Plant Anatomy PDF

What does Plant Anatomy mean? This course is an introduction to the basic internal structure of plants, including their cells, tissues, and organs. Robert Whittaker (1920-1980), an American scientist and the first one to propose a five-kingdom classification of living things. The stru...

What does Plant Anatomy mean? This course is an introduction to the basic internal structure of plants, including their cells, tissues, and organs. Robert Whittaker (1920-1980), an American scientist and the first one to propose a five-kingdom classification of living things. The structure of the plant cell  I. The Protoplast  Protoplast is a biological term used to refer to the entire cell, excluding the cell wall.  It can be classified into cytoplasm, cell organelles and ergastic substances.  Cytoplasm It is viscous, transparent in visible light, circulate (cytoplasmic streaming), chemically composed of water (85-90 %), proteins, organic and inorganic substances.  Plasma membrane or Plasmalemma  is a single, thin, semipermeable membrane, occurs on the outer surface of the cytosol (thus called ectoplast).  provides a surface area for many biochemical processes inside the cell and gives it the flexibility.  regulates the movement of substances into and out of the cell.  is involved in the production of cellulose for cell wall building  There is another single inner cytoplasmic membrane called the tonoplast that surrounds the vacuoles and regulates the movement of substances to inside or outside the vacuole.  Vacuole Occupying more than 90% of the volume of most mature plant cells. Filled with watery fluid called cell sap which is slightly acidic and help to maintain pressures within the cell. Contain inorganic ions, sugars, enzymes and complex organic materials, or water soluble pigments called anthocyanins that are responsible for the red, blue or purple color of many flowers and leaves.  a. Nucleus It is the largest organelle within the cell, easily observed by Microscope. It is spheroid or ovoid in shape. It is bounded by double membranes (nuclear membranes) that are perforated by numerous pores (nuclear pores) that permit the movement of materials from the interior of the nucleus to the cytoplasm It contains one or more nucleoli (that are not bounded by membranes) and chromatin threads which are embedded in a granular fluid called nucleoplasm. Function 1. It is the control center of the cell. 2. It stores the genetic material of the cell (DNA) in the form of chromatin threads which regulate gene expression and cell division.  b. Plastids: Plastids are characteristic of plant cells. They are absent in bacteria, fungi and blue-green algae. They vary in shape, size and pigmentation. They are bounded by double membranes. Types of plastids  1. Chloroplasts (Green plastids): The two membranes surround a fluid called stroma. suspended in the stroma are thylakoides which are discs that form stacks or grana. These stacks contain green chlorophyll (photosynthetic pigment) and other pigments, and are interconnected by tubes (lamellae). The photosynthetic pigments are oriented in the stacks to capture as much light energy as possible.  Etioplasts They are the site of photosynthetic assimilation and the synthesis of starch due to the presence of chlorophyll pigment. Chloroplasts that have not been exposed to light are known as etioplasts. If a plant is kept away from light for several days, its normal chloroplasts will actually convert into etioplasts. Etioplasts lack active pigment and their high concentrations in plant cells will cause leaves to appear yellow rather than green. After exposure to sun light, the stimulation of chlorophyll synthesis takes place and etioplasts are converted again into chloroplasts 2. Chromoplasts (Colored plastids)  They are containing non-photosynthetic pigments (red, yellow or orange) responsible for the color of many flower petals, fleshy fruits and roots of carrot. They sometimes developed from chloroplasts through internal changes.  3. Leucoplasts (non-pigmented plastids): They are confined to colorless organs (such as subterranean parts). They have the capability to develop chlorophyll when exposed to light (e.g. potato tuber). They include the amyloplasts that synthesize and store starch; elaioplasts that synthesize and store fats and lipids; proteinoplasts that store and modify proteins.  C. Mitochondria (sing. Mitochondrion): They are numerous, tiny organelles, like paddles, rods or balls in shape. They accumulate in groups where energy is needed, and are always in constant motion in living cells.  