An Overview of Biological Basics - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 38

FIGURE 2.11 A sketch of green algae. Source: “Siphoneae”, Ernst Haecket, Kunstformen der Natur, 1904.
Molds are used for the production of citric acid (Aspergillus niger) and many antibiotics,
such as penicillin (Penicillium chrysogenum). Mold fermentations make up a large fraction
of the fermentation industry.
Algae are usually unicellular organisms, although some plantlikemulticellular structures are
present in marine waters. Algae can be divided into five groups: Rhodophyta (red algae), Phaeo-
phyta (brown algae), Chlorophyta (green algae), Cyanophyta (blue-green algae), and Bacillario-
phyta (golden-brown algae). Figure 2.11 shows a drawing of typical green algae. The largest
alga is the giant kelp, which can grow over 60-m long. All algae are photosynthetic and contain
chloroplasts, which normally impart a green color to the organisms. The chloroplasts are the
sites of chlorophyll pigments and are responsible for photosynthesis. A typical unicellular
alga is 10 e 30 m m in size. Multicellular algae sometimes form a branched or unbranched fila-
mentous structure. Some algae contain silica or calcium carbonate in their cell wall. Diatoms
containing silica in their cell wall are used as filter aids in industry. Some algae, such as Chlorella,
Scenedesmus, Spirulina,andDunaliella, are used for wastewater treatment while producing
single-cell proteins. Certain gelling agents, such as agar and alginic acid, are obtained from
marine algae and seaweeds. Many algae have been proposed for biofuel production.
Protozoa are unicellular, motile, relatively large (1 e 50 mm) eukaryotic cells that lack cell
walls. Protozoa usually obtain food by ingesting other small organisms, such as bacteria or
other food particles. Protozoa are usually uninucleate and reproduce by sexual or asexual