Double membrane envelope

Inner membrane is folded into cristae

Kreb's cycle enzymes in matrix

As in the case of plastids, mitochondria are bounded by an envelope comprised of two membranes and bounding an inner space, mitochondrial matrix. A characteristic feature of mitochondria is the presence of cristae, which are invaginations (tubules or folds) of the inner membrane. In plant cells the cristae are irregularly distributed. The length and frequency of the cristae vary from plant to plant, from cell to cell and between stages of cell development. Mitochondria are much smaller than chloroplasts and typically have an ellipsoidal form.

Shown here is a group of mitochondria from a secretory cell of the digestive gland of Drosophyllum lusitanicum, a carnivorous plant. Note the continuity of cristae with the inner mitochondrial membrane.

The main function of the mitochondria is the production of ATP via oxidative phosphorylation in a process of cellular respiration. The inner mitochondrial membrane and cristae contain the system for electron transport and oxidative phosphorylation. The mitochondrial matrix contains the enzymes for the Kreb's cycle (or tricarboxylic acid cycle) and is the site of carbon dioxide release.