Day-neutral plant

A plant unaffected by day length.

Death Rate or Mortality Rate

The number of deaths occurring in a period of time.

Debt-For-Nature Swap

A conservation strategy in which a developing country takes steps to preserve its biodiversity in exchange for a reduction in its foreign debt.


A crustacean with five pairs of legs, such as shrimps, crayfish, and lobsters.


Referring to trees that lose their leaves at the end of the growing season.


An organism that obtains nutrients from dead plants and animals.


Removal of trees from a forested area without adequate replanting.


The condition resulting from excessive water loss.

Demographic transition

Hypothesis that countries, as they become industrialized, have declines in death rates followed by declines in birth rates.


A final step in the nitrogen cycle, during which nitrogen gas is returned to the atmosphere.

Density-dependent Factor

A variable related to the density of a population that affects population size.

Density-independent Factor

A variable that affects population size regardless of population density.

Dental Formula

The number, kind, and placement of teeth that are specific for a particular kind of organism.

Deoxyribonucleic Acid (DNA)

A double-helix-shaped nucleic acid.


The result of the extraction of abiotic resources (non-renewable) from the environment or the extraction of biotic resources (renewable) faster than they can be renewed.


A drug that decreases the activity of the central nervous system.

Derived Character

A feature that evolved only within the group under consideration, such as the feathers of birds.

Dermal Tissue System

One type of plant tissue system, which forms the outer covering of plants.

DesalinationThe removal, using any of several processes, of excess salt and other minerals from water in order to obtain fresh water suitable for animal consumption or irrigation, and if almost all of the salt is removed, for human consumption, sometimes producing table salt as a by-product.



An area where rainfall averages less than 25 cm per year.


Conversion of rangeland, rain-fed cropland to desert-like land, with a drop in agricultural productivity of 10% or more. It is usually caused by a combination of overgrazing, soil erosion, prolonged drought, and climate change.

Desired plant community

The plant community that has been determined through a land use or management plan to best meet the plan’s objectives for a site. A desired plant community is consistent with the site’s capability to produce the required resource attributes through natural succession, management intervention, or a combination of both.

Determinate Cleavage

A process in which each cell develops into a specific part of the gastrula.


A consumer that feeds on dead plants and animals.


Macroorganisms that eat decaying matter. Includes ant, beetle, centipede, cricket, earthworm, earwig, enchytraeid worm, millipede, mite, scorpion, slug, snail, spider, springtail, termite, woodlice.


An organism in which the blastopore develops into the anus and the coelom arises by enterocoely and whose embryo has indeterminate cleavage.

Diabetes MellitusA disorder of glucose metabolism caused by insufficient insulin.



A sheet of muscle below the rib cage that functions in inspiration and expiration.


A phase in the heartbeat during which the ventricles relax and the blood flows in from the atria.

Diastolic Pressure

The pressure maintained in the blood when the ventricles are relaxed.


An abundant component of phytoplankton; member of phylum Bacillariophyta.


An angiosperm with two cotyledons, net venation, and flower parts in fours or fives.


In the brain, an area below the cerebral hemisphere that contains the thalamus and the hypothalamus.


A process in which the cells of a multicellular individual become specialized during development.


The process by which molecules move from an area of greater concentration to an area of lesser concentration.


Breaking down food into usable molecules.

Dihybrid Cross

A cross between individuals that involves the pairing of contrasting traits.


The existence of distinct, genetically determined forms of the same species, such as male and female forms.


One of a great variety of terrestrial reptilian forms during the Mesozoic era 245 million to 65 million years ago.


A formation from two amino acids bonded together by means of a condensation reaction.


A cell that contains both chromosomes of a homologous pair.


A double sugar formed from two monosaccharides.


A tractor-drawn implement composed of circular plates arranged at an angle with the soil. Used to prepare the soil for seeding.


The spatial distribution of individuals in a population.

Disruptive Selection

A type of natural selection in which individuals with two extreme forms of a trait have an advantage.


The separating of a molecule into simpler molecules, atoms, radicals, or ions.

dissolved oxygen (DO) content

Amount of oxygen dissolved in a given volume of water at a given temperature and atmospheric pressure; usually expressed in parts per million (ppm).


Divergent Evolution

The process of two or more related species becoming more and more dissimilar.


In taxonomy, a grouping of similar classes of plants.


Hereditary information in the form of a large molecule called deoxyribonucleic acid.

DNA Fingerprint

A pattern of bands made up of specific fragments from an individual’s DNA.

DNA Polymerase

An enzyme that binds to the separated strands of DNA and assembles each strand’s complement in replication.


In the three-domain system of classification, one of three broad groups that all living things fall into on the basis of rRNA analysis.

Domestic price

The price at which a commodity trades within a country,  in contrast to the world price. For those commodities not benefiting from some form of price support, the domestic price is determined by supply and demand. For commodities that receive price support, the domestic price is usually set by the loan rate or some comparable support level that serves as a price floor in the marketplace working in conjunction with any import quota that may be in effect

Domesticated or cultivated species

Species in which the evolutionary process has been influenced by humans to meet their needs.


The adaptation of an animal or plant to life in intimate association with and to the advantage of man.

Dominant Referring

To an allele that masks the presence of another allele for the same characteristic.


A state of decreased metabolism.

Dormant / dormancy

A biological process in which a plant ceases most growth activities and simply maintains existing tissue.


The top of a bilaterally symmetrical animal.

Dorsal Nerve Cord

A neural tube dorsal to the notochord.

Double Cropping

Raising two different crops on the same land in one growing season.

Double Fertilization

In plants, the process in which two types of cell fusion take place in the embryo sac.

Down Feather

One of the soft, fluffy feathers that cover the body of nesting birds and help insulate adult birds.

Down Syndrome

A disorder caused by an extra twenty-first chromosome and characterized by a number of physical and mental abnormalities.


A farm implement for planting seeds which forms a small furrow, deposits the seed in dribbles, covers the seed, and packs soil over it. It can also deposit fertilizer, lime, or other amendments into the soil, alone or with the seed.

Drip irrigation

A method of irrigation used to place irrigation water near plants' roots through pipes or tubes with small holes and eliminate runoff.Through which water trickles drop by drop.


A male bee that develops from an unfertilized egg and functions only to fertilize eggs from the queen.


Any chemical taken into the body that alters the normal processes of either the mind or the body.

Dryland farming

Farming on non-irrigated land. Success is based on rainfall, moisture-conserving tillage, and drought-resistant crops. 

Duchenne Muscular Dystrophy

A form of muscular dystrophy that weakens and progressively destroys muscle tissue.


Disposing of waste illegally by not using bins or official recycling centres, civic amenity sites or landfills.


The first section of the small intestine.

Dura Mater

The outermost of the three sacs that enclose the brain and spinal cord.