Plants Lisa Michalek Introduction to Plants Based on

Plants © Lisa Michalek

Introduction to Plants • Based on weight, plants are the dominant group of organisms on land. • Most plants are photosynthetic. – They produce organic materials from inorganic materials by photosynthesis. • A few plant species live as parasites. – Many parasitic plants cannot photosynthesize.

Introduction to Plants • Plants probably evolved from multicellular aquatic green algae that could not survive on land. • Multicellularity enabled plants to develop features that helped them live more successfully on land. • Before plants could thrive on land, they had to be able to: – Absorb nutrients from their surroundings. – Prevent their bodies from drying out. – Reproduce without water to transmit sperm.

Absorbing Nutrients • On land, most plants take nutrients from the soil with their roots. • Botanists think that fungi may have helped early land plants to get nutrients from Earth’s rocky surface. – Symbiotic relationships between fungi and the roots of plants are called mycorrhizae. – Today, about 80% of all plant species form mycorrhizae.

Preventing Water Loss • The first plants lived at the edges of bodies of water, where drying out was not a problem. • A watertight covering, which reduces water loss, made it possible for plants to live in drier habitats. – This covering, called the cuticle, is a waxy layer that covers the non-woody aboveground parts of most plants.

Preventing Water Loss • The cuticle does not let oxygen or carbon dioxide pass through it. • Pores called stomata permit plants to exchange oxygen and carbon dioxide. – Stomata extend through the cuticle and the outer layer of cells. • A pair of guard cells border each stoma. • Stomata open and close as the guard cells change shape.

Reproducing on Land • Aquatic algae reproduce sexually when sperm swim through the water and fertilize eggs. • The sperm of most plants must be able to move without water. • In most plants, sperm are enclosed in a structure (pollen) that keeps them from drying out. • Pollen permits the sperm of most plants to be carried by wind or animals rather than water.

Vascular Tissue, Seeds and Flowers • As plants adapted to land, they developed many features that helped in their success. • One of the most important changes in plants was the development of conducting tissues that move water and other materials through the plant body.

Advantages of Conducting Tissue • The first plants were small. – Materials were transported within their bodies by osmosis and diffusion. • Today, specialized cells that transport water and other materials within a plant are found in vascular tissues. • The existence of vascular tissue allows for larger and more complex plants.

Advantages of Conducting Tissue • The larger, more complex plants have a vascular system. – A system of well-developed vascular tissue that distributes materials more efficiently. • Three groups of plants alive today lack a vascular system. – These plants are called nonvascular plants. • Plants that have a vascular system are called vascular plants.

Advantages of Seeds • A seed is a structure that contains the embryo of a plant. – An embryo is an early stage in the development of plants and animals. • Most plants living today are seed plants. – Vascular plants that produce seeds. • The first seed plants appeared about 380 million years ago.

Advantages of Seeds • Protection – Seeds are surrounded by a protective cover called the seed coat. – The seed coat protects the embryo from drying out and from mechanical injury and disease. • Nourishment – Most kinds of seeds have a supply of nutrients stored in them. – These nutrients are a ready source of nourishment for a plant embryo as it starts to grow.

Advantages of Seeds • Plant Dispersal – Seeds disperse (spread) the offspring of seed plants. – Many seeds have structures that help wind, water, or animals carry them away from their parent plant. – Dispersal prevents competition for water, nutrients, light, and living space between parents and offspring.

Advantages of Seeds • Delayed Growth – The embryo in a seed is in a state of suspended animation. – Most seeds will not sprout until conditions are favorable. • Such as when moisture is present and the weather is warm. – Seeds make it possible for plant embryos to survive through unfavorable periods such as droughts or cold winters.

Advantages of Flowers • The flower is a reproductive structure that produces pollen and seeds. • Most plants living today are flowering plants – seed plants that produce flowers. • The first flowering plants appeared more than 130 million years ago. – The pollen of the first seed plants was carried by wind. – Large amounts of pollen are needed to ensure cross-pollination by wind – an inefficient system.

Advantages of Flowers • Many flowers attract animals, such as insects, bats, and birds. • Tiny pollen grains stick to animals, which carry pollen directly from one flower to another. • Flowering plants that are pollinated by animals produce less pollen, and cross-pollination can occur between individuals that live far apart.

Plant Life Cycles • Plants have life cycle in which haploid plants that make gametes (gametophytes) alternate with diploid plants that make spores (sporophytes). – A life cycle in which a gametophyte alternates with a sporophyte is called alternation of generations.

