10.2: What are Algae?

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10.2 What are Algae?

Algae are eukaryotic organisms, which are organisms whose cells contain a nucleus and other structures (organelles) enclosed within membranes. They live in moist environments, mostly aquatic, and contain chlorophyll.

Algae are not terrestrial plants, which have 1) true roots, stems, and leaves, 2) vascular (conducting) tissues, such as xylem, and phloem, and 3) lack of non-reproductive cells in the reproductive structures. Algae are not cyanobacteria. Cyanobacteria are prokaryotes, which lack membrane-bound organelles and have a single circular chromosome. Figure 10.1a shows the cellular composition of blue-algae and 1b shows a micrograph of the cells. The cell has a wall with a gelatinous coat. Just beneath the cell wall is a plasma membrane. Within the cell, there are layers of phycobilisomes, photosynthetic lamellae, ribosomes, protein granules, and circular DNA known as nucleoids. These are typical components of growing plants - however, the component we are interested in are lipid droplets, which are oils that can be extracted from the algae.

diagram of cell structure of blue algae, see above text for important information. See link in caption for text description — Figure 10.1a: Cell structure of blue-algae.

Click for a text description of Figure 10.1a.

Cell Structure of blue-algae including liquid droplet, nucleoid (circular DNA), protein granule, ribosome, photosynthetic lamellae, phycobilisomes (cyanosomes), plasma membrane, cell wall, gelatinous coat

*Credit: TutorVista*

micrograph of blue-algae, blue circles with several green dots within them — Figure 10.1b: Micrograph of blue-algae.

*Credit: B.R. Speer*

Algae is composed of ~ 50% carbon, 10% nitrogen, and 2% phosphorus. Table 10.3 shows the composition of various algae looking at the percentages of protein, carbohydrates, lipids, and nucleic acid.

Table 10.3: Composition of algae – protein, carbohydrates, lipids, and nucleic acid.
Species	Protein	Carbohydrates	Lipids	Nucleic acid
Scenedesmus obliquus (green alga)	50-56	10-17	12-14	3-6
Scenedesmus quadricauda	47	-	1.9	-
Scenedesmus dimorphus	8-18	21-52	16-40	-
Chlamydomonas rheinhardii (green alga)	48	17	21	-
Chlorella vulgaris (green alga)	51-58	12-17	14-22	4-5
Chlorella pyrenoidosa	57	26	2	-
Spirogyra sp.	6-20	33-64	11-21	-
Dunaliella bioculata	49	4	8	-
Dunaliella salina	57	32	6	-
Euglena gracilis	39-61	14-18	14-20	-
Prymnesium parvum	28-45	25-33	22-38	1-2
Tetraselmis maculata	52	15	3	-
Porphyridium cruentum (red alga)	28-39	40-57	9-14<	-

So what are the characteristics of algae?

1. Eukaryotic organisms:

As mentioned above, algae are eukaryotic organisms. The structure of a eukaryote (a typical plant cell) is shown in Figure 10.2a. Figure 10.2b shows the cell structure of a prokaryote, a bacterium, one of two groups of the prokaryotic life. Some do not consider the prokaryotes as true algae because they have a different structure, but most include these in the family of algae. There are labels for the different parts of the organisms, but I will not require you to know this information in detail - it is there so if you have a desire to look up more information, you can. Table 10.4 shows a comparison of both these types of cells.

Eukaryote schematic structure as described in the text. See link in caption for text description — Figure 10.2a: Eukaryote schematic structure.

Click for a text description of Figure 10.2a.

Eukaryotic Cell includes: A nucleus (Nuclear pore, nuclear envelope, nucleolus), rough endoplasmic reticulum, ribosomes, smooth endoplasmic reticulum, small membranous vesicles, filamentous cytoskeleton, plasmodesmata, plasma membrane, cell wall, chloroplast (thylakoid membrane, starch grain), vacuole (vacuole, tonoplast), mitochondrion (mitochondria), peroxisome, cytoplasm, golgi vesicles, golgi body (golgi apparatus)

Credit: Eukaryote: from Wikipedia.com

Prokaryote schematic structure. See link in caption for text description — Figure 10.2b: Prokaryote schematic structure.

Click for a text description of Figure 10.2b.

