Plant Cell and Structures - University of Santo Tomas

UNIT II: Plant Cell and Structures Mershen B. Gania, RPh, ClinPharm., MSPharm. Department of Pharmacy, School of Health Sciences University of Santo Tomas - General Santos PLANT CELL It consists of a box-like cell wall surrounding a mass of protoplasm. Function: Physical fr...

UNIT II: Plant Cell and Structures Mershen B. Gania, RPh, ClinPharm., MSPharm. Department of Pharmacy, School of Health Sciences University of Santo Tomas - General Santos PLANT CELL It consists of a box-like cell wall surrounding a mass of protoplasm. Function: Physical framework Plant’s metabolism Nutrient transport Food and Oxygen Production Membranes and Transport Membranes They regulate the passage of molecules into and out of cells and organelles. Divides the cell into numerous compartments, each with a specialized metabolism. Act as surfaces that hold enzymes. Composition of Membrane  Hydrophobic Tail Hydrophilic head Micelle Formation Hydrophobic Tail Hydrophilic head Plasma Membrane Intrinsic Proteins - proteins that are partially immersed in the lipid bilayer. Extrinsic or peripheral proteins - located outside the membrane and merely lying next to it. Glycoproteins – these are oligosaccharides bound to certain intrinsic proteins. Glycolipids – sugars attached to membrane lipids. Fluid Mosaic Model/ Membrane  Transport Mechanism or Movement of Particles in the Membrane. Permeability – movement of particles from the extracellular to intracellular region. Impermeable membrane – nothing passes through Freely permeable – virtually anything can pass through. Compartment – a division with the same specialized process. Selectively permeable membrane – certain substances cross the membrane more easily and rapidly than others. Cellular Transport The Five Different Kinds of Cellular Transport. (2022, October 6). Biopact CT. https://biopactct.com/blog/what-are-the-different-types-of-cellular-transport/  Vesicle Transport Exocytosis – The fusion of a vesicle with the cell membrane, releasing the vesicle contents to the cell exterior. Endocytosis – The invagination of the cell membrane, forming a vesicle that pinches off and carries external material into the cell. Lumen – vesicle contains degrading substances, such as H2O2 Endocytosis Dissimilar vehicle Exocytosis Cell Types Prokaryotic vs Eukaryotic Cells | BioNinja. (2024). Bioninja.com.au. https://old-ib.bioninja.com.au/standard-level/topic-1-cell-biology/12-ultrastructure-of-cells/prokaryotic-versus-eukaryot.html The Plant Cell Prokaryotic vs Eukaryotic Cells | BioNinja. (2024). Bioninja.com.au. https://old-ib.bioninja.com.au/standard-level/topic-1-cell-biology/12-ultrastructure-of-cells/prokaryotic-versus-eukaryot.html Cell Wall Composed of cellulose, a long chain glucose monomer and other components. Provides only strength and protection to the protoplasm inside. Protoplasm A mass of proteins, lipids, nucleic acids, and water within a cell, except for the wall. It is composed of the cytoplasm and the nucleus. Plasma Membrane Completely covers the surface of the protoplasm. Impermeable to harmful materials and permeable to beneficial ones. Selectively permeable Nucleus An archive or permanent storage place, for the organism’s genetic information. All information must be stored in DNA inside every nucleus , and the storage must be safe and permanent. Nucleus Nuclear envelope – composed of an outer membrane and inner membrane. It separates nuclear material from the rest of the cell, and it contains numerous small holes. Nuclear pores – involved in transporting material between the nucleus and the rest of the protoplasm. Nucleoplasm – a complex association of DNA, enzymes and other factors necessary to maintain, repair, and read DNA, histone proteins that support and interact with DNA, several types of RNA, and water and numerous other substances. Nucleoli – the components of ribosomes are synthesized and partially assembled. Central Vacuole Store mostly water and salts. Tonoplast – refers to the vacuole membrane. Digestive organelle – consist of digestive enzymes for lysis. It contains visible crystals, starch, protein bodies, and various types of granules or fibrous materials. It also expand and merge until there is just one large central vacuole. Example: In flower