Animals, plants, fungi, and protozoans are eukaryotes. They are made up of eukaryotic cells, which contain many organelles, as shown here in an animal and a plant cell. Organelles are the membrane-bound compartments of eukaryotic cells that carry out specific functions.
The defining feature of eukaryotic cells is an organelle called the nucleus. The nucleus contains the cells DNA, the stored genetic instructions of each cell, and for this reason is the control center of the cell. Important reactions for interpreting the genetic instructions occur in the nucleus.
The "rough ER" has a rough appearance because it is studded with ribosomes. Ribosomes are protein-making machines, and they pass newly made proteins into the interior of the ER.
In addition to having ribosomes on the endoplasmic reticulum, eukaryotic cells also have ribosomes in the cytoplasm.
The rough ER is contiguous with the "smooth ER," which lacks ribosomes on its surface. The smooth ER is the site of lipid production.
The Golgi apparatus is a series of flattened membrane compartments whose purpose is to process and package proteins produced in the rough endoplasmic reticulum.
Transport vesicles deliver proteins from the rough endoplasmic reticulum, where the proteins were made, to the Golgi apparatus. As the proteins make their way through the Golgi apparatus they are processed. Proteins are then packaged into transport vesicles, which deliver the proteins to their final destination.
An organelle called a chloroplast is found in the cells of plants and algae, but not in animal cells. Chloroplasts are the sites of photosynthesis, the process by which light energy is captured and converted into chemical energy. Chloroplasts allow plants to create the food that all animals depend on for survival.
Lysosomes can also break down and recycle materials from inside the cell, such as worn-out cell parts or molecules.
In a fully hydrated plant, a large water vacuole dominates the plant cell. The vacuole and the cell wall together keep the plant cell rigid, helping the plant stand upright.
Both plants and animals have a cytoskeleton, which is a network of protein fibers that carry out a variety of functions, including cell support and the movement of structures within cells. The cytoskeleton also provides animal cells with cell movement.