Alternation of Generations

Vascular-Plant Sporophyte • Vascular System – Larger bodies require an efficient vascular system for transporting materials internally. – The sporophytes of vascular plants have two types of vascular tissue. – Each type of vascular tissue contains strands of long, tube like cells that are lined up end to end like sections of pipe. – These strands of cells transport water and nutrients within a plant’s body.

Vascular-Plant Sporophyte – Soft-walled cells transport organic nutrients in a tissue called phloem. – Hard-walled cells transport water and minerals nutrients in a tissue called xylem. • The walls of the water-conducting cells in xylem are thickened, which helps support the plant body. – This makes it possible for vascular plants to grow to great heights.

Vascular-Plant Sporophyte

Vascular-Plant Sporophyte • Distinctive Body Form – Nearly all plants have a body that consists of a vertical shaft from which specialized structures branch. – The part of a plant’s body that grows mostly upward is called the shoot. – In most plants, the part of the body that grows downward is called the root.

Vascular-Plant Sporophyte – Zones of actively dividing plant cells, called meristems, produce plant growth. – The vertical body form results as new cells are made at the tips of the plant body. – As vascular plants became better adapted to life on land, most developed the familiar plant structures (roots, stems, and leaves – which are complex structures made of several different types of specialized tissues. )

Nonvascular Plants • Nonvascular plants do not have a vascular system for transporting water and other nutrients within their bodies. • All nonvascular plants lack true roots, stems, and leaves. – Although most have structures that resemble them.

Features of Nonvascular Plants • Small Size – All nonvascular plants are small and relatively simple. – Water and other nutrients are transported within their bodies mostly by osmosis and diffusion, which move materials short distances. – This greatly limits the size of a nonvascular plant’s body.

Features of Nonvascular Plants • Larger Gametophyte – The gametophytes of nonvascular plants are larger and more noticeable than the sporophytes. – Hair-like projections called rhizoids anchor the gametophytes to the surfaces on which they grow. – The smaller, usually nongreen sporophytes grow on the gametophytes and depend on them for nutrients.

Features of Nonvascular Plants • Require Water for Sexual Reproduction – Nonvascular plants must be covered by a film of water in order for fertilization to occur. – Eggs and sperm form in separate structures, which are often on separate plants. – The gametophytes grow in mats of tightly covered by a film of water, the sperm can easily swim to neighboring individuals and fertilize their eggs.

Kinds of Nonvascular Plants • Mosses – Phylum Bryophyta are the most familiar of nonvascular plants. – The “leafy” green plants that you recognize as mosses are gametophytes. – Most sporophytes, which are not green, grow from the tip of a gametophyte. • Each sporophyte consists of a bare stalk topped by a spore capsule.

Kinds of Nonvascular Plants – Most mosses have a cuticle, stomata, and some simple conducting cells. – The walls of the water-conducting cells in mosses are not thickened, as they are in a vascular plant. – Mosses never get very large because their water-containing cells carry water only short distances.

Kinds of Nonvascular Plants • Liverworts – Phylum Hepatophyta grow in mats of many individuals. – They have no conducting cells, no cuticle, and no stomata. – Their gametophytes are green.

Kinds of Nonvascular Plants – In some gametophytes of liverworts are flattened and have lobes. – Structures that resemble stems and leaves make up the gametophytes of most liverworts, like those of the mosses. – The sporophytes of liverworts are very small and consist of a short stalk topped by a spore capsule.

Kinds of Nonvascular Plants • Hornworts – Phylum Anthocerophyta are a small group that completely lack conducting cells. – The sporophyte of a hornwort has both stomata and a cuticle. – The gametophyte of a hornwort is green and flattened. – Green hornlike sporophytes grow upward from the gametophytes.

Mosses and Medicine • Moss has been used as an antiseptic for centuries. • In World War I, moss was used to treat soldier’s wounds in emergency situations. • The antiseptic qualities result from moss’ natural absorbency and acidity.

Mistaken for Mosses • A variety of plants and plantlike organisms are mistakenly called mosses. – Irish moss is a red alga. – Spanish moss is a flowering vascular plant. – Reindeer moss is a lichen.

Seedless Vascular Plants • The earliest known seedless vascular plant is the Cooksonia. • The sporophytes of these ancient plants had branched, leafless stems that were only a few centimeters long. • Spore-forming sporangia were located at the tips of the stems. • Rhynia, another early seedless vascular plant, also had horizontal underground stems, or rhizomes.