buds, petals expand from tiny to full-sized in just few hours by simply enlarging their vacuoles. In seed cells, vacuoles may be filled with protein that will be used when the seed germinates, perhaps 10 to 50 years after the material was deposited in the vacuole. Role of electrolytes Calcium regulates the activity of many enzymes and plant cells keep protoplasmic calcium concentrations at the proper level by moving calcium into the vacuole, where it reacts with oxalic acid and crystallizes into an inert form. Excretion and Storing of Waste Product Metabolic waste products are pumped across the vacuole membrane and stored permanently in central vacuole, hence noxious and bitter taste, deter animals from eating plants. Cytoplasm The gelatinous liquid that fills the inside of a cell. It is composed of water, salts, and various organic molecules, such as intracellular organelles, nucleus and mitochondria. Mitochondria Store energy as highly energetic but fairly unreactive compounds, such as sugar and starches. Also known as the _______________ because it produces Adenosine triphosphate (ATP) Component of the Mitochondria Cristae – folded, forming large sheets or tubes. Matrix – a site of reactions that do not involve highly reactive intermediates take place. Outer mitochondrial membrane – surrounds the cristae and matrix as a second membrane, which gives shape and a little rigidity to the mitochondrion. Inner mitochondrial membrane – forms the cristae, is a selectively permeable and has numerous pumps and channel. Plastids A group of dynamic organelles able to perform many functions. Responsible in carrying out photosynthesis by green plastids, chloroplast. Synthesis, storage, and export of specialized lipid molecules; storage of carbohydrates and iron; and formation of colors in some flowers, and fruits. Site of synthesis of amino acids: isoleucine, valine, phenylalanine, tryptophan, tyrosine, lysine, threonine, and methionine. Parts of Plastids 1. Stroma - An inner fluid 2. Chloroplast 3. Chlorophyll 4. Thylakoids 5. granum Ribosomes Responsible for protein synthesis. A complex aggregates of three RNA (ribosomal RNA) and approximately 50 types of protein that associate and form two subunits. Polysomes – are clustered ribosomes bound together eith messenger RNA. Endoplasmic Reticulum A system of narrow tubes and sheets of membrane that form a network throughout the cytoplasm. ER carries large molecule such as proteins, while small particles are carried by diffusion , such as monosaccharides and cofactors. Rough Endoplasmic Reticulum Large proportion of a cell’s ribosomes are attached to the ER, giving rough appearance, thus this is called rough ER. As an attached ribosome synthesizes a protein, it passes through the membrane and collects in the lumen. If the protein is a storage product, as in seeds of legumes, it merely remains in the ER, which may become quite swollen. Smooth Endoplasmic Reticulum Lacks ribosomes and it is involved in lipid synthesis and membrane assembly. As lipid are produced by SER, they are inserted into the membrane, and then vesicles form and pinch off, carrying the new membrane to other parts of the cell. Produces large amount of fatty acids (cutin, and wax on epidermal cells), oils (palm oil, coconut oil, and safflower oil), and fragrances of many flowers. Dictyosomes Initially modifies materials secreted by a cell. A stack of thin vesicles held together in a flat or curved array. Cisterna – thin vesicle alongside with the endoplasmic reticulum. Forming face –the first cisterna becomes embedded more deeply as more vesicle accumulates. Maturing face – vesicles are being released. Different types if processing may occur within a dictyosome: Modification of the vesicle’s membrane or modification of its contents. Microbodies These are small, spherical bodies approximately 0.5 to 1.5 um in diameter. Two types of Microbodies: Peroxisomes and Glyoxysomes. Produce or use the dangerous compound peroxides, H2O2. Contains the enzyme catalase, which detoxifies peroxide by converting it to water and oxygen Peroxisomes Detoxifies certain products of photosynthesis and are found closely associated with chloroplasts. Glyoxysomes Occur only In plants, which are involved in converting stored fats into sugars. They are more important