Plant Biology and Molecular Biology

Cladode is a type of phylloclade consisting of one internode only. These are cylindrical (not fleshy) and are mistaken for leaves

Verticillaster is a complex inflorescence found in the Ocimum sanctum, a member of family Labiatae.

Caryopsis is a one-seeded fruit where the pericarp (fruit wall) is completely fused with the seed coat, making them indistinguishable. This is characteristic of cereals like wheat and maize. Achene has a separate pericarp, cypsela is similar but found in Asteraceae, and nut is a hard one-seeded fruit with unfused walls.

A cistron is defined as the segment of DNA that contains the complete genetic information required to synthesize one polypeptide chain or functional RNA. Muton is the smallest mutable unit, recon is the smallest recombinable unit, and operon is a cluster of functionally related genes.

Alburnum or sap wood is the outer, lighter-colored wood in tree trunks that conducts water and minerals. It contains living cells and is physiologically active. Heart wood is the inner, non-living part; autumn wood and spring wood refer to growth rings formed in different seasons.

Porogamy is the entry of pollen tube through the micropyle, the most common type of pollen tube entry in flowering plants. Mesogamy is through the integuments, chalazogamy is through the chalaza, and anisogamy refers to gametes of different sizes.

Solanaceae family (e.g., tomato, brinjal, Datura) typically shows bicarpellary syncarpous ovary with axile placentation - where ovules are attached to a central column in a multilocular ovary. Malvaceae has axile placentation but often syncarpous with more carpels; Asteraceae usually shows basal placentation.

Apogamy is the development of a sporophyte (embryo) from a gametophyte without fertilization. Apospory is gametophyte from sporophyte, parthenocarpy is fruit development without fertilization (no embryo formation necessarily), and polyembryony is multiple embryo formation.

Cholodny-Went Theory explains phototropism (bending toward light) through unequal auxin distribution - more auxin accumulates on the shaded side causing cells to elongate more. Photomorphogenesis is light-mediated development, photoperiodism is response to day length, and photorespiration is a wasteful process in C3 plants.

Cleistogamy is seen in underground flowers of Commelina bengalensis which are small and inconspicuous. This plant also bears chasmogamous blue flowers above.

Coconut water (liquid endosperm) is rich in cytokinins, which promote cell division. It's widely used in tissue culture media. Gibberellins promote stem elongation, ethylene controls fruit ripening, and auxin regulates cell elongation and apical dominance.

IAA (Indole-3-Acetic Acid), the natural auxin, is primarily responsible for apical dominance - where the main shoot tip suppresses lateral bud growth. ABA (abscisic acid) is a stress hormone, GA3 promotes elongation and flowering, and C2H4 is ethylene (ripening hormone).

Short day plant (SDP) requires a relatively short day light period (usually 8-10 hrs.) and a continuous dark period of about 14-16 hours for subsequent flowering

After fertilization, the ovary develops into the fruit while the ovules become seeds. The embryo develops from the zygote, and endosperm is the nutritive tissue formed from double fertilization. This is a fundamental concept in plant life cycles.

RuBP (Ribulose-1,5-bisphosphate) is the first compound to accept CO2 in the Calvin cycle (dark phase of photosynthesis). This reaction is catalyzed by RuBisCO enzyme. NADP and Ferredoxin are involved in electron transport, while Cytochrome is part of electron transport chain.

AUG is the universal start codon that codes for methionine and initiates protein synthesis in both prokaryotes and eukaryotes. UUU codes for phenylalanine, UAA is a stop codon, and AAA codes for lysine. The genetic code is nearly universal.

Little leaf disease is a physiological disorder caused by zinc deficiency, where new leaves are extremely small and chlorotic. Zinc is essential for the synthesis of auxin (IAA), and its deficiency leads to stunted growth with characteristic small leaves. Copper, boron, and iron deficiencies cause different symptoms like wilting, corky lesions, or interveinal chlorosis respectively.

Chlorophyll 'a' has the molecular formula C55H72O5N4Mg, containing a porphyrin ring with a magnesium atom at the center. Chlorophyll 'b' differs by having one more oxygen atom (C55H70O6N4Mg). The key difference is the substitution of a formyl group (-CHO) for the methyl group (-CH3) on the porphyrin ring.

Stratification involves exposing seeds to low temperatures and moisture conditions to break seed dormancy and stimulate germination. Scarification involves scratching the seed coat, while vernalization applies to whole plants.

Pyruvic acid from glycolysis enters the mitochondrial matrix and is converted to acetyl-CoA, which then enters the Krebs cycle (citric acid cycle). In this cycle, acetyl-CoA is completely oxidized to CO2 and H2O, generating NADH, FADH2, and GTP/ATP. The Calvin cycle fixes CO2 in photosynthesis, Hill reaction is part of photosynthesis, and nitrogen cycle is a biogeochemical cycle.

Respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed during respiration. For carbohydrates, the ratio is exactly 1 because the molecular formula of glucose (C6H12O6) gives equal moles of CO2 and H2O upon complete oxidation. Fatty acids have RQ less than 1 (about 0.7), organic acids have RQ greater than 1, and nucleic acids have variable RQ depending on their composition.

Kranz anatomy—It is a typical structure in the leaves of plants that have a C₄-pathway of CO₂ fixation. The leaves contain a ring of mesophyll cells, containing a few chloroplasts surroundings a sheath of bundle sheath cells having large chloroplasts involved in the Calvin cycle.

Azotobacter is a free-living, aerobic, nitrogen-fixing bacteria found in soil. Unlike Rhizobium which forms symbiotic associations with legume roots, or Clostridium which is anaerobic, Azotobacter lives independently and fixes atmospheric nitrogen aerobically. Rhodospirillum is a photosynthetic bacteria, not primarily known for free nitrogen fixation.

Sagittaria (arrowhead) is an aquatic plant characteristic of the reed-swamp stage in hydrarch (water-based) succession. Hydrarch succession progresses from phytoplankton to submerged plants to floating plants to reed-swamp stage (with plants like Sagittaria, Scirpus) to sedge meadow to woodland to climax forest. Juncus (rush) is also in reed-swamp, but Sagittaria is more representative. Salix (willow) and Trapa (water chestnut) appear in later stages.

Paddy fields produce methane through anaerobic decomposition of organic matter in flooded soil conditions. Methanogenic archaea break down organic material in the oxygen-depleted environment, releasing methane (CH4) which is a potent greenhouse gas connected with global warming. While CO2 is also a greenhouse gas, paddy fields are specifically noted for methane emissions.