BiologyReviewer

Biology 1 Reviewer Introduction to Biology Biology Bios – Life Logos – To study Biology – The study of living things Characteristics of Living Things With definite organization Compared with non-living matter of similar size, living things are highly complex and organized Parts of living things are arranged in a particular way Atom -> Molecule -> Cell -> Tissue -> Organ -> Organ system -> Organism Molecules -> Cell -> Cell Groups-> Organism -> Population -> Community-> Ecosystem -> Biosphere Irritability/Responsiveness refers to the ability to react to any environmental change or stimulus that often results in movement organisms perceive and respond to stimuli in their internal and external environments the ability to respond helps ensure the survival of the organisms Reproduction Formation of new cells or new organisms In order for life to continue, living things must be able to produce other living things of their kind (Reproduction). Reproduction can be sexual or asexual Growth refers to an increase in size It can result from an increase in cell number, cell size, or the amount of substance surrounding the cells involves the conversion of materials acquired from the environment into the specific molecules of the organism’s body Metabolism refers to sum total of all the chemical reactions needed to sustain an organism’s life Anabolism- building up process Catabolism- breaking down process Adaptation refers to modifications that promote the likelihood of survival living things not suited to a new conditions either move to a better environment or change (evolution) results into unity and diversity of life Maintain homeostasis the existence and maintenance of a relatively constant environment within the body Levels of Taxonomic Classification Domain Danny’s Kingdom Kid Phylum Purchased Class Canned Order Oatmeal Family From Genus Garage Species Sale Linnaeus Plantae Animalia Whittaker Monera Protista Fungi Plantae Animalia Woese Eubacteria Archaebacteria Protista Fungi Plantae Animalia Woese Bacteria Archaea Eukarya Domain Bacteria Archaea Eukarya Kingdom Eubacteria Archaebacteria Protista Fungi Plantae Animalia Cell Type Prokaryote Prokaryote Eukaryote Eukaryote Eukaryote Eukaryote Cell Walls? Cell wall (peptidoglycan) Cell wall Cell wall (cellulose) Cell walls (chitin) Cell walls (cellulose) None Number of Cells Unicellular Unicellular Unicellular (most) Multicellular (most) Multicellular Multicellular Mode of Nutrition Autotroph Heterotroph Autotroph Heterotroph Autotroph Heterotroph Heterotroph Autotroph Heterotroph The Science of Botany The scientific study of plants Also ‘plant biology’ Characteristics of Plants Eukaryote With true nucleus and membrane-bound organelles Multicellular Composed of more than one cells Cellulosic cell wall Cell wall of plants contains the polysaccharide cellulose Autotroph (Photosynthesis) Can produce their own food through photosynthesis Photosynthesis - the process by which plants capture light energy of sunlight and use carbon dioxide and water to make their own food (glucose). With large central vacuole Fluid-filled sacs for storage of water and nutrients needed by the cell; also help support the shape of the cell Plants have large central vacuole Small or absent in animal cells Bacterial cells do not have vacuoles With plastids Chloroplast - Contains chlorophyll a and b as well as carotenoids Amyloplast Chromoplast Sedentary Generally non-motile Not exactly immobile They also exhibit some form of limited movement unidirectional movement of plant parts in response to light, or phototropism the folding of the leaves of Mimosa in response to touch Sub disciplines of Botany Plant Morpho-anatomy form and structures of plants Plant Molecular Biology Structures and functions of important biological molecules (proteins, nucleic acids) in plants Plant Cell Biology Structures, functions, and life processes of plant cells Plant Physiology Deals with how plants function (photosynthesis, mineral nutrition) Plant Genetics Deals with plant heredity and variation Heredity- transmission of traits from parents to offspring Variation- differences in traits among biological organisms Plant Ecology Interrelationships among plants, and between plants ands their environment Plant Pathology Deals with diseases in plants Plant Systematics Deals with plant taxonomy and phylogeny Taxonomy- the description, identification, nomenclature, and classification of organisms Phylogeny- evolutionary history and relationships among individuals or groups of organisms Phycology- study of algae Mycology- study of fungi Pteridology- study of ferns Bryology- study of mosses Dendrology- study of trees The Scientific Method A logical process of learning facts through observation and experimentation from which, certain conclusions or theories are drawn. Steps of Scientific Method Identification of the problem through observation Any scientific process starts with observation using all the senses. From observation a problem or a question may be identified. Formulation of hypotheses Hypothesis is a preliminary conclusion or an educated guess about a scientific problem It is a supposition, based on the previous observations, that is offered as an explanation for the observed phenomenon. Format: “If……then…..because…..” To be useful, the hypothesis must lead to predictions that can be tested by additional controlled observations, or experiments Experimentation or testing of hypotheses Experiment is a special procedure used to test hypotheses. There must be two sets of experiments Control group- test subjects randomly assigned to not receive the experimental treatment. Experimental group- test subjects randomly assigned to receive the experimental treatment. Experimental set-up is similar to the control in every aspect except the presence of the variable The variable is the factor or parameter to be tested Variables are factors in the experiment that can be changed and then measure the effects of the factor or parameter to be tested. Two types: Independent variable is the variable that is changed or controlled in a scientific experiment to test the effects on the dependent variable. Dependent variable is the variable being tested and measured in a scientific experiment. Whatever event you are expecting to change is always the dependent variable. Independent variable causes a change in Dependent Variable and it isn’t possible that Dependent Variable could cause a change in Independent Variable. Controlled experiment vs control group Controlled experiment- one in which everything is held constant except for one variable (independent variable). Control group - the group (in a controlled experiment) that does not receive experimental treatment. All factors are the same with the experimental group except for the variable being tested. Analysis and interpretation of data and results Data/results must be gathered during and after experimentation Data include records collected while making observations during an experiment One way to analyze and interpret records of observation is by using tables and graphs. Generalization or formulation of conclusion Scientific theories have been thoroughly tested. Examples: Atomic Theory- All matter is composed of atoms Cell Theory- All living things are composed of cells Theory may be developed into a scientific law or a scientific principle. Communication of the findings No matter how well designed an experiment is, it is useless it is not communicated thoroughly and accurately. If experiments are not communicated or shared to other scientists in enough detail to be repeated, their conclusions cannot be verified. Without verification, scientific findings cannot be safely used as the basis