during the germination of fat-rich, oily seeds such as peanut, sunflower, and coconut. Cytosol or hyaloplasm Most of the volume of cytoplasm is a clear substance. It is mostly water, enzymes, and numerous chemical precursors, intermediates, and products of enzymatic reactions. Microtubules Structural elements of a cell. It holds certain regions of the cell surface while the parts expand. It assembles into arrays like an antenna that either catch vesicles and guide them to specific sites or cover a region, excluding the vesicles. Microtubules are the means of motility for both organelles and whole cells. The framework that moves chromosomes during division of the nucleus. Two types of Proteins in Microtubules. Alpha-tubulin Beta-tubulin Microfilaments These are constructed by the assembly of globular proteins (Actin). Fungal Cell They do not contain plastids of any type Their walls contain chitin Chitin – similar to cellulose but it contains nitrogen. Growth and Division of the Cell Cell Cycle Cells are initiated by the division of a mother cell, grow for a period, and usually cease to exist by dividing and producing two daughter cells. Cell cycle arrest - refers to when cells stop dividing, a part of the plant their final form. Interphase A period during which chromosomes are not visible with light microscope. The longest phase of the cell cycle and the time in which the physiological function of the cells in undertaken. It is subdivided into three parts: gap (or growth) 1, synthesis, and gap (or growth) 2 periods. Growth Phase of the Cell Cycle G1 Phase – the cell recovers from division and conducts most of its normal metabolism, such as synthesizing nucleotides used for the next round of DNA Replication. S Phase – the genes in the nucleus are replicated. A gene is a polymer of nucleotides, and each gene has a unique sequence of nucleotides. G2 Phase – cells prepare for division. This phase lasts only about 3 to 5 hours. G1 Phase or Gap 1 One important process is the synthesis of the nucleotides used for the next round of DNA replication. The length of the cell cycle varies based on health, age, temperature, and many other factors. G1 is the longest part of the cell cycle. Example: On single-celled organisms such as some algae, the cell cycle may be as brief as several hours; short cycle times also occur rapidly growing embryos and roots. S phase (Synthesis) Genome – an entire complex of genes for an organism. Many higher plants need about 30,000 types of genes to store information required to make the proper enzymes, structural proteins, and hormones. Genes are attached in short pieces of linking DNA. This structure is known as Chromosomes. Chromosomes Formation of Chromosome 1. During the S phase, DNA and genes are replicated. 2. After replication, the duplicated DNA molecules remain attached at the centromere, connected by a protein called Cohesin. 3. Each half of the chromosome is now called a Chromatid. G2 Phase This phase lasts for 3 to 5 hours. The alpha- and Beta-tubulins are necessary for spindle microtubules to be synthesized, and the cell produces proteins essential for processing chromosomes and breaking down the nuclear envelope. Division Phase of the Cell Cycle Mitosis Cells divides almost immediately, producing two new cells. The cells, in turn divide, with each of them producing two more cells. It ensures that the two new cells (daughter cells) resulting from a cell undergoing mitosis each have precisely equal amounts of DNA and certain other substances duplicated during interphase. Mitosis refers to the division of the nucleus alone. Prophase 1. The chromosomes become shorter and thicker, and their two-stranded nature becomes apparent; 2. The nuclear envelope dissociates and the nucleolus disintegrates. Metaphase The alignment of the chromosomes in a circle midway between the two poles around the circumference of the spindle and in the same plane as that previously occupied by the prephase band. Anaphase The briefest of the phases The sister chromatids of each chromosome separating and moving the opposite poles. Telophase 1. Each group of daughter chromosomes becomes surrounded by a reformed nuclear envelope 2. Daughter chromosomes become longer and thinner and finally become indistinguishable. 