BSEH SS Biology flashcards

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

Spermatogenesis outcome

One diploid primary spermatocyte completes meiosis I and II to produce four haploid spermatids, which mature into four functional sperm cells.

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 triploid endosperm.

LH surge

A sharp rise in luteinizing hormone near mid-cycle triggers ovulation, releasing the secondary oocyte from the mature Graafian follicle about 36 hours later.

hCG function

Human chorionic gonadotropin, secreted by the developing placenta, maintains the corpus luteum so it keeps producing progesterone during early pregnancy.

Test cross

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

Hardy-Weinberg equilibrium

Allele and genotype frequencies remain constant across generations only when there is no mutation, no migration, random mating, no selection, and a large population.

Linkage effect on ratios

Genes close together on the same chromosome tend to be inherited together, so dihybrid crosses yield fewer recombinant phenotypes than the expected 9:3:3:1.

Sickle-cell mutation

An autosomal recessive substitution replaces glutamic acid with valine at position six of the beta-globin chain, causing hemoglobin to polymerize and distort red cells.

Sympatric speciation

Formation of new species within the same geographic area, driven by polyploidy, habitat shifts, or behavioral isolation rather than a physical barrier.

Malaria pathogen

Plasmodium species, transmitted by the bite of an infected female Anopheles mosquito, invade red blood cells and cause cyclical fever and chills.

Active acquired immunity

Immunity produced when the body encounters an antigen through infection or vaccination and generates its own antibodies plus memory B and T cells.

Biofortification

Breeding crops to increase their content of vitamins, minerals, or protein, such as iron-rich pearl millet or vitamin A-rich carrots, improving nutritional value.

Composite fish culture

A pond system stocking surface, middle, and bottom feeding fish species together so they use different food niches and raise total yield per pond.

Sticky ends

Short single-stranded overhangs produced when a restriction enzyme cuts DNA at a palindromic site, allowing complementary fragments to base-pair and be ligated.

Ti plasmid

A tumor-inducing plasmid from Agrobacterium tumefaciens used as a vector to transfer foreign genes into dicot plant cells; it is disarmed before use.

PCR steps

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

Bt cotton

A transgenic crop carrying Bacillus thuringiensis cry genes that encode insecticidal proteins killing bollworm larvae that feed on the plant tissue.

RNA interference

Introduction of a complementary RNA that silences a specific target gene, used to block nematode infestation in tobacco plants.

Logistic growth equation

Population growth is dN/dt = rN(K−N)/K, where r is the intrinsic rate and K the carrying capacity; growth slows as population nears K.

Ten percent rule

Only about ten percent of energy at one trophic level transfers to the next, so energy pyramids are always upright and top predators are few.

Primary succession

Colonization of a bare substrate with no existing soil, starting with pioneer species such as lichens and mosses that gradually build soil.

Ozone depletion cause

Chlorofluorocarbons release chlorine atoms in the stratosphere; each chlorine atom catalytically destroys many ozone molecules, thinning the ozone shield.

Fluid mosaic model

The plasma membrane is a phospholipid bilayer with proteins floating in or spanning it, giving a flexible, selectively permeable, mosaic-like structure.

Competitive inhibition

An inhibitor resembling the substrate binds the enzyme active site; raising substrate concentration reduces inhibition because substrate outcompetes the inhibitor.

Oxidative phosphorylation

Electron transport along the inner mitochondrial membrane pumps protons, and ATP synthase uses the returning proton gradient to make most cellular ATP.

Calvin cycle

Stromal reactions using ATP and NADPH to fix carbon dioxide via RuBisCO, producing triose phosphate that builds glucose and other carbohydrates.

Water potential equation

Water potential equals solute potential plus pressure potential; water moves from higher to lower water potential, with pure water at atmospheric pressure set to zero.

Stomatal closure

Abscisic acid triggers potassium ion efflux from guard cells under water stress, lowering turgor pressure and closing the stomatal pore.

C4 photosynthesis

Carbon dioxide is first fixed into oxaloacetate by PEP carboxylase in mesophyll cells, concentrating carbon dioxide around RuBisCO and suppressing photorespiration.

Photoperiodism

Flowering response to relative day and night length; short-day plants require nights longer than a critical duration, and long-day plants require shorter nights.

Counter-current mechanism

Opposite flow in the two limbs of the loop of Henle maintains a medullary salt gradient, enabling the collecting duct to concentrate urine under ADH.

Carbon dioxide transport

About seventy percent of carbon dioxide travels in blood as bicarbonate formed by carbonic anhydrase inside red blood cells, with the rest bound to hemoglobin.