A Prokaryote cell contains: A nucleoid (circular DNA), Ribosomes, Plasmid, Cytoplasm, plasma membrane, Cell wall, Capsule, Pili, Bacterial flagellu

Credit: Prokaryote: from Wikipedia.com

Table 10.4: Comparison of eukaryotic cells and prokaryotic cells.
--	Eukaryotic cells	Prokaryotic cells
Size	Fairly large in size	Very minute in size
Nuclear region	Nuclear materials surrounded by a membrane	Nuclear region (nucleoid) not surrounded by a nuclear membrane
Chromosome	More than one chromosome present	Single chromosome present
Membrane	Membrane-bound cell organelles are present	Membrane-bound cell organelles are absent

2. Live in moist environments

These organisms lack a waxy cuticle (the wax in terrestrial plants prevents water loss). There are a wide variety of growth environments for algae. The typical conditions for algae are moist, tropical regions and they can grow in marine and freshwater. Freshwater algae grow in animals, aquatic plants, farm dams, sewage, lakes, rivers, lagoons, snow, mud/sand, and soil.

3. Contain chlorophyll

Algae are mostly photosynthetic, like plants. They have five kinds of photosynthetic pigments (chlorophyll a, b, c, d, and f) and have many accessory pigments that are blue, red, brown, and gold. Chlorophyll is a green pigment found in almost all plant algae and cyanobacteria. It absorbs light and transfers light energy to ATP (adenosine triphosphate).

So how are algae classified?

Algae belong to the Protista kingdom. Figure 10.3 shows a schematic of where Protista fits with other classifications of Plantae, Animalia, Fungi, Eubacteria, and Archaebacteria.

Algae can also be classified based on chlorophyll content. The first type is chromista. These types of algae contain chlorophylls a and c, and examples of the algae include brown algae (golden-brown algae), kelp, and diatoms. These materials are a division of Phaeophyta. These types have a habitat on rocky coasts in temperate zones or open seas (cold waters). The structure is multicellular and they can grow up to 50 m long.

kingdoms of life 3 initial branches. See link in caption for text description — Figure 10.3: Various kingdoms of life.

Click for a text description of Figure 10.3.

Eubacteria (unicellular, prokaryotic)

Archaebacteria (unicellular, prokaryotic)

Protista (eukaryotic, unicellular and multicellular)

Plantae (multicellular, eukaryotic)

Animalia (multicellular, eukaryotic)

Fungi (multicellular, eukaryotic)

*Credit: By Hull (Google) [Public domain], via Wikimedia Commons*

A phylogenetic tree example with different organisms on different branches of a cartoon tree — Figure 10.4: A phylogenetic tree.

*Credit: Phylogenetic Tree from creationwiki.org*

Red algae are another type and contain chlorophyll a, such as marine algae (seaweed). These organisms are in the division of Rhodophyta, which has over 4000 species. These are some of the oldest eukaryotic organisms on Earth (there are 2 billion-year-old fossils). They are abundant in tropical, warm waters. They act as food and habitat for many marine species. The structure ranges from thin films to complex filamentous membranes. These algae have accessory pigments, and the phycobilins (red) mask chlorophyll a. Figure 10.5b shows various red algae. Dinoflagellates are unicellular protists, and these are associated with red tide and bioluminescence.

A pile of bright yellow kelp — Figure 10.5a: Kelp

*Credit: BEEMS Module A3*

Green algae contain chlorophylls a and b. They are in the division Chlorophyta. This is the largest and most diverse group of algae. It is found mostly in freshwaters and also on land (rocks, trees, and soil). The structures are single cells (Micrasterias), filamentous algae, colonies (Volvox), and leaf-like shape (Thalli). Terrestrial plants arose from a green algal ancestor. Both have the same photosynthetic pigments (chlorophyll a and b). Some green algae have a cell wall made of cellulose, similar to terrestrial plants. Figure 5c shows examples of green algae.

3 different algae’s & magnifications, 1 looks like a branch, 1 is zoomed in to look like branches made of rectangles & 1 is brown dots — Figure 10.5b: Red algae photo- and micrographs.

*Credit: BEEMS Module A3*

Examples of green algae: Chalmydomonas, Volvox, Ulothrix, Fristschiella, Ulva, Hydrodictyon — Figure 10.5c: Examples of green algae.

*Credit: BEEMS Module A3*