3. Nucleoli reappear 4. Many of the spindle fibers disintegrate 5. A cell plate forms. Tissue and Primary Growth Meristematic Tissues These are places in plants where cell division occurred. During cell division, ne cell becomes two cells. Each new cell are called daughter cells, which can also divide. kazilek. (2014, February 3). Cell Division - Mitosis and Meiosis | Ask A Biologist. Asu.edu. https://askabiologist.asu.edu/cell-division Apical Meristems A meristematic tissues found at, or near, the tips of roots and shoots, which increase in length as the apical meristems produce new cells. Also called as primary growth. 3 primary meristems 1. Protoderm 2. Ground meristem 3. Procambium In plants belonging to the DICOT class, apical meristems are located in BOTH the shoot tips and root tips. A shoot is simply a young, leaf-bearing stem. In plants belonging to the MONOCOT class, apical meristems are located ONLY in the root tips.  3 Primary Meristems Primary or Transitional Meristem develop from each apical meristem: Protoderm gives rise to epidermis Ground meristem gives rise to ground tissue Procambium gives rise to vascular tissue Lateral Meristems Composed of the vascular cambium, and cork cambium. Produce tissues that increase the girth (inc. diameter) of roots and stems. Also known as Secondary Growth. Mostly seen in DICOT class. MONOCOT do not have lateral meristems. Vascular Cambium Referred to simply as the cambium. Produces secondary tissues that function primarily in support and conduction. Cork Cambium A thin cylinder that runs the length of roots and stems of woody plants. It lies outside of the vascular cambium, just inside the outer bark, which it produces. Intercalary Meristems They have apical meristems , and near nodes (leaf attachment areas), they have other meristematic tissues. Develop an intervals along stems, where, like the tissues produced by apical meristems, their tissues ass to the length Types of Plant Tissues - Permanent Tissues are None Meristematic - Permanent tissues based on the type of the cell: 1. Simple Permanent Tissues - composed of one kind of cell. 2. Complex Permanent Tissues - composed of several kinds of cell. Simple Tissues 1. Parenchyma 2. Collenchyma 3. Sclerenchyma a. Sclereids b. Fibers 4. Epidermis 5. Secretory Tissues  Composed of parenchyma cells. Parenchyma Generally spherical in shape when they are first produced, but when grow they push against one another, their thin, pliable walls are flattened at the points of contact. For aquatic plants Parenchyma cells have spaces between them. This type parenchyma tissue with extensive connected air spaces is referred to as aerenchyma. Chlorenchyma - parenchyma cells containing numerous chloroplasts. Collenchyma Their walls are generally thicker and more uneven in thickness. This unevenness is generally due to extra primary walls in the corners. They provide flexible support for both growing organs and mature organs, such as leaves and floral parts. Sclerenchyma Consist of cells that have thick, tough, secondary walls, normally impregnated with lignin. Most sclerenchyma cells are dead at maturity and function in Sclereids - “stone” cells support. Two forms: 1. Sclereids - “stone” cells 2. Fibers Fibers Epidermis One cell thick, with fatty cutin (forming the cuticle) within and on the surfaces of the outer walls. It may include guard cells that border pores called stomata; root hairs, which are tubular extensions of single cells; other hairs that consists of one several cells; and glands that secrete protective substances. Periderm Consist of cork cells and loosely arranged groups of cells comprising lenticels involved in gas exchange, constitutes the other bark of woody plants.  