NSEB 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 a diploid zygote, while the second fuses with two polar nuclei to form triploid endosperm.

Porogamy

Entry of the pollen tube into the ovule through the micropyle; the most common route of fertilization in angiosperms.

Spermatogenesis output

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

Site of fertilization

In humans, fusion of sperm and ovum normally occurs in the ampullary-isthmic junction of the fallopian tube, not in the uterus.

Monohybrid genotypic ratio

In the F2 generation of a monohybrid cross the genotypes are in the ratio 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.

Dihybrid F2 ratio

When two independently assorting gene pairs are crossed, the F2 phenotypic ratio is 9:3:3:1, assuming no linkage or lethality.

Test cross

Crossing an individual of unknown genotype with a homozygous recessive partner; a 1:1 ratio reveals a heterozygote.

Semiconservative replication

Each daughter DNA molecule retains one parental strand and one newly synthesized strand, as shown by the Meselson-Stahl experiment.

Chargaff's equivalence rule

In double-stranded DNA the amount of adenine equals thymine and guanine equals cytosine, so purines equal pyrimidines overall.

Lac operon

An inducible operon switched on when lactose binds the repressor, allowing RNA polymerase to transcribe lacZ, lacY and lacA.

Hardy-Weinberg conditions

Allele frequencies stay constant only with no mutation, no migration, random mating, no selection and a very large population.

Hardy-Weinberg equation

p + q = 1 for allele frequencies, and p squared plus 2pq plus q squared = 1 for genotype frequencies in a stable population.

HIV replication

HIV is a retrovirus; reverse transcriptase converts its RNA genome into DNA, which integrates into the host genome and infects helper T cells.

Malaria transmission

Plasmodium species are transmitted by the bite of an infected female Anopheles mosquito, which injects sporozoites into the human blood.

Restriction endonuclease

A bacterial enzyme that cuts DNA at a specific palindromic sequence, producing sticky or blunt ends for recombinant DNA work.

EcoRI recognition site

The enzyme recognizes the palindromic hexanucleotide GAATTC and cuts between G and A, generating complementary sticky ends.

Ti plasmid

A tumour-inducing plasmid from Agrobacterium tumefaciens used as a natural vector to deliver genes into plant cells.

PCR cycle steps

Repeated cycles of denaturation, primer annealing and extension by Taq polymerase double the target DNA each round.

Ten percent law

Only about ten percent of energy at one trophic level is transferred to the next; the rest is lost as heat and respiration.

Net primary productivity

NPP equals gross primary productivity minus the energy lost through respiration by producers; it is the energy available to consumers.

Logistic growth equation

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

Exponential growth equation

dN/dt = rN describes unlimited growth with constant intrinsic rate r, giving a J-shaped curve when resources are abundant.

Loop of Henle counter-current

The descending and ascending limbs maintain a medullary osmotic gradient, allowing concentrated urine to be formed under ADH.

Sinoatrial node

A patch of pacemaker cells in the right atrium that spontaneously depolarizes and sets the rhythm of the heartbeat.

Bohr effect

A fall in pH or rise in carbon dioxide reduces hemoglobin's affinity for oxygen, shifting the dissociation curve to the right.

Transpiration pull

Water is pulled up the xylem by evaporation from leaves, creating tension transmitted through continuous water columns.

Photosystem II role

PSII absorbs light and splits water, releasing oxygen and supplying electrons to the photosynthetic electron transport chain.

Calvin cycle

Light-independent reactions in which RuBisCO fixes carbon dioxide onto RuBP, producing sugars through reduction and regeneration steps.

Glycolysis net yield

One glucose yields two pyruvate, a net two ATP and two NADH during glycolysis in the cytoplasm, independent of oxygen.

Krebs cycle location

In eukaryotes the citric acid cycle occurs in the mitochondrial matrix and yields NADH, FADH2, ATP and carbon dioxide.

Mendel's law of segregation

The two alleles of a gene separate during gamete formation, so each gamete carries only one allele of each pair.

Sex-linked inheritance

Genes on the X chromosome show different inheritance in males and females; affected fathers cannot pass X-linked traits to sons.