Lab 4 Plant Structure and Function

Virtual Lab 4 Plant structure and function Introduction Angiosperms are flowering plants and they make up about 70% of the plant kingdom and they have structures that we can easily recognize such as roots, stems, leaves, fruits and flowers. For these reasons, we will use them as a representative to study the structures and functions of a typical green plant. The two classes of angiosperms are dicotyledonous (dicots) and monocotyledonous (monocots) plants. We will explore the features of these two classes of plants through a close examination of their anatomical features such as roots, stems and leaves. We will then describe the root morphology and identify the growing and absorptive root structures. We will also discuss the sexual reproduction of a flowering plant, using the lily flower as our experimental specimen. Activity I External structure of a dicot The figure below represents for a typical structure of a dicot flowering plant. The plant body consists of shoot system and root system. The shoot system, which is the portion of the plant growing above ground, includes stems, leaves, flowers, and fruits. Organs and organ systems of a flowering plant Videos to watch – plants part 1 The structure of the stem to which leaves, and buds are attached is called node. The portion of the stem between successive nodes is an internode. Leaf structure of a dicot Foliage leaves. All leaves except for cotyledons (the seed leaves) are called foliage leaves. Leaves with a single blade are simple leaves, while with two or more blades are called compound leaves. Petiole (leaf stalk) helps the foliage leaves attach to the stem. At the base of each leaf, in the angle between the petiole and the stem, is an axillary bud. The Axillary bud may remain as a bud for most or all the life, or it may be stimulated to develop into a branch of the stem, which may produce leaves, flowers, and other structures. There are two types of leave arrangements. One is opposite leaves in which leaves are positioned two per node. The other is called alternate leaves in which the leaves are positioned one at a node. Cotyledons are the seed leaves, which serve primarily to store food in the seed and supply it to the young seedling. They are positioned as opposite leaves in bean plant. As represented in the following figure, 1) the embryo’s root emerges first as the seed germinates, followed soon by the hypocotyl (stem region below the point of attachment of the cotyledons). 2) The sunlight influences the growth direction of hypocotyl which then pulls the cotyledon above the ground. 3) As the seedling matures, the cotyledons degenerate and fall off, a leaf scar will appear to mark the location where the cotyledons or other leaves were attached. Cotyledon morphology of a dicot Activity II External structure of a monocot The leaf of monocots has a characteristic pattern with the parallel veins. The leaf blade, which has a much more linear shape than that of bean, is attached to the stem by a leaf sheath which wraps around and strengthens the stem. Leaves of monocots and dicots As a monocot, corns have only single cotyledons. Unlike the bean plant whose cotyledons grow above the ground finally, the cotyledon of corn remains within the “seed” in the ground. Coleoptile is a hollow sheath to protect the young leaves of corn as they emerge through the soil. Exposure to sunlight will stop the growth of coleoptile, while the leaves continue to grow to break through the coleoptile’s tip. Stages of seedling for monocots and dicots Videos to watch – plants part 2 Q1 Search online for images of the corn (monocot) and bean (dicot) plants. Compare their anatomical structures and then, fill out the table below. (6 points) Structures Leaf shape Pattern of leaf veins Number of cotyledons Bean Corn Flower petal arrangements Vascular bundle organization in stems Vascular bundle organization in roots Q2 Take photos of one monocot and one dicot plant that you can find in your neighborhood. Attach the photos here and label as many structures as you can identify such as the shoots, roots, stems, leaves, flowers, fruits, cotyledons, and petioles. (10 points) Activity III External structure of a flower Flowers are characteristic reproductive structures of the angiosperms. The characteristic parts in the flower are shown in the following picture. Reproductive structures of a flower Videos to watch – plants part 1 and part 2 Q3 Fill out the function for each part of the flower in this table (9 points) Parts Pedicel Receptacle Sepals Petals Function Anther Filament Stigma Style Ovary Q4 Take a photo of at least one flower that you can find in your neighborhood. Attach the photos here and label as many reproductive structures that you can find from your flowers. Also identify if the flower is a monocot or dicot (6 points) Q5 What are monoecious and dioecious flowers? (1 point) Q6 Unlike animals, plant sexual reproduction is a double fertilization process. Briefly describe the sequence of events beginning from the landing of a pollen onto the stigma and leading to the double fertilization in the ovule. (5 points) Q7 Although some plants have flowers with both male and female reproductive structures, they still have strategies to increase genetic diversity. How do flowers where both male and female reproductive structures are present, prevent self-fertilization? (2 points) Activity IV External structure of the root The root anchors and supports the plant in the soil. A root also absorbs water and minerals from the soil and plays an important role in food storage. During seed germination, the embryonic root, called the radicle, is usually the first to emerge and develops into an unbranched primary root. Later secondary roots emerge as branches from the primary root, and secondary roots give rise to tertiary roots. When we look at the function and the morphology of the root, there are four regions to consider: Beginning at the tip of the root 1) The root cap, 2) the apical meristematic zone with the apical meristem, 3) the region of cell elongation, and 4) the root hair zone also known as the zone of maturation. Q8 Label the growth regions and the cell types as shown in the image below (7 points) Q9 What is the shape of a root cap cell? And at what stage of the cell cycle do cells at the root cap belong to? (2 points) Cross section of root structure Q10 Why is the root a good model to study plant development? (2 points)