ABE 113 Chapter 2 Plant Anatomy and Morphology PDF

ABE 113 Chapter 2. Plant Growth and Development Topics: Plant anatomy and morphology Photosynthesis and respiration Hormonal regulation of growth Flowering and reproductive development A. Plant anatomy and morphology Definition: Plant anato...

ABE 113 Chapter 2. Plant Growth and Development Topics: Plant anatomy and morphology Photosynthesis and respiration Hormonal regulation of growth Flowering and reproductive development A. Plant anatomy and morphology Definition: Plant anatomy - is the study of the internal structure of plants at the microscopic and macroscopic levels. It involves examining plant tissues, cells, and organs to understand their functions and adaptations. Plant anatomy can be divided into several key components: Divisions of Plant Anatomy 1. Plant Tissues: a. Meristematic Tissues: These are regions of actively dividing cells responsible for plant growth. They are found in areas like the tips of roots and stems. Meristems are classified by their location in the plant as apical (located at root and shoot tips), lateral (in the vascular and cork cambia), and intercalary (at internodes, or stem regions between the places at which leaves attach, and leaf bases, especially of certain monocotyledons—e.g., grasses). b. Dermal Tissues: The dermal tissue system—the epidermis—is the outer protective layer of the primary plant body (the roots, stems, leaves, flowers, fruits, and seeds). The epidermis is usually one cell layer thick, and its cells lack chloroplasts. The outermost layer of plant tissue, called the epidermis, provides protection and regulates gas exchange. They help deter excess water loss and invasion by insects and microorganisms. c. Ground Tissues: Ground tissues make up the bulk of plant organs and are involved in functions like photosynthesis, storage, and support.  d. Vascular Tissues: The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: a. the vascular cambium and b. the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant. 2. Plant Cells a. Cell Wall: A rigid outer layer made of cellulose that provides structural support. A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism b. Cell Membrane: A semi-permeable membrane surrounding the cell, controlling the movement of substances in and out. The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space). c. Chloroplasts: A chloroplast is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in the cells. The ATP and NADPH is then used to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of other functions, including fatty acid synthesis, amino acid synthesis, and the immune response in plants.  d. Vacuole: A large, central organelle responsible for storing water and nutrients. Plant cell vacuoles are large, fluid-filled vesicles that occupy most of the cell's volume and perform various functions. Vacuoles are large organelles in plant cells that occupy a significant volume of the cell. They have various functions, such as: 1. Providing rigidity and turgidity to the cell by developing hydrostatic pressure with water. 2. Storing salts, minerals, nutrients, proteins, pigments, and waste products 3. Breaking down complex molecules and regulating pH and osmotic pressure 4. Helping in plant growth and protection from predators and droughts B. Plant Morphology Plant morphology refers to the external appearance, form, and structure of plants. It encompasses the study of various plant organs, their functions, and adaptations. Key aspects of plant morphology include: 1. Roots: Roots anchor the plant and absorb water and nutrients from the soil. Types of roots include taproots and fibrous roots, each suited to different plant types and environments. Modifications of roots include storage roots (e.g., carrots), aerial roots (e.g., orchids), and pneumatophores (e.g., mangroves). 2. Stems: Stems provide structural support and transport nutrients and water between roots and leaves. Stem types include herbaceous (soft) and woody (hard) stems. Modifications of stems include rhizomes (horizontal underground stems), stolons (horizontal above-ground stems), and tubers (swollen, underground stems). 3. Leaves: Leaves are the primary sites for photosynthesis. They vary in shape, size, and arrangement and can be adapted for specific functions, such as water conservation (e.g., succulent leaves) or climbing (e.g., tendrils). 4. Flowers: Flowers are the reproductive structures of plants. They consist of sepals (protective outermost whorl), petals (often colorful and attracting pollinators), stamens (male reproductive organs), and carpels (female reproductive organs). 5. Fruits: Fruits develop from fertilized flowers and serve as protective structures for seeds. They come in various forms, including fleshy fruits (e.g., apples), dry fruits (e.g., sunflower seeds), and nuts (e.g., acorns). 