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CTYOnline Life Science Lesson 3.3 – Plant Kingdom

SCENE 1-A In the five and six kingdom classification schemes, all plants fit into the kingdom Plantae. Have you ever wondered what really makes a plant a plant? This lesson will answer this question as you learn what makes plants different from organisms in the other kingdoms. First, think of what you already know about plants. All plants are multicellular organisms. They contain nuclei in their cells, so they are eukaryotes. Plant cells have chloroplasts that contain a green pigment called chlorophyll. You should recall that chloroplasts are the structures in plant cells that allow plants to make energy from the sun through photosynthesis. All plants perform photosynthesis and all plant cells have cell walls that surround and protect their cell membranes. Although plants bend in the wind, they cannot move to another place like humans and other organisms. SCENE 2-A There are some plants that look similar to the plant-like members of the kingdom Protista, like the seaweed seen here. However, plants and protists have different types of cell walls, which make them different from one another. You will learn about the plant cell wall soon. Most plants are adapted to life on land, which offers some advantages and disadvantages to plants. One advantage to life on land is that there is usually a lot of sunlight available for photosynthesis. Therefore, it is easier for plants to photosynthesize, make sugars, and survive. One disadvantage to life on dry land is that plants need special structures to prevent themselves from drying out. Land plants also need special structures to keep them from falling over. To learn about some of the specialized structures that help plants live on land, click on each of the boxes. Structures that Conserve Water Plant cell walls are made of a type of sugar compound known as cellulose. Cellulose makes the cell wall rigid, which helps prevent plant cells from collapsing and losing water and other materials that are stored within the cell. On the outside, a waxy layer called the cuticle covers the leaves and stems of many plants. Since the cuticle is thick, it keeps moisture inside the plant and prevents water from easily passing through the leaves and stems. Structures that Transport Materials Specialized tissues, known as xylem and phloem, transport water and nutrients through the body of most plants. However, some plants do not have these specialized tissues. Instead, they are able to absorb water and minerals from their surroundings. You will learn more about the function of xylem and phloem later in this lesson. Structures for Support Stems and roots give most plants structure and support. A sturdy, rigid stem supports the weight of a plant’s leaves. The stem also allows the leaves to grow up above other objects where they are able to reach sunlight. Roots help anchor the plant in the ground to keep the plant from moving and falling over. SCENE 3-A You just learned some features that allow plants to live on land. Some of these features, such as roots, stems, and leaves, are used to classify different types of plants. You will need to know the structure and function of these organs to be able to tell the different types of plants apart. Click on the highlighted regions of the plant to learn about the general structures scientists use to classify plants. Leaves Leaf cells contain most of the chloroplasts found in plants. Since chloroplasts are the site of photosynthesis, it makes sense that they are in cells that receive the most sunlight. Leaves generally provide a wide, flat area for sunlight to be absorbed. They also provide an area for plants to take in carbon dioxide and release the oxygen made when plants produce sugars during photosynthesis. So how do gases get in and out of leaves? The answer is through small openings in leaves called the stomata. The stomata are surrounded by specialized cells called guard cells. Guard cells open and close to control the amount of gas entering or exiting the leaves. Stems Stems allow water and nutrients to be transported between the leaves and roots in plants that have xylem and

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phloem. They also support the weight of the plant. There are two main types of stems: herbaceous and woody stems. Plants that don’t need to support the weight of many leaves tend to have herbaceous stems. These soft, green stems are found in plants such as grasses, sunflowers, and beans. Plants that do have a lot of leaves or heavy fruit usually have woody stems. Woody stems are much harder than herbaceous stems and are found in plants such as pine trees, oak trees, and rose bushes. Roots Roots absorb water and minerals from the soil. They anchor plants in the ground, keeping them from falling over. Roots also store extra sugars made by the leaves during photosynthesis. This food source can later be used to produce energy for the plant. There are two main types of roots: taproots and fibrous roots. Plants with taproots have one main root that extends into the ground. Taproots allow the plant to reach a deep water source. The carrot is a common taproot. Plants with fibrous roots have many smaller roots branching from the stem that extends into the ground. Fibrous roots allow the plant to spread out and absorb water that is close to the surface. Many grasses have fibrous roots. SCENE 4-A In addition to general differences in stems, leaves, and roots, scientists have divided the kingdom Plantae into four major categories based on their characteristics. To learn why plants can be organized into four categories, click on each of the boxes below. Vascular vs. Non-vascular The presence or absence of what is known as vascular tissue helps classify plants. Plants with vascular tissue have the specialized tissues called xylem and phloem that transport water and nutrients throughout their bodies. Xylem transports the water and minerals absorbed from the roots up the stem and to the leaves of a plant. Phloem transports sugars produced in the leaves down the stem and to the roots of a plant. It might help you to remember that xylem starts with the letter in the alphabet next to the “w” in water. Xylem carries water and minerals up the plant. Phloem sounds like it is spelled with the letter “f”, like food. Phloem carries food, or sugars, made in the leaves down the plant. Xylem and phloem are vascular tissues and are sometimes bundled together in what are known as vascular bundles. Vascular plants have vascular tissue. Non-vascular plants do not have vascular tissue. Seedbearing vs. Seedless The presence or absence of seeds is a characteristic helpful in classifying plants. Seeds contain an outer covering known as the seed coat. The seed coat surrounds stored food for the developing plant, known as the embryo. The embryo uses this stored food until it grows its first leaves and is able to make its own food through photosynthesis. Some seeds are “naked”, meaning they do not have a fruit surrounding them. Other seeds have the added protection of a fruit, which you will learn more about later in this lesson. Plants that have seeds are called seedbearing plants. Plants that lack seeds are called seedless plants. Flowering vs. Non-flowering The presence or absence of flowers also helps classify plants. Flowers contain some plants’ reproductive structures. Flowers can be very large and colorful or small and almost unnoticeable. You will learn about the roles that particular flower structures play later in this lesson. Plants that produce flowers are called flowering plants. Plants that lack flowers are called non-flowering plants. SCENE 4-B Scientists classify plants into the four main categories based on whether or not they have vascular tissues, seeds, or flowers. Remember that in plants, a division is equivalent to a phylum for other types of organisms in the hierarchical classification scheme. There are at least three divisions of plants included in each of the four main categories. Next you will begin learning about the first category: the non-vascular, seedless, non-flowering plants. SCENE 5-A To learn about non-vascular seedless plants, please click on the highlighted box now. SCENE 5-B Non-vascular seedless plants have three divisions. Members in each of the three divisions are commonly known as mosses, liverworts, and hornworts. They are non-vascular seedless plants since they lack xylem and phloem and do not produce seeds. They also lack true roots, stems, and leaves. Instead of roots, these organisms have hair-like structures called rhizoids. Rhizoids resemble roots and help anchor plants in the soil. However, they do not play a major role in absorbing water and minerals.

