Mold is a type of fungus that grows in multicellular filaments called hyphae. These tubular branches have multiple, genetically identical nuclei, yet form a single organism, known as a colony. In contrast, yeast is a type of fungus that grows as a single cell.
Molds secrete hydrolytic enzymes, usually from hyphal tips, that degrade biopolymers such as starch, cellulose and lignin into simper substances that can be absorbed. This plays a role in the decomposition of organic material.
Yeasts can produce energy aerobically (with oxygen) or anaerobically (without oxygen). In anaerobic respiration, yeasts convert carbohydrates to carbon dioxide and alcohols to produce energy. Yeasts also obtain carbon from hexose sugars.
Molds reproduce by producing small spores, which can be either sexual (reproducing using meiosis) or asexual (reproducing using mitosis).
Most yeasts reproduce asexually. The most common process is known as “budding,” when a small bud forms on the parent cell. The parent nucleus splits in two and the daughter nucleus moves into the bud cell, which continues to grow until it splits from the parent cell.
Molds are often used in the production of food and drinks, such as soy sauce, sake, quorn, cheese, rennet and salami. They are also used in antibiotics such as penicillin, cholestoral-lowering drugs such as Lovastatin, and immunosuppressants such as cyclosporine.
Yeasts are used for producing ethanol for alcoholic beverages such as beer, as leavening agents in baking, and as a nutritional supplement for vegans. Their simple cellular structure also makes them valuable resources for geneticists, and they are used to study processes such as the cell cycle, DNA replication and recombination.
Certain types of mold can be hazardous to human health in large quantities and can cause allergic reactions and respiratory problems. Some molds also produce mycotoxins, which pose a serious risk to humans and animals. Symptoms of mold allergies include Symptoms of a mold allergy are watery, itchy eyes, chronic coug, headaches or migraines, difficulty breathing, tiredness, rashes, sinus problems, nasal blockage, and frequent sneezing.
Yeasts can cause infection in people with compromised immune systems. They can cause the disease cryptococcossis, which is found in 7-9% of AID patients in the US. The yeast candida can also cause candidiasis in humans.
Video explaining the differences
Here's a good video that talks about the different types of Fungi: Mold, Yeast and Mushrooms and their benefits and health hazards: