Tamil Nadu HSE Second Year Botany flashcards

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

Heterospory

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

Coralloid roots

Specialised dichotomously branched roots of Cycas that grow upward near the soil surface and contain nitrogen-fixing cyanobacteria in a symbiotic association.

Lichen symbiosis

Mutualistic association of a fungus and an alga. The fungus provides shelter and absorbs minerals; the alga photosynthesises and supplies carbohydrate. Lichens are pollution indicators.

Protonema

The first stage of a moss gametophyte, a green branched filament that develops from a germinating spore and later produces the leafy shoot.

Binomial nomenclature rules

Each species has a two-word Latin name: genus capitalised, specific epithet lower case, both italicised or underlined, followed by the author's abbreviated name.

Holotype

The single specimen designated by the author as the permanent reference for a new species name; it anchors the identity of that name in nomenclature.

Bentham and Hooker system

A natural classification published in Genera Plantarum that arranges dicotyledons before monocotyledons, based mainly on floral and seed characters.

Numerical taxonomy

Classification using many equally weighted characters, each scored and compared numerically, so that overall similarity determines grouping rather than a few key features.

Fluid mosaic model

Description of the plasma membrane as a phospholipid bilayer with proteins floating in or spanning it; explains selective permeability and membrane fluidity.

Synaptonemal complex

Protein structure formed between paired homologous chromosomes during zygotene of prophase I; it holds homologues together and enables crossing over.

Cell plate formation

Cytokinesis in plant cells, where vesicles from the Golgi apparatus fuse at the equator to build a new cell wall between daughter nuclei.

Cristae

Infoldings of the inner mitochondrial membrane that increase surface area for the electron transport chain and ATP synthase during oxidative phosphorylation.

Test cross

Crossing an individual of unknown genotype with a homozygous recessive parent; appearance of recessive offspring shows the unknown was heterozygous.

Incomplete dominance

Condition where the heterozygote shows an intermediate phenotype, as in pink Snapdragon flowers; F2 gives 1 red : 2 pink : 1 white.

Semi-conservative replication

Each new DNA molecule keeps one parental strand and one newly synthesised strand; proved in E. coli by the Meselson and Stahl density experiment.

Okazaki fragments

Short DNA pieces synthesised discontinuously on the lagging strand during replication, later joined by DNA ligase into a continuous strand.

Kranz anatomy

Arrangement in C4 leaves where bundle sheath cells with large chloroplasts surround vascular bundles, and mesophyll cells fix CO2 into four-carbon acids.

Photorespiration

RuBisCO fixes O2 instead of CO2, forming phosphoglycolate and wasting energy; high in C3 plants at high temperature and high oxygen concentration.

Water potential

The sum of solute potential and pressure potential; water moves from regions of higher water potential to lower water potential across membranes.

Plasmolysis

Shrinkage of protoplast away from the cell wall when a plant cell loses water in a hypertonic solution; reversed by placing the cell in pure water.

Apical dominance

Suppression of lateral bud growth by auxin produced in the shoot apex; removing the apex releases lateral buds.

Vernalization

Induction of flowering by exposure to low temperature in biennials such as winter wheat; perceived at the shoot apex and remembered through subsequent growth.

Phytochrome

Pigment existing as Pr and Pfr forms; red light converts Pr to the active Pfr form, which regulates flowering, seed germination and photomorphogenesis.

Richmond-Lang effect

Delay of leaf senescence by cytokinins, which maintain protein and chlorophyll levels in treated leaves.

Double fertilization

In angiosperms, one male gamete fuses with the egg and the second fuses with two polar nuclei, forming zygote and triploid endosperm nucleus.

Polygonum type embryo sac

The common eight-nucleate, seven-celled embryo sac with three antipodals, two synergids, one egg and a central cell with two polar nuclei.

Cleistogamy

Condition in which flowers never open and self-pollination occurs within the closed bud, ensuring seed set without pollinators.

Apomixis

Formation of seeds without fertilisation, as by nucellar embryony in Citrus; offspring are genetically identical to the mother plant.

Ten per cent law

Rule that only about ten per cent of energy at one trophic level is transferred to the next, so food chains rarely exceed four or five levels.

Biological magnification

Increase in concentration of non-degradable pollutants such as DDT along a food chain, reaching highest levels in top carnivores.

In-situ conservation

Conservation of species within their natural habitat through national parks, wildlife sanctuaries and biosphere reserves, allowing natural evolution to continue.

Bt cotton

Transgenic cotton carrying cry genes from Bacillus thuringiensis that make the plant toxic to bollworm larvae, reducing insecticide use.