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Since mosses, liverworts, and hornworts do not have true roots, they must absorb water and minerals directly from their surroundings. This is why you find them in very moist areas, like along steam banks. These plants are limited to a small size because they do not have vascular tissues to transport water and nutrients. SCENE 5-C Mosses, liverworts, and hornworts grow quickly and play an important role in holding down soil and preventing it from being washed or blown away. They are often the first to live in areas that are newly uncovered or exposed, like a newly formed island. These tiny plants are even important after they die because they provide new soil for other plants to grow where mosses once lived. Now you know the structure and importance of mosses, liverworts, and hornworts. In the next scene, you will learn the general lifecycle of mosses. SCENE 6-A The general life cycle of a moss is often referred to as an “Alternation of Generations.” A moss alternates stages as it spends part of its life as a mature individual—the sporophyte stage—and the majority of its life as an immature plant in the gametophyte stage. Moss sporophytes produce spores, which are small reproductive cells. Spores released from the sporophyte travel through the air. In they land on a moist area, they can crack open and develop into one of two types of leafy gametophytes. The male gametophytes produce sperm. The female gametophytes produce egg cells. The sperm from one gametophyte then swim through a thin layer of water to the egg cells of another gametophyte and join in a process known as fertilization. The fertilized egg then develops into the mature sporophyte that is able to start the process over. SCENE 6-B See how well you remember the characteristics and life cycle of the non-vascular, seedless plants. Click under the options that apply to the nonvascular seedless plants. SCENE 7-A To learn about vascular seedless plants, please click on the highlighted box now. SCENE 7-B The next category of plants you will explore is the vascular seedless plants. This group includes three divisions that are commonly known as club mosses, horsetails, and ferns. Each of the three divisions has vascular tissue and they lack seeds. Click on each box to learn more about the representatives of each division. When you are finished, you can explore the important roles these plants play. Club Mosses Club mosses are not true mosses. Unlike true mosses, club mosses have vascular tissue that transports water and nutrients through their bodies. However, like mosses, they produce spores on the tips of their stems. The spores are contained in structures that appear to be cones. Horsetails Horsetails produce spores in what looks like cones on the tip of their stems. Their stems are hollow and pop when pulled apart. The horsetail’s stem contains silica, which is a substance found in sand and also in glass. The silica in their stems makes them rough to the touch. In fact, North American pioneers used the stems to clean their pots and they referred to the plants as “scouring rushes.” Ferns Ferns are the largest division of vascular, seedless plants. They have an underground stem called a rhizome. Leaves grow from the underground rhizome. Fern leaves are often referred to as fronds. If you have ever turned over a fern frond, you might have noticed some interesting little dots. Those dots are called sori. Sori are the ferns’ reproductive structures that contain a fern’s spores. SCENE 7-C Club mosses, horsetails, and ferns are important because, like the non-vascular seedless plants, they too help in forming soil. Their roots and rhizomes help hold the soil in place and prevent it from washing away. Many ferns are used as houseplants. You might even have a fern in your own house. Perhaps the most important contribution of this group is fossil fuels. The remains of these organisms that lived over 300 million years ago provide a source of fuel that you know as coal which can be burned for energy.

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Now you know the structure and importance of club mosses, horsetails, and ferns. In the next scene, you will learn the general life cycle of ferns. SCENE 8-A The lifecycle of a fern is an “Alternation of Generations” similar to that of mosses. There is a sporophyte stage and a gametophyte stage. However, unlike mosses, ferns spend the majority of their life in the sporophyte stage. A fern’s life cycle begins when spores are produced in the sori of the adult fern plant, which is the sporophyte. When released spores land in a moist area, they develop into a heart-shaped gametophyte, called a prothallus. The prothallus contains both the male and female gametophytes that produce sperm and egg cells. Sperm released from the male structure swim through a thin layer of water to join the egg cell in the female structure. This fertilized egg then develops into a mature sporophyte, starting the cycle over. SCENE 8-B See how well you remember the characteristics and the life cycle of the vascular seedless plants. Click under the options that apply to the vascular seedless plants. SCENE 9-A To learn about vascular, non-flowering, seedbearing plants, please click on the highlighted box now. SCENE 9-B The third category you will explore are the vascular, non-flowering, seedbearing plants. This category of plants is often referred to as the gymnosperms. In Greek, the term “gymnosperm” means “naked seed.” The description fits because the seeds of gymnosperms are not enclosed in fruits. Instead, many gymnosperms produce their seeds in cones. Most gymnosperms have scale-like or needle-like leaves that stay green throughout the year. They have the ability to grow very tall and have vascular tissue to transport the water and nutrients needed to keep them alive. Gymnosperms are some of the oldest