for new hypotheses and further experiments. The Plant Cell Cell The basic structural and functional unit of every organism Types of cells (based on the presence or absence of true nucleus) Eukaryotic Prokaryotic Common Features of all Cells Molecular components Proteins, amino acids, lipids, carbohydrates, sugars, nucleotides, DNA and RNA–All cells have chromosomes, which carry genes in the form of DNA All cells use DNA as a hereditary blueprint that stores the instructions for making other parts of the cell and for producing new cells Structural components Plasma membrane, cytoplasm and ribosomes Metabolism Extracts energy and nutrients from the environment; uses energy and nutrients to build, repair, and replace cellular parts (to maintain their complexity) Essentially all of the energy powering life on Earth originates in sunlight. Characteristics PROKARYOTIC CELL EUKARYOTIC CELL Greek words pro-before karyon-nucleus eu-true karyon-nucleus General characteristics without true nucleus nuclear membrane absent with true nucleus nuclear membrane present Exemplified by: Bacteria and Archaeans Protists, Fungi, Plants and Animals Chromosomes Single circular composed of only nucleic acid Multiple linear composed of nucleic acid + protein Location of DNA Found in the nucleoid not membrane-bound Found in the nucleus bound by double membrane Membrane-bound organelles absent present Mitochondria absent present Ribosomes small large Microtubules usually absent present Cytoplasm No cytoskeleton With cytoskeleton Cell wall peptidoglycan cellulose (plants and protists) chitin (fungi) Reproduction Binary fission Involves mitosis and meiosis Size Smaller (0.2-2 um in diameter) Larger (10-100 um in diameter) The Cell Theory Robert Hooke coined the word ‘cell’. He is a British scientist, observed mass of tiny cavities from thin slices of cork with his self-made microscope. He named these structures “CELLS” since these structures reminded him of the small rooms in a monastery Anton van Leeuwenhoek is a Dutch tradesman and scientist. Using handcrafted microscopes, was the first person to observe and describe single celled organisms, which he originally referred to as ‘animalcules’ (which we now refer to as microorganisms). He was also the first to record and observe muscle fibers, bacteria, spermatozoa and blood flow in capillaries. Matthias Schleiden (1838), a botanist, and Theodor Schwann (1839), a zoologist, proposed the cell theory. Rudolph Virchow (1855), a physician, modified the theory. Three Tenets of Cell Theory: Schleiden & Schwann Cells are the basic units of life All living organisms are composed of one or more cells Virchow Cells arise from previously existing cells Eukaryotic Cell Structures and Functions Plasma membrane (or cell membrane) the outermost component of a cell encloses the cytoplasm and forms the boundary between material inside the cell and materials outside it, hence it is called the “gatekeeper of the cell” Selectively permeable which regulates the exchange of essential substances between the cell’s contents and the external environment Also known as “plasmalemma” in plants. Nucleus the most distinct (usually the largest) organelle in a eukaryotic cell, averaging about 5 um in diameter usually situated at the center of the cell, bounded by a double membrane (nuclear membrane) contains most of the genes in the eukaryotic cell (some genes are located in mitochondria and chloroplasts) Controls and regulates the functions of other organelles, thus called the “governor or the control center of the cell” Nuclear envelope/membrane Double membrane that encloses the nucleus separating its contents from the cytoplasm isolates the nucleus from the rest of the cell and allows selective exchange of materials perforated with tiny membrane-lined channels called nuclear pores Nucleolus diffuse body with no surrounding membrane that is found at the center of the nucleus Functions: Ribosomal RNA (rRNA) synthesis and Site of ribosome assembly Chromatin The DNA is organized into chromosomes, structures that carry the genetic information. Each chromosome is made up of a material called chromatin, a complex of proteins and DNA. Cytoplasm consists of all materials inside the plasma membrane and outside the nucleus Has semifluid, jellylike substance called cytosol the most active region of the cell because most of the cell’s metabolic activities---the biochemical reactions that support life--- occur in cell cytoplasm Contains the different organelles of the cell Organelles are physiologically active, permanent sub-cellular structures performing metabolic functions Endoplasmic reticulum Endoplasmic means "within the cytoplasm”, and reticulum is Latin for "little net” network of membranous tubules and sacs called cisternae accounts for more than half the total membrane in many eukaryotic cells the ER membrane is continuous with the nuclear membrane Smooth ER (without ribosomes) Rough ER (with ribosomes) synthesis of lipids (oils, phospholipids, and steroids) metabolism of carbohydrates detoxification of drugs and poisons Store calcium ions Transport by vesicle formation Abundant in liver and muscle cells The ribosomes on the outside of rough ER are used to synthesize both secretory proteins and phospholipids Membrane factory of the cell (grows in place by adding membrane proteins and phospholipids to its own membrane) Transport by vesicle formation Ribosomes spherical bodies that may be attached to the Endoplasmic Reticulum or nuclear envelope (Attached ribosomes) or free in the cytoplasm (Free ribosomes). The two types of ribosomes are structurally identical aggregates of rRNA and protein Function: site of protein synthesis in the cell Proteins synthesized from free ribosomes function within the cytosol (e.g. enzymes) Proteins from attached ribosomes are for use within the cell membrane components export from the cell or for secretion Golgi bodies (or golgi apparatus) named for the Italian physician and cell biologist Camilo Golgi, who discovered in the late 1800s membrane-bound vesicles of flattened sacs and stacks (cisternae) parallel to each other Unlike in ER, the cisternae of Golgi appartus are not physically connected derived from endoplasmic reticulum Otherwise known as dictyosomes in plants Entry or cis face (convex) a cisterna that faces the rough ER Medial cisternae Sacs between the entry and exit faces Exit or trans face (concave) a cisterna that faces the plasma membrane Functions of Golgi apparatus separates (sorts) proteins and lipids received from the ER according to their destinations modifies some molecules (For instance, it adds sugars to proteins to make glycoproteins) manufactures certains molecules (polysaccharides) packages these materials into vesicles that are then transported to other parts of the cell or to the plasma membrane for export Synthesized by: Free Ribosomes Attached Ribosomes Occupy storage vesicles that become lysosomes Function within the cell (e.g. enzymes) Secreted from the cell by exocytosis Incorporated into the plasma membrane Mitochondria Singular: ‘mitochondrion’ double-membrane organelle, smooth outer membrane and folded inner membrane (cristae) found in almost all living cells The outer membrane is smooth, but the inner membrane forms deep folds called cristae. Pair of membranes enclosing two fluid compartments: the intermembrane compartment between the outer and inner membrane matrix within the inner membrane Abundant in liver cells Also contain ribosomes Have their own DNA Site of cellular aerobic respiration (convert energy stored in sugar to ATP) major site of ATP synthesis “powerhouse of the cell” found in large number of metabolically active cells Peroxisomes are small, single