From http://www.youtube.com/user/ouliogroove
Passage 4: Listen to part of lecture in biology class. “Algae”
Today, we are going to talk about algae. First, you must remember that ‘alga’ is singular and ‘algae’ the plural. Algae are aquatic organisms. They are plant species that may be uni- or multi-cellular, and they contain chlorophyll thriving wet conditions, and usually lack roots, stems, and leaves. They can range in size from tiny single cell organisms to huge giant kelp. The term algae apply to several groups of aquatic organisms, which are capable of photosynthesis or manufacturing their own food. Algae are interesting because they can be colorful. Most people think of algae as green see weed, but algae can not only be green, but it can also be red, brown, or blue-green. The main focus of this lecture will be on the types of colored algae. Later lectures will be directed to other characteristics of algae.
Brown algae are chromists. The name chromista means ‘color’. Most chromists are colored, but some such as maldu may be colorless. They do not store their energy in the form of starch like other plants. And in addition to containing chlorophyll, they contain other pigments which give them in golden or brown color. Some chromists are not photo-synthetic, and in the past where class does animal or fungi or other does plant. However, today it is recognized that all of the chromista may have developed from independent evolutionary line from a common ancestor of plants, animals and fungi. And thus the new kingdom of chromista was born. Even though there was not complete agreement on how all of the chromists are inter-related, new researches being conducted which may explained the inter-relationships between them.
Green algae is very diversed. They are more than 7000 species of green algae and they are growing in very diversed habitats. They contain two forms of chlorophyll: capture light energy and manufacture to their own food. They are also mainly aquatic, but don’t share a common relationship with the chromists or the Rhodophyta organisms. Some of you may have seen green wroth attached to rocks in ocean. This may be sea lettuce, both green wroth and lettuce are examples of green algae. There sizes can be microscopic or giant and they are very important in aquatic ecosystems.
Kelp is chromist. And in fact coast lines in continents which are cool and tempered often have an abundance of kelp forests which are important source of food for marine and fresh water organisms. Chromists can occur in fresh water or salt water. Some are planktonic and float near the water surface while others attached themselves to the bottom of the ocean, and become so large they are referred to as forest. They are also many fossils associated with this group because of the ability of organisms to secret the calcium carbonate or lime deposits. Because of the algae’s ability to secret the carbonate, some of these group are thought to be responsible for so called embotrolium deposits.
Red algae are red because of pigment which absorbs blue light and reflects red light. They live in deeper depth than most algae because of their photosynthetic pigments. Most red algae live in tropical marine environment rather than in fresh water, but some do live in fresh water. Red algae are classified as Rhodophyta and they are important for different reasons. They are important in the formation of coral leaves because they secrete a shell of carbonate around themselves. Scientists are completely sure about how the organisms precipitate the calcium carbonate, but because they do and because fossils have resulted, it is believed that they may have association with petroleum deposit. In some areas, the red algae or coral leaf algae as they are referred to have been known to contribute more to the composition of leaf structure than coral does. In the South Pacific, giant clam shells have been found which contain a pink crystal material on the outside of the shells. This material is an example of calcium carbonate which has been deposited by red algae. Red algae can also be an important source of food. Nori (김) as a red algae is an important source of food for Asians. It has been cultivated in Japan for hundreds of years, but the industry started in 1950s, one of discoveries was made about the different stages in the organisms lives. When it was discovered that one phase of red algae’s life cycle was considered in edible stage, cultivation of the organism for food began on a much larger scale. Nori has many benefits as a food source. First, it is easy to cultivate, second, it is in high vitamin content, and third, it is high in protein content. The last colored algae I want to talk about today is the blue-green algae.
Blue-green algae are classified as Cyanobacterium. They are aquatic bacteria and make their own food. They get their name from pigment, which captures light for the process of photosynthesis. They are considered bacteria and they are quite small, usually microscopic. Although they are usually unicellular, they often grow into colonies, which are large enough to be seen. They are some of the oldest known fossils in the world and they are important for virus of nitrogen fertilizer used and been in rice cultivation. Cyanobacteria are living plants in formed chloroplast with which plants make food. Some of the cyanobacteria are good food sources because they are high in protein and can be cultivated easily in ponds. In the US, these organisms are considered as health food. But in ancient culture of Aztecs in Mexico they were dietary staple. While some of these algae are considered nutritious. Others such as Honscum(?) are known to be toxic to both humans and animals. And some can cause problems to those who come in contact with them. If you have ever been swimming, and later develop swimmer’s itch? You have probably encountered some blue-green algae, which has caused you skin irritation. On that note we will conclude today’s lecture. See you next class….!
Now get ready to answer the questions. You may use your notes to help you to answer.
18. What aspect of the algae does the professor mainly discuss?
19. What does the professor say about brown algae?
20. What is the evidence that the green algae diversed in size?
Listen again to part of lecture. Then answer the question:
”And some can cause problems to those who come in contact with them. If you have ever been swimming, and later develop swimmer’s itch? You have probably encountered some blue-green algae, which has caused you skin irritation.“
21. What does the professor imply when she says this?
” You have probably encountered some blue-green algae”
22. Why does the professor mention blue-green algae are classified as cyanobacteria?
23. How does the professor explain the purpose of the lecture?