and largest plants alive today. SCENE 9-C The gymnosperms include four divisions that are commonly known as conifers, ginkgoes, cycads, and gnetophytes. Click on each box to learn more about the representatives in each division. Conifers This Ponderosa pine is an example of a conifer. Conifers are the largest group of gymnosperms. They get their name from the Greek word meaning “carry cones.” This name fits because you have probably noticed that most conifers do carry cones. The leaves of most conifers stay green throughout the year, and so they are commonly called evergreens. People tend to think that conifers are the only evergreens. However, it is important to remember that other types of plants can also be evergreens. Ginkgoes Ginkgo biloba is the only living example of a Ginkgo. Ginkgoes are the smallest division of gymnosperms since it has only one living species. However, Ginkgoes are fairly common because they are often used in parks where their leaves make beautiful fall colors. If you buy a Ginkgo someday, be careful. There are separate male and female trees. The female trees produce a very smelly seed. People use compounds from Ginkgo biloba leaves as an herbal medicine to potentially increase blood flow to the brain and possibly improve memory. Cycads Cycads are often mistaken for palm trees. They might look like palm trees, but they are smaller and produce comes instead of flowers, which are present in palm trees. Cycads grow in tropical locations and were more common millions of years ago. Gnetophytes Gnetophytes come in many different shapes and sizes. The gnetophyte seen here is the Welwitschia plant. This plant only has two leaves throughout its entire life. Although it only has two leaves, it can live for about one hundred years. Like other gymnosperms, it does not produce flowers and has seeds that are not enclosed in fruits.

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SCENE 9-D If you look around, you can probably find something that is made from the wood of a gymnosperm. In fact, the paper you write on and the books you read are made from the wood of gymnosperms. The wood of gymnosperms is also used to make houses and buildings. Now you know the structure and importance of conifers, ginkgoes, cycads, and gnetophytes. In the next scene, you will learn the general life cycle of a pine tree. SCENE 10-A The general lifecycle of a conifer is similar to the previous life cycles you have learned in that it has both a sporophyte stage and a gametophyte stage. However, unlike ferns, the sporophyte and the gametophyte are found on the same tree. The cycle begins when the adult sporophyte, a pine tree, produces both male and female cones. Male cones produce pollen grains that are similar to spores. Unlike spores, however, pollen grains cannot develop into new organisms. Instead, pollen grains contain sperm cells and protect them for transport. The female cones produce egg cells. The pollen grains and the egg cells are the gametophytes. Wind transports pollen grains from the male cones to the egg cells in the female cones. The sperm inside the pollen grain fertilizes the egg in a process known as fertilization. The fertilized egg then develops into a seed. When the seed drops, if the conditions are right, it eventually develops into a young sporophyte that grows to be an adult sporophyte that can start the cycle over. SCENE 10-B See how well you remember the characteristics and the life cycle of the vascular, non-flowering, seedbearing plants. Click under the options that apply to the vascular, non-flowering, seedbearing plants. SCENE 11-A To learn about vascular, flowering, seedbearing plants, please click on the highlighted box now. SCENE 11-B The fourth category of plants is the vascular, flowering, seedbearing plants. These plants are often called angiosperms. In Latin, “angi” means “enclosed,” and in Greek “sperma” means “seed.” All angiosperms have flowers and enclose their seeds in fruits. Flowers contain the reproductive structures of the plant. Fruits cover and protect the seeds. Even the smallest flowers produce fruits that you may not notice. You will learn more about these structures later in this lesson. SCENE 11-C Angiosperms are broken into two separate groups: monocots and dicots. They differ in several ways. For example, monocots and dicots differ in the arrangement of their vascular bundles. They also differ in the number of first leaves that emerge from the seed. These “seed leaves” are called cotyledons. They supply the seedling with nutrients it needs until it can grow its first true leaves and photosynthesize on its own. To learn more about these two groups and the number of cotyledons they have, click on the two labels. Monocots Monocots only have one cotyledon. Flower parts of monocots usually come in groups of three. For example, some monocots have flowers with three petals, some have six, and some have nine and so on. Their leaves usually have veins going up and down and their bundles of xylem and phloem are scattered throughout the stem. Palm trees, corn, grasses, and irises are all examples of monocots. Dicots Dicots have two cotyledons. The flower parts of dicots are usually arranged in groups of fours or fives. For example, if you see a flower with four, eight, five, or ten petals, you know it comes from a dicot. Their leaves usually have veins that branch in many directions and their bundles of xylem and phloem are arranged in a ring. Apple trees, roses, beans, and peanuts are all examples of dicots. SCENE 11-D You probably recognized some of the plants used as examples of monocots and dicots. All fruits, vegetables, wheat, rice, and other food products come from angiosperms. Flowering plants also supply cotton fiber from the cotton plant. Among other things, some angiosperms are used in medicine. For example, aspirin was originally made from chemicals found in the willow tree.

