Complex sentence: Bacteria which produce only lactic acid during fermentation are homofermentative; those that also produce lactic acid and other compounds such as carbon dioxide, alcohol, aldehydes and ketones are heterofermentative.
Split into simpler sentences: Bacteria which produce only lactic acid during fermentation are homofermentative. Those that produce lactic acid and other compounds such as carbon dioxide, alcohol, aldehydes and ketones are heterofermentative.