Tamil Nadu HSE First Year Botany flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Binomial nomenclature

System of naming organisms with two Latin words, genus and species epithet, devised by Linnaeus; genus is capitalised, species lower-case, and both are italicised.

Heterospory

Production of two kinds of spores, microspores and megaspores, by the same plant; seen in Selaginella and Salvinia, and it is the precursor to the seed habit.

Coralloid roots

Specialised dichotomously branched roots of Cycas that grow above ground and harbour nitrogen-fixing cyanobacteria such as Anabaena and Nostoc in a symbiotic association.

Phylloclade

A flattened, green, fleshy stem that performs photosynthesis and stores water, as in Opuntia; leaves are reduced to spines to limit transpiration.

Free central placentation

Type of placentation where ovules are borne on a central axis that is not connected to the ovary wall by septa, as in Dianthus and Primrose.

Pneumatophores

Negatively geotropic, breathing roots that grow vertically above the soil or water surface in mangrove plants such as Rhizophora, helping in gaseous exchange.

Fluid mosaic model

Model proposed by Singer and Nicolson describing the plasma membrane as a fluid phospholipid bilayer with proteins floating in or spanning it, allowing lateral movement.

Enzyme active site

Specific pocket of an enzyme where substrate binds and catalysis occurs; its shape is complementary to the substrate, explaining the lock-and-key specificity.

Ribosome

Non-membranous organelle that is the site of protein synthesis; prokaryotic cells have 70S ribosomes while eukaryotic cells have 80S ribosomes.

Crossing over

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during pachytene of prophase I, producing new allele combinations.

Apical dominance

Inhibition of growth of lateral buds by auxin produced in the terminal bud; removing the apex releases lateral buds and makes the plant bushy.

Vernalisation

Promotion of flowering by exposing plants to a period of low temperature, as in winter wheat; it prevents flowering until after winter cold.

Cyclic photophosphorylation

Light-driven electron flow involving only photosystem I, returning electrons to the same reaction centre and generating ATP without NADPH or oxygen release.

RuBisCO

Enzyme that catalyses carbon fixation in the Calvin cycle by attaching CO2 to RuBP; it can also bind oxygen, initiating photorespiration.

Respiratory quotient

Ratio of carbon dioxide released to oxygen consumed during respiration; about 1.0 for carbohydrates, less than 1.0 for fats and proteins.

Water potential

Measure of free energy of water per unit volume, expressed as solute potential plus pressure potential; pure water at atmospheric pressure has a value of zero.

Cohesion-tension theory

Explanation of ascent of sap in which transpiration pull creates tension in xylem, and cohesion between water molecules keeps the continuous water column intact.

Guttation

Loss of water as liquid droplets from hydathodes at leaf margins, caused by root pressure when transpiration is low, commonly seen in grasses.

Hydroponics

Technique of growing plants in a nutrient solution without soil, used to identify essential mineral elements and their deficiency symptoms under controlled conditions.

Nitrogenase

Oxygen-sensitive enzyme complex that catalyses biological nitrogen fixation, reducing atmospheric nitrogen to ammonia in organisms such as Rhizobium and Azotobacter.

Critical concentration

Minimum concentration of an essential element in plant tissue below which normal growth and metabolism are impaired, producing deficiency symptoms.

Double fertilisation

Process unique to angiosperms in which one male gamete fuses with the egg and the second fuses with two polar nuclei, forming zygote and triploid endosperm.

Apomixis

Formation of seeds without fertilisation, producing embryos genetically identical to the mother plant; it is exploited to preserve hybrid vigour in crops.

Polyembryony

Occurrence of more than one embryo in a single seed, as in Citrus, caused by cleavage of the zygote or development of synergids or nucellar cells.

Law of segregation

Mendel's principle that the two alleles of a gene separate during gamete formation, so each gamete receives only one allele of each pair.

Semi-conservative replication

Mode of DNA replication in which each parent strand serves as a template, so every daughter DNA molecule contains one old and one new strand.

Restriction endonuclease

Enzyme that recognises a specific palindromic DNA sequence and cuts the double strand at or near it, producing fragments used in recombinant DNA technology.

Agrobacterium tumefaciens

Soil bacterium whose Ti plasmid transfers T-DNA into plant cells; modified, it is a widely used vector for producing transgenic plants.

Micropropagation

Rapid clonal multiplication of plants from small explants grown on sterile nutrient medium under controlled conditions, using totipotency of plant cells.

Bt cotton

Transgenic cotton carrying cry genes from Bacillus thuringiensis that produce insecticidal proteins toxic to bollworm larvae, reducing pesticide use.

Biofertiliser

Preparation containing living microorganisms such as Rhizobium, Azotobacter or mycorrhizal fungi that enrich soil nutrients and improve plant growth without chemical fertilisers.

Polar nuclei

Two nuclei present in the central cell of the mature embryo sac; they fuse with one male gamete during triple fusion to form the triploid primary endosperm nucleus.