Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Essentials of Biology Sylvia S. Mader Chapter 20 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20.1 Plant Organs • Flowering plants have two major components to their structure. – A root system – A shoot system composed of the stem, leaves, and reproductive organs. • At the end of the root and shoot system is a terminal bud from which vertical growth, called primary growth, occurs. 20.1 The Body’s Organization (cont.) Leaves • Recall that photosynthesis, the process by which plants make carbohydrates, occurs in the leaves. • To conduct photosynthesis, leaves need solar energy, water, and carbon dioxide. • Photosynthetic leaves share similar structural components. – The blade, the wide part of the leaf – The petiole, the stalk connecting leaf to stem. Leaves (cont.) • There is tremendous diversity in leaf structure between plant species. • In some plant species, leaves may serve additional functions, such as storage. • Some plants are deciduous, meaning that they drop their leaves during certain seasons. Leaves (cont.) Stems • The stem is the main axis of the plant. • Stems can produce side (lateral) branches from lateral (axillary) buds. • Nodes are the points where leaves attach to stems. • An internode is the region between nodes. Stems (cont.) • The stem also contains the vascular tissue that transports water and nutrients to leaves to support photosynthesis. • In some plant species, stems may also carry out photosynthesis or serve as a storage organ. Roots • Roots anchor plants to the soil. • Roots also absorb water and nutrients from the soil. • The surface area of roots is greatly increased by the production of root hairs. Roots (cont.) • There are different types of root systems. – Some plants have a single taproot. – Grasses have fibrous root systems. – Some plants have prop roots for support. • For perennial plants, the roots act as a storage order that allows the shoot system to regrow each year. Roots (cont.) Monocot Versus Eudicot Plants • Flowering plants are divided into two major groups based upon the difference in embryonic leaves (cotyledons). – Plants that produce a single cotyledon are called monocots. – Plants that produce two cotyledons are called eudicots. • Cotyledons provide developing plants with nutrients and serve other roles. Monocot Versus Eudicot Plants (cont.) • The arrangement of the vascular tissue differs between monocots and eudicots. • Plants have two types of vascular tissue. – The xylem transports water and minerals. – The phloem transports organic nutrients. • The vascular tissues serve as a type of circulatory system for plants. Monocot Versus Eudicot Plants (cont.) • The pattern of venation in the leaves of monocots and eudicots differs. – Monocots have parallel venation. – Eudicots have a net-like pattern. • The number of species also differs between monocots and eudicots. – Eudicots include a large number of species. – There are fewer monocots species. Monocot Versus Eudicot Plants (cont.) 20.2 Plant Tissues and Cells • Plant growth occurs continually from dividing cells called the meristem. • The apical meristems are located at the tip of the root and shoot. • Cellular division of the apical meristems increase the length of the root and shoot. 20.2 Plant Tissues and Cells (cont.) • The outer cell layer of plant tissues is the epidermis. • The root epidermis can also have epidermal root hairs to increase surface area. 20.2 Plant Tissues and Cells (cont.) • The leaf epidermis is covered with a waxy cuticle, providing a barrier to water loss. • The leaf epidermis also have stomata which regulate gas and water exchange. 20.2 Plant Tissues and Cells (cont.) • In tree trunks, epidermis is replaced by cork, produced by the cork cambium. • Cork is waterproof because of a chemical called suberin. 20.2 Plant Tissues and Cells (cont.) • The interior of the plant leaves, stems, and roots is composed of ground tissue. • There is also a meristematic vascular tissue called the vascular cambium, which produces new vascular tissue. • There are three cell types in ground tissue. – Parenchyma – Collenchyma – Sclerenchyma 20.2 Plant Tissues and Cells (cont.) • Parenchyma cells are the least specialized cell type. • Parenchyma cells are photosynthetic cells found throughout the plant. 20.2 Plant Tissues and Cells (cont.) • Collenchyma cells have thick cell walls. • Collenchyma cells are arranged in bundles to provide flexible support below the epidermis. 20.2 Plant Tissues and Cells (cont.) • Sclerenchyma cells have cell walls reinforced with lignin. • Sclerenchyma cells are often dead cells. • Sclerenchyma cells provide support in mature tissues. 20.2 Plant Tissues and Cells (cont.) • The xylem is the vascular tissue that transport water and minerals from roots. • Vessel elements are one type of xylem with large, perforated cell walls. • Tracheids are smaller xylem cells whose walls have numerous pits. 20.2 Plant Tissues and Cells (cont.) 20.2 Plant Tissues and Cells (cont.) • The phloem of the vascular system is composed of sieve-tube members. • The sieve-tube members have perforated plates on each end of the cell. • Each sieve-tube member has a companion cell which controls the activity of the enucleated sieve-tube member. 20.2 Plant Tissues and Cells (cont.) 20.3 Organization of Leaves • Leaf structure varies from plant species to plant species. • There may be a single blade of the leaf or multiple blades, forming a compound leaf. 20.3 Organization of Leaves (cont.) 20.3 Organization of Leaves (cont.) • The top and bottom of a typical eudicot leaf is composed of epidermis – The epidermis often has hairs or glands. – Stomata are located on the lower epidermis. • The interior of the leaf is composed of photosynthetic mesophyll cells. – The spongy mesophyll is arranged randomly to increase surface area for gas exchange. – The palisade mesophyll is comprised of elongated, vertically-oriented cells. 