Secretory Tissues Occurs in various places in plants. They secrete substances such as nectar, oils, mucilage, latex and resins. Secretory Tissues Examples: 1. Nectar (flowers) from nectaries 2. Oils (peanuts, oranges, citrus) from accumulation of glands and elaioplasts 3. Resins (Conifers) from resin canals 4. Lactifiers (latex - milkweed, rubber plants, opium poppy) 5. Hydathodes (opening for secretion of water) 6. Digestive glands of carnivorous plants (enzymes) 7. Salt glands that shed salt (especial in plants adapte to environments laden with salt) Complex Tissues 1. Xylem 2. Phloem Xylem The “plumbing” and storage systems of a plant and is the chief conducting tissue in all organs for water and minerals absorbed by the roots. It consist of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. Types of Tracheids Xylem The “plumbing” and storage systems of a plant and is the chief conducting tissue in all organs for water and minerals absorbed by the roots. It consist of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. The flow of fluid through the vessels is not blocked by perforation plates. However, perforation plates may block the movement of objects, such as fungal spores, that may invade the xylem. Phloem It conducts dissolved food materials (primarily sugars) produced by photosynthesis throughout the plant, is composed mostly of two types of cells without secondary walls. It is composed of sieve tubes, companion cells, parenchyma, ray cells, and fibers. Callose aids in plugging injured sieve tubes. Roots Anchor the plant Absorb water and nutrients Embryonic Root or Radicle Radicle is the embryonic root of the plant, which develops into the future root of the plant. It is the first part of the embryo to develop into the root system of plants. These embryonic roots grow deep into the soil and absorb all the essential minerals, water and other nutrients required for their growth and development. The Root System Within a germinating seed, an embryo (immature plant) contains a tiny, rootlike radicle. This radicle develops into a root. Different types of a root. 1. Taproot 2. Adventitious root 3. Fibrous root 4. Prop root  THE ROOT STRUCTURE/ EXTERNAL ANATOMY 1. Root cap 2. Region of Cell division 3. Region of elongation 4. Region of Maturation THE ROOT CAP - Composed of a cluster of parenchyma cells covering the tip of the root. - Its function is to protect the delicate tissues behind it as the young tip pushes through abrasive soil particles. - The dictyosomes of the root cap’s outer cells secrete and release a slimy substances that lodges in the walls and eventually passes to the outside.  THE REGION OF CELL DIVISION - Composed of an apical meristem in the center of the root tips, produce the surrounding root cap. - Three subdivision of apical meristem: 1. Protoderm - gives rise to an outer layer of cells, the epidermis. 2. Ground meristem - produces parenchyma cells of the cortex. 3. Procambium - produces primary xylem and primary phloem. A Cross Section of a Monocot Root THE REGION OF ELONGATION - In this region, the cells become several times their original length and wider. - Normally it increases the girth gradually through addition of secondary tissues produced by the cambium.  THE REGION OF MATURATION - Most of the cells mature, or differentiate, into the various distinctive cell types of the primary tissues. - Also known as, region of differentiation, or root-hair zone. - Root hairs, which absorb water and minerals, adhere tightly to soil particles with the aid of microscopic fibers they produce and greatly increase the total absorptive surface of the root. Internal Structure Internal Structure The Casparian Strip Modified Roots Food storage Propagative roots Pneumatophores Aerial Roots Photosynthetic roots of some orchids Contractile roots some herbaceous dicots and monocots Buttress roots looks Parasitic roots Symbiotic roots –mycorrhizae or “fungus roots” –Legumes (e.g., pea, beans, peanuts) and bacterium form root nodules.  Modified Roots Food storage Pneumatophores Aerial Roots  Modified Roots Buttress Roots Symbiotic Roots Photosynthetic Roots Modified Roots Parasitic Roots STEM External Form of a Woody Twig Node - the area, or region (notstructure), of a stem where a leaf or leaves are attached. Internode - a stem region between node. Terminal bud - present at the tip of each twig. Bud scale scars - tiny scars from around the twig when they fall off. Counting the number of groups of bud scale scars on a twig can reveal the age of the twig. External Form of a Woody Twig Axil - an angle between a petiole and the stem which contains a bud. The bud located at the axil is an axillary bud. Terminal Bud - present at the tip of each twig. The meristems within them normally produce tissues that make the twig grow longer during the growing season. Stem Extensions Blade - a broad and flat surface of the leaf. Petiole - the attachment