History of Plant Classification

History of Classification

• Gaspard Bauhin grouped morphologically similar species together in the same genus.
• Carolus Linnaeus (Father of Taxonomy) developed the binomial system of nomenclature for efficiently grouping and naming organisms. He wrote "Species Plantarum" in 1753.
• Antoine-Laurent de Jussieu organized plants systematically in botanical gardens based on their characteristics.
• Charles Edwin Bessey introduced the phylogenetic system of classification to the US and focused on the systematic study of plant morphology.
• Arthur Cronquist wrote "The Evolution and Classification of Flowering Plants" in 1988, which was a groundbreaking work in plant classification.
• Armen Takhtajan is considered one of the greatest botanists in the world, writing about the evolution of plants and publishing "Diversity and Classification of Flowering Plants" in 1997.
• Adolf Engler and Karl Prantl developed a popular system of classification based on the phylogenetic system.

Microscopes

• Scanning Electron Microscope (SEM) uses beam transmission to produce images by detecting secondary electrons. It can magnify objects up to 10,000 times their original size.
• Mechanical Parts of the Microscope:
  • Base: U or V-shaped, provides a stable foundation for the microscope.
  • Arm: Connects the base and the tube, serving as a handle for carrying the microscope.
  • Stage: Holds the slide containing the specimen, with an opening in the center for light to pass through.
  • Stage Clips: Secure the specimen on the stage.
  • Substage: Located below the stage, holds the Abbe condenser and the iris diaphragm.
  • Body Tube: Connects the objective to the eyepiece, allowing light to pass from the objective to the eyepiece.
  • Coarse Adjustment: Used for low power objective (LPO) focusing.
  • Fine Adjustment: Used for high power objective (HPO) focusing.
  • Maturing Face: Also called the Trans face or concave, where vesicles start to swell and are released.
• Magnifying Parts of the Microscope:
  • Eyepiece or Ocular: Detachable cylinder located at the top of the tube with a pointer that rotates.
  • Objectives: Two or three objectives attached to the revolving nosepiece.
    • Scanner Objective: Shortest cylinder with a large opening for low magnification (marked "5x").
    • Low Power Objective: Used to observe the general outline of the specimen.
    • High Power Objective: Longest cylinder with a small opening for higher magnification, used to study detailed parts of the specimen.
    • Oil Immersion Objective: Important for the germination of oily seeds.

Cell Structures

• Endoplasmic Reticulum (ER): A network of narrow tubes and sheets of membrane throughout the cytoplasm.
  • Rough Endoplasmic Reticulum (RER): Has ribosomes attached and is involved in protein synthesis.
  • Smooth Endoplasmic Reticulum (SER): Does not have ribosomes attached and is involved in lipid synthesis.
• Ribosomes: Responsible for protein synthesis, found dispersed in the cytoplasm or attached to the ER.
• Golgi Apparatus: Packages and modifies proteins and enzymes, sorts them into vesicles, and releases them into the cytoplasm.
• Peroxisomes: Detoxify some products of photosynthesis, specialized for oxidative reactions using molecular oxygen. They contain the enzyme catalase.
• Enzyme Catalase: Detoxifies peroxides through chemical reactions, converting it to oxygen and water.
• Plastids: Found in plants and algae, surrounded by inner and outer membranes. Have circular DNA not associated with histones.
  • Stroma: Inner fluids that encircle the grana and thylakoids.
  • Chloroplasts: Disc-shaped, contain chlorophyll for photosynthesis.
  • Chromoplasts: Contain different pigments that give plants their colors.

Nucleus

• Nucleus: The cell’s command center, surrounded by the nuclear envelope, filled with nucleoplasm.
• Four Main Parts of the Nucleus:
  • Nuclear Envelope: Composed of a membrane perforated by numerous pores.
  • Nucleoplasm: Granular fluid inside the nucleus, a type of protoplasm.
  • Chromatin: Contains DNA and proteins, involved in protein synthesis.
  • Nucleolus: The largest and most prominent domain in the nucleus, where ribosomal RNA synthesis occurs.
• Heterochromatin: Tightly packed, less accessible for transcription, restrains the activity of transposable elements.
• Underlying Nuclear Lamina: A fibrous meshwork that provides structural support to the nucleus.
• Nuclear Pore Complexes: Large protein complex controlling the exchange of components between the nucleus and the cytoplasm.

Plant Tissues

• Meristematic Tissues: Cells actively divide and are responsible for the production of new cells.
  • Location:
    • Apical Meristem: Found at the tips of roots and shoots, responsible for growth in length.
    • Lateral Meristem: Located along the sides of roots and stems, responsible for growth in width.
    • Intercalary Meristem: Found at the nodes of stems, responsible for growth in length.
• Permanent Tissues: Mature cells that have lost the ability to divide.
  • Simple Permanent Tissues:
    • Parenchyma: The most abundant tissue type, responsible for food and waste storage.
    • Collenchyma: Provides structural support and flexibility, commonly found in stems and leaves.
    • Sclerenchyma: Provides strength and rigidity to the plant, found in stems, roots, and leaves as fibers and sclereids.
  • Complex Permanent Tissues:
    • Xylem: Transports water and minerals upwards from the roots.
    • Phloem: Transports food downwards from the leaves to other parts of the plant.

Water Relations in Cells and Tissues

• Water: Involved in transport processes within cells.
• Endodermis: The innermost layer of the cortex, a single layer of closely packed barrel-shaped cells with no intercellular spaces. Passage cells, located opposite the protoxylem, are thin-walled.
• Stele or Vascular Cylinder: Occupies the central portion of the root, consisting of the pericycle and vascular tissues.
• Pericycle: Lies internal to the endodermis, a single layer of thin-walled parenchyma cells.
• Root System:
  • Taproot System: Has a main root with lateral branches. Common in dicot plants.
  • Fibrous Root System: Consists of a network of fine roots, common in monocot plants. Important for stabilizing soil and preventing erosion.
  • Lateral Roots: Originating from the pericycle.
• Radicle: The embryonic root, which emerges first from the seed.