20.3 Organization of Leaves (cont.) 20.4 Organization of Stems • Primary growth, driven by cell division in the apical meristem, contributes to the growth of stems. • The organization of the terminal bud protects the apical meristem. Nonwoody Stems • Plant stems that do not contain wood are called herbaceous stems. • The vascular bundles of herbaceous eudicot stems are arranged in a ring under the epidermal layer. • The vascular bundles of herbaceous monocot stems are randomly distributed. Nonwoody Stems (cont.) Nonwoody Stems (cont.) Woody Stems (cont.) • Woody stems undergo both primary and secondary growth. • Secondary growth is an increase in girth. • The vascular cambium of woody plants is meristematic and produces new xylem and phloem cells each year. Woody Stems (cont.) • Woody stems have three distinct regions. – Bark – Wood – Pith • The vascular cambium occurs between the bark and the wood. Woody Stems (cont.) Bark • Tree bark contains several cell types. – Cork – Cork cambium – Cortex – Phloem • The cork cells have several functions. – Cork cells protect the stem – Specialized cork cells form lenticels to facilitate gas exchange. Wood • Wood is composed of the secondary xylem produced each year by the stem. • Spring wood has wide xylem vessels with thin walls, due to transport of large amounts of water. • When water is scarce later in the summer, the xylem vessels of summer wood become narrower with thicker walls. • Spring and summer wood together make an annual ring. 20.5 Organization of Roots • Within the eudicot root, there are longitudinal zones where cells are in different stages of differentiation. – The apical meristem is composed of dividing cells protected by a root cap. – Cells in the next zone are elongating vertically. – In the last zone, the cells mature before completing their development. 20.5 Organization of Roots (cont.) Tissues of the Eudicot Root • The eudicot root has several tissue types. – The epidermis is the outermost layer. – The cortex in the center of the root is comprised parenchyma cells. – The endodermis is an internal cell layer that regulates the movement of water and nutrients into the vascular tissue. – The pericycle is an inner ring of dividing cells that can produce lateral roots. – The vascular tissue in the center of the root contains xylem and phloem for transport. Tissues of the Eudicot Root (cont.) Organization of Monocot Roots • Monocots have the same growth zones as eudicot roots but do not undergo secondary growth. • The center of monocot roots is composed of ground tissue called pith. • The pith is surrounded by a vascular ring with alternating bundles of xylem and phloem. Comparison With Stems • Roots and stems are both produced by primary growth from apical meristems. • However, the branching of roots and stems occur differently. – Stems branch from buds on the stem. – Roots branch from the internal pericycle. • The vascular cambium of eudicot stems and roots produces secondary growth. 20.6 Plant Nutrition • Plants are unique in that they require only inorganic nutrients to survive. • Plants convert these inorganic nutrients to the organic compounds needed for life. • Some inorganic elements are essential, meaning that plants have an absolute requirement for those elements. 20.6 Plant Nutrition (cont.) • The essential nutrients are divided into two categories based upon their relative concentrations in plant tissues. – Macronutrients are elements that are required in large amounts. – Micronutrients are required in small amounts for specialized functions. 20.6 Plant Nutrition (cont.) • There are nine macronutrients. – Carbon – Hydrogen – Oxygen – Phosphorus – Potassium – Nitrogen – Sulfur – Calcium – Magnesium 20.6 Plant Nutrition (cont.) • There are seven micronutrients, which serve primarily as enzyme cofactors. – Iron – Boron – Manganese – Copper – Zinc – Chloride – Molybdenum 20.6 Plant Nutrition (cont.) • Deficiencies in one or more of these nutrients can stunt plant growth. Adaptations of Roots for Mineral Uptake • Mineral nutrients enter plants through the root system. • Roots have several modifications that enhance their ability to acquire nutrients. • Some of those modifications involve specific symbiotic relationships. Adaptations of Roots for Mineral Uptake (cont.) • In plants such as legumes, specialized bacteria reside in root nodules. • These bacteria are capable of converting atmospheric nitrogen gas into a form useable by the plants. • The plant roots provide carbohydrates to the bacteria to support their growth. Adaptations of Roots for Mineral Uptake (cont.) • Most plants have a symbiotic relationship with mycorrhizal fungi. • The fungal hyphae increases the surface area available for water and nutrient uptake. • The plant roots provide the fungi with carbohydrates and amino acids. Adaptations of Roots for Mineral Uptake (cont.) 20.7 Transport of Nutrients • The water and nutrients taken up by roots and root hairs are transported to leaves via the interconnected vessel elements of the xylem. • This movement is provided in part by root pressure, a positive pressure created when water enters the root by osmosis. 20.7 Transport of Nutrients (cont.) • The cohesion-tension model explains how water travels up the xylem to leaves. • Recall that leaves have numerous openings called stomata. • When these stomata are open, water evaporates from the interior of the leaf to the outside air, a process called transpiration. 20.7 Transport of Nutrients (cont.) • As plant leaves transpire water, a tension is created that pulls water from roots to leaves. • This tension is maintained because water molecules display an attraction to one another called cohesion. • Water also adheres to the xylem elements in a process called adhesion. 20.7 Transport of Nutrients (cont.) Opening and Closing of Stomata • The opening and closing of the leaf stomata is controlled by turgor pressure within the guard cells. • As water enters the guard cells, these cells swell, opening the stomate. • As water exits the guard cells, the loss of turgor causes the stomate to close. Opening and Closing of Stomata (cont.) Organic Nutrients in the Phloem • The phloem transport carbohydrates from photosynthesizing leaves to roots, young leaves, and other tissues that require carbohydrates. • The transport of carbohydrates through the phloem occurs by a mechanism called the pressure-flow model. Organic Nutrients in the Phloem (cont.) • Phloem transport is considered source to sink transport. • As mature leaves photosynthesize, they become a source of sugar. • The carbohydrates in the phloem are transported to tissues that require sugars, called sink tissues. Organic Nutrients in the Phloem (cont.)