membrane-bound vesicle containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H2O2) Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell. The enzymes in peroxisomes break down hydrogen peroxide to water and oxygen. Peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen. Peroxisomes do not bud from the endomembrane system. They grow larger by incorporating proteins made primarily in the cytosol, lipids made in the ER, and lipids synthesized within the peroxisome itself Cytoskeleton Cell support Cell shape Cell and organelle motility (movement) Cell division Thin Microfilaments small fibrils formed from protein subunits Cell shape Cell motility (movement) Cell division Medium-sized intermediate filaments provide mechanical support to the cell and maintenance of cell shape Thick microtubules hollow structures formed from protein subunits Cell shape Cell motility (movement) Chromosome movements in cell division Organelle movements Forming essential components of certain organelles, such as cilia and flagella (in animal cells) Structures only present in: Animal Cell Plant Cell Lysosomes Centrioles Flagella Cilia Cell wall Plasmodesmata Large central vacuole Plastid Chloroplast, the most important plastid Chromoplast Amyloplast Cell Wall extracellular structure of plant cells that distinguishes them from animal cells Prokaryotes, fungi, and some protists also have cell walls Almost all plant cells have a cell wall; only sperm cells of some seed plants lack one Much thicker than the plasma membrane, ranging from 0.1 um to several micrometers Composition of Cell Wall Cellulose main composition of plant cell wall; a polysaccharide tough, inflexible, and insoluble in water Adjacent, parallel cellulose molecules crystallize into an extremely strong microfibril (cellulose microfibril) Hemicellulose Another kind of polysaccharide that bound together the cellulose microfibril deposited between the cellulose microfibrils and bind chemically to the cellulose, producing a solid structure that resembles reinforced concrete Lignin Usually found in the secondary wall of plant cell walls Resists chemical, fungal, and bacterial attack Pectin A sticky polysaccharides composing the middle lamella layer Layers of Cell Wall Primary wall relatively thin and flexible wall Secondary wall Located between the plasma membrane and the primary wall Usually much thicker than the primary wall almost always impregnated with the compound lignin, which makes the wall even stronger than hemicelluloses alone can make it. often deposited in several laminated layers, has a strong and durable matrix that affords the cell protection and support Both primary and secondary cell walls are permanent; once deposited, they are almost never degraded or depolymerized, as can be done with microtubules and microfilaments. Middle lamella a thin layer rich in sticky polysaccharides called pectins located in between primary walls of adjacent cells The cementing substance between plant cells as it glues adjacent cells together brought about by pectin Responsible for the organized arrangement of plant cells When the cell matures and stops growing, it strengthens its wall. Some plant cells do this simply by secreting hardening substances into the primary wall. Functions of Cell Wall Protects the plant cell Provides strength Maintains the shape of the cell Prevents excessive uptake of water On the level of the whole plant, the strong walls of specialized cells hold the plant up against the force of gravity. Considerable metabolism occurs in the wall, and it should therefore be considered a dynamic, active organelle. Plasmodesmata (singular, plasmodesma; from desmos, to bind). Channels or fine holes perforating the cell walls between adjacent cells Plasma membrane of one cell passes through it and is continuous with the plasma membrane of the adjacent cell and thus are continuous. Cytosol passes through the plasmodesmata and connects the chemical environments of adjacent cells. These connections unify most of the plant into one living continuum. Water and small solutes can pass freely from cell to cell, and recent experiments have shown that in some circumstances, certain proteins and RNA molecules can also do this Desmotubules- give stability to plasmodesmata Central Vacuole develops by the coalescence of smaller vacuoles, themselves derived from the endoplasmic reticulum and Golgi apparatus. The vacuole is thus an integral part of a plant cell's endomembrane system. Have single membrane called tonoplast (vacuolar membrane) Like all cellular membranes, the vacuolar membrane is selective in transporting solutes Cell sap- the solution inside the central vacuole differs in composition from the cytosol Vacuoles often appear to be empty because they store mostly water and salts that cannot be preserved for microscopy. However, they sometimes contain visible crystals, starch, protein bodies, and various types of granules or fibrous materials in addition to water and salts. Functions of the Vacuole Storage of both nutrient reserves and waste products. In seed cells, vacuoles may be filled with starch or protein that will be used when the seed germinates 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 Main repository of inorganic ions, such as potassium and chloride. Metabolic waste products are pumped across the vacuole membrane and stored permanently in the central vacuole. Holding waste inside forever does not sound like an optimal situation, but it actually may be selectively advantageous: Because most of these compounds are noxious and bitter, they deter animals from eating the plants. Mutations that result in excretion might make the cells taste good, which would be selectively disadvantageous Vacuole is the lysosome in plants Cell growth The vacuole has a major role in the growth of plant cells, which enlarge as their vacuoles absorb water, enabling the cell to become larger with a minimal investment in new cytoplasm. The cytosol often occupies only a thin layer between the central vacuole and the plasma membrane, so the ratio of plasma membrane surface to cytosolic volume is great, even for a large plant cell. Over a long period, plants must produce additional proteins, membranes, and organelles or they would become almost pure water. Cellular digestion As organelles age and become impaired, they fuse with the tonoplast and are transported into the central vacuole, where digestive enzymes break them down. Some vacuoles contain pigments that color the cells, such as the red and blue pigments of petals that help attract pollinating insects to flowers. Plastids A dynamic group of organelles able to perform various functions. Each type of plastid is associated to a particular function which may include: synthesis, storage, and export of specialized lipid molecules storage of carbohydrates and iron formation of colors in some flowers and fruits Like mitochondria, plastids always have an inner membrane and an outer membrane and an inner fluid called stroma. In chloroplasts the inner membrane is extensive and highly folded. Plastids also have ribosomes and circular DNA that is not associated with histones. Plastids grow and reproduce by pulling apart Chloroplasts lens-shaped organelles are found in leaves and other green organs of plants and in algae concentrated in the mesophyll layer of the leaf larger than mitochondria, about 4 to 6 ? m in diameter. An individual leaf cell may contain as many as 50 chloroplasts. Site of photosynthesis in plants When chloroplasts photosynthesize rapidly, they produce sugar faster than the cell can use it, so it is temporarily polymerized into starch grains inside the chloroplasts. composed of two membranes (outer and inner) separated by a narrow