Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview What is a Plant? Lesson Overview An Introduction to Plant Diversity

Lesson Overview Lesson Overview What is a Plant? THINK ABOUT IT Plants have adapted so well to so many environments that they dominate much of the surface of our planet.

Lesson Overview Lesson Overview What is a Plant? The Plant Kingdom Plants are classified as members of the kingdom Plantae. Plants are eukaryotes that have cell walls containing cellulose and carry out photosynthesis using chlorophyll a and b.

Lesson Overview Lesson Overview What is a Plant? All plants have the same basic needs: sunlight, a way to exchange gases with the surrounding air, water, and minerals. What Plants Need

Lesson Overview Lesson Overview What is a Plant? Sunlight Plants use the energy from sunlight to carry out photosynthesis. Leaves are typically broad and flat and are arranged on the stem so as to maximize light absorption.

Lesson Overview Lesson Overview What is a Plant? Gas Exchange Plants require oxygen to support cellular respiration, as well as carbon dioxide to carry out photosynthesis. Plants must exchange these gases with the atmosphere and the soil without losing excessive amounts of water through evaporation.

Lesson Overview Lesson Overview What is a Plant? Water and Minerals Land plants have evolved structures that limit water loss and speed the uptake of water from the ground. Minerals are nutrients in the soil that are needed for plant growth.

Lesson Overview Lesson Overview What is a Plant? Many plants have specialized tissues that carry water and nutrients upward from the soil and distribute the products of photosynthesis throughout the plant body.

Lesson Overview Lesson Overview What is a Plant? Origins in the Water The ancestors of today’s land plants were water-dwelling organisms similar to today’s green algae. Although not as large and complex as many plants, green algae have cell walls and photosynthetic pigments that are identical to those of plants. Green algae also have reproductive cycles that are similar to plants. Studies of the genomes of green algae suggest that they are so closely related to other plants that they should be considered part of the plant kingdom.

Lesson Overview Lesson Overview What is a Plant? An Overview of the Plant Kingdom The relationship of plant groups is shown below

Lesson Overview Lesson Overview What is a Plant? The Plant Life Cycle The life cycle of land plants has two alternating phases, a diploid (2N) phase and a haploid (N) phase. The shift between the haploid phase–a cell that contains half the genetic information with only one copy of each chromosome, and the diploid phase –a cell that contains two copies of each chromosome. This is known as the alternation of generations, as shown in the figure.

Lesson Overview Lesson Overview What is a Plant? The Plant Life Cycle The multicellular diploid phase is known as the sporophyte, or spore-producing plant.

Lesson Overview Lesson Overview What is a Plant? The Plant Life Cycle The multicellular haploid phase is known as the gametophyte, or gamete- producing plant.

Lesson Overview Lesson Overview What is a Plant? Trends in Plant Evolution An important trend in plant evolution is the reduction in size of the gametophyte and the increasing size of the sporophyte.

Lesson Overview Lesson Overview What is a Plant? The First Plants Green algae are mostly aquatic. They are found in fresh and salt water, and in some moist areas on land. Ancient green algae shared the ocean floor with corals and sponges. Green algae absorb moisture and nutrients directly from their surroundings and do not contain the specialized tissues found in other plants.

Lesson Overview Lesson Overview What is a Plant? Multicellularity Green algae can form colonies. Spirogyra forms long threadlike colonies called filaments.

Lesson Overview Lesson Overview What is a Plant? Multicellularity Volvox colonies consist of as few as 500 to as many as 50,000 cells arranged to form hollow spheres. Volvox shows some cell specialization and straddles the fence between colonial and multicellular life.

Lesson Overview Lesson Overview What is a Plant? Mosses and Other Bryophytes Mosses, hornworts, and liverworts all belong to a group of plants known as bryophytes. Bryophytes have specialized reproductive organs enclosed by other, non- reproductive cells. Bryophytes show a higher degree of cell specialization than do the green algae and were among the first plants to become established on land.

Lesson Overview Lesson Overview What is a Plant? Mosses and Other Bryophytes Mosses have a waxy, protective coating that makes it possible for them to resist drying, and thin filaments known as rhizoids that anchor them to the soil. Rhizoids also absorb water and minerals from the soil.

