Bihar BSEB Intermediate Biology flashcards

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

Double fertilization

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

Tapetum function

The innermost microsporangium wall layer that nourishes developing pollen grains and supplies sporopollenin for the exine. Its degeneration is normal after pollen maturation.

LH surge

A sharp rise in luteinizing hormone around mid-cycle that triggers ovulation and converts the ruptured follicle into the corpus luteum, which secretes progesterone.

Lactational amenorrhea

A natural contraceptive effect in which intense breastfeeding suppresses ovulation through prolactin, preventing conception for up to about six months after delivery.

Test cross

Crossing an individual of unknown genotype with a homozygous recessive partner; offspring ratios reveal whether the tested individual was homozygous dominant or heterozygous.

Chargaff's rule

In double-stranded DNA the amount of adenine equals thymine and guanine equals cytosine, so purines equal pyrimidines and the ratio A/T equals G/C equals one.

Lac operon inducer

Lactose (allolactose) binds the repressor protein, releasing it from the operator so RNA polymerase transcribes lacZ, lacY and lacA for lactose metabolism.

Hardy-Weinberg equilibrium

Allele and genotype frequencies stay constant across generations in a large randomly mating population with no mutation, migration or selection; p squared plus 2pq plus q squared equals one.

Secondary immune response

A faster, stronger antibody response on second exposure to an antigen, produced by memory B and T cells and the basis of vaccination.

Cyclosporin A source

An immunosuppressive drug produced by the fungus Trichoderma polysporum, used to prevent rejection after organ transplantation by suppressing T cell activity.

Rhizobium role

A symbiotic bacterium that infects legume roots, forms nodules and fixes atmospheric nitrogen into ammonia using the enzyme nitrogenase, acting as a biofertilizer.

Single cell protein

Protein extracted from mass-cultured microorganisms such as Spirulina or Methylophilus, used as nutritious animal feed and a partial substitute for conventional protein sources.

EcoRI sticky ends

This restriction enzyme cuts the palindromic sequence GAATTC between G and A, producing complementary single-stranded overhangs that can be joined by DNA ligase.

Taq polymerase

A heat-stable DNA polymerase from Thermus aquaticus that survives PCR denaturation cycles at about 94 degrees Celsius and extends primers at about 72 degrees.

Bt cotton

A transgenic crop carrying Bacillus thuringiensis cry genes that produce insecticidal crystal proteins toxic to bollworm larvae but harmless to mammals.

RNA interference

Silencing of a specific gene by introducing double-stranded RNA, used to block nematode infestation in tobacco and to study gene function.

Logistic growth equation

dN/dt equals rN times (K minus N) divided by K, describing population growth that slows as size N approaches carrying capacity K and forms a sigmoid curve.

Ten percent law

Lindeman's rule that only about ten percent of energy at one trophic level is transferred to the next, so food chains rarely exceed four or five levels.

Competitive exclusion principle

Gause's principle that two species competing for identical limited resources cannot coexist indefinitely; one is eliminated or shifts to a different niche.

Biomagnification

Progressive increase in concentration of non-biodegradable pollutants such as DDT or mercury along a food chain, harming top consumers most severely.

Fluid mosaic model

Singer and Nicolson's description of the plasma membrane as a fluid phospholipid bilayer with integral and peripheral proteins able to move laterally.

S phase

The interphase stage in which DNA replicates and histone proteins are synthesized, doubling the DNA content before the cell enters G2 and mitosis.

Crossing over

Exchange of segments between non-sister chromatids of homologous chromosomes during pachytene of meiosis I, producing new allele combinations and genetic variation.

Competitive inhibition

An inhibitor resembling the substrate binds the enzyme's active site, slowing the reaction; raising substrate concentration can overcome this inhibition.

Casparian strip

A waxy suberin band in root endodermal cell walls that blocks apoplastic water movement, forcing water and minerals through the symplast for selective uptake.

RuBisCO

The enzyme that fixes carbon dioxide onto ribulose bisphosphate in the Calvin cycle; it is the most abundant protein on Earth and also binds oxygen.

Respiratory quotient values

The ratio of carbon dioxide released to oxygen consumed: about 1.0 for carbohydrates, 0.7 for fats and 0.9 for proteins, indicating the substrate being respired.

Apical dominance

Suppression of lateral bud growth by auxin produced in the shoot apex; removing the apex allows side branches to grow, as used in tea plantations.

Bile function

Bile salts emulsify fats into small droplets, increasing surface area for lipase, and help absorption of fat-soluble vitamins; bile also neutralizes acidic chyme.

Glomerular filtration rate

About 125 millilitres of plasma filtrate formed per minute in both kidneys, roughly 180 litres daily, most of which is reabsorbed in the tubules.

Sliding filament theory

Muscle contraction occurs as myosin heads bind actin and pull thin filaments toward the sarcomere centre, shortening the sarcomere while filament lengths stay constant.

SA node

The sinoatrial node in the right atrial wall generates the heartbeat's electrical impulse, setting the rhythm and acting as the natural pacemaker of the heart.