According to Dictionary.com, the function of stroma in both humans and plant cells is as a supportive matrix. In people, stroma is the connective and supportive tissue of organs. In plants, the stroma is the cytoplasm in a cell's chloroplasts, according to the University of Illinois.
According to About.com, stroma is an important element in plants and is critical to the role of photosynthesis. The stroma, a very dense fluid within the chloroplast, is part of the supporting matrix of a plant cell and is also where carbon dioxide is turned into sugar. The University of Illinois calls this process part of the dark reactions, because this part of photosynthesis does not depend on light.
Organs consist of two tissues. One deals with the function of the organ, and the other, the stroma, comprises the rest of the tissues, such as blood vessels and nerves. This stroma varies depending on the organ. For instance, the spleen is made up almost wholly of connective tissue. The bulk of the spleen consists of lymphocytes and other blood cells, while the stroma tissue is the supporting connective tissue. The main part of the brain consists of nerve cells and glia, while the stroma is the connective tissue and blood vessels.