Mitochondria
I think you are referring to the cristae. These are the folded parts of the inner membrane. The purpose is to increase surface area of the inner membrane against the matrix. The membrane is the site of the energy transfer in the mitochondria, so having more surface area is a plus.
The organelle that contains a smooth outer membrane and a folded inner membrane in a cell is the mitochondrion. Mitochondria are responsible for producing energy in the form of ATP through a process called cellular respiration.
The inner membrane folds in a mitochondrion are called cristae.
The outer membrane is smooth, while the inner membrane is convoluted into folds called cristae in order to increase the surface area
to give it more sure area
Cristae (singular; crista)
The inner mitochondrial membrane is highly folded
Cristae (singular; crista)
It is mitochondria.
The area enclosed by the highly folded inner mitochondrial membrane is known as the cristae. These folds increase the surface area of the inner membrane, allowing for more space for proteins and enzymes involved in energy production through oxidative phosphorylation. The highly folded structure of the cristae enhances the efficiency of ATP production within the mitochondria.
It is the mitochondria
This description matches the structure of mitochondria. The outer membrane of mitochondria surrounds the organelle, while the inner membrane is folded into numerous layers called cristae, which help increase the surface area for energy production through oxidative phosphorylation.