They are bounded by double membranes (the outer membrane is smooth, while the inner is folded to form cristae which project into the inner space (stroma or matrix) to increase the surface area available for the enzymes. They contain DNA, RNA, ribosomes and proteins. Functions: They are the power houses of the cell. The main center of respiration (i.e. converting the energy stored in reserve substances like lipids, starch and carbohydrates, into high energy molecules (ATPs).  d. Endoplasmic Reticulum (ER): ER is the largest membrane-bound organelle in eukaryotic cells, forming a continuous network of membrane-enclosed sacs called cisternae. It may be associated with the nuclear envelope, or it may be at the cell periphery (plasma membrane). Functions: The ER may be divided into two types: a. Rough ER: appears rough due to the presence of ribosomes on its outer surface. It is the main site for protein synthesis, secretion and storage. b. Smooth ER: appears smooth due to lack of ribosomes. It is the site of lipid synthesis (as phospholipids in plasma membranes).  e-Ribosomes Ribosomes are the protein builders or protein synthesizers of the cell. They are tiny bodies assemble proteins, made up of RNA and proteins, have no boundary membrane, that is why some scientists prefer not to call them organelles. They occur free in the cytoplasm or on the outside of the rough endoplasmic reticulum. They consist of two major components: Small ribosomal subunits: which read the messenger RNA (mRNA). Large ribosomal subunits: which join amino acids to form a polypeptide chain.  F. The Golgi apparatus (Dictyosomes): They are organelles, appear as flattened disc-like membranes (cisternae). Each cisterna is bounded by a single membrane. At the edge of these membranes, small vesicles appear. Function: When proteins come out of the endoplasmic reticulum, they go into the Golgi for further processing. The vesicles used to transport material from the endoplasmic reticulum to Golgi, and transport of synthesized product from Golgi to cell membrane. The vesicles also package proteins that will be used in constructing primary cell wall.  G. Microbodies: They are small, spherical organelles, move freely in the cytoplasm, and bounded by a single membrane. They contain enzymes to carry out specific functions. Peroxisomes Glyoxysomes Lysosomes Peroxisomes: are present in almost all eukaryotic cells. They contain enzymes that detoxify the cell and get rid of toxic hydrogen peroxide produced during metabolism. Glyoxysomes: are specialized peroxisomes found only in plants (particularly in the fat storage tissues of germinating seeds) and filamentous fungi. They contain enzymes that aid in the lipid biosynthesis. Lysosomes: function as the digestive system of the cell. They contain hydrolytic enzymes that can break down many kinds of biomolecules and destroy invading viruses and bacteria. h. The cytoskeleton: It is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells. It extends from the cell nucleus to the cell membrane. It is responsible for contraction, cell motility, movement of organelles and vesicles through the cytoplasm, establishment of the intracellular organization of the cytoplasm and cell polarity, and to give the cell mechanical support.  It is composed of three main components: 1. Microfilaments (actin filaments): They are the main component in the cytoskeleton. They occur in the cell in the form of bundles of parallel fibers. They are composed of the most abundant cellular protein known as actin. They determine the shape of the cell, and help in cell motility. 2. Intermediate filaments: They are very stable structures that form the true skeleton of the cell. They anchor the nucleus and position it within the cell, and they give the cell its elastic properties and its ability to withstand tension. 3. Microtubules: They are longer filaments formed of thin, hollow, tube-like structures, composed of alpha and beta tubulin. They play a crucial role in moving the daughter chromosomes to the newly forming daughter cells during mitosis. They are commonly found inside the plasma membrane to control the addition of cellulose to cell wall, and control the movement of cilia and flagella. Ergastic substances Reserve food materials Secretory products Excretory products  1. Carbohydrates (saccharides): They include soluble monosaccharides (glucose); disaccharides (sucrose), both are commonly referred to as ‘sugars’, in addition to nonsoluble polysaccharides (starch and cellulose). Sucrose is often stored as a food reserve (in sugar beet and sugar cane), while glucose and fructose are often stored in many fruits.  