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Transcript
Gymnosperms evolved seeds as a way to protect their young After mosses and ferns, the next group of plants to evolve was the gymnosperms [JIM-nuh-sperms] . This group includes pine trees and other conifers (conebearing plants ; see Figure 3 .8), as well as cycads and ginkgos. Gymnosperms were the first plants to evolve seeds, structures in which plant embryos are encased in a protective covering and provided with a stored supply of nutrients (Figure 3 .10) . Gymnosperms (gymno, "naked"; sperm, "seed") have seeds that are relatively unprotected compared with those of angiosperms, the next major group of plants to arise . Gymnosperms were the dominant plants 250 million years ago, and the evolution of seeds was probably an important part of their success . Seeds provided nutrients that plant embryos could use to grow before they were able to produce their own food via photosynthesis . Seeds also provided embryos with protection from drying or rotting and from attack by predators. Angiosperms produced the world's first flowers Although typically we think of flowers when we think of plants, flowering plants are a relatively recent development in the history of life . Today the flowering plants, or angiosperms [Awjee-oh-sperms], are the most dominant Light-gathering leaves are the main site of photosynthesis . Leaves absorb carbon dioxide through tiny openings. A waxy covering (cuticle) on leaves and stems prevents unnecessary water loss by evaporation . Most plants possess vascular tissues . The vascular system transports water and minerals throughout the plant and adds to its sturdiness. Flowers are the structures in which reproduction takes place and in which fruits are produced. Fruits contain the young of the next generation, the seeds . j The stem provides support and extends the plant toward the sun. Roots anchor plants to the ground and allow them to absorb water and critical nutrients from the soil. and diverse group of plants on the planet, including orchids, grasses, corn plants, and apple and maple trees. Angiosperms produce seeds that are well protected (angio means "vessel," referring to the tissues that encase the plant's embryo). Highly diverse in size and shape, angiosperms live in a wide range of habitats—from mountaintops to deserts to salty marshes and fresh water. Almost any plant we can think of that is not a moss, a fern, or a cone-producing tree is an angiosperm . The key to the Figure 3 .9 The Basic Structures of a Plant Shown here is a familiar garden vegetable, a pepper plant . Because it is a member of the angiosperms, the last of the major plant groups to evolve, all the evolutionary innovations that distinguish plants can be shown on this one plant. success of angiosperms, and their defining feature, is the flower . Flowers are specialized structures for sexual reproduction, or pollination, where the male and the female gametes meet (Figure 3 .11). Some flowers provide food, such as the sugary liquid known as nectar, to attract animals to visit them and in the process transport pollen (male gametes) from flower to flower. The transported pollen can fertilize another flower's ovules (structures containing female gametes). Thus animals can provide a means of sexual reproduction between even very distant plants . Plants also use wind to disperse their pollen from flower to flower. People with hay fever are reacting to this method of plant sex, which sends nose-irritating pollen blowing through the air. In addition to increasing the efficiency of fertilization through flowers, angiosperms have evolved a variety of ways to distribute their seeds to distant places in order to get their young off to a good start . One of these is the use of tasty fruits that attract animals . As the embryos of some angiosperms are developing, the surrounding ovary develops into a ripening fruit (see Figure 3 .11). Animals eat the fruit and later excrete the seeds in their feces . These nutrient-rich wastes provide a good place for the seeds to begin life, often far from their parent plant where they will not compete with that parent for water, Chapter 3 Major Groups of Living Organisms 3.5 Figure 3 .12 Getting Around Plants have evolved many ways of spreading to new areas. (a) A palm tree seed in a coconut can float for hundreds of miles until it reaches a new beach where it can take root and grow . (b) Some seeds have wings (for example, maple "keys") or other structures (such as dandelion fluff, shown here) that allow them to be carried by the wind, sometimes over great distances . nutrients, or light . But hitching a ride in an animal's gut is not the only means plants have for overcoming their immobility ; plant seeds have evolved many other ways to travel (Figure 3 .12). Plants are the basis of land ecosystems and provide many valuable products It is difficult to overstate the significance of plants . As photosynthesizing organisms, plants use sunlight and carbon dioxide to make sugars, food that they and the organisms that eat them can use. Nearly all organisms on land ultimately depend on plants for food, either directly by eating plants or indirectly by eating other organisms (such as animals) that eat plants or that eat other organisms that eat plants, and so on . Many organisms live on or in plants, or on or in soils largely made up of decomposed plants. Flowering plants provide humans with materials such as cotton for clothing and with pharmaceuticals such as morphine. Essentially all agricultural crops are flowering plants, and the entire floral