Practical Plant Diversity . By studying the morphological characteristics as well as adaptations to the mode of life of different species of algae in this experiment, it gives us a chance to discover more about the significant of algae contributing to our

Organisms and Environment

Practical Plant Diversity No.1

The Algae

Introduction:

Algae are simple living organisms which are photosynthetic protists. They capture light energy and convert inorganic substances into simple sugars using the captured energy. Some of them are plant-liked while some of them are more animal-liked. Thus , they are defined as groups of eukaryotes that are classified in 12 phyla according to their morphological characteristics. Algae range from single-celled organisms to multi-cellular organisms.They range in size from 50 um in diameter, to giant one whose length may even exceed 60m.Algae are usually found in damp places or bodies of water , so they are common in terrestrial as well as aquatic environments. However, terrestrial algae are usually not easy to find and far more common in moist and tropical regions than dry ones as they do not have vascular tissues and other adaptations to live on land.

Objectives:

To study the general and unique morphological characteristics of the five major phyla of algae, and
The adaptations to their mode of life

The followings are the five major phyla of algae that were studied:

Results & Discussion :

1. The origin of the diatomaceous earth is freshwater. For the diatom slide of freshwater, pennate diatoms were found which are long and bilaterally symmetrical in shape. While for the diatom slide of marine, centric diatoms were found which are round and radically symmetrical in shape. In the slide of diatomaceous earth, we observed that there are mainly pennate diatoms with only small amount of centric diatoms. Therefore, by comparing the three diatom slides and the composition of pennate and centric diatoms in the diatomaceous earth slide, we can surely deduce the origin ...

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Results & Discussion :

2. Under the light microscope (up to x1000 magnification), the morphological features of these green algae, Chlorella , Chlamydomonas and Spirogyra, can be resolved are in the following:

For Chlorella, it is unicellular, small and oval in shape. A single nucleus was found which lies in the cavity of the chloroplast. Moreover, cup-shaped chloroplasts, which are dark green in color inside the cell wall can also been seen. However, no flagellum can be found indicating that they are non-motile and have to move by water current.

For Chlamydomonas, it is small. It is also unicellular and contained the cup-shaped chloroplast where a single large pyrenoid can also been found inside the chloroplast. There is also a pair of long, whiplike flagella indicating that they are motile.

For Spirogyra, it is an unbranched filamentous form which is multicellular and relatively larger in size compared with Chlorella and Chlamydomonas. It has a thick cell wall and the chloroplasts are in spiral forms. The small round bodies in the chloroplasts are pyrenoids. Nucleus can be seen in the middle of each cell. Moreover, a large vacuole can also be observed.

3. First, they are most similar to plants as they exhibit apical growth, their bodies are differentiated into nodal and internodal regions and whorls of short branches also arise in the nodal regions.

Second, they have root-liked structures which are called rhizoids for anchorage. These rhizoids have the similar function to roots in plants.

Third, they have a similar reproduction system with plants. Male gametes are produced in antheridia (contain sperm), while female gametes are produced in oogonia (contain eggs) which are surrounded by several types of sterile accessory cells. These sex organs make just like those in some plants which carry our sexual reproduction.

4. For similarities, both of their fronds are soft, translucent and membranous with no definite shape.Second, they both have rhizoidal holdfast for attachment to the substratum.Third, they both are thallus.

For differences, Ulva is bright green as it contains chlorophyll a and b whereas Porphyra is red which contains chlorophyll a and Phycobilins. Second, for the size of each frond, Ulva is relatively much bigger than Porphyra. The thallus of Ulva is flat and broad(>1m long) while the thallus of Porphyra is sheet-like(>15m long) Third, cell division of Porphyra is confined to one plane and cells are packed together into 1-2-layered sheet whereas cell division of Ulva is confined to two planes results in a flattened sheet of two cells thick.

5. For Laminaria,

Holdfasts are present for attachment to the rocks firmly even at extreme low tide.
It has a slippery texture as mucilage is secreted to the surface for protection from other organisms which may attach or attack them and to prevent desiccation at extreme low tide..
Splits can be found on large lamina to reduce water resistance, which prevent breakage easily because of the water current and waves.

For Fucus,

Holdfasts are present for attachment to the rocks firmly in the intertidal zone and withstand mechanical stress caused by water wave and current
Air bladders are frequently present to reduce the weight so that it can float on water to maximize the absorption of light for photosynthesis.
Thirdly, the dichotomously-branched thallus and the presence of midrib help to support itself so that damage by waves and water current can be minimized.

For Sargassum,

Presence of berry-liked air bladders provides buoyancy for them to float freely in the warm region of water to maximize the sunlight absorption for photosynthesis.
The sporophyte is highly differentiated, with stem-liked stipe which gives support to it and helps to withstand wave action.
There are many leaf-like appendages which are small in size which increase the surface area for sunlight absorption to carry out photosynthesis and reduce water resistance for free-floating in the water.

6. Algae play an important role in ecosystem. As all of them contain chlorophyll, they are photosynthetic which absorb carbon dioxide and release oxygen. The oxygen supply in the environment can be maintained.

They are phytoplankton which carry out photosynthesis to produce food. Therefore, they act as a primary producer in the food chain which contains a lot of nutrients. For example, phytoplankton such as diatoms and dinoflagellates act as the food source for zooplankton. Aquatic animals such as shrimps feed on diatoms and dinoflagellates and fishes which at a higher trophic level will further feed on shrimps. Algae such as laminaria ,Ulva and porphyra are also the food for human which is nutritious to us. Thus, they are significant in ecosystem. Without it, the ecosystem will be upset.

The mucilage called algin extracted from brown algae such as Laminaria can act as a stabilizer and emulsifier for food industry. And the mucilage extracted form red algae can also used to make agar which can be used as a , a substitute, a thickener for soups, in , and desserts such as , as a clarifying agent in , and for fabrics.

As Kelps are the largest known algae which form Kelp forest in marine, it can acts as the shelter for other small organisms.

Conclusion:

By studying the morphological characteristics as well as adaptations to the mode of life of different species of algae in this experiment, it gives us a chance to discover more about the significant of algae contributing to our life as well as the ecosystem.

Reference:

http://www.microscopy-uk.org.uk/mag/artjan99/gyra.html

http://www.mbari.org/staff/conn/botany/reds/lisa/chem.htm

Biology of Plants