intermembrane space that constitutes an outer compartment. The inner membrane encloses a second compartment containing the fluid called stroma. Grana- stacks of discs structures Thylakoid- each individual disc in a grana Free ribosomes; copies of the chloroplast genome (DNA) and enzymes The stroma surrounds a third compartment- the thylakoid space, delineated by the thylakoid membrane. Therefore, the membranes of the chloroplast divide the chloroplast space into three compartments: the intermembrane space, the stroma, and the thylakoid space Pigments are located in the thylakoid membrane Photosynthetic pigments are chlorophyll a - the main light-capturing pigment in land plants chlorophyll b carotenoids Chlorophyll, the key light-capturing pigment molecule in chloroplasts, strongly absorbs violet, blue, and red light but reflects green. Chlorophyll is responsible for the green color of the chloroplasts. Chromoplasts Plastid containing accumulated colored lipids bright red, yellow, or orange It has no grana but with an extensive system of membranes. The pigments can be part of the membrane or present as plastoglobuli (droplets). Found mostly in flowers and fruits. Amyloplasts Plastids found in plant tissues that cannot photosynthesize (roots, bark, wood) Accumulate sugar to produce large starch grains. Constitute the bulk of the tissue in starchy vegetables. If exposed to light, amyloplasts can be converted to chloroplasts. Membranous Structure of Cells Double Membrane Single Membrane cell membrane cell wall nuclear membrane mitochondria plastids endoplasmic reticulum lysosomes (found only in animal cell) peroxisomes golgi apparatus Biological Membranes Plasma Membrane encloses the cytoplasm and forms the boundary between material inside the cell and materials outside it, hence it is called the “gatekeeper of the cell” Controls traffic into and out of the cell it surrounds. Selectively permeable (semi-permeable) allows some substances to cross it more easily than others selectively isolates the cell’s contents from the external environment regulates the exchange of essential substances between the cell’s contents and the external environment allows communication with other cells gives strength, shape, and protection to the cell Biological membranes are mostly composed of lipids (42%), proteins (55%), and some carbohydrates (3%). Phospholipids are the most abundant lipid in the plasma membrane Proteins determine most of the membrane's functions. The Fluid Mosaic Model Fluid Mosaic Model describes the structure of the plasma membrane developed by cell biologists S.J. Singer and G.L. Nicholson in 1972 The membrane is a fluid structure with a “mosaic" of various proteins embedded in or attached to a fluid phospholipid bilayer (double layers). Membrane proteins are dispersed, individually inserted into the phospholipid bilayer with their hydrophilic regions protruding. This molecular arrangement would maximize contact of hydrophilic regions of proteins and phospholipids with water in the cytosol and extracellular fluid, while providing their hydrophobic parts with a nonaqueous environment Phospholipid Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions. Consists of two very different parts: a polar, hydrophilic head which forms the outer borders and non-polar hydrophobic tails which “hide inside Fluidity of Membranes Hydrophobic interactions hold membranes together which are much weaker than covalent bonds. Most of the lipids, and some proteins, can shift about laterally. Rarely, a lipid may flip-flop transversely across the membrane. Adjacent phospholipids switch positions rapidly, about 107 times per second. Proteins are much larger than lipids and move more slowly, but some membrane proteins do drift As temperatures cool, membranes switch from a fluid state to a solid state. The temperature at which a membrane solidifies depends on the types of lipids. Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids. Membranes must be fluid to work properly; they are usually about as fluid as salad oil. The steroid cholesterol has different effects on membrane fluidity at different temperatures. At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids. At cool temperatures, it maintains fluidity by preventing tight packing. Cholesterol is a "temperature buffer”, resisting changes in membrane fluidity that can be caused by changes in temperature. Cholesterol is only found in the plasma membranes of animal cell When a membrane solidifies, its permeability changes, and enzymatic proteins in the membrane may become inactive-for example, if their activity requires them to be able to move laterally in the membrane Two Types of Membrane Proteins Integral proteins penetrate the hydrophobic core of the lipid bilayer Many are transmembrane proteins, which span the membrane; other integral proteins extend only partway into the hydrophobic core. Peripheral proteins not embedded in the lipid bilayer at all loosely bound to the surface of the membrane, often to exposed parts of integral proteins Most of the proteins within membranes have both hydrophobic and hydrophilic regions. Functions of Membrane Proteins Transport A hydrophilic channel can be provided by a protein that spans the membrane. (Channel proteins) Other proteins transport substances by changing shape. (Carrier protein) Some hydrolyzes ATP to actively pump substances across the membrane Enzymatic activity A membrane protein can be an enzyme with its exposed active site in the extracellular matrix. This protein can be a part of a metabolic pathway. Signal transduction A membrane protein can act as a receptor with a binding site for a specific chemical messenger. (Receptor proteins) The external messenger (signaling molecule) may cause a shape change in the protein that relays the message to the inside of the cell, usually by binding to a cytoplasmic protein. Cell-cell recognition Some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells. Intercellular joining Membrane proteins of adjacent cells can associate with each other to form junctions. This is evident in the gap and tight junctions of animal cells. Attachment to the cytoskeleton and extracellular matrix (ECM) Membrane proteins can help in maintaining the cell’s shape by binding non covalently with microfilaments and other elements of the cytoskeleton. Role of Membrane Carbohydrates in Cell to Cell Recognition Cell-cell recognition, a cell's ability to distinguish one type of neighboring cell from another, is crucial to the functioning of an organism. It is also the basis for the rejection of foreign cells (including those of transplanted organs) by the immune system in humans. Cells recognize other cells by binding to surface molecules, often to carbohydrates, on the plasma membrane. The diversity of the molecules and their location on the cell's surface enable membrane carbohydrates to function as markers that distinguish one cell from another. Membrane structure results in selective permeability The Permeability of the Lipid Bilayer Nonpolar molecules are hydrophobic and can therefore dissolve in the lipid bilayer of the membrane and cross it easily, without the aid of membrane proteins. Examples: hydrocarbons, carbon dioxide, and oxygen Polar molecules are hydrophilic do not cross the membrane easily. Examples are glucose (and other sugars) and water Hydrophobic core of the membrane impedes the direct passage of ions and polar molecules, which are hydrophilic, through the membrane. Transport Proteins Cell membranes are permeable to specific ions and a variety of polar molecules. These hydrophilic substances can avoid contact with the lipid bilayer by passing through transport proteins that span the membrane. Transport