22–1 Introduction to Plants

22–1 Introduction to Plants
Photo Credit: © Terry Donnelly/Dembinsky Photo Associates Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall
What Is a Plant? What is a plant? Copyright Pearson Prentice Hall

What Is a Plant? What Is a Plant? Plants are multicellular eukaryotes that have cell walls made of cellulose. Plants develop from multicellular embryos and carry out photosynthesis using the green pigments chlorophyll a and b. Copyright Pearson Prentice Hall

What Is a Plant? Plants include trees, shrubs, and grasses, as well as other organisms, such as mosses and ferns. Most plants are autotrophs, although a few are parasites or saprobes that live on decaying materials. Copyright Pearson Prentice Hall

The Plant Life Cycle The Plant Life Cycle Plant life cycles have two alternating phases, a diploid (2N) phase and a haploid (N) phase, known as alternation of generations. Copyright Pearson Prentice Hall

The Plant Life Cycle Alternation of Generations All plants have a life cycle with alternation of generations, in which the haploid gametophyte phase alternates with the diploid sporophyte phase. Copyright Pearson Prentice Hall

The Plant Life Cycle During the two phases of the life cycle, mitosis and meiosis alternate to produce the two types of reproductive cells—gametes and spores. The diploid (2N) phase is called the sporophyte, or spore-producing plant. The haploid (N) phase is called the gametophyte, or gamete-producing plant. Copyright Pearson Prentice Hall

The Plant Life Cycle Plant spores are haploid (N) reproductive cells formed in the sporophyte by meiosis. The spores can grow into new organisms called gametophytes. A gamete is a reproductive cell produced by mitosis, and it can fuse with another gamete to produce the sporophyte. Copyright Pearson Prentice Hall

What Plants Need to Survive
What do plants need to survive? Copyright Pearson Prentice Hall

In order to survive, plants need: sunlight water and minerals gas exchange transport of water and nutrients throughout the plant body Copyright Pearson Prentice Hall

Sunlight Plants use energy from sunlight to carry out photosynthesis. Photosynthetic organs such as leaves are broad and flat to maximize light absorption. Copyright Pearson Prentice Hall

Water and Minerals All cells require a constant supply of water. Water is used up quickly when the sun is shining. As a result, plants have structures that limit water loss. Copyright Pearson Prentice Hall

As they absorb water, plants also absorb minerals. Minerals are nutrients in the soil needed for plant growth. Copyright Pearson Prentice Hall

Gas Exchange Plants require oxygen to support cellular respiration as well as carbon dioxide to carry out photosynthesis. They must exchange these gases with the atmosphere without losing excessive amounts of water through evaporation. Copyright Pearson Prentice Hall

Movement of Water and Nutrients Plants take up water and minerals through their roots, but they make food in their leaves. Most plants have specialized tissues that carry water and nutrients from the soil and distribute products of photosynthesis throughout the plant body. Simpler plants carry out these functions by diffusion. Copyright Pearson Prentice Hall

Early Plants Early Plants When plants first appeared, life on Earth changed. As plants colonized the land, they changed the environment so other organisms could develop. New ecosystems arose, and organic matter began to form soil. Copyright Pearson Prentice Hall

Early Plants How did the first plants evolve? Copyright Pearson Prentice Hall

Early Plants The first plants evolved from an organism similar to the multicellular green algae living today. Copyright Pearson Prentice Hall

Early Plants Multicellular green algae have the size, color, and appearance of plants. They have reproductive cycles similar to those of plants. Green algae also have cell walls and photosynthetic pigments that are identical to those of plants. Copyright Pearson Prentice Hall

Early Plants The First Plants DNA sequences confirm that plants are closely related to certain groups of green algae, suggesting that the ancestors of the first plants were indeed algae. Copyright Pearson Prentice Hall

Early Plants The oldest known plant fossils, about 450 million years old, are similar to today’s mosses. They had a simple structure and grew close to the ground. One of the earliest fossil vascular plants was Cooksonia, which looked similar to mosses living today. Copyright Pearson Prentice Hall

