Morphology and Morpho-anatomy of Plant Cells

Morphology and Morpho-anatomy

• Morphology is the study of the physical form and structure of organs
• Morpho-anatomy studies the visible and microscopic parts of commodities

Cell Structure

• A cell consists of: • Cell wall • Cytoplasm • Organelles (plastids, mitochondria, vacuole)
• Cell wall components: • Cellulose (most abundant fibrillar component) • Hemicellulose (heterogenous group of polysaccharides) • Pectin (diverse group of hydrophilic, gel-forming polysaccharides)
• Changes in cell wall composition and structure affect fruit and vegetable texture
• Excessive degradation of the structure reduces postharvest life and enhances decay organisms

Plasma Membrane

• Outer fluid boundary of the living cytoplasm
• Selective barrier that allows entry of oxygen, nutrients, and waste
• Consists of a phospholipid bilayer

Cytoplasm

• Contains proteins, carbohydrates, amino acids, lipids, nucleic acids, and other water-soluble substances
• Cytosol: semi-fluid substance filling the interior of the cell and embedding other organelles and subcellular compartments

Mitochondria

• Site of cellular respiration that uses oxygen to produce ATP from sugars, fats, and other fuel sources
• "Powerhouse of the cells"

Plastids

• Cell organelles that only occur in plant cells
• Descended from proplastids in egg cells, becoming various types of plastids (e.g., chloroplasts, chromoplasts, amyloplasts)

Vacuoles

• Occupies 95% of the cell volume, surrounded by a membrane (tonoplast)
• Increase in cell volume is primarily due to enlargement of vacuoles
• Maintain cell turgor by accumulating salts from organic and inorganic acids

Dermal Tissue/Dermal System

• Outer protective layer of the plant, composed of: • Epidermis (tight arrangement of epidermal cells with points of interruption for gas and moisture exchange) • Hypodermis (layer below epidermal cells, where oil cells of citrus are found) • Cuticular membrane (extracellular composite structure with cutin and wax, resisting water loss and pathogen invasion) • Trichomes (single-celled or multicellular appendages on stems and fruits, preventing water loss) • Stomata (opening in epidermis of leaves, fruits, and stems, regulating gas exchange and transpiration) • Lenticels (pores that are always open, permitting oxygen entry and carbon dioxide and water vapor output)

Ground Tissues

• Fill out the three-dimensional bulk of the plant
• Types of ground tissues: • Parenchyma (thin and flexible primary walls; storage site for starches, proteins, oils, etc.) • Collenchyma (elongated cells with thick walls; provide support to elongated stems) • Sclerenchyma (thickened lignified walls; provide permanent support and aid in conduction of water as in xylem)