across a semipermeable membrane from an area of higher concentration to an area of lower concentration, driven by the concentration gradient. In simple diffusion, molecules move randomly and spontaneously through the lipid bilayer of the membrane or through aqueous channels formed by integral membrane proteins. No energy input (ATP) is required for simple diffusion, as it occurs down the concentration gradient, from regions of high to low concentration, until equilibrium is reached. Simple diffusion is a fundamental process involved in the exchange of gases (e.g., oxygen, carbon dioxide) in the respiratory system, the absorption of nutrients and ions in the digestive system, the reabsorption of water and solutes in the kidneys, and the movement of signaling molecules across cell membranes. The rate of simple diffusion depends on factors such as the concentration gradient, temperature, molecular size, lipid solubility, and membrane surface area and permeability. Simple diffusion contrasts with facilitated diffusion, which involves the movement of molecules across membranes facilitated by transport proteins but still occurs down the concentration gradient without the expenditure of energy.

Cytokinesis is the final stage of cell division in which the cytoplasm and organelles are partitioned between two daughter cells, resulting in the formation of two new cells. In animal cells, cytokinesis involves the formation of a contractile ring composed of actin and myosin filaments at the equatorial plane of the cell, which contracts to create a cleavage furrow that pinches the cell membrane inward. This process eventually separates the parent cell into two distinct daughter cells, each containing a complete set of chromosomes and organelles. In plant cells, cytokinesis occurs differently due to the presence of a rigid cell wall. During telophase, the nuclear envelope reforms around the separated chromosomes, and the nucleoli reappear. Chromatin begins to decondense, and the spindle fibers disassemble. As telophase progresses, cytokinesis completes the cell division process, resulting in the formation of two genetically identical daughter cells. Telophase is preceded by anaphase, during which sister chromatids are pulled apart toward opposite poles of the cell by spindle fibers, and followed by cytokinesis, which completes the cell division process initiated during mitosis.

Cells require a large surface-to-volume ratio to facilitate efficient exchange of nutrients, gases, and waste products with their environment. As cells grow larger, their volume increases more rapidly than their surface area. A large surface-to-volume ratio allows for a greater surface area through which substances can enter and exit the cell, enabling rapid exchange of molecules essential for cellular metabolism. Nutrients such as glucose and oxygen must diffuse into cells, while waste products such as carbon dioxide and metabolic by-products must diffuse out of cells. A large surface-to-volume ratio ensures that cellular processes such as cellular respiration, photosynthesis, and protein synthesis can occur efficiently by providing sufficient surface area for nutrient uptake and waste removal. Additionally, a large surface-to-volume ratio supports cellular communication and signaling by allowing cells to interact with their environment and neighboring cells more effectively.

In the taxonomic hierarchy, the family represents a higher-level grouping that includes related genera. In the classification provided, Elephantidae represents the family, encompassing all elephants. The specific epithet "indicus" refers to the Indian elephant, which is a subspecies of the Asian elephant.