Early Plants Fossils suggest that the first plants needed water to complete their life cycles. The demands of life on land favored the evolution of plants that were: more resistant to the drying rays of the sun. more capable of conserving water. more capable of reproducing without water. Copyright Pearson Prentice Hall

Early Plants From these plants, several major groups of plants evolved. One group developed into the mosses and their relatives. Another group gave rise to all other plants. All plants have evolved different adaptations for a variety of terrestrial environments. Copyright Pearson Prentice Hall

Overview of the Plant Kingdom
Plants are divided into four groups based on these features: water-conducting tissues seeds flowers Plants are also classified by other features, including reproductive structures and body plan. Copyright Pearson Prentice Hall

Evolutionary Relationships Among Plants Flowering plants Cone-bearing plants Ferns and their relatives Flowers; Seeds enclosed in fruit Mosses and their relatives This cladogram shows the evolutionary relationships among the various groups of plants. The four main groups of living plants are mosses and their relatives, ferns and their relatives, cone-bearing plants, and flowering plants. Seeds Water-conducting (vascular) tissue Green algae ancestor Copyright Pearson Prentice Hall

Today, scientists can classify plants more precisely by comparing the DNA sequences of various species. Copyright Pearson Prentice Hall

22–1 Copyright Pearson Prentice Hall

22–1 Most plants alive today are cone-bearing. flowering. ferns. mosses. Copyright Pearson Prentice Hall

22–1 The two phases of a plant's life cycle are referred to as alternation of generations. spontaneous generation. biogenesis. sexual and asexual. Copyright Pearson Prentice Hall

22–1 Which statement accurately describes a way that plants meet their basic needs? Plants take in carbon dioxide from soil through their roots. Plants obtain the energy for photosynthesis from sunlight. Plants obtain minerals by exchanging gases with the atmosphere. Plants absorb water through their broad, flat leaves. Copyright Pearson Prentice Hall

22–1 The first group of plants to evolve from green algae were the cone-bearing plants. ferns. mosses. flowering plants. Copyright Pearson Prentice Hall

22–1 The diploid phase of the plant life cycle is known as the sporophyte. gametophyte. egg. spore. Copyright Pearson Prentice Hall

22–2 Bryophytes Photo Credit: Terry Donnelly/Dembinsky Photo Associates Copyright Pearson Prentice Hall

Groups of Bryophytes Mosses and their relatives are called bryophytes, or nonvascular plants. They do not have vascular tissues, or specialized tissues that conduct water and nutrients. Copyright Pearson Prentice Hall

Groups of Bryophytes What adaptations of bryophytes enable them to live on land? Copyright Pearson Prentice Hall

Groups of Bryophytes Bryophytes have life cycles that depend on water for reproduction. Bryophytes draw up water by osmosis only a few centimeters above the ground. Copyright Pearson Prentice Hall

Groups of Bryophytes During one stage of their life cycle, bryophytes produce sperm that swim through water to reach eggs of other individuals. Therefore, bryophytes must live where there is rainfall or dew for part of the year. Copyright Pearson Prentice Hall

Groups of Bryophytes Groups of Bryophytes Bryophytes are low-growing plants found in moist, shaded areas. Copyright Pearson Prentice Hall

Groups of Bryophytes What are the three groups of bryophytes? Copyright Pearson Prentice Hall

Groups of Bryophytes The three groups of bryophytes are: mosses liverworts hornworts Copyright Pearson Prentice Hall

Groups of Bryophytes Mosses The most common bryophytes are mosses. Mosses: are adapted to life in wet habitats and nutrient-poor soils. can tolerate low temperatures. are clumps of gametophytes growing together. Copyright Pearson Prentice Hall

Groups of Bryophytes Capsule The Structure of a Moss Sporophyte Stalk Stemlike structure Gametophyte Leaflike structure This illustration shows the structure of a typical moss plant. The green photosynthetic portion is the gametophyte. The brown structure on the tip of the gametophyte is the sporophyte. Rhizoid Copyright Pearson Prentice Hall

Groups of Bryophytes Each moss plant has a shoot that looks like a stem with leaves. These are not true stems or leaves, because they do not contain vascular tissue. Copyright Pearson Prentice Hall

