cells

• Plants

  • Bryophytes (liverworts, hornworts, mosses)
  • Pteridophytes (ferns)
  • Gymnosperms (cycads, pines)
  • Angiosperms (seed plants that bear flowers)
• Cell wall

  Rigid outer layer of the cell that surrounds the plasma membrane, protects the cell, and provides mechanical support
• Animal cells do not possess cell walls
• Lignin is a compound in cell walls of plant parts that provides mechanical support
• Cotton thread is made up of one billion cellulose chains, a vital raw material used in textile industries
• Features of plant cells

  • Cell wall, chloroplasts, large vacuoles, plasmodesmata, chemical nature of the intercellular substance
• Lignin is a phenolic compound consisting of para-hydroxybenzoic acid, syringic acid, and vanillic acid
• Plants are unique because they are involved in the biochemical process of photosynthesis
• Main feature that distinguishes animal cells from cells of plants, fungi and bacteria

  • Possession of cell walls surrounding the plasma membrane
• Organisms possessing cell walls

  • Plants
  • Fungi
  • Bacteria
• Plant cells contain all organelles found in animal cells except for lysosomes
• Timber used in building and furniture manufacture comprises tissues made of lignified cell walls
• In some plant tissues like xylem and sclerenchyma, cell walls are impregnated with lignin, providing rigidity
• Syringic acid is a 'taxonomic marker' found only in lignin from angiosperm plants
• Cell wall and chloroplasts only occur in plant cells of leaves and herbaceous stems
• The main function of the vacuoles is to store primary metabolites such as sugars, organic acids and reserve proteins
• A marker is a DNA sequence with a known location in a genome
• Acids


  • para-hydroxybenzoic acid
  • syringic acid
  • vanillic acid
• Chloroplasts are abundantly found in cells of leaf tissues and stems of some herbaceous plants; they are the sites for photosynthesis
• Chlorophyll pigments impart the green colour to the leaves, herbaceous stems and thalli (singular: thallus) of liverworts and fern prothalli (singular: fern prothallus)
• Immature plant cells contain numerous small vacuoles; but as the cell increases in size, these small vacuoles fuse to form a large single vacuole
• Vacuole

  • It is bounded by a membrane technically known as the tonoplast
  • It contains a fluid called the cell sap which contains water, sugars, organic acids, amino acids and inorganic ions
• Recent studies have revealed that 1 mm2 of the leaf area can contain up to 500,000 chloroplasts
• The intercellular substance, which is also called the middle lamella and found in plant cells, binds the adjacent cells together
• The grana [singular: granum] are stacks of flattened vesicles within the chloroplast
• The vacuole is also the site where certain plant pigments are stored
• Pectin is an acidic polysaccharide, also known as polygalacturonic acid
• Anthocyanins are responsible for the various colours exhibited in flowers, fruits and other plant organs
• Fungal cells are different from plant and animal cells in that the cell walls of most fungi, particularly the higher groups of fungi, such as the Zygomycetes Ascomycetes
• Chloroplasts


  • They are characterised by being bounded by two membranes
  • They contain their own variant of DNA
• Another role of the vacuoles is to remove toxic secondary metabolites, such as nicotine and tannin from the rest of the cytoplasm
• Chloroplasts are green organelles (plastids) that contain chlorophylls and carotenoid pigments
• A single mesophyll cell may contain about 50 chloroplasts
• Syringic acid is known as a 'taxonomic marker' because it only occurs in lignin obtained from angiosperm plants (flowering plants), but it is absent in lignin obtained from gymnosperm plants (non-flowering plants e.g. the pines)
• When a particular substance is present in high concentrations, such a compound tends to form crystals, e.g. crystals of calcium oxalate
• The vacuole is a liquid-filled cavity that is located within the cytoplasm
• Plasmodesmata provide a pathway for the transport of molecules from one cell to another neighbouring cell
• In mature cells about 90% of the cell is occupied by the vacuole
• For instance, the blue, purple, violet, and red anthocyanins are located in the vacuole
• Each granum contains structures called thylakoids; they are rich in chlorophylls and carotenoid pigments