Starch is a polysaccharide chain formed of glucose subunits. It is a temporary product of photosynthesis, formed in chloroplasts, and stored in leucoplasts (amyloplasts). Starch molecules arrange themselves in the plant in semi-crystalline granules (starch grains). Starch grains are spherical, pear-shaped or angular under the microscope. The deposition of starch occurs around a point called hilum. Successive layers of starch encircle the hilum, the position of the hilum may be concentric or eccentric.  potato starch grain It comprises three types; simple ,semicompound and compound starch grains Eccenteric pointed hilum Oval in shape  wheat starch grain concentric pointed hilum spherical in shape  Phaseolus starch grain concentric fissured hilum  Zea starch grains concentric x- or y-shaped hilum  Rice starch grains Copmound starch grains – angular outline , smallest in size, no hilum.  2. Fats, oils and waxes: Fats, oils and waxes are examples of lipids. These are esters with long-chain carboxylic acids and long-alcohols. Fat is the name given to a class of triglycerides that appear as solid or semisolid at room temperature, thus called saturated(with the fatty acid chains have all single bonds). They are mainly present in animals. While, oils are triglycerides that appear as a liquid at room temperature, thus called unsaturated (with one or more double or triple bonds between the molecules). They are mainly present in plants (e.g. soy beans, cotton seeds, nuts, olive, coconuts, palms…etc.).), and fatty fish (e.g. salmon). In plants, the fats and oils are produced by elaioplasts. potato starch grain wheat starch grain Phaseolus starch grain Waxes are widespread in plants, form protective coatings of fatty substances on the epidermis of stems, leaves and fruits.  They divided into three main groups:- (oils ,fats, waxes) (phospholipids) (cholesterol and steroids)  3. Proteins: Proteins are large macromolecules, consisting of one or more long chains of amino acid residues. Plastids that synthesize and store protein are known as proteinoplasts. In many seeds, protein granules are found in solid state and differentiated into globoid and crystalloid bodies and known as aleurone grains (e.g. Castor seeds), or may appear undifferentiated or amorphous (e.g. Wheat grains). 4. Inulin: It is a polysaccharide, occurs in the storage organs of many plants (e.g. onion, banana, garlic, asparagus, wheat, artichoke). For these plants, inulin is used as an energy reserve and for regulating cold resistance. Most plants that synthesize and store inulin do not store other forms of carbohydrate such as starch.  5. Crystals: They are the waste or excretory products of the cytoplasm. They are located primarily in the vacuole but can be found in cytoplasm and cell wall. They provide a reserve of calcium in the cell, in addition to providing a means of removing toxic accumulations of oxalates. They differ in shape and size, and are often deposited within particular cells known as idioblasts. The most common are those composed of Calcium Oxalate salts which are widely distributed metabolic end products (e.g. Druses, Raphides, Solitary…etc.). Also Ca-carbonate crystals are formed in some plants called also (cystolith) and formed in enlarged epidermal cell and has stalk. Ca-oxalate (solitary crystal) e.g. onion scale leaf Ca-oxalate (Raphides crystal) Ca-carbonate crystal (cystolith) Ca-oxalate (druses)  6. Tannins: A heterogenous group of phenol derivatives, appears as granular mass, yellow, red or brown in color, usually formed in idioblasts. May be found in the vacuole, in the cytoplasm or cell wall of leaves, unripe fruits and seed coats (the bitter taste in pomegranate and tea is due to tannins). It protects plant against dehydration, rotting by fungi and bacteria and damage by animals.  7. Other materials: Alkaloids: Nitrogenous compounds, produced by many plant species (e.g. caffeine, nicotine, cocaine, morphine). Flavonoids: They are water soluble compounds, include many pigments (e.g. flavones, anthocyanins), found in flowers, fruits and leaves of many plants and color cell sap with red, purple, violet and blue colors. Glycosides: They are organic compounds, consist of sugar (glucose) combined with an aromatic or any other organic substance. They include many medicinal compounds (e.g. amygdalin, salicin, saponin).