Assam HS Class 11-12 Biology flashcards

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

Five-kingdom classification

Whittaker's system dividing organisms into Monera, Protista, Fungi, Plantae and Animalia, based on cell type, cell wall, body organisation, nutrition mode and phylogenetic relationships.

Binomial nomenclature

Two-part Latin naming system where the genus name is capitalised and the species epithet is lowercase, both italicised in print or underlined separately when handwritten, with author abbreviation following.

Prokaryotic cell features

Cells lacking a membrane-bound nucleus and organelles, having 70S ribosomes, a single circular DNA molecule, and usually a peptidoglycan cell wall in bacteria; mesosomes are infoldings of the plasma membrane.

Epithelial tissue

Closely packed cells resting on a basement membrane that cover or line body surfaces, lack direct blood supply, and are joined by tight and adhering junctions; classified by cell shape and layer number.

Light reaction products

ATP, NADPH and oxygen generated in thylakoid membranes through photosystems I and II, water photolysis and cyclic or non-cyclic electron transport, supplying reducing power for carbon fixation.

Calvin cycle

Stromal carbon-fixation pathway in which RuBisCO attaches CO2 to ribulose-1,5-bisphosphate; carboxylation, reduction and regeneration steps consume ATP and NADPH to build sugar.

Kranz anatomy

C4 plant leaf arrangement with a ring of large bundle-sheath cells around vascular bundles and mesophyll cells; PEP carboxylase fixes CO2 first, reducing photorespiration and raising photosynthetic efficiency.

Glycolysis net yield

Cytoplasmic breakdown of one glucose into two pyruvate molecules, producing a net gain of two ATP and two NADH after the two ATP consumed in the preparatory phase are subtracted.

Respiratory quotient

Ratio of carbon dioxide released to oxygen consumed in respiration; approximately 1.0 for carbohydrates, less than 1 for fats and proteins, and zero in anaerobic fermentation.

Enzyme inhibition types

Competitive inhibitors resemble substrate and bind the active site, raising Km without changing Vmax; non-competitive inhibitors bind elsewhere and lower Vmax; feedback inhibition regulates pathways.

Cardiac cycle phases

A 0.8-second cycle at 72 beats per minute comprising atrial systole (0.1 s), ventricular systole (0.3 s) and joint diastole (0.4 s), with valves ensuring one-way blood flow.

Countercurrent in gills

Water flows opposite to blood in fish gill lamellae, maintaining a concentration gradient so oxygen diffuses into blood along the entire length, achieving high oxygen extraction.

Law of segregation

Mendel's principle that the two alleles of a gene separate during gamete formation in meiosis, so each gamete carries only one allele and random fusion restores pairs.

Water potential

Chemical potential of water expressed in pressure units, equal to solute potential plus pressure potential; pure water at atmospheric pressure has zero, and water moves toward lower values.

Nitrogen fixation

Conversion of atmospheric nitrogen to ammonia by free-living bacteria such as Azotobacter or symbiotic Rhizobium in root nodules, using nitrogenase protected from oxygen by leghaemoglobin.

Double fertilisation

Angiosperm process where one male gamete fuses with the egg to form a diploid zygote and the second fuses with two polar nuclei to form triploid endosperm.

LH surge effect

A sharp rise in luteinising hormone around mid-cycle ruptures the mature Graafian follicle, releasing the oocyte at ovulation and converting the remnant into a progesterone-secreting corpus luteum.

Menstrual cycle phases

Sequence of menstrual, follicular, ovulatory and luteal phases; oestrogen thickens the endometrium, progesterone maintains it, and falling progesterone causes shedding if fertilisation does not occur.

Spermatogenesis sequence

Formation of sperm from spermatogonia through mitotic multiplication, meiotic primary and secondary spermatocytes, spermatids, and spermiogenesis; Sertoli cells nourish and Leydig cells secrete testosterone.

Linkage

Tendency of genes located on the same chromosome to be inherited together; recombination frequency rises with distance between loci and is used to construct genetic maps.

Pleiotropy

Condition where a single gene mutation affects several apparently unrelated phenotypic traits, illustrated by phenylketonuria or sickle-cell anaemia affecting many body systems simultaneously.

Semi-conservative replication

Each daughter DNA molecule retains one parental strand and one newly synthesised strand, demonstrated by Meselson and Stahl using nitrogen isotope labelling in E. coli.

Genetic code properties

Triplet codons read continuously without overlap or punctuation; the code is degenerate, nearly universal, with AUG as initiator and UAA, UAG, UGA as stop codons.

Lac operon regulation

Inducible negative control system in E. coli where the repressor blocks transcription without lactose; lactose binding releases the repressor, allowing RNA polymerase to transcribe structural genes.

Hardy-Weinberg principle

Allele and genotype frequencies remain constant across generations in a large randomly mating population without mutation, migration or selection; genotype frequencies follow p squared plus 2pq plus q squared.

Homologous versus analogous

Homologous organs share structural origin but may differ in function, indicating common ancestry; analogous organs share function but differ in structure, indicating convergent evolution.

Acquired immunity

Pathogen-specific defence involving B lymphocytes producing antibodies (humoral) and T lymphocytes mediating cell contact killing (cell-mediated), with memory cells giving a rapid secondary response.

Restriction endonuclease

Enzyme recognising a specific palindromic DNA sequence and cutting it, often producing sticky ends that allow insertion of DNA fragments into vectors for cloning.

PCR steps

Repeated cycles of denaturation near 94 degrees Celsius, primer annealing near 50 to 60 degrees, and extension near 72 degrees by Taq polymerase, doubling target DNA each cycle.

Bioreactor purpose

Vessel maintaining controlled temperature, pH, oxygen and substrate for large-scale culture of microbes or cells to produce antibiotics, enzymes, vaccines or recombinant proteins.

Logistic growth equation

Population growth described by dN/dt equals rN times (K minus N) over K, giving an S-shaped curve that levels off at carrying capacity K as resources become limiting.

Ten percent energy law

Only about ten percent of energy at one trophic level transfers to the next, so food chains rarely exceed four or five levels and top consumers receive very little energy.