The correct answer is Parenchyma.Concept:Parenchyma is a living, simple permanent tissue composed of thin-walled cells.Parenchyma is also called primary tissue or ground tissue.It is present in the cortex, pith, palisade, mesophyll, and some other parts of the flower.It is mostly produced by the ground tissue.The parenchyma forms the major part of the plant organs.Explanation:In aquatic plants, large air sacs give them buoyancy effects. These sacs are surrounded by parenchyma tissues, also known as aerenchyma.Basically, in aquatic plants, aerenchyma is parenchyma tissue. Aerenchyma cells form a network with large air spaces or air cavities for gaseous exchange.These air cavities in aquatic plants allow the plant to be light and buoyant, allowing it to float easily in water.Additional InformationCollenchyma:Collenchyma is a simple, living mechanical tissue.Its cell is composed of more or less elongated cells with thick, primary non-lignified walls.Intercellular spaces are found to be absent.Sclerenchyma:The sclerenchyma consists of long, narrow cells with thick and lignified cell walls having a few or numerous pits.These are dead cells and do not perform any metabolic function.Complex tissue:Complex permanent tissues are a group of more than one type of cells having a common origin and working together as a unit.The main complex tissues in vascular plants are xylem and phloem.Xylem is a complex permanent tissue which conducts water and mineral nutrients upwards from the root to all aerial parts of the plant.Phloem is a food conducting complex permanent tissue.