proteins include: Channel and carrier proteins Thus, the selective permeability of a membrane depends on: discriminating barrier of the lipid bilayer specific transport proteins built into the membrane Types of Transport Mechanisms across the Plasma membrane Passive Transport substances move into or out of cells down concentration gradients (from higher concentration to lower concentration) A difference in concentration between two adjacent regions is called a concentration gradient. DOES NOT require energy Examples: Simple Diffusion, Osmosis, and Facilitated diffusion Diffusion Movement of molecules or substances from an area of higher concentration to an area of a lower concentration The net (or overall) movement of molecules or ions down a concentration gradient until equilibrium is achieved Results from the constant random motion of all solutes in a solution Each molecule moves randomly, yet diffusion of a population of molecules may be directional Principles of Diffusion In the absence of other forces, molecules or ions tend to move “down” their concentration gradient, from a region of higher concentration to one of lower concentration (assuming that the membrane is permeable to that substance). Diffusion is a spontaneous process, needing no input of energy. After a substance has diffused completely through a space, removing its concentration gradient, molecules will still move around in the space, but there will be no net movement of the number of molecules from one area to another, a state known as dynamic equilibrium. Each substance diffuses down its own concentration gradient, unaffected by the concentration differences of other substances Factors Affecting Diffusion Steepness of the concentration gradient. The greater the difference in concentration between the two sides of the membrane, the higher is the rate of diffusion Temperature. The higher the temperature, the faster the rate of diffusion Size (mass) of the diffusing substance. The larger the mass of the diffusing particle, the slower its diffusion rate Solvent density As the density of a solvent increases, the rate of diffusion decreases. The molecules slow down because they have a more difficult time getting through the denser medium. If the medium is less dense, diffusion increases. Solubility Nonpolar or lipid-soluble materials pass through plasma membranes more easily than polar materials, allowing a faster rate of diffusion. Surface area. The larger the membrane surface area available for diffusion, the faster is the diffusion rate Diffusion distance (thickness of plasma membranes) The greater the distance over which diffusion must occur, the longer it takes Tonicity Tonicity refers to the ability of a solution to cause a cell to gain or lose water. The tonicity of a solution depends on: Solute concentration that cannot cross the membrane (non penetrating solutes), relative to that inside the cell. Membrane permeability Isotonic “having the same strength” Solution whose concentration of water and solute inside the cell (intracellular fluid) is THE SAME as the concentration outside the cell (extracellular fluid). Example: 0.9% NaCl (normal physiologic saline solution) There will be no net movement of water across the plasma membrane. Water flows across the membrane, but at the same rate in both directions. In an isotonic environment, the volume of an animal cell is stable while flaccid in plant cell. Hypertonic “having greater strength” Solution that has a HIGHER concentration of solute and a LOWER concentration of water than does a cell cytoplasm Example: 2% NaCl solution It will cause water to leave the cell and the cell will shrink or crenate in animal cell and plasmolyzed in plant cell Hypotonic “having lesser strength” Solution that has a LOWER concentration of solute and HIGHER concentration of water than does a cell cytoplasm Example: pure water It will cause water to enter the cell, and thus the cell will swell or even burst (lysis) in animal cell but is normal for plant cell (because of its cell wall). Significance of Plasmolysis Plasmolysis is helpful in determining whether a particular cell is living or dead as plasmolysis does not occur in a dead or nonliving cell. Salting of prickles, meat, fishes etc. and addition of sugar to jams jellies cut fruits etc. prevent their decay by microbes as the latter get killed due to plasmolysis or due to high concentration of salts and sugar. By salting, weeds can be killed from tennis courts and the growth of plants can be prevented in the cracks of the wall. It shows that the cell wall is elastic and permeable Absorption of water by roots hairs. Cell to cell movement of water occurs throughout the plant body. Opening of the stomata through its regulation of the turgidity of guard cells. This turgidity of guard cells is due to osmotic entry of water in guard cells. Osmotic pressure helps in the growth of young cells by playing role in cell elongation. Turgidity of plant cells. High osmotic concentration in plants increases the resistance against freezing temperature and drought. Osmosis keeps all the organs of plant body fully expanded. Autochory (self-dispersal of seeds) of some fruits is dependent upon release of turgor pressure, which is developed due to osmotic entry of water. Osmosis provides mechanical support to non woody plants by making its cells fully turgid Simple Diffusion Movement of solute molecules from an area of higher concentration to an area of a lower concentration of that solute in solution Substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins Osmosis Movement of water (solvent) across a semi-permeable membrane from an area of high water concentration to an area of low water concentration water diffuses from the less concentrated solution (fewer solute molecules and more water molecules), into the more concentrated solution (more solute molecules and fewer water molecules) until the solute concentrations on both sides of the membrane are equal. Conditions to occur: The cell membrane is less permeable, selectively permeable, or not permeable to solutes A concentration gradient for water exists across cell membrane Facilitated Diffusion assists a specific substance into or out of cells from a higher to lower concentration of that substance With the aid of one of two types of transport proteins: channel and carrier proteins Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion move through this process Channel-mediated Facilitated Diffusion A solute moves down its concentration gradient across the lipid bilayer through a membrane channel Function by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane Aquaporins -passage of water molecules through the membrane in certain cells Ion channels/gated channels - open or close in response to a stimulus (electrical/chemical) Examples of substance that pass through Channel-mediated FD: Ions (Na+, K+, Ca+) and water Carrier-mediated Facilitated Diffusion A carrier (also called a transporter) moves a solute down its concentration gradient across the plasma membrane Carriers are integral membrane proteins that undergo changes in shape in order to move substances across the membrane by facilitated diffusion. Example of substance that pass through carrier-mediated FD: glucose and other sugars Active Transport movement of solutes against a concentration gradient (from lower concentration to higher concentration gradient) across a cell membrane; “uphill” movement uses CELLULAR ENERGY (in the form of ATP) to move molecules across the plasma membrane a carrier-mediated processuses active transport-proteins which span the width of the membrane Example: Na+K+ pump Active transport enables a cell to maintain internal concentrations of