i think what you're really wanting to ask is
what organelle prevents cells from falling apart
the cellular membrane keeps its contents (cytoplasm) inside, it is support by an infrastructure called the cytoskeleton, which is made of proteins that are in a constant state of flux (consantly changing to meet the needs of the cell)
ATP production happens in the cristae of the "mitochondria"
In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 10 micrometers (μm) in diameter. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth.
ribosomes are responsible for protein synthtesis, which most often happens in the "rough endoplasmic reticulum"
Ribosomes are the components of cells that make proteins from amino acids. One of the central tenets of biology is that DNA makes RNA, which then makes protein. The DNA sequence in genes is copied into a messenger RNA (mRNA). Ribosomes then read the information in this RNA and use it to produce proteins. Ribosomes do this by binding to a messenger RNA and using it as a template for the correct sequence of amino acids in a particular protein. The amino acids are attached to transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA sequence. The attached amino acids are then joined together by another part of the ribosome. The ribosome moves along the mRNA, "reading" its sequence and producing a chain of amino acids.
but although both ribosomes and rough ER are both organelles, it would be more exact to say that
"the function of ribososmes is protein synthesis"