Features of Seedless Vascular Plants • Vascular System – Have both xylem and phloem. – The water-conducting cells in the xylem are reinforced with lignin, a major part of wood. – Because of their vascular system, they grow much larger than nonvascular plants and also develop true roots, stems, and leaves.

Features of Seedless Vascular Plants • Larger Sporophyte – The sporophytes of seedless vascular plants are larger than the gametophytes. • Their larger size makes it easier for the wind to carry away spores, which makes dispersal more efficient. – The much smaller gametophytes develop on or below the surface of soil. – Water is needed for fertilization. • When there is enough water on or in the soil, the sperm swim to eggs and fertilize them.

Features of Seedless Vascular Plants • Drought-Resistant Spores – The spores of the seedless vascular plants have thickened walls that are resistant to drying. – Such spores make it possible for a plant to live in drier habitats.

Kinds of Seedless Vascular Plants • Ferns – Phylum Pterophyta are the most common and most familiar seedless vascular plants. – Ferns grow throughout the world, but they are most abundant in the tropics. – The plants that are recognized as ferns are sporophytes.

Kinds of Seedless Vascular Plants – Most fern sporophytes have rhizomes that are anchored by roots and leaves called fronds. • The coiled young leaves of a fern are called fiddleheads. – Spores are produced in sporangia that grow in clumps on the lower side of fronds. – The gametophytes of ferns are flatted, heartshaped green plants that are usually less than 1 cm across.

Kinds of Seedless Vascular Plants • Club Mosses – Phylum Lycophyta have roots, stems and leaves. – Their leafy green stems branch from an underground rhizome. – Spores develop in sporangia that form on specialized leaves. – In some species, clusters of nongreen spore-bearing leaves form a structure called a cone.

Kinds of Seedless Vascular Plants • Horsetails – Phylum Sphenophyta have roots, stems and leaves. – The vertical stems grow from a rhizome, are hollow and have joints. – Whorls of scale like leaves grow at the joints. – Spores form in cones located at the tips of stems.

Kinds of Seedless Vascular Plants • Whisk Ferns – Phylum Psilotophyta most closely resemble the earliest vascular plants. – Whisk ferns have highly branched stems and no leaves or roots. – They produce spores in sporangia that form at the tip of short branches.

Gymnosperms • Seed plants whose seeds do not develop within a sealed container (a fruit). • The word comes from the Greek words gymnos, meaning “naked, ” and sperma, meaning “seed. ”

Features of Gymnosperms • Seeds – All gymnosperms produce seeds. – Seeds protect plant embryos, provide them with nutrients, and permit them to survive long periods of unfavorable conditions. – In some plants, seeds also disperse new plants far from their parents.

Features of Gymnosperms • Greatly Reduced Gametophytes – All seed plants produce very tiny gametophytes of two types. • Male and female. – The gametophytes form within the tissues of the sporophytes. – Grains of pollen are male gametophytes. – Female gametophytes form within structures that become seeds. – In all but one species of gymnosperm, male and female gametophytes develop in male and female cones.

Features of Gymnosperms • Wind Pollination – The sperm of gymnosperms do not swim through water to reach and fertilize eggs. – Instead, the sperm are carried to the structures that contain eggs by pollen, which can drift on the wind. – Wind pollination makes sexual reproduction possible even when conditions are very dry.

Kinds of Gymnosperms • Conifers – Phylum Coniferophyta are the most familiar and most successful gymnosperms. – Conifers have leaves that are either needle-like or reduced to tiny scales. • These leaves are an adaption for limiting water loss.

Kinds of Gymnosperms – Some of the tallest living plants, the redwoods of coastal California and Oregon are conifers. – The oldest trees in the world are thought to be bristlecone pines, a species of conifer that grows in the Rocky Mountains and Great Basin. • Some bristlecone pines are about 5, 000 years old. – Vast forests of conifers grow in cool, dry regions of the world.

Kinds of Gymnosperms • Cycads – Phylum Cycadophyta have short stems and palm-like leaves. – Cones that produce pollen and those that produce seeds develop on different plants. – Cycads are widespread throughout the tropics.

Kinds of Gymnosperms • Gnetophytes – Phylum Gnetophyta are a diverse group of trees, shrubs, and vines that produce pollen and seeds in ones that resemble flowers. – One type, Ephedra, is common in the Western US.

