Tamil Nadu HSE Second Year Zoology 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 unicellular organism such as Amoeba or Paramecium divides into two identical daughter cells after nuclear division, producing rapid population growth without fertilisation.

Menstrual cycle phases

Ordered sequence of menstrual, follicular (proliferative), ovulatory and luteal (secretory) phases; oestrogen peaks before ovulation, progesterone dominates after it, driven by FSH and LH.

Placental hormones

Human chorionic gonadotropin maintains the corpus luteum early in pregnancy; the placenta also secretes human placental lactogen, oestrogen and progesterone to sustain pregnancy.

Spermatogenesis outcome

One diploid primary spermatocyte completes meiosis I and II to yield four haploid spermatids, which mature into sperm by spermiogenesis without unequal cytoplasmic division.

Test cross

Crossing an individual showing a dominant phenotype with a homozygous recessive partner; a 1:1 offspring ratio reveals the unknown parent was heterozygous.

Incomplete dominance

Condition in which the heterozygote shows an intermediate phenotype, as with pink Antirrhinum flowers from red and white parents, so the F1 does not resemble either homozygote.

Semiconservative replication

Each daughter DNA molecule retains one parental strand and one newly synthesised strand; helicase unwinds, polymerase extends 5' to 3', and ligase joins Okazaki fragments.

Lac operon

Inducible operon of E. coli lactose genes; lactose binds the repressor, freeing the operator so RNA polymerase transcribes the structural genes for lactose metabolism.

Hardy-Weinberg equilibrium

Allele and genotype frequencies stay constant across generations only with no mutation, migration, selection, or genetic drift and with random mating in a large population.

Homologous versus analogous organs

Homologous organs share ancestry but may differ in function, indicating divergent evolution; analogous organs share function but not ancestry, indicating convergent evolution.

Miller-Urey experiment

Laboratory simulation passing electric sparks through methane, ammonia, hydrogen and water vapour, which produced amino acids and supported chemical evolution of organic molecules on early Earth.

Natural selection conditions

Heritable variation, overproduction of offspring, differential survival and differential reproduction must all operate for allele frequencies to shift toward better-adapted traits over generations.

Widal test

Serological agglutination test detecting antibodies against Salmonella typhi antigens in blood serum, used to support the diagnosis of typhoid fever.

AIDS diagnostic criterion

AIDS is diagnosed when an HIV-positive person has a CD4 helper T-cell count below about 200 per microlitre, or develops opportunistic infections or cancers.

Metastasis

Spread of malignant cells from a primary tumour to distant sites through blood or lymphatic vessels, where secondary tumours form; a hallmark of malignant rather than benign tumours.

Passive immunity

Protection conferred by antibodies from another source, such as maternal IgG across the placenta or injected antiserum; it acts immediately but is short-lived and gives no memory.

Secondary immune response

Faster, stronger antibody response on re-exposure to an antigen, dominated by IgG, because memory B and T cells from the primary response expand rapidly.

Toxoid vaccine

Vaccine made from a chemically inactivated bacterial toxin, as in tetanus and diphtheria immunisation, which induces antibodies that neutralise the active toxin.

Antibody classes

IgG crosses the placenta and dominates secondary responses; IgM appears first; IgA is secreted in milk and mucus; IgE mediates allergy; IgD sits on B-cell surfaces.

BOD in sewage treatment

Biochemical oxygen demand measures oxygen consumed by microbes decomposing organic matter; secondary aerobic treatment with bacterial flocs sharply reduces it before discharge.

Biofertilisers

Microbial inoculants that enrich soil nutrients: Rhizobium and Azotobacter fix nitrogen, Anabaena and Nostoc add nitrogen in paddy fields, and Glomus mycorrhiza improves phosphorus uptake.

Cyclosporin A

Immunosuppressant drug obtained from the fungus Trichoderma polysporum, used to prevent rejection of transplanted organs by suppressing T-cell-mediated immune responses.

Bt toxin

Crystal protein from Bacillus thuringiensis, encoded by cry genes; inactive in the bacterium but solubilised by alkaline insect gut pH, it forms pores that kill lepidopteran larvae.

Restriction endonuclease

Enzyme that recognises a specific palindromic DNA sequence and cuts it, often producing sticky ends; EcoRI is used to create recombinant DNA in cloning.

Polymerase chain reaction

In vitro DNA amplification using Taq polymerase and primers through repeated cycles of denaturation, primer annealing and extension, doubling target DNA each cycle.

Logistic growth equation

dN/dt = rN(K−N)/K describes population growth slowing as size N approaches carrying capacity K, producing a sigmoid (S-shaped) curve.

Competitive exclusion principle

Gause's principle that two species competing for the same limiting resource cannot coexist indefinitely; the weaker competitor is excluded or shifts to another niche.

Ten per cent law

Lindeman's rule that only about ten per cent of energy at one trophic level is transferred to the next, the rest lost as heat and respiration, so energy pyramids are upright.

Species-area relationship

log S = log C + Z log A relates species richness S to area A; slope Z is about 0.1-0.2 for small areas and 0.6-1.2 for continents.

Biomagnification

Progressive increase in concentration of persistent, fat-soluble pollutants such as DDT at successive trophic levels because they are not metabolised or excreted.

Water vascular system

Network of canals and tube feet unique to echinoderms, used for locomotion, feeding and respiration; it is a key diagnostic feature of the phylum.

Sliding filament theory

Muscle contraction model in which myosin heads bind actin and pull thin filaments toward the sarcomere centre, shortening it using ATP and calcium ions.