Secretory vesicles carry materials within and for transfer out of the eukaryotic cytoplasm. Lysozomes are drived from the ER and carry lysozyme, used in intra- and extracellular digestion and nonspecific external defense against disease in the human body. Peroxisomes are derived from the cytoplasm and carry oxidase (superoxide dismutase) and catalase, both of which are used to decompose toxic oxygen containing by-products of respiration.
Vacuoles are membrane sacs found in plant and plant-like algal cells. They serve as storage sites for carbohydrates, lipids and other substances synthesized by the cells. Vacuoles can also be found in the cells of some animals, such as in adipose tissue, as well as in animal-like protists.
Mitochondria serve as the site of the final oxidation of food in most eukaryotic cells. They are composed of an outer membrane surrounding an inner membrane folded into cristae that increase the surface area for the placement of membrane-bound molecules involved in energy transfer. The inner fluid, called the mitochondrial matrix, contains enzymes, circular DNA and 70S ribosomes.
Chloroplasts, found in plant and plant-like protists, are similar to mitochondria in that they are composed of both an inner and outer layer of membrane. The inner membrane is folded into layers called thylakoids that are stacked together, forming grana. Photosynthetic pigments lie between the thylakoids and membrane-bound molecules embedded in them serve in the production of energy carrying molecules during the light reactions of photosynthesis. The cytoplasm-like stroma is the site of the dark reactions where carbohydrates are synthesized for export either as stored products in vacuoles or as components of the cell wall. Photosynthetic prokaryotes lack chloroplasts, but do have foldings of the cell membrane called photosynthetic lamellae.