6. Adaptations: Plants exhibit various adaptations based on their environment. Examples include the development of thorns or spines for defense, specialized leaves for water storage (e.g., succulents), and aerial roots for support and access to air (e.g., banyan trees). Summary Understanding plant anatomy and morphology is essential for plant scientists, botanists, horticulturists, and farmers. It provides insights into plant growth, development, and adaptations, aiding in plant breeding, cultivation practices, and the overall study of plant biology. B. Photosynthesis and Respiration 1. PHOTOSYNTHESIS Photosynthesis - is the process by which green plants and certain other organisms transform light energy into chemical energy. Photosynthesis - is a biological process used by many cellular organisms to convert light energy into chemical energy, which is stored in organic compounds that can later be metabolized through cellular respiration to fuel the organism's activities. The term usually refers to oxygenic photosynthesis, where oxygen is produced as a byproduct, and some of the chemical energy produced is stored in carbohydrate molecules such as sugars, starch, glycogen and cellulose, which are synthesized from endergonic reaction of carbon dioxide with water.  Here are the key mechanics of photosynthesis: 1. Light Absorption: Photosynthesis begins when chlorophyll, a green pigment found in chloroplasts within plant cells, absorbs sunlight. Chlorophyll molecules capture energy from photons (light particles), primarily in the blue and red regions of the light spectrum. 2. Light-Dependent Reactions: In the thylakoid membranes of chloroplasts, the absorbed light energy is used to split water molecules (photolysis) into oxygen, protons (H+ ions), and electrons. The electrons are passed through a series of protein complexes known as the electron transport chain (ETC), releasing energy in the process. This energy is used to pump protons across the thylakoid membrane into the thylakoid space, creating a proton gradient. 3. ATP and NADPH Formation: As protons accumulate in the thylakoid space, they create a proton motive force (PMF) that drives the enzyme ATP synthase, generating adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (Pi). Meanwhile, electrons reduce nicotinamide adenine dinucleotide phosphate (NADP+) to form NADPH, which carries high-energy electrons. 4. Calvin Cycle (Light-Independent Reactions): ATP and NADPH produced in the light-dependent reactions are used in the Calvin cycle, which takes place in the stroma of the chloroplast. Carbon dioxide (CO2) from the atmosphere is fixed into organic molecules, eventually forming glucose and other sugars through a series of enzyme-driven reactions. 5. Glucose Production: The glucose and other carbohydrates produced in the Calvin cycle store chemical energy derived from sunlight.  Most plants, algae and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the biological energy necessary for complex life on Earth. How does photosynthesis occur in plants? During photosynthesis, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds. The process can be summarized in the following equation: 6CO2+6H2O+lightenergy→C6H12O6+6O2 In this equation, carbon dioxide and water are converted into glucose and oxygen using light energy. The process of photosynthesis occurs in the chloroplasts of plant cells, which contain chlorophyll, a green pigment that absorbs light energy from the sun. The oxygen produced during photosynthesis is released into the atmosphere, while the glucose is used by the plant as a source of energy for growth and other metabolic processes Photosynthesis Stages I and II The two stages of photosynthesis are: Stage I. The light-dependent reactions, which capture the energy of light and use it to make the hydrogen carrier Nicotinamide adenine dinucleotide phosphate hydrogen(NADPH) and the energy-storage molecule Adenosine triphosphate (ATP). Stage II. The Calvin cycle, which uses these products to capture and reduce carbon dioxide. This stage can proceed without sunlight. Photosynthesis Stage II. The Calvin Cycle The Calvin cycle is a series of chemical reactions that occurs in photosynthesis and involves the fixation of carbon dioxide into organic compounds that can be used to make sugars and other molecules. 3-Phosphoglyceric acid (3PG, 3-PGA, or PGA) is a biochemically significant metabolic intermediate in both glycolysis and the Calvin-Benson cycle. It is the conjugate acid of 3-phosphoglycerate or glycerate 3-phosphate (GP or G3P) 12. In the Calvin-Benson cycle, 3-phosphoglycerate is typically the product of the spontaneous scission of an unstable 6-carbon intermediate formed upon CO2 fixation. Thus, two equivalents of 3-phosphoglycerate are produced for each molecule of CO2 Adenosine triphosphate (ATP) is an organic compound that provides energy to drive and support many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer.  Nicotinamide adenine dinucleotide phosphate hydrogen(NADPH) plays a crucial role in many of the chemical reactions that make up the procedure of the photosynthesis. NADPH is a product of the first level of photosynthesis. It helps to fuel the reactions that occur in the second stage of the process of photosynthesis. Plant cells require light energy, water, and carbon dioxide for carrying out the steps of the photosynthesis process.  