1 The kidneys are used to remove excess water and ions from the blood. 2  These are then expelled as urine. 3  The kidneys perform a vital role in homeostatic regulation in mammals, removing excess water, salt, and urea from the blood.
Ectoparasites Parasites that live on the outside of the host, either on the skin or the outgrowths of the skin, are called ectoparasites. They are directly transmitted between hosts.
subÂ·strate. 1. The material or substance on which an enzyme acts. See Note at enzyme. 2. The surface on which plants, algae, or certain animals, such as barnacles, live or grow. A substrate may serve as a source of food for an organism or simply provide support. - The surface on which an organism lives or moves.. The surface on which plants, algae, or certain animals, such as barnacles, live or grow. A substrate may serve as a source of food for an organism or simply provide support.