Angiosperms • Most seed plants are flowering plants or angiosperms. • Angiosperms produce seeds that develop enclosed within a specialized structure called a fruit. • The word comes from the Greek words angeion, meaning “case, ” and sperma, meaning “seed. ”

Features of Angiosperms • Flowers – The male and female gametophytes of angiosperms develop within flowers which promote pollination and fertilization more efficiently than do cones. – Some flowers, such as roses, are brightly colored or have strong scents. • This attracts insects and other animals that carry pollen and increases the likelihood of crosspollination, which often occurs before the flowers open.

Features of Angiosperms – The flowers of many angiosperms, such as oaks and grasses, have small greenish flowers that are adapted for wind pollination. – The female reproductive part of a flower also provides a pathway that enables sperm to reach and fertilize eggs without swimming through water.

Features of Angiosperms • Fruits – Although fruits provide some protection for developing seeds, their primary function is to promote seed dispersal. – The angiosperms produce many different types of fruits, which develop from parts of flowers. – Many fruits are eaten by animals. • The seeds are dispersed as they pass undigested from the animals’ bodies. – Other fruits have structures that help them float on wind or water. – Some fruits even forcefully eject their seeds, flinging them away from the parent plant.

Features of Angiosperms • Endosperm – The seeds of angiosperms have a supply of stored food called endosperm at some time during their development. – In many angiosperms, the endosperm is absorbed by the embryo before the seeds mature.

Kinds of Angiosperms • Botanists divide the angiosperms into two subgroups, monocots and dicots. • The monocots are flowering plants that produce seeds with one seed leaf (cotyledon). – Most monocots also produce flowers with parts that are in multiples of three and have long, narrow leaves with parallel veins.

Kinds of Angiosperms • The dicots are flowering plants that produce seeds with two seed leaves. – Most dicots also produce flowers with parts in multiples of two, four, or five and have leaves with branching veins.

Familiar Families of Angiosperms Subgroup Monocots Family Examples Iridaceae (Iris) Irises, gladiolus, crocus Liliaceae (Lily) Daylilies, tulips, asparagus, aloe vera (class Monocotyledonae) Poaceae (Grass) Wheat, corn, rice, lawn grasses Dicots Asteraceae (Aster) Daisies, sunflowers, lettuce, ragweed Brassicaceae (Mustard) Broccoli, cauliflower, turnips, cabbage Fabaceae (Legume) Beans, clovers, peanuts, soybeans Rosaceae (Rose) Roses, apples, peaches, pears, plums Solanaceae (Nightshade) Potatoes, tomatoes, peppers, petunias (class Dicotyledonae)

Plants as Food • Humans depend on plants in many ways. • Plants store the extra nutrients they make or absorb in their bodies. • Plant parts contain organic nutrients (carbohydrates, fats, and proteins) and minerals (calcium, magnesium, and iron). • All types of plant parts – roots, stems, leaves, flowers, fruits, and seeds – are eaten as food.

Fruits and Vegetables • To a botanist, a fruit is the part of a plant that contains seeds. • A vegetative part is any nonreproductive part of a plant. • The foods that you think of as fruits (such as apples, bananas, and melons) are also fruits in the botanical sense. • Vegetables may be any botanical part of a plant. • Fruits and vegetables provide dietary fiber and are important sources of essential vitamins and minerals.

Root Crops • Potatoes are an important food staple in many parts of the world. – Rich in calories and easy to grow, potatoes are an ideal crop for a small farm. – They are classified as root crops because they grow underground. – Potatoes are actually tubers, modified underground stems that store starch. • Yams, an essential food crop in many tropical parts of the world, are roots. • Sweet Potatoes, carrots, radishes, turnips, beets, and cassava are important root crops. – These vegetables are enlarged roots that store starch.

Legumes • Many members of the pea family, which are called legumes, produce protein-rich seeds in long pods. – About 45% of a soybean, the most important legume grown for food, is protein. • Soybeans are often cooked and pressed into cakes called tofu. • Peas, peanuts, and the many different types of beans are the seeds of legumes. • Alfalfa, which is fed to livestock, is another important legume. – Like many legumes, alfalfa has nitrogen-fixing bacteria, which add nitrogen compounds to the soil, in its roots. • Alfalfa is also grown to enrich the soil.

Cereals • Cereals are grasses that are grown as food for humans and livestock. • Cereal grasses produce large numbers of type of edible, dry fruit called a grain. • A grain contains a single seed with a large supply of endosperm. • Each grain develops from a flower. • The flowers of cereal grasses form in tightly packed clusters of many individual flowers.

