Many single-celled protists have a projection called a flagellum. What is its purpose?

Glycolysis is the first step in the process of cellular respiration, which is the metabolic pathway by which cells generate ATP (adenosine triphosphate), the energy currency of the cell. Glycolysis occurs in the cytoplasm and involves the breakdown of glucose, a six-carbon sugar, into two molecules of pyruvate, a three-carbon compound. During glycolysis, glucose is oxidized and ATP is produced through substrate-level phosphorylation. Glycolysis is anaerobic, meaning it does not require oxygen, and is common to both aerobic and anaerobic respiration pathways.

The slide, containing the specimen to be observed, is placed on the stage of a light microscope. The stage is a flat platform located beneath the objective lenses and above the light source. It typically has a mechanical stage control that allows precise movement of the slide in both the x-axis (side to side) and y-axis (front to back). The stage clips or a stage holder secure the slide in place during observation, ensuring that the specimen remains in focus under the objective lenses.

The cell membrane, also known as the plasma membrane, contains two layers of phospholipids arranged in a bilayer structure. Each phospholipid molecule consists of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. In the bilayer structure, the hydrophilic heads face outward, interacting with the aqueous environments both inside and outside the cell, while the hydrophobic tails face inward, shielded from the surrounding water. This arrangement forms a barrier that separates the internal environment of the cell from the external environment, regulating the passage of substances into and out of the cell.

The process described, where many solute particles must use a channel protein to move from a high concentration inside the cell to a lower concentration outside the cell, is called "Facilitated diffusion." This process involves the passive movement of molecules across a biological membrane with the assistance of transport proteins. Channel proteins are one type of transport protein that facilitates the diffusion of specific molecules, such as ions or polar molecules, across the membrane by providing a channel through which these molecules can pass. Facilitated diffusion does not require energy input from the cell and occurs down the concentration gradient, from areas of higher concentration to areas of lower concentration.