The photosystem that creates NADPH during the light reactions of photosynthesis is Photosystem I. Photosystem I is one of two protein complexes involved in the light reactions of photosynthesis, with the other being Photosystem II. Here is a step-by-step explanation of how NADPH is created in Photosystem I: 1. Light energy is absorbed by chlorophyll molecules in Photosystem I. 2. This absorbed light energy excites electrons in the chlorophyll molecules, causing them to move to a higher energy level. 3. These high-energy electrons are transferred to an electron carrier molecule called ferredoxin.  4. The electrons are then passed from ferredoxin to an enzyme called ferredoxin-NADP+ reductase. 5. Ferredoxin-NADP+ reductase uses the high-energy electrons to reduce NADP+ (nicotinamide adenine dinucleotide phosphate) to NADPH. NADPH plays a crucial role in photosynthesis as it serves as a source of high-energy electrons and reducing power. These electrons are used in the Calvin cycle, the second stage of photosynthesis, to convert carbon dioxide into glucose and other organic molecules. In summary, NADPH is created by Photosystem I in the light reactions of photosynthesis. The absorbed light energy excites electrons in chlorophyll, which are then transferred to ferredoxin and eventually used by ferredoxin-NADP+ reductase to reduce NADP+ to NADPH. 2. CELLULAR RESPIRATION Cellular respiration is the process by which cells, including plant cells, extract energy from glucose and other organic molecules. It involves a series of chemical reactions that release energy in the form of adenosine triphosphate (ATP). Here are the key mechanics of cellular respiration: A. Glycolysis (in the Cytoplasm): Glucose, typically derived from photosynthesis, is broken down into two molecules of pyruvate. This process yields a small amount of ATP and generates high-energy electrons, which are carried by molecules like nicotinamide adenine dinucleotide (NADH). B. Citric Acid Cycle (Kreb’s Cycle, in the Mitochondria): Pyruvate enters the mitochondria and is further oxidized into carbon dioxide. High-energy electrons are transferred to molecules like NADH and flavin adenine dinucleotide (FADH2), releasing additional ATP. C. Electron Transport Chain (in the Inner Mitochondrial Membrane): Electrons from NADH and FADH2 move through a series of protein complexes in the inner mitochondrial membrane, releasing energy. This energy is used to pump protons (H+ ions) across the inner mitochondrial membrane, creating a proton gradient. D. ATP Synthesis: As protons flow back into the mitochondrial matrix through ATP synthase, ATP is generated from ADP and Pi. This process is known as oxidative phosphorylation and is the primary source of ATP production in cellular respiration. E. Release of Energy: Cellular respiration - is the process by which cells, including plant cells, extract energy from glucose and other organic molecules. Summary Photosynthesis and cellular respiration are interconnected processes, with the products of one (glucose and oxygen) serving as the reactants for the other. Together, these processes enable the flow of energy through ecosystems and sustain life on Earth. C. Hormonal Regulation of Plant Growth Hormonal regulation is crucial for the growth and development of plants. Plants produce and respond to a variety of hormones that control processes such as seed germination, stem elongation, flowering, and fruit development. These hormones act in concert to coordinate growth and respond to environmental cues. Here are the main plant hormones and their roles in growth regulation: Main Plant Hormones 1. Auxins (e.g., Indole-3-Acetic Acid, IAA): Role: Auxins primarily promote cell elongation and control the direction of growth. They are responsible for tropisms (responses to environmental stimuli), such as phototropism (growth toward light) and gravitropism (response to gravity). Functions: Promoting cell elongation by acidifying the cell wall, allowing it to expand. Apical dominance, where auxins inhibit lateral bud growth in favor of the main shoot. Root development and formation of adventitious roots. Stimulating fruit development and preventing premature fruit drop. 2. Cytokinins: Role: Cytokinins promote cell division and differentiation, particularly in meristematic tissues (regions of active growth). They interact with auxins to regulate various aspects of growth. Functions: Stimulating cell division and shoot formation in tissue culture. Delaying senescence (aging) in leaves and promoting chloroplast retention. Counteracting apical dominance when present in higher concentrations than auxins. 3. Gibberellins (GA): Role: Gibberellins regulate stem elongation, seed germination, and flowering. Functions: Promoting stem elongation by cell division and expansion. Breaking seed dormancy and promoting germination. Stimulating flowering in some plants. Inducing the production of enzymes that break down stored nutrients in seeds. 