industry rests on the reproductive structures of angiosperms . Gymnosperms such as pines, spruces, and firs are the basis of forestry industries, providing wood and paper. As valuable as plants are when harvested, they are also valuable when left in nature . By soaking up rainwater in their roots and other tissues, for example, plants prevent runoff and erosion that can contaminate streams. Plants also produce the crucial gas oxygen. The Fungi : A World of Decomposers Most people are familiar with fungi as the 'BACTERIA' 'ARCHAEA) mushrooms sliced on their pizza or sprouting from their lawns . However, the Fungi, a kingdom within the domain Eukarya, also includes yeasts (single-celled fungi) and molds . In fact, the familiar mushroom is just a small part of a fungus. Most fungal 'BACTERIA' (ARCHAEA) EUKARYA PROTISTA (PLANTAE FUNGI tissues typically are woven through whatc2 ever substance—often the tissues of another organism—the fungus is digesting and making its living from . Because fungal tissues are largely hidden from view, fungi are among the most poorly understood of the major groups of organisms. Fungi can be costly to human society. They can cause diseases, contaminate crops, rot food, and force us to clean our bathrooms more often than we might like. Other fungi are beneficial, providing us with pharmaceuticals, including antibiotics such as penicillin . Yeasts such as Saccharomyces cerevisiae [sAK-ah-roh-MICE-eez Bair-uhVEE-see-eye] can feed on sugars and produce two important products : alcohol and the gas carbon dioxide, both crucial to the rising of bread and the brewing of beer. Fungi also provide highly sought-after delicacies such as truffles, whose underground growing locations can be found only by specially trained dogs or pigs. As Figure 3 .13 shows, the fungi are divided into three distinct groups : zygomycetes, which evolved first, ascomycetes, and basidiomycetes . Each group differs in— and is named for—its unique reproductive structures. Fungi play several roles in terrestrial ecosystems. Many fungi are decomposers . Playing the role of garbage processor and recycler, these fungi speed the return of the nutrients in dead and dying organisms to the ecosystem. Some fungi are parasites (organisms that live in or on other organisms and harm them), while others are mutualists (organisms that benefit from, and provide benefits to, the organisms they associate with) . Sometimes the benefits and harms in these associations involve nutrition, sometimes not . Do not confuse these terms, however, with the categories of decomposer, consumer, and producer, even though they describe how organisms get their nutrition . Mutualist and parasite are a separate, unrelated pair of words to describe whether organisms are good or bad for the organisms they associate with. For example, consumers can be mutualists or parasites; likewise, mutualists can be consumers, producers, or decomposers . Chapter 3 Major Groups of Living Organism AI stars, s ously a 'Ph( In humans, fungi can cause mild diseases such as athlete's foot . Fungal diseases can also be deadly, like the pneumonia caused by the fungus Pneumocystis carinii [woo-moh-szss-tiss kuh-REE-nee], the leading killer of people suffering from AIDS . Fungi attack plants, too. Ceratocystis ulmi [BARE-uh-toh-srss-tiss ooL-mee] causes Dutch elm disease, which has nearly eliminated the elm trees that once formed arching canopies over streets all across the United States. Rusts and smuts are fungi that attack crops . Still other fungi are specialized for eating insects, and biologists are trying to use these fungi to kill off insects that are crop pests (Figure 3.16). were t 3 .18 of ians I anem next € comp ing nr ment spidE Thee off tc Some fungi live in beneficial associations with other species Some fungi are mutualists, living in association with other organisms to their mutual benefit . One broad group of mutualists—found in all three groups of fungi (zygomycetes, ascomycetes, and basidiomycetes)—is known as mycorrhizal [MY-koh-RYE-zul] fungi . These species live in mutually beneficial associations with plants . The fungi form thick, spongy mats of mycelium on and in the plants' roots that help the plants absorb more water and nutrients . The fungi receive sugars and amino acids, the building blocks of proteins, from the plants . More than 95 percent of ferns (and their close relatives), gymnosperms, and angiosperms have mycorrhizal fungi living in association with their roots. Figure 3 .17 Mutua list Fungi A lichen consists of an alga and a fungus intimately entwined In a mutually beneficial association . This lichen, known as British soldiers is shown growing on an old log. For example, morels—a group of mushrooms highh prized as food by some—are the reproductive structures of mycorrhizal fungi. Another familiar fungal association is the lichen [akin], a lacy, orange or gray-green growth often seen on tree trunks or rocks . A lichen is an association of an alga (a photosynthetic protist, as we learned earlier) anda fungus (Figure 3 .17) . Both ascomycetes and basidiomycetes are known to form lichens . The alga and fungus in a lichen grow with their tissues intimately entwined, allowing the fungus to receive sugars and other carbon compounds from the alga . In return, the fungus produces lichen acids, a mixture of chemicals that scientists believe may function to protect both the fungus and the alga from being eaten by predators. 