Class XI Biology Core Concepts Vocabulary Flashcards

Comprehensive vocabulary flashcards covering key definitions, specialized terminology, and physiological concepts across Class XI Biology units.

Binomial Nomenclature

The system of naming living organisms using a two-word format consisting of the Generic name and the specific epithet, introduced by Carolus Linnaeus.

Systematics

The branch of biology dealing with the identification, nomenclature, classification, and evolutionary relationships among diverse organisms.

Taxon

A distinct biological unit or category at any rank within the taxonomic hierarchy (e.g., species, genus, family).

Archaebacteria

Specialized bacteria characterized by a distinct cell wall structure that enables them to survive in extreme habitats like salty areas (halophiles), hot springs (thermoacidophiles), and marshy places (methanogens).

Heterocysts

Specialized cells present in filamentous cyanobacteria such as Nostoc and Anabaena that perform atmospheric nitrogen fixation.

Diatomaceous Earth

The gritty, indestructible cell wall deposits rich in silica left behind by diatoms in their natural habitat over billions of years.

Contagium vivum fluidum

The phrase meaning 'infectious living fluid', coined by M.W. Beijerinck in $1898$ to describe the infectious extract of tobacco plants affected by mosaic disease.

Lichen

A symbiotic association between an algal partner (phycobiont) which prepares food and a fungal partner (mycobiont) which provides shelter and absorbs nutrients.

Hydrocolloids

Water-holding substances commercially obtained from marine algae, such as algin from brown algae and carrageen from red algae.

Protonema

The creeping, green, branched, and filamentous first stage of the moss gametophyte that develops directly from a germinating spore.

Prothallus

An inconspicuous, small, multicellular, free-living, and mostly photosynthetic thalloid gametophyte formed upon germination of pteridophyte spores.

Choanocytes

Specialized collar cells lining the spongocoel and canals of sponges (Phylum Porifera) that facilitate water current and food capture.

Cnidoblasts

Stinging cells containing nematocysts found on the tentacles and body of cnidarians, used for anchorage, defense, and capturing prey.

Metagenesis

The phenomenon of alternation of generations in certain cnidarians where asexual polyps produce sexual medusae, which then reproduce sexually to form polyps.

Flame Cells

Specialized excretory cells found in flatworms (Phylum Platyhelminthes) that function in osmoregulation and excretion.

Radula

A file-like rasping organ located in the mouth of most molluscs, used for feeding.

Water Vascular System

A distinctive hydraulic system found in echinoderms that assists in locomotion, capture and transport of food, and respiration.

Pulvinus

A swollen leaf base found in certain leguminous plants.

Phyllotaxy

The pattern or arrangement of leaves on a stem or branch (e.g., alternate, opposite, or whorled).

Aestivation

The mode of arrangement of sepals or petals in a floral bud with respect to other members of the same whorl.

Placentation

The arrangement of ovules within the ovary of a flower (e.g., marginal, axile, parietal, free central, or basal).

Stomatal Apparatus

The structure consisting of a stomatal aperture, two surrounding guard cells, and adjacent specialized subsidiary cells.

Bulliform Cells

Large, empty, colourless adaxial epidermal cells in grass leaves that absorb water to expose the leaf surface or turn flaccid during water stress to curl leaves inward.

Mesosome

A specialized infolding of the plasma membrane in prokaryotes that functions in cell wall synthesis, DNA replication, respiration, and secretion.

Fluid Mosaic Model

The cell membrane structure model proposed by Singer and Nicolson in $1972$, describing a quasi-fluid lipid bilayer with laterally moving integral and peripheral proteins.

Tonoplast

The single membrane bounding the central vacuole in plant cells, facilitating active transport of ions against concentration gradients.

Axoneme

The core of eukaryotic cilia and flagella containing a $9+2$ array of radially arranged peripheral microtubule doublets and two central microtubules.

Secondary Metabolites

Organic compounds produced by plants, fungi, and microbes (e.g., alkaloids, flavonoids, rubber, essential oils) that do not play direct roles in primary physiological processes.

RuBisCO

Ribulose bisphosphate carboxylase-oxygenase, the most abundant protein in the biosphere, responsible for catalyzing carbon dioxide fixation in the Calvin cycle.

Quiescent Stage ($G_0$)

An inactive phase of the cell cycle where cells exit the $G_1$ phase and remain metabolically active without proliferating unless stimulated.

Synaptonemal Complex

A complex protein structure formed between paired homologous chromosomes during the zygotene stage of meiotic prophase I.

Chiasmata

X-shaped structures formed during the diplotene stage of meiosis representing the sites where crossing over occurred between homologous chromosomes.

Kranz Anatomy

A specialized leaf anatomy in $C_4$ plants featuring large bundle sheath cells with abundant chloroplasts surrounding vascular bundles in a wreath-like arrangement.

Photorespiration

A light-dependent pathway occurring in $C_3$ plants where RuBisCO binds oxygen instead of carbon dioxide, consuming energy and releasing $\text{CO}_2$ without producing sugars, ATP, or NADPH.

EMP Pathway

The glycolytic pathway named after Embden, Meyerhof, and Parnas that partially oxidizes glucose into two molecules of pyruvic acid in the cytoplasm.

Respiratory Quotient (RQ)

The ratio of the volume of $\text{CO}_2$ evolved to the volume of $\text{O}_2$ consumed in cellular respiration per unit time.

Plasticity

The capacity of plants to follow different developmental pathways in response to environmental conditions or life phases, resulting in varied structures such as heterophylly.

Respiratory Climacteric

The marked increase in the rate of respiration in fruits during ripening, induced by the plant hormone ethylene.

Erythroblastosis Foetalis

A severe hemolytic condition in an $\text{Rh-positive}$ fetus caused by maternal $\text{Rh-negative}$ antibodies crossing the placenta during subsequent pregnancies.

Cardiac Output

The volume of blood pumped out by each ventricle of the heart per minute, calculated as stroke volume times heart rate (approx. $5\text{ litres}$ per minute in a healthy individual).

Ammonotelism

The process of excreting nitrogenous waste primarily as soluble and highly toxic ammonia, typical of aquatic invertebrates, bony fishes, and aquatic amphibians.

Juxtaglomerular Apparatus (JGA)

A specialized regulatory cellular structure formed by the contact of the distal convoluted tubule and afferent arteriole, which secretes renin to maintain GFR.

Sarcomere

The functional anatomical unit of muscle contraction located between two successive Z lines within a myofibril.

Action Potential

A rapid reversal of electrical charge across a nerve cell membrane triggered by a stimulus that increases sodium ion permeability, creating a nerve impulse.

Corpus Callosum

A thick band of nerve fibres that connects the left and right cerebral hemispheres in the human brain.

Diabetes Insipidus

A metabolic disorder caused by diminished synthesis or release of antidiuretic hormone (ADH), leading to excessive water loss and dehydration.