There are always some exceptions found in the nature. For example, there are a group of plants called 'parasitic plants' which are unable to perform photosynthesis, a characteristic function of majority members of the plant kingdom. These parasitic plants depend on other living plants for their food and nutritional requirements. Parasitic plants that depend totally on other plants for their food and nutritional requirements are known as total parasites or holoparasites or obligately parasitic plants. Parasitic plants that depend partially on other plants for their food and nutritional requirements are called partial parasites or hemiparasites.