Reading Essentials for Biology Glencoe (794133), страница 51
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One of the toxic species is responsible for an event that iscalled red tide. In a red tide, the organisms become so numerousthat the ocean turns a reddish color. During a red tide, humansrun the risk of being poisoned if they eat shellfish, such as clamsor mussels, which have fed on the toxic algae. Because of this,harvesting shellfish is usually banned during a red tide.How can red algae survive in deep water?The next three phyla, red algae, brown algae, and green algae,are multicellular organisms.
Red algae are seaweeds. The bodyof the seaweed is called a thallus. Seaweeds lack roots, stems,214Chapter 19READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Fusion ofgametesNameDateClassSection19.2Algae: Plantlike Protists, continuedor leaves. Red algae use structures called holdfasts to attach torocks. Red algae grow in tropical waters or along rocky coasts incold water.Red algae can survive in deep water where most other seaweeds cannot live.
This is because red algae have some photosynthetic pigments that absorb green, violet, and blue light. Thatis the only part of the light spectrum that can penetrate waterbelow 100 m.Can algae create a forest?4. What do red algae havethat allows them to survive in deep water?________________________________________________________________________The second of the multicellular phyla are the brown algae.They are usually found in cool ocean water. Many types of brownalgae have air bladders that keep their bodies floating near thesurface where light is available. The largest of the brown algae iskelp.
It can grow to be 60 m long. In some places kelp formshuge, dense, underwater forests. Kelp forests are ecosystems thatprovide homes for many saltwater organisms.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are the characteristics of green algae?Most green algae live in freshwater, so you may have seen themat the edges of ponds or lakes.
Surprisingly, green algae can livein many different environments. Some live in salt water, some insnow, and some on tree trunks. There is even one species of greenalgae that lives in the fur of an animal.Green algae are the most diverse of all the algae. They can beunicellular or multicellular. They may live in colonies.
A colonyis a group of cells that lives together in close association.There is a species of green algae called Volvox. It is composedof hundreds of cells. Each cell has flagellates. Together the cellsform a hollow, ball-shaped structure. The cells are connected bycytoplasm. The flagella of the individual cells face the outside ofthe ball-shaped structure. To move the colony, the flagella beattogether, spinning the ball through the water. Small balls of daughter colonies form inside the larger ball. Eventually the larger ballbreaks open and releases the daughter colonies.How do green algae reproduce?Green algae can reproduce sexually or asexually.
One methodof asexual reproduction in green algae is called fragmentation.During fragmentation an individual organism breaks into piecesand each piece forms a new organism.READING ESSENTIALS5. What is one method ofasexual reproduction ingreen algae?________________________________________________________________________Chapter 19215NameDateClassSection19.2Algae: Plantlike Protists, continuedAlternation of Generations6. What is the name of thelife cycle of green algae?________________________________________________________________________Green algae have a complex life cycle.
This life cycle alternatesbetween individuals that produce spores and individuals that produce gametes. This pattern is called alternation of generations.It means the generations alternate between haploid and diploid.Remember that haploid forms of cells are sex cells or gametes.They contain half the number of chromosomes as the parentorganism. Diploid forms are the body cells. They contain the sameamount of chromosomes as the parent.How does alternation of generations work?Use the illustration below to help you understand alternation ofgenerations.
The haploid form of the algae is called the gametophyte because it produces gametes. The gametes join to form azygote, which is a fertilized cell. From the zygote, the diploid formof the algae will develop. The diploid form is called the sporophyte. Certain cells in the sporophyte undergo meiosis. Thesespores are haploid spores that develop into new gametophytes.Gametophyte (n)Gametophyte (n)FemalegametophyteSporophyte (2n)SporeGamete GameteFertilizationnZygoteMeiosisSpore216Chapter 19n2n2n2nREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.MalegametophyteNameDateClassSection19.2Algae: Plantlike Protists, continued◗ After You ReadMini Glossaryalternation of generations: type of life cyclefound in green algae and all plants wherean organism alternates between a haploidgametophyte generation and a diploidsporophyte generationcolony: group of cells that live together in closeassociationfragmentation: type of asexual reproduction inalgae where an individual breaks into piecesand each piece grows into a new individualgametophyte: in algae, the haploid form of anorganism in alternation of generations thatproduces gametessporophyte: in algae, the diploid form of anorganism in alternation of generations thatproduces sporesthallus: body structure produced by plants andalgae that lacks roots, stems, and leaves1.
Review the terms and their definitions in the Mini Glossary above. Circle the three wordsthat relate to the life cycle of green algae. Then describe the process on the lines belowusing your own words.________________________________________________________________________________________________________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.2.
Place the six phyla of algae in the appropriate column in the idea map below. One of thealgae will be used twice.red algaegreen algaeeuglenoidsbrown algaediatomsdinoflagellatesPlantlike Protists: Algae• Major producer of oxygen• Important part of food chainOne-celledMulticellularVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about algae, the plantlike protists.READING ESSENTIALSChapter 19217NameDateClassSection19.3 Slime Molds, Water Molds, andDowny MildewsSC.G.1.4.1 The student knows of the great diversity and interdependence of living things.Also covers SC.D.1.4.4, SC.F.2.4.1◗ Before You ReadYou may have seen commercials on television about household cleaners that can rid a home of moldand mildew.
From what you may have observed, where do you think molds and mildew most oftenare found? Write on the lines below what conditions might play a part in making a good environment for molds and mildew.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCreate a Quiz After youhave read this section, createa quiz based on what youhave learned. After you havewritten the quiz questions, besure to answer them.Certain groups of protists have features like those of a fungus.Funguslike protists consist of the slime molds, the water molds,and the downy mildews.
Like fungi, the funguslike protistsdecompose organic material for food.There are three phyla of funguslike protists. Two of the phylaconsist of slime molds. The third phylum is made up of the watermolds and downy mildews.Slime Molds1. Name the two differenttypes of slime mold.________________________________________________________________________218Chapter 19Many slime molds are beautifully colored, ranging from brilliant yellow or orange to rich blue, violet, and jet black.
They livein cool moist places where they grow on damp, organic matter,such as rotting leaves or decaying tree stumps and logs.There are two major types of slime molds. One type, theplasmodial slime molds, belong to one phylum. The other typeof slime molds, the cellular slime molds, belong to a differentphylum.Slime molds are animal-like during much of their life cycle.They move about and surround food in a way similar to amoebas.However, like fungi, slime molds make spores to reproduce.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are funguslike protists?NameDateClassSection19.3Slime Molds, Water Molds, and Downy Mildews, continuedWhat is plasmodial slime?SporesBAPlasmodial slime molds get theirname because they form a plasmodium(plaz MOH dee um).
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