Plant BiologyPlant Biology

Understanding the structural organization of plants through meristematic and permanent tissues.

• Meristematic Tissues: Actively dividing cells responsible for plant growth. Classified into apical (length), lateral (girth/secondary growth), and intercalary (internodal elongation).
• Simple Permanent Tissues: Comprise Parenchyma (living, storage, photosynthesis), Collenchyma (living, flexible mechanical support), and Sclerenchyma (dead, rigid support containing lignin).
• Complex Permanent Tissues: Xylem transports water and minerals (composed of tracheids, vessels, xylem parenchyma, and xylem fibers). Phloem transports organic food (composed of sieve tubes, companion cells, phloem parenchyma, and phloem fibers).
• Stomata and Transpiration: Microscopic pores on leaves regulated by guard cells that control gaseous exchange and transpiration. Potassium ions ($K^+$) play a key role in the opening and closing mechanism.

Core biochemical processes enabling plant survival, energy conversion, and nutrient uptake.

• Photosynthesis Equation: $6CO_2 + 6H_2O \xrightarrow{Light/Chlorophyll} C_6H_{12}O_6 + 6O_2$. Oxygen released comes from water photolysis, not carbon dioxide.
• Photosynthetic Pigments: Chlorophyll 'a' is the primary photosynthetic pigment. Chlorophyll 'b', carotenoids, and xanthophylls act as accessory pigments absorbing different light spectra.
• C3 and C4 Pathways: C3 plants (wheat, rice) fix $CO_2$ directly via RuBisCO. C4 plants (maize, sugarcane) have Kranz anatomy and use PEP carboxylase for efficient carbon fixation in high temperatures.
• Respiration in Plants: Occurs via Glycolysis (in cytoplasm) and Krebs cycle / Electron Transport System (in mitochondria), releasing energy as ATP.

Chemical messengers regulating growth, development, flowering, and stress responses in plants.

• Auxins: Discovered by F.W. Went. Promotes cell elongation, apical dominance, and root initiation. Example: Indole-3-acetic acid (IAA).
• Gibberellins (GA): Promotes stem elongation, seed germination, and bolting in rosette plants. Breaks seed dormancy.
• Cytokinins: Promotes cell division (cytokinesis), delays leaf senescence (aging), and overcomes apical dominance.
• Ethylene and Abscisic Acid (ABA): Ethylene is a gaseous hormone promoting fruit ripening. Abscisic Acid (ABA) is a stress hormone inducing stomatal closure and seed dormancy.

Classification of plant kingdom and reproductive mechanisms in flowering and non-flowering plants.

• Plant Kingdom Classification: Divided into Cryptogams (non-seed bearing: Thallophyta, Bryophyta, Pteridophyta) and Phanerogams (seed bearing: Gymnosperms, Angiosperms).
• Bryophytes and Pteridophytes: Bryophytes ('Amphibians of plant kingdom') lack true vascular tissue. Pteridophytes are the first vascular cryptogams possessing xylem and phloem.
• Gymnosperms vs Angiosperms: Gymnosperms bear naked seeds without fruits (e.g., Pinus, Cycas). Angiosperms bear seeds enclosed within fruits, further divided into Monocots and Dicots.
• Sexual Reproduction in Flowering Plants: Stamen is the male reproductive organ (produces pollen); Pistil/Carpel is the female reproductive organ (ovary, style, stigma). Double fertilization is unique to angiosperms.