A symbiotic relationship is a close and long-term biological interaction between two biological organisms of different species, termed symbionts, be it mutualistic, commensalistic, or parasitic. Mutualistic symbiosis is a type of symbiotic relationship where both species involved benefit from their interactions. In some cases, the species are entirely dependent on each other (obligate mutualism) and in others, they derive benefits from their relationship but could survive without each other (facultative mutualism). An example of mutualistic symbiosis is the relationship between nitrogen-fixing bacteria and leguminous plants. The bacteria provide the plants with nitrogen, which is essential for plant growth, while the plants provide the bacteria with carbohydrates. Another example is the relationship between oxpeckers and large mammals in Africa. The birds remove parasites from the mammals skin, while the mammals provide the birds with food and a place to live. Commensalistic symbiosis is a type of symbiotic relationship where one species benefits from the interaction, while the other is neither helped nor harmed. An example of commensalistic symbiosis is the relationship between remoras and sharks. Remoras attach themselves to sharks and feed on the scraps of food left over from the sharks meals, while the shark is not affected by the remoras presence. Parasitic symbiosis is a type of symbiotic relationship where one species benefits from the interaction, while the other is harmed. An example of parasitic symbiosis is the relationship between ticks and mammals. Ticks feed on the blood of mammals, which can transmit diseases to the mammals.