Swim Bladder, also called air bladder, is an expandable gas-filled sac that helps many bony fishes to control their buoyancy in order to stay at their current water depth without having to waste energy in swimming. A swim bladder is similar to a lung in structure and function in some primitive fishes, but it is not a lung because most cases its primary role is not respiration. Continue reading What are Swim Bladders?
The continued secondary growth of vascular cylinder in many older roots and stems exerts a pressure which results in the stretching and rupturing of the epidermis, cortex and other tissues outside the secondary phloem. To avoid such breaking of external tissues, the plant organs develop a secondary protective covering by replacing epidermis and other external tissues. This protective secondary covering (tissues) of certain plants, especially woody plants, is called Periderm. Continue reading What is Periderm in Plants?