The nucleus, mitochondria and chloroplasts are the three organelles that have two membranes. They are present only in eukaryotic cells.
Nucleus
The nucleus, which is the largest organelle in a cell, functions as the control center, regulating all characters and functions of cells in the body. It houses thin, thread-like essential structures called chromosomes. These chromosomes carry genes, which are the hereditary unit in all organisms. The double-membrane of the nucleus separates the chromosomes from the cytoplasm and other cellular components. Tiny holes in the nuclear envelope that connect the outer and inner membrane also facilitate the selective flow of proteins and other materials in and out of the nucleus. A perinuclear space separates the two membrane layers.
Mitochondria
Called the powerhouses of the cell, mitochondria are the primary sites for cellular respiration. They have their own DNA and ribosomes and are responsible for providing energy in the form of ATP for all critical cellular activities. The outer and inner membrane, which are composed of proteins and phospholipid layers, are separated by an intermembrane space. The porous outer membrane surrounds the surface of the mitochondrion completely forming a continuous boundary with the cytoplasm. The inner membrane features deep folds known as cristae, which increase the internal surface and act as the sites for ATP-generating chemical reactions.
Chloroplasts
Chloroplasts are only found in plant cells, where they play a role in trapping solar energy to be converted into glucose and oxygen through the process of photosynthesis. The outer and inner membrane divide the chloroplast into two distinct regions – grana, which are stacks of flattened membranous sacs called thylakoids, and stroma, a homogenous mixture in which the grana are embedded.