Plant Cell Structure Quiz

Medicinal Plants - Lecture Notes

• Medicinal plants are used to cure or prevent disease.
• Their action is through chemicals called active constituents.
• Plants can be annual, biennial, or perennial.
• Annuals live for one year and die after producing flowers, fruits, and seeds.
• Biennials live for two seasons.
• Perennials live for more than two years.

The Cell and Cell Differentiation

• A cell is the fundamental unit of a living organism (plants and animals).
• It's composed of a cell wall, nucleus, cytoplasm, vacuoles (containing crystals and aleurone grains), mitochondria, Golgi bodies, lysosomes, and plastids.
• A group of identical cells performing a specific function is called tissue.
• The cell wall of mature cells consists of the middle lamella (intercellular substance), primary wall (cellulose and pectin), secondary wall (primarily cellulose with polysaccharides), and tertiary wall (thinner cellulose layer).
• Modifications like lignin, suberin, and cutin can occur in the secondary and tertiary walls.

Cell Wall Properties

• Cellulosic Walls: Mostly cellulose, possibly with hemicellulose and pectin (a polysaccharide composed of linear chains of glucose residue).

• These walls stain blue with iodine and sulfuric acid.

• They also stain blue with chloro-zinc-iodine.

• Cellulosic walls don't react with aniline, phloroglucin, or HCl.

• They dissolve in CuO in an ammonia solution.

• Mucilaginous Walls: Certain cellulosic cell walls can be transformed into gums and mucilages.

• These stain with ruthenium red, iodine sulfuric acid, or corallin soda.

• Lignified Walls: Lignin is a strengthening material forming a complex polymer of phenylpropanoid.

• Stain magenta red with phloroglucin and hydrochloric acid.

• Suberized and Cutinized Walls: Suberin and cutin are mixtures of polymerized fatty acids and suberic acid.

• Stain red with alkanna tincture and Sudan III.

• Chitinous Walls: Chitin is a polysaccharide derivative found in insects and fungi.

• Heated with 50% potash at 160-170°C, it's converted into chitosan, ammonia, and acids (acetic and oxalic).

• Gives a deep violet coloration with iodine solution followed by dilute sulfuric acid.

Plant Tissues

• Parenchyma: Is the fundamental or ground tissue with isodiametric or slightly elongated cells. Contains starch granules and calcium oxalate crystals.
• Collenchyma: Is a living mechanical tissue with unevenly thickened, non-lignified walls, found in the angles (angular collenchyma) or tangential walls (lamellar collenchyma) of herbaceous stems, petioles, and leaf midribs.
• Sclerenchyma: Thick-walled, dead, lignified cells primarily meant for support. Sclereids are short, isodiametric cells; Fibres are long, thin, and tapering.

Secretory Tissues

• Found as isolated cells or rows with suberized walls.
• Contents can include volatile oils, resins, gum-resin, mucilage, enzymes, tannins.
• Secretory Cavities (Glands): Internal structures embedded in tissue, containing cavities where secretions (volatile oils, oleoresins, etc.) are secreted. Formed via:
  • Schizogenous (splitting of cells to form a cavity).
  • Schizolysigenous (first schizogenous, then cells break down).
  • Lysigenous (cells break down to form a cavity).
• Secretory Ducts: Tube-like structures, may extend through the entire plant (e.g., in leaves of Pinus). Develop schizogenously, lysigenously, or schizolysigenously (e.g., in Capaifera).
• Laticiferous Structures: Tube-like cells containing latex (colorless, milky emulsion).

Primary Metabolites - Carbohydrates

• Carbohydrates are organic compounds containing C, H, and O. Primary example is starch.
• Starch: A polysaccharide (polymer of glucose) formed through photosynthesis. Plants absorb CO2 and water in presence of chlorophyll & sunlight. Starch molecules link together to form granules.
• Amylose: inner layers of starch granules, soluble in water.
• Amylopectin: outer layers of starch granules, insoluble in water.

Microscopical and Macroscopic Characters of Starch

• Starch occurs as granules in various shapes (irregular, angular, oval).
• Insoluble in cold water but forms a colloidal solution in boiling water.
• Staine deep blue/violet with iodine.
• Gelatinizes on heating with water thus swelling first then dissolving.

Proteins

• Proteins are nitrogenous compounds composed of amino acids. Found in seeds as aleurone grains.
• Aleurone Grains: Small solid protein particles often in seeds. Consist of: ground substance (soluble protein), crystalloid (albumin, insoluble protein), and globoids (containing globulin and calcium/magnesium hexaphosphoric acid).