of the leaf from the stem. Stipules - the base of a petiole. Origin and Development of Stems Origin and Development of Stems Three Primary Meristems Maturation of Protoderm Procambium Ground primordia Meristem (embryonic Gives rise to the Located at the Apical leaves that Mitosis epidermis. interior of the Produces two meristem will develop protoderm. tissues: into mature Protected by a leaves after cuticle (thin, It produces water Pith - center the bud waxy, protective -conducting Cortex - scales drop layer.) primary xylem extensive off) cells and primary phloem cells Origin and Development of Stems As each leaf and bud develop, a strand of xylem and phloem extending , called a trace, branches off from the cylinder of the xylem and phloem extending up and down the stem and enters the leaf of the bud. As the traces branch from the main cylinder of the xylem and phloem, each trace leaves a little, thumbnail-shaped gap in the cylinder of vascular tissue. LEAVES All leaves originate on the shoot’s apical meristem as a bulge of tissue called Leaf primordia. External Morphology Stipule Petiole Sessile - petiole is absent Petiolate - petiole is present Leaf Base Leaf blade/ Lamina Sessile or apetiolated  Monocot leaf Supported by leaf sheath Ligules and auricles Functions: 1. protection from dirt water External Morphology 2. Phyllotaxy Opposite: 2 leaves at a node, on opposite sides of the stem. Alternate: 1 leaf per node, with the second leaf being above the first but attached on the opposite side of the stem. Whorled: 3 or more leaves at a node Identify the arrangement. External Morphology 3. Leaf Types A B Leaf Types A. Simple leaf - one blade or lamina B. Compound leaf -blade is divided into two or more leaflets or (pinnae) -petiolule Rachis – continuation of the petiole where the leaflets are attached  TWO TYPES OF COMPOUND LEAVES: A. Pinnately Compound - leaflets are arranged laterally along the rachis (featherlike fashion) External Morphology Three types of PINNATELY compound leaves: 1. Unipinnate 2. Bipinnate 3. Tripinnate Pinnately Compound Leaves 1. Simple Pinnate a. Even pinnate -each leaflet has a pair b. Odd pinnate -terminal leaflet has no pair Pinnately Compound Leaves 2. Bipinnate -primary rachis branches into secondary rachis that bears the leaflets 3. Tripinnate -with primary, secondary and tertiary rachises  TWO TYPES OF COMPOUND LEAVES: B. Palmately Compound - leaflets radiate from a common point LEAF VENATION A. Netted/Reticulate –venation main vein branches forms network common to dicots and some nonflowering plants. NETTED/ RETICULATE VENATION 1. Pinnately netted main vein veins and veinlets arise from the midrib and ramify throughout the lamina. NETTED/ RETICULATE VENATION 2. Palmately netted principal veins arise at one point at the base of the leaf B. Parallel venation - characteristics of many monocots (e.g., grasses, cereal grains); veins are parallel to one another. Shape Margin  Leaves - Comparisons Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves Most dicots have branch-like Monocots have parallel leaf veins and palmate leaf shape veins and longer, slender blades Internal Anatomy chloroplasts  Structure of a Leaf 1. Upper Epidermis – a single layer of similar cells covering the upper surfaces of the leaf, generally with a waxy cuticle. Consists of closely-packed cells and usually contains no chloroplasts Stomata are usually absent 2. Mesophyll – between the epidermal layers. It contains palisade parenchyma that are tall, tightly packed, and filled with chloroplasts for photosynthesis. It also has spongy parenchyma which are irregularly shaped, have large air spaces between them, and fewer chloroplasts. Structure of a Leaf 3. Veins – contain the vascular tissue that is continuous with that in the stem. Xylem carries water and minerals upward. Phloem carries dissolved food throughout the plant. 