4. Abscisic Acid (ABA): Role: ABA is primarily involved in stress responses and dormancy. Functions: Inducing stomatal closure in response to water stress (drought). Promoting seed dormancy and inhibiting germination under unfavorable conditions. Regulating responses to environmental stressors such as salinity and cold. 5. Ethylene (C2H4): Role: Ethylene is a gaseous hormone involved in various aspects of plant growth and stress responses. Functions: Promoting fruit ripening by accelerating the breakdown of cell wall components. Inducing leaf abscission (shedding) in deciduous trees in preparation for winter. Regulating responses to environmental stress, such as flooding or mechanical damage. 6. Brassinosteroids (BRs): Role: Brassinosteroids promote cell elongation and division, as well as various developmental processes. Functions: Enhancing stem elongation and cell expansion. Promoting root growth and development. Affecting pollen tube elongation and seed development. 7. Jasmonic Acid (JA) and Salicylic Acid (SA): Role: These hormones are involved in plant defense responses to pathogens and herbivores. Functions: Activating defense mechanisms, including the production of protective compounds and proteins. Regulating responses to herbivore damage and pathogen infection. Plant Hormones Functions Summary Plant hormones interact in complex ways, and their levels can be influenced by environmental factors. The balance between these hormones plays a critical role in regulating plant growth, development, and responses to external stimuli. D. Flowering and reproductive development Flowering and reproductive development in plants is a highly regulated process that involves the transformation of vegetative structures into reproductive structures, ultimately leading to the production of seeds and fruits. This process is controlled by a combination of genetic, hormonal, and environmental factors. Here's an overview of the key stages and factors involved: 1. Vegetative Growth: In the early stages of a plant's life, it undergoes vegetative growth, where the emphasis is on the development of leaves, stems, and roots. During this phase, the plant establishes its root system, grows its leaves, and prepares itself for future reproductive growth. 2. Floral Initiation: Floral initiation marks the transition from vegetative to reproductive growth. It is influenced by various factors, including day length (photoperiodism), temperature, and hormonal signals. In response to specific environmental cues, the plant undergoes a genetic program that leads to the formation of flower buds at specific sites called meristems. 3. Flower Development: Once the floral initiation has occurred, the plant's meristems differentiate into floral organs, including sepals, petals, stamens (male reproductive organs), and carpels (female reproductive organs). These organs develop in whorls or layers, with sepals on the outermost layer, followed by petals, stamens, and carpels toward the center of the flower. Parts of a Flower and Its Function 4. Pollination: Pollination is the transfer of pollen (containing male gametes) from the anthers (part of the stamen) to the stigma (part of the carpel) in a process called fertilization. Pollination can occur through various mechanisms, including wind, insects, birds, and other pollinators. 5. Fertilization: After successful pollination, the pollen tube grows down the style (a part of the carpel) to reach the ovule inside the ovary. Fertilization occurs when the male gametes from the pollen fuse with the female gametes in the ovule, forming a zygote. 6. Fruit Development: Following fertilization, the ovary develops into a fruit, which protects and nourishes the developing seeds. The fruit can take various forms, such as berries, drupes, pods, or nuts, depending on the plant species. 7. Seed Maturation: As the fruit develops, the seeds inside undergo maturation, accumulating nutrients and becoming viable for future germination. 8. Seed Dispersal: Once the fruit is mature, it facilitates the dispersal of seeds to new locations. This can occur through various mechanisms, including wind, animals, and water. 9. Germination: When conditions are favorable (e.g., adequate moisture, temperature, and light), seeds germinate. This involves the growth of a new plant from the embryo within the seed. 10. Repetition: - In many plants, the cycle of flowering, pollination, fertilization, fruit development, and seed dispersal repeats seasonally or as dictated by environmental cues. Summary It's important to note that the timing and regulation of flowering and reproductive development can vary widely among plant species. Some plants are annuals, completing their life cycle in one growing season, while others are perennials, flowering and reproducing over several years. Additionally, plants have evolved various adaptations to optimize reproduction and ensure the survival of their species in diverse ecosystems. -----------end of presentation----------- Quiz No. 2