Lipids

• Lipids include fixed oils, fats, and waxes. Fixed oils are liquids while fats are solids. Waxes are esters.
• Fixed oils and fats hydrolyze to form glycerol and soap with aqueous alkali Hydrolysis by aqueous caustic alkali forms soap and glycerol (specification).

Secondary Metabolites - Special Focus

• Alkaloids: Naturally occurring, nitrogen-containing organic compounds often having marked effects on organisms and may be basic.
• Glycosides: Organic compounds consisting of a sugar part (glycone) and a non-sugar part (aglycone).
• Volatile Oils/Essential Oils: Volatile oils are often aromatic mixtures of hydrocarbons and oxygenated compounds.
• Tannins: Water-soluble polyphenol compounds that bind to proteins (e.g., in tanning leather). Can be classified as hydrolysable (which are hydrolyzed with acids/enzymes) or condensed (not hydrolyzed).

Crystals of Calcium Oxalate

• Calcium oxalate is a common plant component that may be of crystalline structures. They are insoluble and found in many diverse plant parts.
• Forms: Includes acicular (needle shaped), prismatic, rosette, and cluster types (various shapes, orientations, and sizes).

The Stem

• The stem is the main axis of the plant, generally above ground.
• Functions: Support leaves and flowers, conduct water and minerals, and transport food.
• Shapes: Cylindrical, angular, triangular, quadrangular.
• Types: Herbaceous (soft), succulent (fleshy), woody (hard)
• Branching types: Monopodial (main axis continues growing) Sympodial (apical bud stops growing, axillary buds develop into new branches.)

The Root

• The root is the underground portion of the plant.
• Functions: Absorbs water and minerals from the soil, anchors the plant, and stores food.
• Types: Primary roots (main central root—e.g. tap root), Secondary roots (branches).
• Adventitious roots (arise from non-root parts of the plant, e.g., stem).
• Fibrous roots (a system of thin roots).

The Leaf

• Leaves are flattened, lateral outgrowths from the stem usually bearing chlorophyll and serving for photosynthesis and transpiration.
• Parts of the leaf: Lamina (blade—the flattened part), Petiole (stalk), and Base (connection of leaf to stem.)
• Types: Simple (undissected leaf blade), Compound (blade dissected into leaflets)
• Edges of leaves: can have distinct margins (e.g., entire, crenate, dentate, serrate).
• Shape of leaf bases to tips include: ovate, obcordate, etc.
• Types of venation: parallel, reticulate.
• Surface characteristics: smooth, punctate, pubescent etc.

The Flower

• Flowers are specialized structures on plants that facilitate reproduction.
• Floral Parts: Receptacle (support structure), Calyx (sepals—often green), Corolla (petals—often colored), Androecium (male reproductive parts, stamens) Gynaecium (female reproductive parts, the pistil),
• Types of Flowers: Complete (all four whorls), Incomplete (lacking one or more whorls), Regular (actinomorphic, can be divided into two symmetrical halves), Irregular (zygomorphic, division into symmetrical halves is only in one plane).

Inflorescence

• Arrangement of flowers on the plant.
• Two main branching types: Racemose (older flowers generally at the base of the axis or the central axis), Cymose (generally with older flowers at the apex and newer flowers lower down the stem). Capitula (a condensed inflorescence with sessile florets, surrounded by bracts). 

Chromatography

• Chromatography is a lab technique used for separating components of a mixture.
• Main Phases: Stationary phase (a non-moving component, often solid or a liquid coating), Mobile phase (moving substance which may carry various compounds away). 
• Types: Thin layer chromatography (TLC) and Column chromatography,  Gas Liquid Chromatography (GLC).

Crude drug considerations

• Quality control is an important step in using plants for medicinal purposes. 
• Important stages for production: Cultivation, Collection, Drying, Packing, and Preserving.
• The stage of maturity often influences the production and the presence of active substances.
• Environmental Factors including soil health, and season are key to quality.
• Various methods of collection; collection times; processing needs.

Evaluation of Crude Drugs

• Examining crude drugs for identification using various methods (e.g., morphological, microscopic, chemical, biological, or physical characteristics).
• Establishing quality control (checking for impurities and proper storage and handling techniques).
• Ensuring that active constituents are present at proper levels. Aromatic quality; composition; structure; possible adulteration; purity considerations.

Test your knowledge on plant cell structure and composition. This quiz covers components like the cell wall, middle lamella, and the differences between various plant phyla. Brush up on your understanding of mucilaginous walls and lignin characteristics in plant biology.