Groups of Bryophytes When mosses reproduce, they produce thin stalks, each containing a capsule. This is the sporophyte stage. Copyright Pearson Prentice Hall

Groups of Bryophytes The “leaves” of mosses are one cell thick, so they lose water quickly if the surrounding air is dry. Mosses have rhizoids, which are long cells that anchor them in the ground and absorb water and minerals from the soil. Water moves through rhizoids and into the rest of the plant. Copyright Pearson Prentice Hall

Groups of Bryophytes Liverworts Liverworts’ gametophytes form broad, thin structures that draw up moisture from the soil surface. Mature gametophytes produce structures that look like tiny green umbrellas. These carry the structures that produce eggs and sperm. Copyright Pearson Prentice Hall

Groups of Bryophytes Some liverworts can reproduce asexually by means of gemmae. Gemmae are small multicellular reproductive structures. In some species, gemmae form in gemma cups. When washed out of the cup, the gemmae can divide by mitosis to produce a new individual. Copyright Pearson Prentice Hall

Groups of Bryophytes Hornworts Hornworts are found only in soil that is damp nearly year-round. Their gametophytes look like those of liverworts. The hornwort sporophyte looks like a tiny green horn. Copyright Pearson Prentice Hall

Life Cycle of Bryophytes
How do bryophytes reproduce? Copyright Pearson Prentice Hall

Bryophytes reproduce and develop by alternation of generations. The gametophyte is the dominant stage of the life cycle and is the stage that carries out most of the plant's photosynthesis. Copyright Pearson Prentice Hall

Life Cycle of a Moss The life cycle of a moss illustrates how bryophytes reproduce and develop. Copyright Pearson Prentice Hall

Life Cycle of a Bryophyte Mature sporophyte (2N) Gametophyte (N) In bryophytes, the gametophyte is the dominant, recognizable stage of the life cycle and is the form that carries out photosynthesis. Sporophytes, which produce haploid spores, grow at the top of the gametophyte plant. When the spores are ripe, they are shed from the capsule like pepper from a shaker. In some species, gametes (sperm and eggs) are produced on separate male and female gametophyte plants. Gametophyte (N) Copyright Pearson Prentice Hall

Human Use of Mosses Human Use of Mosses Sphagnum mosses thrive in the acidic water of bogs. Dried sphagnum acts as a natural sponge. It can accumulate to form peat deposits. Peat can be cut from the ground and used as fuel. Peat can be used to improve the soil’s ability to retain water and to increase soil acidity. Copyright Pearson Prentice Hall

22–2 Unlike all other plants, bryophytes do NOT have vascular tissue. chlorophyll. gemmae. cell walls. Copyright Pearson Prentice Hall

22–2 Water moves from the soil into the stemlike and leaflike structures of bryophytes by osmosis. active transport. specialized conducting structures. vascular tissue. Copyright Pearson Prentice Hall

22–2 The most abundant bryophytes are the liverworts. mosses. hornworts. ferns. Copyright Pearson Prentice Hall

22–2 Fertilization in bryophytes is dependent upon the presence of water. sunlight. nutrients. wind. Copyright Pearson Prentice Hall

22–2 The stage of a moss plant that carries out most photosynthesis is the green gametophyte. sporophyte. protonema. zygote. Copyright Pearson Prentice Hall

22–3 Seedless Vascular Plants
Photo Credit: ©Terry Donnelly/Dembinsky Photo Associates Copyright Pearson Prentice Hall

Evolution of Vascular Tissue
420 million years ago, mosslike plants on land were joined by taller plants. Evidence shows that these plants had vascular tissue, which is specialized to conduct water and nutrients throughout the plant. Copyright Pearson Prentice Hall

The first vascular plants contained tracheids which are cells specialized to conduct water. Tracheids make up xylem, a transport subsystem that carries water from the roots to every part of a plant. Copyright Pearson Prentice Hall

Tracheids are hollow with thick cell walls that resist pressure. They connect end to end to allow water to move efficiently. Copyright Pearson Prentice Hall

Vascular plants have a second transport subsystem composed of vascular tissue called phloem. Phloem transports solutions of nutrients and carbohydrates produced by photosynthesis. Copyright Pearson Prentice Hall

