OUAT cheat sheet

Law of diminishing returns: as a variable input is added to fixed inputs, marginal product eventually declines; apply until marginal value product equals input price.

Soil pH ranges: strongly acid below 5.5, near neutral 6.5-7.5; most field crops perform best at pH 6.0-7.0, and legumes tolerate slightly higher pH.

C:N ratio of organic residues: below about 25:1 favors net nitrogen mineralization; above about 30:1 favors immobilization and temporary N deficiency.

NPK fertilizer grades are expressed as percent N, percent P2O5 (available phosphate), and percent K2O (water-soluble potash), always in that order.

Crop rotation with legumes fixes atmospheric nitrogen via Rhizobium symbiosis, breaking cereal disease and pest cycles and reducing soil nitrogen depletion.

Critical period of weed competition is generally the early crop growth stage; weeds removed within the first 3-6 weeks cause the greatest yield loss.

Seed germination requires adequate moisture, suitable temperature, and oxygen; dormant seeds may need scarification, stratification, or light exposure to break dormancy.

Integrated pest management uses economic threshold levels: chemical control is justified only when pest density threatens to exceed the cost of treatment.

Ruminant digestion: rumen microbes ferment cellulose to volatile fatty acids; rumination and buffering by saliva maintain rumen pH near 6.0-7.0.

Rumen acidosis occurs when pH falls below about 5.5 after abrupt intake of readily fermentable carbohydrates; signs include reduced feed intake and diarrhea.

Major vaccine types: live attenuated (strong, long-lasting immunity, may revert), killed/inactivated (safe, needs boosters), and toxoid (against toxins, e.g., tetanus).

Passive immunity in neonates comes from colostrum within the first hours of life; failure of passive transfer raises susceptibility to infection.

Normal vital signs in cattle: rectal temperature about 38-39 degrees C, heart rate 60-70 beats per minute, respiration 10-30 breaths per minute.

Zoonosis is a disease transmissible from animals to humans, such as rabies, brucellosis, anthrax, and tuberculosis.

Estrous cycle length: cattle about 21 days, sheep about 17 days, swine about 21 days; ovulation occurs near the end of estrus in most species.

Inbreeding depression reduces fertility and vigor; crossbreeding exploits heterosis, giving hybrid offspring superior performance to parental averages.

Pond fertilization promotes phytoplankton growth; inorganic fertilization typically uses N:P ratio near 4:1 to 8:1, while organic manures supply both nutrients and detritus.

Dissolved oxygen below about 3 mg/L stresses most cultured fish; values above 5 mg/L are generally safe, and oxygen is lowest before dawn due to night respiration.

Water pH for most freshwater aquaculture should stay between 6.5 and 9.0; acidic ponds require liming with agricultural lime or dolomite.

Ammonia toxicity rises with high pH and temperature because un-ionized ammonia (NH3) increases; keep total ammonia low by aeration and water exchange.

Carp polyculture stocks surface, column, and bottom feeders together (e.g., catla, rohu, mrigal) to use all pond niches and raise total yield.

Induced breeding uses pituitary gland extract or synthetic hormones (e.g., ovaprim) to trigger spawning in fish that do not breed naturally in captivity.

Fish age is commonly estimated from scales or otoliths by counting annuli; growth rings reflect seasonal changes in growth rate.

Bycatch is non-target catch; selective gear such as larger mesh size and turtle excluder devices reduces discard and mortality of juveniles.

Mendel's law of segregation: alleles separate during gamete formation; law of independent assortment applies to genes on different chromosomes.

Hardy-Weinberg equilibrium frequencies hold when there is no mutation, migration, selection, or genetic drift and mating is random: p^2 + 2pq + q^2 = 1.

Photosynthesis light reactions occur in thylakoid membranes producing ATP and NADPH; the Calvin cycle in the stroma fixes CO2 using RuBisCO.

Cellular respiration: glycolysis in cytoplasm, Krebs cycle in mitochondrial matrix, and oxidative phosphorylation on the inner mitochondrial membrane.

pH = -log[H+]; a change of one pH unit means a tenfold change in hydrogen ion concentration.

Newton's second law F = ma; work W = Fd cos(theta); kinetic energy KE = 1/2 mv^2, and power P = W/t.

In classical genetics, a test cross uses a homozygous recessive individual to reveal the genotype of an unknown dominant phenotype.

Humanities reasoning: correlation does not imply causation; a valid argument requires true premises plus a logical form such as modus ponens.