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Now you know the structure and importance of angiosperms. In the next scene, you will learn the general lifecycle of a flowering plant. SCENE 12-A In order to understand the lifecycle of a flowering plant, you need to know the different parts of a flower. As you have heard several times in this lesson, the flower contains the plant’s reproductive structures. Click on each of the highlighted structures to explore the flower parts. When you are finished, click continue to begin learning the life cycle of a flowering plant. Stamen Stamens are the male reproductive structures of a flower. They consist of long filaments that have pollen-filled anthers at the top. The pollen contains sperm cells that are the flower’s male reproductive cells. Pistil Pistils are the female reproductive structures of a flower. They consist of the stigma, style, and ovary. The stigma is the top of the pistil and is sticky so pollen grains stick to it. The long part holding up the stigma is called the style. The round part at the bottom is called the ovary. The ovary contains one or more ovules that enclose the egg cells. Sepal Sepals form the bottom of a flower. They often look like small leaves. They are the protective covering for the immature flower before it begins to bloom. Petal Petals are often the bright colors you see on flowers. They are used to attract insects and other potential animal pollinators. SCENE 12-B You can now begin exploring the lifecycle of flowering plants. To do so, drag the bee to the anther of this flowering plant. Pollen is the male gametophyte. Pollen from the anther gets on the bee’s head and legs when it tries to get food from the flower. Now drag the bee with pollen to the flower on the other side of the screen. Place the bee on the stigma of this flower. When the bee reaches in to get more food, it will release some pollen grains onto the sticky stigma of this flower. SCENE 12-C Now click on the flower to see how sperm cells in the pollen reach the female gametophyte, which are the egg cells. The pollen creates a pollen tube that grows from the stigma, through the style, and down toward the ovary. The sperm then moves down this tube and fertilizes the eggs within the ovules. Click on the ovary to see what happens once the egg cells are fertilized. Once the egg cells are fertilized, the petals and stamens begin falling off. The ovary develops into the fruit. The fruit surrounds and protects the seeds and provides nourishment for the embryo inside. SCENE 12-D Click on the fruit to see what happens once it ripens. Wind, animals, and other methods help spread the seeds of ripened fruits to other areas. Each seed can grow into a new flowering plant and start the process over. Take a minute to review this lifecycle and recall the main points in this summary picture. Flowering plants exhibit an alteration of generations lifecycle that is dominated by the sporophyte stage. Notice that the pollen and egg cells are the gametophytes and the adult flowering plant is the sporophyte. SCENE 12-E See how well you remember the characteristics and the life cycle of the vascular, flowering, seedbearing plants. Click under the options that apply to the vascular, flowering, seedbearing plants. SCENE 13-A You have now learned characteristics, importance, and a general lifecycle of each of the four main plant categories. Can you remember what makes them different from one another? Throughout this program, you

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have built tables. Now take some time to look at the tables together. Compare each group and observe what makes them different from one another to complete this lesson.