Final answer:
Capacitation is essential for enhancing sperm motility and altering the membrane for acrosome reaction, which allows sperm to penetrate the oocyte's protective layers and ensure fertilization. Only a few hundred sperm reach the oocyte, with just one succeeding in fusing with the oocyte to start forming a zygote.
Step-by-step explanation:
Capacitation and Its Importance in Fertilization
Capacitation is a vital physiological process that sperm must undergo to successfully fertilize an oocyte (egg). During capacitation, sperm's motility is enhanced and the membrane surrounding the acrosome is altered. The acrosome is a cap-like structure on the sperm's head that contains digestive enzymes critical for penetrating the protective layers around the oocyte. The importance of capacitation lies in its role in preparing the sperm to break through the corona radiata and zona pellucida so that it can fuse with the oocyte plasma membrane, initiating fertilization.
Events of Sperm Fertilizing an Oocyte
Upon ejaculation, hundreds of millions of sperm face a challenging journey to reach the oocyte. Many are obstructed by the acidity of the vagina, cervical mucus, or attacked by phagocytic leukocytes in the uterus. The few hundred that reach the oocyte must pass through the surrounding corona radiata and zona pellucida. Then, the acrosomal reaction occurs, allowing the sperm to penetrate the oocyte's extracellular matrix. Once a sperm binds to the zona pellucida and the acrosome releases its enzymes, the sperm and oocyte plasma membranes can fuse, leading to the exchange of haploid genomes to form a diploid zygote. It is critical that only one sperm fertilizes the oocyte to ensure proper genetic composition.