Lesson Overview Lesson Overview What is a Plant? Why Bryophytes Are Small Bryophytes do not make lignin, a substance that hardens cell walls, and do not contain true vascular tissue. Because of this, bryophytes cannot support a tall plant body against the pull of gravity.

Lesson Overview Lesson Overview What is a Plant? Vascular Plants About 420 million years ago, plants for the first time were able to grow high above the ground. Fossil evidence shows these plants were the first to have a transport system with true vascular tissue. Vascular tissue carries water and nutrients much more efficiently than does any tissue found in bryophytes.

Lesson Overview Lesson Overview What is a Plant? Evolution of a Transport System Vascular plants are known as tracheophytes, after a specialized type of water-conducting cell they contain. These cells, called tracheids, are hollow tubelike cells with thick cell walls strengthened by lignin. Tracheids are found in xylem, a tissue that carries water upward from the roots to every part of a plant.

Lesson Overview Lesson Overview What is a Plant? Evolution of a Transport System Vascular plants also have a second transport tissue called phloem that transports solutions of nutrients and carbohydrates produced by photosynthesis.

Lesson Overview Lesson Overview What is a Plant? Seedless Vascular Plants Among the seedless vascular plants alive today are three phyla commonly known as club mosses, horsetails, and ferns. The most numerous of these are the ferns.

Lesson Overview Lesson Overview What is a Plant? Seedless Vascular Plants Ferns have true vascular tissues, strong roots, creeping or underground stems called rhizomes, and large leaves called fronds, shown in the figure. Ferns can thrive in areas with little light and are most abundant in wet habitats.

Lesson Overview Lesson Overview What is a Plant? The Importance of Seeds A seed is a plant embryo and a food supply, encased in a protective covering. The living plant within a seed is diploid and represents the early developmental stage of the sporophyte phase of the plant life cycle.

Lesson Overview Lesson Overview What is a Plant? The First Seed Plants Today’s seed plants are all descended from common ancestors. The fossil record indicates that ancestors of seed plants evolved new adaptations that enabled them to survive on dry land.

Lesson Overview Lesson Overview What is a Plant? Cones and Flowers In seed plants, the male gametophytes and the female gametophytes grow and mature directly within the sporophyte. The gametophytes usually develop in reproductive structures known as cones or flowers. Nearly all gymnosperms bear their seeds directly on the scales of cones. Flowering plants, or angiosperms, bear their seeds in flowers inside a layer of tissue that protects the seed.

Lesson Overview Lesson Overview What is a Plant? Pollen In seed plants, the entire male gametophyte is contained in a tiny structure called a pollen grain. Pollen grains are carried to the female reproductive structure by wind or animals such as insects. The transfer of pollen from the male reproductive structure to the female reproductive structure is called pollination.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Flowers and Fruits The origin of flowering plants is the most recent among the origins of all plant phyla. Flowering plants originated on land and soon came to dominate Earth’s plant life.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Flowers and Fruits Angiosperms develop unique reproductive organs known as flowers, shown in the figure. Flowers contain ovaries, which surround and protect seeds.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Advantages of Flowers Flowers are an evolutionary advantage to plants because they attract animals that carry pollen with them to the next flower they visit. This means of pollination is much more efficient than the wind pollination of most gymnosperms.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Advantages of Fruits After pollination, the ovary develops into a fruit, a structure containing one or more matured ovaries. The wall of the fruit helps disperse the seeds contained inside it. The development of the multiple ovaries of a blackberry flower into the cluster of fruits that make up one berry is shown.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Advantages of Fruits When an animal eats a fleshy fruit, seeds from the fruit enter the animal’s digestive system. By the time the seeds leave the digestive system, the animal may have traveled many kilometers. By using fruit, flowering plants increase the ranges they inhabit.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Angiosperm Classification When an animal For many years, flowering plants were classified according to the number of seed leaves, or cotyledons, in their embryos. Those with one seed leaf were called monocots. Those with two seed leaves were called dicots.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Monocots and Dicots The differences between monocots and dicots include the distribution of vascular tissue in stems, roots, and leaves, and the number of petals per flower.

Lesson Overview Lesson Overview What is a Plant? Lesson Overview Lesson Overview Flowering Plants Monocots and Dicots The characteristics of monocots and dicots are compared in the table below.