small solutes that differ from concentrations in its environment. Bulk Transport Active process in which substances move into or out of cells in vesicles that bud from plasma membrane Particles are transported in large amounts or in bulk without actually passing or crossing the membrane Requires energy supplied by ATP Examples of substance pass through bulk transport: proteins and polysaccharides Exocytosis Particles are transported in large amounts or in bulk “out of the cell” A membrane-enclosed vesicle carrying material to be expelled moves to the cell surface, where the vesicle’s membrane fuses with the cell’s plasma membrane. The vesicle then opens to the extracellular fluid, and its contents diffuse out. Used to dispose of unwanted materials such as products of digestion When plant cells are making walls, exocytosis delivers proteins and carbohydrates from Golgi vesicles to the outside of the cell All cells carry out exocytosis, but it is especially important in two types of cells: secretory and nerve cells (in animals) Endocytosis particles are transported in large amounts or in bulk “into the cell” uptake of material through the cell membrane by formation of vesicle The cell membrane invaginates to form a vesicle containing the material to be taken by the cell. The vesicle then moves into the cytoplasm Phagocytosis the particle to be engulfed is in solid form or chunks of matter. Example: WBC and some other cell types phagocytize bacteria, cell debris, and foreign particles Pinocytosis The particle to be engulfed is in liquid form or a droplet of extracellular fluid Receptor-mediated Endocytosis selectively concentrate specific molecules inside a cell Plasma membranes bear many receptor proteins on their outside surfaces, each with a binding site for a particular molecule Summary Carrier-mediated Energy- requiring Both Transport Mechanism Movement Needs carrier molecule? Requires energy? Simple Diffusion Higher to lower concentration of solute No No Osmosis Higher to lower concentration of water (solvent) No No Facilitated diffusion Higher to lower concentration of molecules Yes No Active transport Lower to higher concentration of substance Yes Yes Endocytosis “into the cell” No Yes Exocytosis “out of the cell” No Yes Photosynthesis The process by which green plants convert light energy into chemical energy stored in the bonds of glucose and releases oxygen food-manufacturing process in plants happens in the chloroplast located in the mesophyll layer of the leaves of plants The reverse process of photosynthesis is Cellular respiration. Photosynthesis - chloroplast Cellular respiration - mitochondria The two can occur at the same time in plant cells since plants have both chloroplast and mitochondria The O2 given off by plants is derived from H2O and not from CO2. 6CO2+6H2O ?C6H12O6+ 6O2 Chloroplasts: The Site of Photosynthesis Chloroplasts are double membranous organelle concentrated in the mesophyll layer of the leaf The leaves are the major sites of photosynthesis in most plants. All green parts of a plant, including green stems and unripened fruit, have chloroplasts Color of leaf is from chlorophyll, the green pigment located within chloroplasts. Chlorophyll resides in the thylakoid membranes Carbon dioxide enters the leaf, and oxygen exits, by way of microscopic pores called stomata (singular, stoma; from the Greek, meaning "mouth"). Water absorbed by the roots is delivered to the leaves in veins. Leaves also use veins to export sugar to roots and other non-photosynthetic parts of the plant. Nature of Sunlight Light is a form of energy known as electromagnetic energy, also called electromagnetic radiation. Electromagnetic waves are disturbances of electric and magnetic fields The distance between the crests of electromagnetic waves is called the wavelength. Wavelengths range from less than a nanometer (for gamma rays) to more than a kilometer (for radio waves). This entire range of radiation is known as the electromagnetic spectrum. The segment most important to life is the narrow band from about 380 nm to 750 nm in wavelength. This radiation is known as visible light because it can be detected as various colors by the human eye. Photosynthetic pigments: the light receptors When light meets matter, it may be reflected, transmitted, or absorbed. Substances that absorb visible light are known as pigments. Different pigments absorb light of different wavelengths, and the wavelengths that are absorbed disappear. If a pigment is illuminated with white light, the color we see is the color most reflected or transmitted by the pigment. If a pigment absorbs all wavelengths, it appears black. We see green when we look at a leaf because chlorophyll absorbs violet-blue and red light while transmitting and reflecting green light. The ability of a pigment to absorb various wavelengths of light can be measured with an instrument called a spectrophotometer. A graph plotting a pigment's light absorption versus wavelength is called an absorption spectrum. The absorption spectra of chloroplast pigments provide clues to the relative effectiveness of different wavelengths for driving photosynthesis, since light can perform work in chloroplasts only if it is absorbed. Light in the violet-blue and red portions of the spectrum is most effective in driving photosynthesis since they are absorbed. Green is the least effective color since they are reflected. Photosynthetic Elements Chlorophyll a main light-capturing pigment in land plants absorbs violet, blue, and red light and reflects blue-green Chlorophyll b absorbs violet, blue, and red light and reflects olive green Chlorophyll a and chlorophyll b differ only in one of the functional groups bonded to the organic structure called a porphyrin ring. Carotenoids hydrocarbons that are various shades of yellow and orange because they absorb violet and blue-green light more important function of at least some carotenoids seems to be photoprotection. These compounds absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen, forming reactive oxidative molecules that are dangerous to the cell. Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes Photosystems are composed of a protein complex called a reaction-center complex surrounded by several light-harvesting complexes Reaction-center complex includes: a special pair of chlorophyll a molecules Light-harvesting complex consists of various pigment molecules (which may include chlorophyll a, chlorophyll b, and carotenoids) bound to proteins. Photosystems are found in the thylakoid membrane. Together, these light-harvesting complexes act as an antenna for the reaction center complex. When a pigment molecule absorbs a photon, the energy is transferred from pigment molecule to pigment molecule within a light-harvesting complex, somewhat like a human "wave” at a sports arena, until it is passed into the reaction center complex. The reaction-center complex contains a molecule capable of accepting electrons and becoming reduced; it is called the primary electron acceptor. These two pigments, P680 and P700, are nearly identical chlorophyll a molecules. However, their association with different proteins in the thylakoid membrane affects the electron distribution in the two pigments and accounts for the slight differences in their light-absorbing properties. Photosystem II Also known as P680 This pigment is best at absorbing light having a wavelength of 680 nm (in the red part of the spectrum). Photosystem I Also known as P700 Most effectively absorbs light of wavelength 700 nm (in the far-red part of the spectrum). Light Reaction (Light-dependent) the photo part of photosynthesis also called Hill’s reaction in honor of Robert Hill, British biochemist