ProtistsI After completing this exercise, you will be able to 1. define phytopla

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ProtistsI After completing this exercise, you will be able to 1. define phytoplankton, phyt, phycobilin, agar,gametangium, oogonia, antheridia 2. recognize and classify selected members of the phyla represented in this exercise; istingish among the structures associated with asexual and sexual reproduction described in this exercise o4. identify the structures of the algae (those in boldface in the procedure sections). Introduction The organisms in this exercise make an enormous impact on the biosphere, both positively and negatively. Among their greatest contibuion is the production of oxygen, because most are the photosynthetic protistans. Many are given the common name "algae. Pond scum, frog spittle, seaweed, the stuff that clogs your aquarium if it's not cleaned routinely, the debris on an ocean beach after a storm at sea, the nuisance organisms of a lake--these are the images that pop into our minds when we first think about the organisms called algae. But many algae are also phytoplankton, the weakly swimming or floating algae, at the base of the aquatic food chain. included are amoebozoans, organisms lacking cell walls in their nonreproductive state that are the shape-shifters of the protistan world. We'll examine the following organisms in this exercise: Common Name Red algae Green algae Desmids and stoneworts Amoebas and slime molds Phylum Note the ending -phyta for several of the phylum names. This derives from the Greek root word phyt, which means "plant." In the not too distant past, these organisms were considered plants because they were photo- synthetic. By contrast, the ending-zoa means "animal." While the endings remain, today these organisms are considered to be members of the kingdom Protista. 5.1 Phylum Rhodophyta: Red Algae (About 15 min.) Although commonly called red algae, members of the Rhodophyta vary in color from red to green to purple to greenish-black. The color depends on the quantity of their photosynthetic accessory pigments, the phycobilins which are blue and red. These accessory pigments allow capture of light energy across the entire visible spec- trum. This energy is passed on to chlorophy'll for photosynthesis. One phycobilin, the red phycoerythrin, allows some red algae to live at great depths where red wavelengths, those of primary importance for green and brown algae, fail to penetrate Which wavelengths (colors) would be absorbed by a red pigment? 67

Explanation / Answer

Phytoplanktons are single-celled free floating minute organisms found in lakes, streams and oceans. They make their own food from sunlight through photosynthesis. They use carbon dioxide like plants and release oxygen. The most commonly-occurring are cyanobacteria (blue-green algae), dinoflagellates and diatoms. They form foundation of terrestrial ecosystem. They are considered as primary producers because they convert solar energy into food that is used by animals. They move up and down depending on the availability of sunlight. Dinoflagellates move actively using flagella. Phytoplankton or their byproducts are used by humans. Phytoplanktons are eaten as food or act as nutritional supplements, fertilizer. Carrageenan, a derivative of phytoplankton is used as a thickening agent in ice cream, sauces and puddings. Diatoms are rich source of diatomaceous earth, which is used as an abrasive and form an component of toothpaste.

Light capturing water-soluble pigment found mostly in stroma of chloroplast of cyanobacteria and some red algae is referred as phycobilins. These molecules consist of a chromophore which gives them color. They are bonded to water-soluble proteins called as phycobiliproteins. They pass the light energy to chlorophylls for photosynthesis. They are efficient in absorbing red, orange, yellow, and green light. Phycobilins are pigments found in cyanobacteria and Rhodophyta. Phycobilins are of two types - phycocyanin and phycoerythrin. Phycocyanin is a blue pigment found in cyanobacteria (blue-green algae) while phycoerythrin is a red pigment found in Rhodopyta (red algae). Both the pigments help to carry out photosynthesis in deep waters. They act as antennae for capturing light energy during photosynthesis.
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Agar is a jelly-like substance obtained from algae belonging to phylum Rhodophyta (red algae). It is an unbranched polysaccharide obtained from the cell walls of red algae primarily Gelidium and Gracilaria. Agar consist of two components a linear polysaccharide agarose and a heterogeneous mixture of smaller molecules called agaropectin. It forms an important component of culture media and acts as a substrate to support microbial growth. It is also used as a laxative, substitute of gelatin (used for thickening of soups) and an essential ingredient of ice creams.

An organ or cell producing gametes is referred as gametangium. It is found in many multicellular protists, algae, fungi. It is a haploid structure. Female gametangia is called as archegonia and produces egg cells and act as the site for fertilization. Archegonia are common in algae. The male gametangia are called antheridia. They produce sperm cells. Antheridia that produce non-motile sperms (spermatia) are called spermatangia.

Porphyridium is a species of red alga (family Porphyridiophyceae). The microalga is a source of fatty acids, lipids, cell-wall polysaccharides and pigments. The polysaccharides are sulphated and their structure gives them unique properties for industrial and pharmaceutical applications. Carbohydrates and exopolysaccharides provide good source for bio-fuel and pharmaceutics. The cell structure contains unique features such as

Chloroplast contain small granules (about 320 A) regularly arranged along the parallel chloroplast lamellae. The granules differ in size and staining intensity depending upon the ribosomes located in the cytoplasm.
presence of two tubular elements- one associated with the Golgi bodies (450 to 550 A) and another present in the cell periphery (350 A). They connect the endoplasmic reticulum and the cell membrane.
The plastid are structurally similar to that in the Chlorophyceae.
The phycobilins are found to be associated with the lamellae of the plastid.
The pyrenoid contains no tubules and does not appear to function in synthesis or storage of reserve material.

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