During which phase does DNA synthesis occur?

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.

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.

In the life cycle of humans, only sperm and eggs, the gametes, have a haploid number of chromosomes. Haploid cells contain half the number of chromosomes found in diploid cells, which have two sets of chromosomes (one from each parent). During sexual reproduction, haploid gametes from each parent fuse to form a diploid zygote, which then develops into a new organism with a complete set of chromosomes. This process ensures genetic diversity and contributes to the variation observed within populations of sexually reproducing organisms.

Exocytosis is the process by which materials are released from a cell by fusing vesicles containing the materials with the plasma membrane, causing the vesicle contents to be expelled into the extracellular environment. It is a form of bulk transport that is used by cells to export molecules such as proteins, neurotransmitters, hormones, and waste products. Exocytosis plays essential roles in various cellular functions, including secretion, cell communication, and the removal of cellular waste.