for measuring oxygen production in isolated chloroplast Convert light (solar) energy to the chemical energy of ATP and NADPH Do not produce sugar takes place at the THYLAKOIDS of chloroplasts Light energizes electrons in the reaction center Water molecule is splitted by an enzyme into two electrons, two hydrogen ions, and an oxygen atom. These electrons are supplied one by one to the P680+. Hence, water supplies the électrons lost in the P680+. In certain cases, photoexcited electrons can take an alternative path called cyclic electron flow, which uses photosystem I but not photosystem II. There is no production of NADPH and no release of oxygen. Cyclic flow does, however, generate ATP. Example of organisms undergoing cyclic electron flow without photosystem II photosynthetic bacteria can also occur in photosynthetic species that possess both photosystems prokaryotes cyanobacteria Photophosphorylation refers to the use of light energy from photosynthesis to ultimately provide the energy to convert ADP to ATP, thus replenishing the universal energy currency in living things. Chemiosmosis is the movement of ions across a semipermeable membrane, down their electrochemical gradient. Reactants Products Light Reaction Light energy Water ATP (Photosystem II) NADPH (Photosystem I) Oxygen Dark Reaction Carbon Dioxide ATP (Photosystem II) NADPH (Photosystem I) Glucose ADP NADP+ Dark Reaction (Calvin Cycle) the synthesis part uses ATP and NADPH to convert CO2 to sugar otherwise known as Calvin Cycle (or Calvin-Benson Cycle) or the C3 Cycle of Carbon Fixation Occur independently of light as long as ATP and NADPH are available. takes place at the STROMA of chloroplasts Carbon enters the Calvin cycle in the form of CO2 and leaves in the form of sugar. The cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high-energy electrons to make the sugar. Take note: The carbohydrate produced directly from the Calvin cycle is actually not glucose, but a three-carbon sugar glyceraldehyde-3-phosphate (G3P). Recall that carbon fixation refers to the initial incorporation of CO2 into organic material. For the net synthesis of one molecule of G3P, the cycle must take place three times, fixing three molecules of CO2 As we trace the steps of the cycle, keep in mind that we are following three molecules of CO2 through the reactions. For the net synthesis of one G3P molecule, the Calvin cycle consumes a total of: 9 molecules of ATP 6 molecules of NADPH The light reactions regenerate the ATP and NADPH. The G3P spun off from the Calvin cycle becomes the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates. Neither the light reactions nor the Calvin cycle alone can make sugar from CO2, Photosynthesis is an emergent property of the intact chloroplast, which integrates the two stages of photosynthesis. Phase 1: Carbon Fixation The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose 1,5 bisphosphate (RuBP). The enzyme that catalyzes this first step is RuBP carboxylase, or rubisco. (This is the most abundant protein in chloroplasts and is also said to be the most abundant protein on Earth.) The product of the reaction is a six-carbon intermediate so unstable that it immediately splits in half, forming two molecules of 3-phosphoglycerate (for each CO2 fixed). Phase 2: Reduction or Synthesis of G3P Each molecule of 3-phosphoglycerate receives an additional phosphate group from ATP, becoming 1,3-bisphosphoglycerate. Next, a pair of electrons donated from NADPH reduces 1,3-bisphosphoglycerate, which also loses a phosphate group, becoming glyceraldehyde-3-phosphate (G3P). Specifically, the electrons from NADPH reduce a carboyxl group on 1,3-bisphosphoglycerate to the aldehyde group of G3P, which stores more potential energy. G3P is a sugar-the same three-carbon sugar formed in glycolysis by the splitting of glucose. Note: For every three molecules of CO2 that enter the cycle, there are six molecules of G3P formed. But only one molecule of this three-carbon sugar can be counted as a net gain of carbohydrate. The cycle began with 15 carbons’ worth of carbohydrate in the form of three molecules of the five-carbon sugar RuBP. Now there are 18 carbons' worth of carbohydrate in the form of six molecules of G3P. One molecule exits the cycle to be used by the plant cell, but the other five molecules must be recycled to regenerate the three molecules of RuBP. Phase 3: Regeneration of the CO2 acceptor (RuBP) In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle into three molecules of RuBP. Through a series of reactions requiring ATP energy, 10 of the 12 molecules of G3P (10 x 3 carbons) regenerate the six molecules of RuBP (6 x 5 carbons). The remaining molecules of G3P will be used to synthesize glucose. To accomplish this, the cycle spends three more molecules of ATP. The RuBP is now prepared to receive CO2 again, and the cycle continues. Photorespiration and Carbon Fixation in C3, C4, CAM Plants A wasteful pathway that occurs when the Calvin cycle carbon-fixing enzyme rubisco, acts on oxygen rather than carbon dioxide. It uses up fixed carbon, wastes energy, and tends to happens when plants close their stomata (leaf pores) to reduce water loss. High temperatures make it even worse A biochemical process in plants in which, especially under conditions of water stress, oxygen inhibits the Calvin cycle, the carbon fixation portion of photosynthesis. right635000C3 Plants 85% of the plant species in the planet “Normal" plants—one that doesn't have photosynthetic adaptations to reduce photorespiration Rice, wheat, and soybeans are C3 plants that are important in agriculture In most plants, initial fixation of carbon occurs via rubisco, the Calvin cycle enzyme that adds CO2 to ribulose bisphosphate. Such plants are called C3 plants because the first organic product of carbon fixation is a three-carbon compound, 3-phosphoglycerate. When their stomata partially close on hot, dry days, C3 plants produce less sugar because the declining level of CO2 in the leaf starves the Calvin cycle. In addition, rubisco can bind O2 in place of CO2. As CO2 becomes scarce within the air spaces of the leaf, rubisco adds O2 to the Calvin cycle instead of CO2. right698400The product splits, and a two-carbon compound leaves the chloroplast. Peroxisomes and mitochondria rearrange and split this compound, releasing CO2. The process is called photorespiration because it occurs in the light (photo) and consumes O2 while producing CO2 (respiration). Unlike normal cellular respiration, photorespiration generates no ATP; in fact, photorespiration consumes ATP. Unlike photosynthesis, photorespiration produces no sugar. In fact, photorespiration decreases photosynthetic output by siphoning organic material from the Calvin cycle and releasing CO2 that would otherwise be fixed. C4 Plants so named because they preface the Calvin cycle with an alternate mode of carbon fixation that forms a four-carbon compound as its first product. Several thousand species in at least 19 plant families use the C4 pathway. Among the C4 plants important to agriculture are sugarcane and corn, members of the grass family. right-228600A unique leaf anatomy is correlated with the mechanism of C4 photosynthesis. Two distinct types of photosynthetic cells: Bundle-sheath cells arranged into tightly packed sheaths around the veins of the leaf. Mesophyll cells Between the bundle sheath and the leaf surface More loosely arranged CAM Plants right31178500Many succulent (water-storing) plants, numerous cacti, pineapples, and representatives of several other plant families that uses Crassulacean acid metabolism (CAM) pathway to minimize photorespiration during hot, arid day. Named after the plant family Crassulaceae, the succulents