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Home >>Biology Dictionary >> Annelida - Antagonism
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Anisopetra
A suborder of the order Odonata containing the larger dragonflies in which the fore and hind wings are of different shapes and the nymphs posses a rectal gill.
Annelida
A phylum of invertebrates comprising the segmented worms (bristleworms, earthworms, leeches). Phylum of soft-bodied, elongated animals with well-marked metameric segmentation, unlike flatworms and roundworms. They differ from theses also in having a coelom (but small in leeches), a blood system, nephridia, and a central nervous system of well-defined cord(s) ventral to the gut with a dorsal brain.
There is a muscular body-wall, and the cuticle is not of chitin (as in Arthropoda) but of a collagen-like protein. Includes three main classes, Polychaeta, Oligochaeta and Hibrudinea.
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Annual
Plant that completes its life-cycle, from seed germination to seed production, followed by death, within a single season
Annual rhythm
Any activity or process that an organism experiences on a yearly basis, e.g. courtship, migration, shedding of leaves.
Annal ring
A cylinder of secondary xylem cut by the cambium in a dicot stem in one year, comprises earlywood (spring wood) and latewood (autumn wood). Occurs as a result of distinct variation in seasonal activity of the cambium.
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Annulus
(Ring of tissue surrounding the stalk (stipe) of fruit bodies of certain basidiomycete fungi, e.g. mushroom; (2) The region of cells concerned in the opening of moss capsules and fern sporangia to liberate spores.
Anoplura
Sucking lice. Order of small exopterygote insects. Wingless; thoracic segments not differentiated. Ectoparasitic on mammals, whose blood they suck. Include human louse (the carrier of typhus).
Anoxia
Lack of oxygen in the tissues.
Ant
An insect of the superfamily Formicoidea with a single family, Formicidae. Hymenoptera with elbowed antennae and with a very narrow abdominal constriction of ‘waist’ sometimes known as the petiole. There are no solitary ants; they invariably live in highly organized colonies containing many types or castes.
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Antagonism
(1) Interaction with, or inhibition of, growth of one kind of organism, by another through the creation of unfavourable conditions, e.g. by exhaustion of food supply or by production of a specific antibiotic substance (e.g. penicillin).
(2) Of drugs, hormones, etc., producing opposing effects (of Synergism).
(3) Of muscles, producing opposite movements so that contraction of one must be accompanied by relaxation of the other (and reflexes usually assure this). The normal way in which muscles regain their relaxed shape after contraction is by contraction of antagonistic muscles.
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Antenna
A long whiplike jointed mobile paired appendage on the head of many arthropods, usually concerned with the senses of smell, touch, etc. In insects, millipedes, and centipedes they are the first pair of head appendages and are specialised and modified in many insects. In crustaceans they are the second pair of head appendages, the first pair (the antennules) having the sensory function, while the antennae are modified for swimming and for attachment.
Antennule
First appendage (paired) of head of Crustacea, usually sensory and antenna - like.
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Antherozoid
A small motile male gamete with flagella, and produced in an antheridium.
Anthesis
Flowering.
Anthocerotae
A class of the division Bryophyta containing the hornworts.
Anthocyanin
One of a group of flavonoid pigments. Anthocyanins occur in the cell vacuoles of various plant organs ad are responsible for many of the blue, red, and purple colours in plants (particularly in flowers).
Anterior
(1) Of lateral flowers, that part furthest away from the main axis, i.e. facing the bract. (2) Of animals, situated at, or relatively nearer to, the front (head) end usually the end directed forward when the animal is moving). In human anatomy, the anterior side is however the front surface, which is equivalent to the ventral side of other Mammals.
Anther
It is a part of the flower borne at the end of stamen. It produces the pollen grains.
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