plant kingdom

• Artificial system of classification:

  • Earliest system of classification
  • Given by Carolus Linnaeus
  • Based on superficial morphological characters or vegetative characters such as habit, color, number, and shape of leaves
  • Drawbacks:
  • Separated closely related species as they were based on few characteristics
  • Equal weightage to both sexual and vegetative characters, which is unacceptable as vegetative characters depend on habitat and easily change
• Natural system of classification:

  • Based on natural affinities among the organisms
  • Considers not only external features but also internal features like structure, anatomy, embryology, and phytochemistry
  • Classification for flowering plants was given by George Bentham and Joseph Dalton Hooker
• Phylogenetic system of classification:

  • Based on evolutionary relationships between various organisms
  • Assumes that organisms belonging to the same taxa have a common ancestor
• Numerical Taxonomy:

  • Classifying with the help of computers
  • Number and codes are assigned to all the characters
  • Each character is given equal importance
• Algae:

  • Chlorophyll-bearing, simple, thalloid organisms
  • Photosynthetic autotrophic and symbiotic
  • Largely aquatic, occurring in freshwater, marine environments, moist stones, soils, and wood
  • Variable in form and size, ranging from unicellular microscopic algae to few meters long
  • Commonly found green algae: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara
• Algae Reproduction:

  • Vegetative reproduction:
  • By fragmentation, each fragment develops into a thallus
  • Asexual reproduction:
  • Production of different types of spores, with zoospores being the most common
  • Zoospores are flagellated and germinate to give rise to new plants
  • Sexual Reproduction:
  • Fusion of two gametes, which can be flagellated and similar in size (isogamous) or dissimilar in size (anisogamous)
  • Fusion between a large, non-motile female gamete and a smaller, motile male gamete is termed oogamous
• Benefits of Algae:

  • Half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis
  • Increase the level of dissolved oxygen in their immediate environment
  • Primary producers in aquatic environments
  • Some species used as food, others produce hydrocolloids commercially
  • Algae like Chlorella and spirulina are used as food supplements
• Classes of Algae:

  • Chlorophyceae (Green algae):
  • Plant body may be unicellular, colonial, or filamentous
  • Chloroplasts may have different shapes
  • Most members have storage bodies called pyrenoids
  • Phaeophyceae (Brown algae):
  • Found primarily in marine habitats
  • Range from simple branched forms to large kelps
  • Food stored as complex carbohydrates
  • Rhodophyceae (Red algae):
  • Majority are marine, especially in warmer areas
  • Multicellular with complex body organization
  • Food stored as floridean starch
• Reproduction in Algae:

  • Chlorophyceae:
  • Vegetative reproduction by fragmentation or spores
  • Asexual reproduction with flagellated zoospores
  • Sexual reproduction with variation in sex cell formation
  • Phaeophyceae:
  • Vegetative reproduction by fragmentation
  • Asexual reproduction with pear-shaped biflagellated zoospores
  • Sexual reproduction can be isogamous, anisogamous, or oogamous

  
  

  • Rhodophyceae:
  • Vegetative reproduction by fragmentation
  • Asexual reproduction by non-motile gametes
  • Sexual reproduction is oogamous
• Bryophytes:

  • Divided into mosses and liverworts
  • Occur in damp, humid, and shaded localities
• Algae:

  • Green algae (Chlorophyceae)
  • Brown algae (Phaeophyceae)
  • Red algae (Rhodophyceae)
• Major pigments:

  • Green algae: Chlorophyll a,b
  • Brown algae: Chlorophyll a,c, fucoxanthin
  • Red algae: Chlorophyll a,d, Phycoerythrin
• Stored food:

  • Green algae: Starch
  • Brown algae: Mannitol, laminarin
  • Red algae: Floridean starch
• Cell wall composition:

  • Green algae: Cellulose
  • Brown algae: Cellulose and algin
  • Red algae: Cellulose
• Flagellar number & position of insertion:

  • Green algae: 2-8, equal, apical
  • Brown algae: 2, unequal, lateral
  • Red algae: Absent
• Habitat:

  • Green algae: Fresh water, salt water, & brackish water
  • Brown algae: Fresh water (rare), salt water & brackish water
  • Red algae: Fresh water (some), salt water (most), & brackish water
• Bryophytes:

  • Amphibians of the plant kingdom because they can live in soil but need water for sexual reproduction
  • Body is more differentiated than algae with thalloid structure and prostrate or erect, attached to the substratum by rhizoids
  • Lack true roots, stem, or leaves, may possess root-like, leaf-like, or stem-like structures
  • Main body is haploid and produces gametes, called a gametophyte
• Economic importance of bryophytes:

  • Used as peat
  • High water holding capacity so used in packing
• Reproduction in bryophytes:

  • Sex organs are multicellular
  • Male sex organ is antheridium, produces anterozoids
  • Female sex organ is archegonium, produces a single egg
  • Zygotes do not undergo reduction division immediately, produce a sporophyte attached to the gametophyte
• Liverworts:

  • Simpler than mosses
  • Found in moist shady areas like banks of streams, marshy ground, damp soil, bark of trees, and deep in the woods
  • Plant body is thalloid, dorsiventral, and closely appressed to the substrate
• Reproduction in liverworts:

  • Asexual reproduction by fragmentation of thalli or with gemmae
  • Sexual reproduction with male and female sex organs produced on the same or different thalli
• Mosses:

  • Main body is a gametophyte
  • Predominant stage is the gametophyte stage
  • Gametophyte stage has protonema stage and leafy stage
  • Attached to soil through rhizoids
• Reproduction in mosses:

  • Reproduction through fragmentation and budding in secondary protonema
  • Sexual reproduction with antheridium and archegonium
• Pteridophytes:

  • Have true roots, stems, leaves
  • Found in cool, shady, damp areas and sandy soil conditions
  • Main sporophyte phase is diploid
  • Body is well-differentiated
• Reproduction in pteridophytes:

  • Sporophytes bear sporangia subtended by sporophylls
  • Sporangia produce spores by meiosis, germinate to give rise to gametophytes
  • Gametophytes bear antheridia and archegonia, require cool, damp, shady places to grow
• Gymnosperms:

  • Ovules not enclosed by ovary wall, remain exposed
  • Roots generally tap roots, some have mycorrhizal association
  • Always woody or tall plants, no herbaceous plants
  • Leaves adapt, needle-like leaves reduce surface area, thick cuticle and sunken stomata reduce water loss
• Reproduction in gymnosperms:

  • Heterosporous, produce haploid microspores and megaspores
  • Some leaves modified into sporophylls arranged to form lax cones