in which the process was first discovered. These plants open their stomata during the night and close them during the day, just the reverse of how other plants behave. Closing stomata during the day helps desert plants conserve water, but it also prevents CO2 from entering the leaves. During the night, when their stomata are open, these plants take up CO2 and incorporate it into a variety of organic acids. This mode of carbon fixation is called crassulacean acid metabolism, or CAM The mesophyll cells of CAM plants store the organic acids they make during the night in their vacuoles until morning, when the stomata close. During the day, when the light reactions can supply ATP and NADPH for the Calvin cycle, CO2 is released from the organic acids made the night before to become incorporated into sugar in the chloroplasts C3 Plants C4 Plants Photosynthesis occurs in mesophyll tissues Photosynthesis occurs both in mesophyll and bundle sheath cells The carbon dioxide acceptor is RuBisco The carbon dioxide acceptor is PEP carboxylase Krantz anatomy is absent Krantz anatomy is present The 1st stable compound formed is 3C compound called 3-Phospho Glyceric Acid (PGA) The 1st stable compound is 4-carbon Oxaloacetic acid (OAA) The optimum temperature is 20-25 degrees Celsius The optimum temperature is 35-44 degrees Celsius Photorespiratory loss is high Photorespiration does not take place. Basic Plant Cell and Tissue Types Root Root System Stem Shoot System Leaves Plant Tissues Permanent Dermis Tissue System Epidermis Periderm Ground Tissue System Parenchyma Chlorenchyma Storage Parenchyma Aerenchyma Stellate Parenchyma Collenchyma Sclerenchyma Fibers Bast Fibers Hard Fibers Sclereids Brachysclereids Macrosclereids Osteosclereids Astrosclereids Vascular Tissue System Xylem Tracheids Vessel elements Phloem Sieve-tube elements Companion cells Meristem Apical Meristem Protoderm Ground Meristem Procambium Lateral Meristem Cork Cambium Vascular Cambium Intercalary Meristem Dermal Tissue System The plant's outer protective covering. forms the first line of defense against physical damage and pathogens. Functions: Protection Prevention of water loss Epidermis Periderm Characteristics Cuticle; stomata guard cells; trichomes cork tissue (phellem), cork cambium (phellogen) phelloderm Location Outermost layer of cells of the primary plant body (roots, stems, and leaves) Initial periderm generally beneath epidermis; subsequently formed periderms deeper in bark Functions Protection Prevention of water loss (cuticle) Replaces epidermis as protective tissue in roots and stems Epidermis The outermost cell layer that covers the leaves, stems, and roots of young plants but also covers flowers, seeds and fruit. Composed of tightly packed cells In herbaceous (nonwoody) plants The epidermis forms the outer covering of the entire plant body throughout its life. Features of Epidermis Cuticle Waterproof covering of the epidermal tissue of leaves and stems characteristic of all plant surfaces exposed to air, even extending through the stomatal pores. Function: Prevents water loss; protects plants from desiccation Trichomes Hair-like outgrowths of the shoot epidermis Plants growing in arid habitats tend to have hairier leaves than similar plants from more mesic habitats. Functions: reduce water loss reflect excess light can also provide defense against insects by forming a barrier or by secreting sticky fluids and toxic compounds Stomata (singular: stoma) openings or pores in the epidermis, each bounded by two guard cells. The primary role of stomata is to regulate the exchange of water vapor and of CO2 between the internal tissues of the plant and the atmosphere. Stomata occur on all aerial parts of the primary plant body but are most abundant on leaves. Guard cells kidney shaped cells surrounding the stoma regulate the opening and closing of the stomata using turgor pressure. Periderm Protective tissue that replaces epidermal tissue on the roots and stem of woody plants as they age Herbaceous (nonwoody) plants do not have periderm composed primarily of: cork cell (phellem), which have thick, waterproof walls and are dead at maturity. cork cambium (phellogen) that gives rise to cork cells. Ground Tissue System Make up the bulk of a young plant Consists of all non-dermal and nonvascular tissues Otherwise known as the fundamental tissue system includes the tissues that form the ground substance of the plant but at the same time show various degrees of specialization. Pith Ground tissue that is internal to the vascular tissue Cortex ground tissue that is external to the vascular tissue Parenchyma Collenchyma Sclerenchyma Fiber Sclereid Shape Polyhedral (many-sided) Elongated Very long Shorter than fibers Cell wall Primary (most) primary and secondary lignified or cutinized Unevenly thickened Primary cell wall only Non-lignified Primary and thick secondary lignified Primary and thick secondary lignified At maturity Living Living Dead Living/Dead Functions Photosynthesis Storage Respiration Digestion Division Protection Secretion of hormones; and excretion Support in the primary plant body Flexible support to young parts or growing regions of the plant shoot Support and strengthening the plant body Storage Support and strengthening the plant body Protection Location Pith and cortex Mesophyll of leaves Flesh of succulent fruits Endosperm of seeds In xylem and phloem Sides of the young stems and in the stalk and midrib of leaves On the periphery (beneath the epidermis) in young elongating stems Sometimes in cortex of stems Most often associated with xylem and phloem In leaves of monocots Throughout the plant body Parenchyma Most common and most abundant of the ground tissues constituting all soft parts of the plant body Fundamental or ground tissue in which other tissues, notably the vascular tissue, are embedded. Although most parenchyma cells only have relatively thin and flexible primary, nonlignified cell walls, certain parenchyma cells especially those associated with the secondary xylem develop secondary wall and become lignified. Specialized Parenchyma Cells Chlorenchyma Photosynthetic parenchyma cells that contain chloroplasts regardless of their location. Photosynthesis Storage Parenchyma Abundant in starch-containing amyloplasts, protein, and oil bodies, e.g. seeds Chromoplast-containing cells, e.g. flowers and fruits Storage Aerenchyma Parenchyma cells with large air spaces Enhances the diffusion of air from the leaves to the roots and enables wetland and waterlogged plants to maintain levels of oxygen sufficient to support respiration. Respiration Stellate Parenchyma Highly branched parenchyma cells, with adjacent cells connected to each other by means of the branches A form of aeration tissue (aerenchyma) in plants, which helps with internal air circulation in plants The tissue is typical of aquatic and wetland plants, and consists of cells with large intercellular spaces that allow air supply to underwater plant parts. Collenchyma A living tissue composed of more or less elongated cells with unevenly thickened and nonlignified primary walls. It is a simple tissue being composed of a single cell type, the collenchyma cell. Collenchyma cells are similar with parenchyma cells in having complete protoplasts capable of meristematic activity and photosynthesis. The chief difference lies in the unevenly thickened, thicker walls of collenchyma cells Lack secondary walls, and lignin is absent from their primary walls. Collenchyma cells are found in groups along the sides of the young stems and in the stalk and midrib of leaves, where they provide support. Cell wall thickening begins early in the shoot development and increases simultaneously as the organ elo