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Organelles are membrane bound structures found in the cytoplasm of cells that carry out specific functions. Those functions include storing and breaking down food, storing DNA, producing proteins, and capturing the sun's energy through photosynthesis. Just like their name states, they act as little organs within each cell. The nucleus, mitochondria, and chloroplasts are the only organelles that contain DNA. The Endosymbiotic Theory explains why mitochondria and chloroplasts contain DNA.

Types of Organelles

Organelle Description Function in cell
Nucleus Sphere at center of cell surrounded by nuclear membrane Controls most cellular functions
Nucleolus Solid sphere within nucleus Begins production of ribosomes
Rough Endoplasmic Reticulum Membrane system attached to nucleus Holds ribosomes (where protein synthesis occurs), modifies proteins
Smooth Endoplasmic Reticulum Same as Rough Endoplasmic Reticulum, but void of ribosomes Bonds membrane lipids, detoxifies drugs
Golgi Bodies / Golgi Apparatus Stack of membranes Packages proteins and other molecules for export out of cell
Lysosomes (only in animal cells) Small spheres Break down dead organelles and no longer useful molecules
Vacoules Membrane covered sacs Store food and water
Mitochondria Membrane covered, and composed of a folded membrane Change chemical energy from food into forms the cell can use
Chloroplasts (only in plant, algae, and protist cells) Green, membrane enclosed sacs Contain the chlorophyll involved in photosynthesis
Chromoplasts (only in plant cells) Membrane enclosed sacs Contain other pigments involved in photosynthesis
Leukoplasts (only in plant cells) Membrane enclosed sacs Convert glucose into starch
Centrioles (only in animal cells) Cylindrical, found in pairs Assist in cellular division


1. Miller, Kenneth, et al. Biology. Boston: Prentice Hall, 2006.