4. Lower epidermis – similar to the upper epidermis, except that it has thinner cuticle and its pores or stomata is larger in number. These small pores control the gas exchanger of gases in and out of the leaf and the loss of water vapor. Each stoma is surrounded by two kidney- shaped cells called guard cells. Typical Dicot Leaf Cross-Section Cuticle Epidermis Palisade Parenchyma Vascular bundles Guard Spongy Cells Parenchyma Stoma  Typical Monocot Leaf Cross-Section Midvein Vein Bundle Epidermis sheath cell Phloem Xylem Bulliform Stoma Cells Function of the Leaf Photosynthesis Gaseous exchange Water Vapour can be lost from the surface of the leaf in a process known as Transpiration. Stomatal control Almost all leaf transpiration results from diffusion of water vapor through the stomatal pore waxy cuticle Provide a low resistance pathway for diffusion of gases across the epidermis and cuticle Regulates water loss in plants and the rate of CO2 uptake Stomatal control When water is abundant: Temporal regulation of stomata is used: OPEN during the day CLOSED at night Stomatal control When water is limited: Stomata will open less or even remain closed even on a sunny morning Plant can avoid dehydration Stomatal resistance can be controlled by opening and closing the stomatal pores. GUARD CELLS AND PLANT HOMEOSTASIS Guard cells are kidney-shaped with thick inner walls and thin outer walls. When they become full of water (turgid) the unevenness of the walls causes them to bow outward and the stomate opens. When they lose water they become less turgid and the stomate closes. Guard cells gain and lose water by osmosis.  Stomatal guard cells Guard cells act as hydraulic valves Environmental factors are sensed by guard cells Integrated into well defined responses Ion uptake in guard cell Biosynthesis of organic molecules in guard cells This alters the water potential in the guard cells Water enders them Swell up 40-100% Specialized Leaves 1. Reproduction 2. Aeration 3. Support 4. Protection 5. Storage 6. Attraction 7. Absorption TRANSPIRATION Plants must supply water to all their tissues. It moves from the roots up the stem to the leaves by capillary action. Most of the water plants take up is lost to the atmosphere by evaporation. Most takes place through stomata.  The rate of transpiration is regulated by the size of the opening of the stomates. They are usually closed when there is too little water available, temperature is low, or there is little light. Most plants open their stomates during the day and close them at night. Relationship between water loss and CO2 gain Effectiveness of controlling water loss and allowing CO2 uptake for photosynthesis is called the transpiration ratio. There is a large ratio of water efflux and CO2 influx Concentration ratio driving water loss is 50 larger than that driving CO2 influx CO2 diffuses 1.6 times slower than water Due to CO2 being a larger molecule than water Water Status of Plants Cell division slows down Reduction of synthesis of: Cell wall Proteins Closure of stomata Due to accumulation of the plant hormone Abscisic acid Naturally more of this hormone in desert plants Plants and water Water is the essential medium of life. Land plants faced with dehydration by water loss to the atmosphere There is a conflict between the need for water conservation and the need for CO2 assimilation This determines much of the structure of land plants 1: extensive root system – to get water from soil 2: low resistance path way to get water to leaves – xylem 3: leaf cuticle – reduces evaporation 4: stomata – controls water loss and CO2 uptake 5: guard cells – control stomata. Photosynthesis One of the most important biochemical process in plants. Among the most expensive biochemical processes in plant in terms of investment The biochemical process that has driven plant form and function  General overall reaction 6 CO2 + 6 H2O C6H12O6 + 6 O2 Carbon dioxide Water Carbohydrate Oxygen Photosynthetic organisms use solar energy to synthesize carbon compounds that cannot be formed without the input of energy. More specifically, light energy drives the synthesis of carbohydrates from carbon dioxide and water with the generation of oxygen. C3 and C4 Leaf structure The C4 carbon Leaf C4 leaves have TWO chloroplast containing cells ○ Mesophyll cells ○ Bundle sheath (deep in the leaf so atmospheric oxygen cannot diffuse easily to them) C3 plants only have Mesophyll cells Operation of the C4 cycle requires the coordinated effort of both cell types ○ No mesophyll cells is more than three cells away from a bundle sheath cells Many plasmodesmata for communication Sexual Reproduction External Structure Internal Structure Other Type or modification Pharmacognosy