Kerala Plus Two Biology (DHSE) flashcards

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

Double fertilisation

In angiosperms, one male gamete fuses with the egg (syngamy) to form a diploid zygote, while the second fuses with two polar nuclei (triple fusion) to form a triploid primary endosperm nucleus.

Apomixis

Asexual production of seeds without fertilisation, producing genetically identical offspring; seen in some species of Citrus and mango (polyembryony).

Corpus luteum

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

Saheli

A non-steroidal oral contraceptive pill developed in India (centchroman); it prevents pregnancy by blocking ovulation and implantation with fewer side effects.

Law of segregation

Alleles of a gene separate during gamete formation, so each gamete receives only one allele; the pair is restored at fertilisation. It explains 3:1 phenotypic ratios in monohybrid crosses.

Incomplete dominance

A pattern where the heterozygote shows an intermediate phenotype between the two homozygotes, e.g., pink flowers in Snapdragon (Antirrhinum).

Hardy-Weinberg equilibrium

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

Lac operon

An inducible operon in E. coli with regulatory, promoter, operator, and structural genes (z, y, a); lactose acts as inducer by binding the repressor, allowing transcription of lactose-metabolising enzymes.

Analogous organs

Structures with different evolutionary origins but similar functions, such as wings of butterflies and birds; they indicate convergent evolution, not common ancestry.

Malaria

A disease caused by Plasmodium species, transmitted by the bite of an infected female Anopheles mosquito; symptoms include fever and chills due to haemozoin release from infected RBCs.

Passive immunity

Immunity acquired by receiving ready-made antibodies from another source, such as colostrum or antivenom; it provides immediate but short-lived protection.

Cyclosporin A

An immunosuppressant drug produced by the fungus Trichoderma polysporum, used to prevent rejection in organ transplant patients.

Restriction endonuclease

An enzyme that cuts DNA at specific palindromic recognition sequences, producing sticky or blunt ends; used in recombinant DNA technology (e.g., EcoRI).

PCR

Polymerase chain reaction: in vitro amplification of DNA using Taq polymerase through repeated cycles of denaturation, primer annealing, and extension.

RNA interference

A technique using double-stranded RNA to silence a specific mRNA, preventing translation; used to develop nematode-resistant tobacco.

Bt toxin

A crystal protein (protoxin) produced by Bacillus thuringiensis; it becomes active in the alkaline gut of insects and kills them, providing pest resistance in transgenic crops.

Logistic growth

Population growth model with limited resources, described by dN/dt = rN((K−N)/K), producing an S-shaped curve that levels off at carrying capacity K.

Ecological succession

The gradual and directional change in species composition of an ecosystem over time; primary succession starts on bare rock, secondary succession follows a disturbance.

Species-area relationship

The observation that species richness increases with area, described by log S = log C + Z log A; the slope Z is steeper for larger areas such as continents.

In situ conservation

Conservation of biodiversity within natural habitats, e.g., biosphere reserves, national parks, wildlife sanctuaries, and sacred groves.

Synaptonemal complex

A protein structure that forms between homologous chromosomes during zygotene of prophase I, holding them together for crossing over at pachytene.

K_m

Michaelis–Menten constant: the substrate concentration at which an enzyme reaches half its maximum velocity; a low K_m indicates high affinity of enzyme for substrate.

Denaturation

Loss of the three-dimensional structure of a protein due to heat, pH change, or chemicals, destroying its function while the primary amino acid sequence remains intact.

Water potential

The chemical potential of water relative to pure water at the same temperature and pressure; pure water has Ψ_w = 0, and solutes lower it (negative solute potential).

Photorespiration

A wasteful process in C3 plants where RuBisCO fixes O2 instead of CO2, consuming ATP and releasing CO2; it is absent in C4 plants due to Kranz anatomy and PEP carboxylase.

Kranz anatomy

The arrangement in C4 plant leaves of bundle-sheath cells surrounded by mesophyll cells, enabling initial CO2 fixation by PEP carboxylase and reduced photorespiration.

Apical dominance

Inhibition of lateral bud growth by auxin produced at the shoot apex; removing the apex promotes branching.

Placentation

The arrangement of ovules within the ovary; types include marginal (pea), axile (China rose), parietal (mustard), free central (Dianthus), and basal (sunflower).

Malpighian tubules

Excretory organs in insects such as cockroach; they remove nitrogenous wastes from the haemolymph and empty into the hindgut.

Binomial nomenclature

The system of naming species with two Latin words: genus (capitalised) and species (lowercase); printed in italics or underlined in handwriting, e.g., Homo sapiens.

Viroids

Infectious agents consisting of free RNA without a protein coat, smaller than viruses; they cause diseases such as potato spindle tuber.

Water vascular system

A unique network of canals and tube feet in echinoderms (e.g., starfish) used for locomotion, feeding, and respiration.