3 .6 IBACTERIA] I ARCHAEAII IBACTERIAL ARCHAEAL ire 3.16 Fungal Parasites e fungi are parasites, making their living by attacking the tissues her living organisms . This beetle, a weevil in Ecuador, has been 1 by a Cordyceps [Koe-duh-seps] fungus, the stalks of which are ring out of its back . Unit 1 The Diversity of Life The Animalia : Complex, Diverse, and Mobile EUKARYA PROTISTA PLANTAEI FUNGI ] 11 The Animalia, or the animals, are a kingdom within the domain Eukarya . The Animalia is the most familiar major group, and the one to which humans belong. All animals are multicellular, and many of them are quite complex . The animals include flashy creatures such as Bengal tigers, peacocks, and you, as well as worms, sea fron part that echi the tebr and I are of o an( ani pla of E sit stars, snails, insects, and other creatures that are less obviously animal-like, such as sponges and corals. The sponges, the most ancient of animal lineages, were the first to branch off the evolutionary tree (Figure 3 .18 on the next page) . Next to evolve were the cnidarians [nye-DARE-ee-uns] (including jellyfish, sea anemones, and corals), and then the flatworms . The next group to evolve was the protostomes, a group that comprises more than 20 separate subgroups, including mollusks (such as snails and clams), annelids (segmented worms), and arthropods (including crustaceans, spiders, and insects), the three shown in Figure 3 .18. These three protostome groups are depicted branching off together because it is unclear which of them evolved from the others first . What is known is that they are part of a single lineage descending from an ancestor that branched off the tree after flatworms, but before echinoderms [ee-KYE-noh-derms] . Next to evolve were the echinoderms (sea stars and the like) and the vertebrates (animals with backbones, such as fish, birds, and humans), both deuterostomes [ g oo-ter-oh-stomes]. Like all fungi and some bacteria and protists, animals are consumers, making their living by eating the tissues of other organisms, from which they derive both carbon and energy. Animals differ from fungi and plants in that animal cells do not have cell walls surrounding their plasma membranes . Typically mobile and often in search of either food or mates, animals have evolved a huge diversity in their ways of life. Outgoing water One type of specialized cell, the collar cell, has a tail-like appendage, known as a flagellum, which keeps water flowing through the sponge. Collar cells also trap food and pass it to other cells, which i digest it. Figure 3 .19 Sponges Have Specialized Cells but Lack Tissues Sponges are loose associations of cells . Although some of these cells are specialized, none are organized as tissues, as in most other animals . Animals evolved organs and organ systems Animals evolved true tissues Sponges are among the simplest of animals . They represent a time in the evolution of animals before tissues— specialized, coordinated collections of cells—had evolved. A sponge is a loose collection of cells (Figure 3 .19) . If it is put through a sieve and broken apart into individual cells, it will slowly reassemble as a whole sponge. Widespread and highly successful, sponges feed on amoebas and other tiny organisms in their aquatic environment, filtering a ton of water just to get enough food to grow an ounce. One of the earliest animal groups to evolve true tissues was the cnidarians . Their name—Cnidaria—comes from the Greek word for "nettle," a stinging plant found on land. Cnidarians are characterized by stinging cells they use to immobilize prey and to protect themselves from predators. Like other cnidarians, jellyfish (Figure 3 .20) have specialized nervous tissues, musclelike tissues, and digestive tissues. This specialization allows behavior—such as gracefully and rapidly swimming away from predators— that requires the coordination of many cells . After tissues, the next level of complexity to evolve was organs and organ systems . Recall that organs are body parts composed of different tissues organized to carry out specialized functions . Usually organs have a defined boundary and a characteristic size and shape ; an example is the kidney. An organ system is a collection of organs functioning together to perform a specialized task . The human digestive system, for example, is an organ system that includes the stomach as well as other digestive organs, such as the pancreas, liver, and intestines . Flatworms, a group of fairly simple wormlike animals, were one of the earliest groups to evolve true organs and organ systems (Figure 3 .21). Animals evolved complete body cavities Still later in the history of this group, animals evolved a complete body cavity—an interior space with a mouth at one end and an anal opening at the other . The two distinct evolutionary lineages that exhibit such cavities are the protostomes and the deuterostomes (see Figure 3 .18). Protostomes include such animals as insects, worms, and Chapter 3 Major Groups of Living Organisms riew the tissue wrs of a jellyfish . I The endoderm is specialized to facilitate digestion, discharging proteins that break down food, which is then taken up by the cells f The mesoglea is an inner layer of jellylike material . The tentacles contain specialized stinging cells that are used to inject poisons into prey and subdue them. Figure 3 .20 Jellyfish Have True Tissue Layers Cnidarians (including jellyfish) were one of the earliest groups to evolve true tissues . These tissues include the ectoderm (ecto, "outer"; derm, "skin") and the endoderm (endo, "inner") . For clarity, these two layers are color-coded blue and yellow, respectively . Sandwiched between them is an inner (red) layer of secreted