Karnataka II PUC Biology (KSEAB) flashcards

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

Binary fission

Asexual reproduction in which a parent cell divides into two identical daughter cells; seen in Amoeba and bacteria, and distinct from budding and fragmentation.

Oestrus cycle

Cyclic reproductive changes in non-primate mammals, with a defined breeding season; differs from the menstrual cycle of primates, which occurs throughout the year.

Tapetum

Innermost layer of the microsporangium wall that nourishes developing pollen grains; its degeneration is linked to pollen maturity and anther dehiscence.

Double fertilisation

Unique to angiosperms: one male gamete fuses with the egg to form the diploid zygote, and the second fuses with two polar nuclei to form triploid endosperm.

Apomixis

Formation of seeds without fertilisation, producing offspring genetically identical to the parent; useful in agriculture to preserve hybrid vigour across generations.

Spermiogenesis

Transformation of haploid spermatids into motile spermatozoa; involves acrosome formation, nuclear condensation, and development of a flagellum, without further division.

Corpus luteum

Temporary endocrine gland formed from the ruptured follicle after ovulation; secretes progesterone, which maintains the endometrium for possible implantation.

Amniocentesis

Prenatal diagnostic technique that samples amniotic fluid for fetal chromosomal analysis; in India it is legally restricted to prevent misuse for sex determination.

Test cross

Cross of an individual with a homozygous recessive partner; a 1:1 phenotypic ratio in offspring indicates the tested individual was heterozygous for the trait.

Hardy–Weinberg equilibrium

Allele and genotype frequencies in a population remain constant across generations in the absence of mutation, migration, selection, drift, and non-random mating; p² + 2pq + q² = 1.

Homologous organs

Structures with similar embryonic origin and basic plan but different functions, such as forelimbs of vertebrates; they indicate common ancestry and divergent evolution.

Passive immunity

Protection acquired by receiving antibodies from another source, such as colostrum or antiserum; it acts immediately but provides no immunological memory.

Biofortification

Plant breeding strategy to increase the vitamin, mineral, or protein content of crops; examples include iron-rich bajra and vitamin A-rich carrot.

Restriction endonuclease

Enzyme that recognises a specific palindromic DNA sequence and cuts it, often producing sticky ends; used to insert genes into cloning vectors.

Polymerase chain reaction

In vitro DNA amplification using repeated cycles of denaturation, primer annealing, and extension by Taq polymerase; produces millions of copies of a target sequence.

Bt cotton

Genetically modified cotton carrying Bacillus thuringiensis cry genes; the toxin kills bollworm larvae that feed on the plant by damaging their gut lining.

RNA interference

Gene-silencing mechanism in which double-stranded RNA causes degradation of complementary mRNA; used to engineer nematode resistance in tobacco.

Carrying capacity

Maximum population size an environment can sustain indefinitely given available resources; symbol K in the logistic growth equation.

Species–area relationship

Species richness increases with area according to log S = log C + Z log A; the slope Z is steeper for islands and fragmented habitats.

Biomagnification

Increase in concentration of a persistent pollutant at successive trophic levels; DDT concentration rises from water to fish to fish-eating birds.

Fluid mosaic model

Description of the plasma membrane as a phospholipid bilayer with embedded proteins that move laterally; explains selective permeability and membrane fluidity.

Crossing over

Exchange of segments between non-sister chromatids of homologous chromosomes during pachytene of prophase I; generates genetic recombination.

Semi-conservative replication

DNA replication mode in which each daughter molecule contains one parental strand and one newly synthesised strand; demonstrated by the Meselson–Stahl experiment.

Photorespiration

Wasteful process in C3 plants where RuBisCO binds oxygen instead of carbon dioxide, consuming ATP and releasing CO₂; reduced in C4 plants by Kranz anatomy.

Water potential

Potential energy of water per unit volume relative to pure water at atmospheric pressure; solutes lower it, and water moves from higher to lower water potential.

Abscisic acid

Plant hormone that acts as a stress signal; closes stomata during drought, promotes seed dormancy, and inhibits growth, countering gibberellin effects.

Kranz anatomy

Arrangement in C4 leaves where bundle-sheath cells surround vascular bundles and are encircled by mesophyll cells; concentrates CO₂ for the Calvin cycle.

SA node

Sinoatrial node in the right atrium that generates electrical impulses setting heart rate; known as the natural pacemaker of the mammalian heart.

Counter-current mechanism

Arrangement in the loop of Henle where filtrate and blood flow in opposite directions; maintains an osmotic gradient for concentrating urine.

Sliding filament theory

Explanation of muscle contraction: myosin heads bind actin and pull thin filaments toward the sarcomere centre, shortening the muscle using ATP.

Saltatory conduction

Rapid propagation of nerve impulses by jumping between nodes of Ranvier in myelinated axons; faster and more energy-efficient than continuous conduction.

Photoperiodism

Response of plants to relative lengths of day and night; short-day plants flower when day length is below a critical value, long-day plants above it.