OUAT flashcards

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

Law of diminishing returns

As successive units of a variable input are added to fixed inputs, marginal product eventually declines, so additional input yields progressively smaller output increases.

Soil pH

A measure of soil acidity or alkalinity on a 0-14 scale; most field crops grow best between pH 6.0 and 7.0, where nutrients are most available.

C:N ratio

The ratio of carbon to nitrogen in organic matter; below about 25:1 nitrogen is released, while above about 30:1 soil microbes tie up nitrogen.

Fertilizer grade

The percentage of nitrogen, available phosphate as P2O5, and water-soluble potash as K2O in a fertilizer, always stated in that order.

Biological nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by symbiotic bacteria such as Rhizobium in legume root nodules, making nitrogen available to plants.

Integrated pest management

A strategy combining cultural, biological, and chemical controls, applying pesticides only when pest numbers exceed an economic threshold that justifies treatment cost.

Seed dormancy

A resting state in which viable seeds fail to germinate despite favorable conditions; broken by scarification, stratification, light, or after-ripening.

Crop rotation

Growing different crops in sequence on the same land to interrupt pest and disease cycles, improve soil structure, and balance nutrient use.

Rumen fermentation

Microbial breakdown of plant fiber in the rumen into volatile fatty acids, the main energy source for cattle, sheep, and goats.

Rumen acidosis

A digestive disorder in which rumen pH falls below about 5.5 after sudden intake of fermentable carbohydrates, causing reduced appetite and diarrhea.

Colostrum

The first milk produced after birth, rich in antibodies; newborn animals must consume it early to acquire passive immunity against infection.

Live attenuated vaccine

A vaccine made from weakened pathogens that replicate in the host, producing strong and long-lasting immunity but carrying a small risk of reversion.

Toxoid vaccine

A vaccine prepared from chemically inactivated bacterial toxins, used to protect against diseases such as tetanus and diphtheria.

Zoonosis

An infectious disease that can be transmitted from animals to humans, including rabies, brucellosis, anthrax, and tuberculosis.

Heterosis

The superior performance of crossbred offspring compared with the average of their parents, exploited in animal and crop breeding to improve vigor and yield.

Estrous cycle

The recurring reproductive cycle in non-primate mammals, about 21 days in cattle and swine and about 17 days in sheep, ending in ovulation.

Dissolved oxygen

The concentration of oxygen gas in water, measured in milligrams per liter; most cultured fish are stressed below about 3 mg/L and thrive above 5 mg/L.

Pond liming

Application of agricultural lime or dolomite to raise the pH of acidic pond water and soil, improving nutrient availability and fish growth.

Un-ionized ammonia

The toxic form of ammonia in water; its proportion rises with higher pH and temperature, making it a key water-quality hazard in aquaculture.

Carp polyculture

Stocking surface, mid-water, and bottom-feeding carp species together so each uses a different pond niche, increasing total fish yield.

Induced breeding

Triggering spawning in captive fish with pituitary gland extract or synthetic hormones when natural breeding does not occur in pond conditions.

Otolith

A calcium carbonate structure in the inner ear of fish whose growth rings are counted to estimate age and growth history.

Bycatch

Non-target organisms caught incidentally in fishing gear; reduced by selective devices such as larger mesh and turtle excluder devices.

Pond fertilization

Adding inorganic nutrients or organic manure to a pond to stimulate phytoplankton growth, forming the base of the food chain for cultured fish.

Law of segregation

Mendel's principle that the two alleles of a gene separate during gamete formation, so each gamete carries only one allele.

Hardy-Weinberg equilibrium

Allele and genotype frequencies remain constant across generations in a large, randomly mating population without mutation, migration, selection, or drift.

Calvin cycle

The light-independent stage of photosynthesis in the chloroplast stroma, where RuBisCO fixes carbon dioxide into sugars using ATP and NADPH.

Test cross

A cross between an individual of unknown genotype and a homozygous recessive individual, used to reveal whether the unknown carries a dominant allele.

Oxidative phosphorylation

The final stage of aerobic respiration on the inner mitochondrial membrane, where electron transport drives ATP synthesis through a proton gradient.

pH scale

A logarithmic measure of hydrogen ion concentration, pH = -log[H+]; a one-unit change represents a tenfold change in acidity.

Kinetic energy

The energy possessed by a moving body, calculated as one-half mass times velocity squared, KE = 1/2 mv^2.

Correlation versus causation

A statistical association between two variables does not prove that one causes the other; a hidden third factor may explain both.