Semen is the cloudy white bodily fluid that is emitted from the urethra and out of the penis during ejaculation. Semen contains citric acid, free amino acids, fructose, enzymes, phosphorylcholine, prostaglandin, potassium, and zinc. The average volume of semen produced in a single ejaculation varies from 2 to 5 ml. The semen from a single ejaculation may contain between 40 million and 600 million sperm ​depending both upon the volume of the ejaculate and the length of time since the last ejaculation.