Cereals • A grain is covered by a dry, papery husk called the bran, which includes the wall of the ovary and the seed coat. • Cereal grains are rich in carbohydrates and also contain protein, vitamins, and dietary fiber. • More than 70% of the world’s cultivated farmland is used for growing cereal grains. • More than half of the calories that humans consume come from just three cereal grasses: wheat, corn, and rice.

Wheat • For more than 1/3 of the world’s population, wheat is the primary source of food. • The endosperm of wheat grains, which is high in carbohydrates, is commonly ground into white flour and used to make breads and pasta. • Vitamin-rich wheat germ consists of the embryos of wheat grains. • Whole-wheat flour consists of the endosperm plus the germ and bran layers.

Wheat • Wheat grains are not always ground into flour. – In the Middle East, wheat grains are often boiled or soaked, dried and then pounded until they crack. • Most wheat is grown in temperate regions that have fertile soil and moderate rainfall. – One of the world’s best wheat-growing areas is the Great Plains region of the US and Canada.

Corn • Corn is the most widely cultivated crop in the US. • American colonists of the 1600 s and 1700 s first learned how to grow corn from Native Americans. • In the southeastern US, corn was more widely grown than wheat, which does not grow as well in hot climates. • Foods that are made from corn include corn bread, corn pone, hominy, and grits.

Corn • About 70% of the corn crop harvested in the US is consumed by livestock. • Other uses for corn include the production of corn syrup, margarine, corn oil, cornstarch, and fuel-grade ethanol. • Most of the corn grown in the US today comes from a region known as the Corn Belt, which includes Iowa, Nebraska, Minnesota, Illinois, and Indiana.

Rice • For more than half of the people in the world, rice is the main part of every meal. • Although it is low in protein, rice is an excellent source of energy rich carbohydrates. • While brown rice still has its vitamin-rich bran layers, white rice has been processed to remove the bran layers. – This processing helps to prevent spoilage in stored rice. – In societies where people eat mainly rice, vitamin-rich sauces such as soy sauce are often added to white rice to make meals more nutritious.

Rice • The white rice you buy at a grocery store is enriched with added vitamins. • Rice is often added to processed foods such as breakfast cereal, soup, baby food, and flour. • In the US, rice is grown in central California, in the Southeast, and along the Gulf Coast in fields.

Nonfood Uses of Plants • Wood – After food, wood is the single most valuable resource obtained from plants. • Many products such as furniture, buildings, boats, cabinets, and violins are made from wood. – The wood from trees that have been cut down and sawed into boards, is called lumber. • Nearly 75% of the lumber cut in the US is used for building construction. • The rest is used to make products that contain wood, or it is ground and moistened to make wood pulp. • Wood pulp is made into paper, rayon, and many other products. – For more than a quarter of the world’s people, wood is still the main source of fuel for heating and cooking.

Nonfood Uses of Plants • Medicines – By studying the plants traditionally used to treat human ailments, researchers have developed many “modern” medicines. Name Source Action Caffeine Tea leaves Acts as a stimulant Codeine Poppy fruits Relieves pain Cortisone Yam tubers Relieves symptoms of allergies Digitalis Foxglove leaves Stabilizes irregular heartbeats and treats cardiac disorders Ephedrine Ephedra stems Acts as a decongestant Salix Bark of willow trees Relieves aches and pains (aspirin) Taxol Yew tree bark Reduces the size of cancerous tumors

Nonfood Uses of Plants • Fibers – Fibers are strands of cellulose, which is a component of the cell walls of plants. – In plants, fibers help provide support for plant body. – The strength and flexibility of plant fibers make them ideal materials for making paper, cloth, and rope. • Most of the fibers used to make paper come from wood. – Paper-making fibers are also obtained from many other plants, including cotton, flax, rice, bamboo, and papyrus.

Nonfood Uses of Plants – For centuries, people have made clothing with cloth made of cotton, the world’s most important plant fiber. • White fibers fill up the inside of a cotton boll, the fruit of the cotton plant. • Cotton thread is spun from the fine white fibers, which grow on cotton seeds. – The stems of flax yield softer, more durable fibers that are used to make linen. – More than 30% of the world’s clothing is now made of synthetic fibers, but natural plant fibers are still prized for their durability and comfort. – Sturdy fibers of hemp and sisal plants are used to make rope.