How is vascular tissue important to ferns and their relatives? Copyright Pearson Prentice Hall

Both xylem and phloem can move fluids through the plant body, even against the force of gravity. Copyright Pearson Prentice Hall

Together xylem and phloem move water, nutrients, and other materials throughout the plant. In many plants, xylem and lignin (a substance that makes cell walls rigid) enable them to grow upright and tall. Copyright Pearson Prentice Hall

Ferns and Their Relatives
What are the characteristics of the three phyla of seedless vascular plants? Copyright Pearson Prentice Hall

Seedless vascular plants include: club mosses horsetails ferns Copyright Pearson Prentice Hall

The most numerous phylum is the ferns. Ferns and their relatives have true roots, leaves, and stems. Copyright Pearson Prentice Hall

Roots are underground organs that absorb water and minerals. Leaves are photosynthetic organs that contain one or more bundles of vascular tissue. Tissue is gathered into veins made of xylem and phloem. Stems are supporting structures that connect roots and leaves, carrying water and nutrients between them. Copyright Pearson Prentice Hall

Club Mosses Ancient club mosses grew into trees and produced forests. Fossilized remains of these exist today as huge beds of coal. Today, club mosses are small plants that live in moist woodlands. Copyright Pearson Prentice Hall

Horsetails The only living genus of Arthrophyta is Equisetum. Equisetum has true leaves, stems, and roots. Equisetum is called horsetail, or scouring rush. Copyright Pearson Prentice Hall

Ferns probably evolved 350 million years ago, when club moss forests covered Earth. Ferns thrive in wet areas with little light. Copyright Pearson Prentice Hall

Life Cycle of Ferns Ferns have vascular tissues, strong roots, underground stems called rhizomes, and leaves called fronds. Photo credit: ©Peter Chadwick/Dorling Kindersley Copyright Pearson Prentice Hall

Life Cycle of Ferns What are the stages in the life cycle of ferns? Copyright Pearson Prentice Hall

Life Cycle of Ferns Life Cycle of Ferns Ferns and other vascular plants have a life cycle in which the diploid sporophyte is the dominant stage. Copyright Pearson Prentice Hall

Life Cycle of Ferns Fern sporophytes develop haploid spores on the underside of their fronds in structures called sporangia. Sporangia are grouped into clusters called sori. Copyright Pearson Prentice Hall

Life Cycle of Ferns The Underside of a Fern Frond Sporangia Photo Credit: left: ©Biophoto Associates/Photo Researchers, Inc.; right: ©Ed Reschke/Peter Arnold, Inc. Sorus Copyright Pearson Prentice Hall

Life Cycle of Ferns Fern Life Cycle Sporangium (2N) Frond Young gametophyte (N) Spores (N) Mature sporophyte (2N) Developing sporophyte (2N) Mature gametophyte (N) Antheridium In the life cycle of a fern, the dominant and recognizable stage is the diploid sporophyte. The tiny, heart-shaped gametophyte grows close to the ground and relies on dampness for the sperm it produces to fertilize an egg. The young sporophyte grows from the gametophyte. Sperm Gametophyte (N) Egg Sporophyte embryo (2N) Archegonium Copyright Pearson Prentice Hall

22–3 Plant cells specialized to conduct water are called tracheids. veins. sori. phloem. Copyright Pearson Prentice Hall

22–3 The presence of vascular tissue enables a plant to carry on photosynthesis. carry on lactic acid fermentation. conduct water and nutrients. make chlorophyll. Copyright Pearson Prentice Hall

22–3 Ferns are different from mosses because they carry out photosynthesis using chlorophyll. have vascular tissue to conduct water and nutrients. help expose more of the plant’s surface area to sunlight. exchange carbon dioxide and oxygen with the atmosphere. Copyright Pearson Prentice Hall

22–3 Club mosses and horsetails are similar to ferns because they have vascular tissue. seeds. sori. fronds. Copyright Pearson Prentice Hall

22–3 When fern spores germinate, they develop into diploid gametophytes. haploid gametophytes. haploid sporophytes. diploid sporophytes. Copyright Pearson Prentice Hall

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22–1 Introduction to Plants

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