material known as the mesoglea (meso, "middle" ; glee, "jelly") . In addition to serving as nervous tissue, the ectoderm coordinates with the endoderm to contract like muscle tissue . Tentacles bring food into the internal cavity through a single opening, which serves as both a mouth and an anus. Figure 3 .21 Flatworms Evolved Organs and Organ Systems One of several organ systems in the flatworm is the reproductive system . It contains both male and female structures, since every flatworm can function as both a male and a female . For clarity, we have color-coded the female structures pink (ovary, oviduct, and genital pore) and the male structures blue (penis and testis). Unit 1 The Diversity of Life snails. Deuterostomes include animals such as sea stars (echinoderms) and all the animals with backbones (vertebrates), such as humans, fish, and birds. The names for these two lineages refer to which of the two openings in the early embryo becomes the mouth . In protostomes (from proto, "first" ; stome, "opening"), the mouth forms from the first opening to develop, and the anus forms elsewhere later . hn deuterostomes (deutero, "second"), the first opening develops into the anus, while the second opening becomes the mouth. This developmental difference has led to radically different patterns of tissue organization in these two groups. Animal body forms exhibit variations on a few themes Animals exhibit a great variety of shapes and sizes, many of which are variations on a few basic body plans. Arthropods (arthro, "jointed" ; pod, "foot") have a hard outer skeleton called an exoskeleton (exo, "outer"), which is made of chitin [KYE-tin], the same material found in the cell walls of fungi. One feature that has facilitated the evolution of arthropod bodies is their segmented body plan . Over time, individual body segments have evolved different combinations of legs, antennae, and other specialized appendages, resulting in a huge number of different types of animals, some of them extremely successful . Probably the bestknown arthropod group is the insects (grasshoppers, beetles, butterflies, and ants, among others), which have six legs and live on land . Whereas prokaryotes dominate Earth in sheer numbers of individuals, insects dominate in number of species, having many more species than any other group of organisms. Other arthropod groups include the arachnids [uhRACK-nids] (spiders, scorpions, and ticks), which have eight legs and also live on land ; the crustaceans (lobsters, shrimps, and crabs), which have ten or more legs and live primarily in water ; and millipedes and centipedes, which live on land and have many more legs— but less specialization—than the previously mentioned groups . Arthropods are a wonderful illustration of how evolution can modify a basic body plan to produce many variations over time (Figure 3 .22) . Looking just at the evolution of the last segment (the rear ends) of these animals, one can see that the changes support a huge variety of shapes and lifestyles . The last segment has evolved into the delicate abdomen of a butterfly, the piercing abdomen of a wasp (which has a huge structure eat prey, avoid being captured, attract mates and care for young, and migrate to new habitats . As we saw earlier, animals are quite useful to immobile organisms, such as plants, which have evolved ways to get animals to carry their pollen and seeds. Animals play key roles in ecosystems and provide products for humans Because they live by eating other organisms, and because most are mobile, animals play many roles in ecosystems . Most serve as consumers, preying on many species of plants and animals . Some animals, such as carrion beetles, serve as decomposers of dead animals. Figure 3.22 Variations on a Theme From a simple segmented body plan, arthropods have evolved a huge diversity of forms and sizes . The millipede can be viewed as the simplest form of these segmented animals, as all of its segments are similar. As segments have evolved and diversified, a variety of organisms have arisen, from lobster to swallowtail butterfly to parasitoid wasp. for inserting and laying eggs deep in another animal's body), and the delicious tail of the lobster. Such segmentation can also be seen in the annelids (segmented worms ; see Figure 3 .18) . This group includes the familiar earthworm, whose body is made up of a repeated series of segments (Figure 3 .23a). Vertebrates—animals with an internal backbone— are also built on a (less obvious) segmented body plan (Figure 3.23b) . The major vertebrate groups include fish, amphibians (frogs and salamanders), reptiles (snakes, lizards, turtles, and crocodiles), birds, and mammals (including humans and kangaroos) . Like annelids and arthropods, vertebrates illustrate how a variety of very different forms can evolve from one basic body plan . The front appendage of vertebrates has evolved as an arm in humans, a wing in birds, a flipper in whales, an almost nonexistent nub in snakes, and a front leg in salamanders and lizards. Animals exhibit an astounding variety of behaviors Another fascinating characteristic of animals is their ability to move, which allows for a wide range of behaviors . Animals have evolved varied ways to capture prey, Test your knowledge of the properties of multicellular eukaryotes . (a) (b) Figure 3.23 Many Animals Are Segmented Segmentation, a body plan in which segments repeat and often can evolve independently of one another, is shown here in (a) an earthworm (an annelid, or segmented worm), and (b) a vertebrate. Chapter 3 Major Groups of Living Organisms