Biology 1030 Glossary
Copyright © Michael Shaw 2007 (Images and Text)

A B C D E F G H I J K L M N O P R S T U V W X Y Z


A

abdomen
The part of the body of vertebrates containing the viscera, that is the kidneys, liver, stomach, and intestines. In arthropods the abdomen is the part of the body directly behind the thorax, and in many other invertebrates it is divided into segments.

aboral, or dorsal
Toward the back, or upper surface.

acoelomate
A solid-bodied animal lacking a cavity between the gut and outer body wall.

adductor muscle
1. a muscle which pulls something towards the main part of the body.
2. a muscle which pulls two structures together, like the two valves of a shell.

adrenal gland
An endocrine gland located adjacent to the kidney in mammals; composed of two glandular portions: an outer cortex, which responds to endocrine signals in reacting to stress and effecting salt and water balance, and a central medulla, which responds to nervous inputs in reacting to stress.

adventitious roots
Roots that have differentiated from the kinds of tissue other than root tissue.

agranulocyte
A type of leukocyte (white blood cell) with nongranular cytoplasm and a large spherical nucleus. They are produced either in the lymphatic system or in the bone marrow.

albumen
(egg white) A solution of protein in water that is secreted by the oviduct of birds and some reptiles. Albumen surrounds the embryo and yolk, which it cushions within the shell of the egg. It is eventually absorbed by the embryo as food.

alimentary canal
A tubular passage which extends from the mouth to the anus. Found in organisms with complete digestive systems.
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allantois
One of four extraembryonic membranes; serves as a repository for the embryo's nitrogenous waste.

allele
an alternative form of a gene.

alpha male
the dominant male in a pack.

amictic egg
A thin shelled diploid egg which cannot be fertilized. Instead, it develops by parthenogenesis. It is produced by rotifers when living conditions are optimal, and will develop to produce amictic females.

amnion
The innermost of four extraembryonic membranes; encloses a fluid-filled sac in which the embryo is suspended.

amniotic fluid
Watery-fluid that bathes the fetus keeping it suspended to act as a protective cushion.

ampulla
Any small vesicle or sac-like offshoot. Some examples include the dilation at the end of the semicircular canal of the ear, or the internal expansion of the echinoderm tube foot.

Anabaena
a genus of filamentous cyanobacteria in which filaments when viewed under the microscope resemble strings of beads. Thick-walled, clear heterocysts can be seen at intervals along or at the ends of the filaments.

anabolism
Metabolic reactions that require energy and result in the biosynthesis of needed compounds. An example of this is photosynthesis, in which solar energy is incorporated into complex compounds such as glucose and its derivatives.

Angiosperm
Any plant that is a member of the class Angiospermae, in which the seeds are enclosed in an ovary. Each member of the class is either a monocotyledon (grasses, tulips) or a dicotyledon (apple, primrose).

annulus
The ring of cells in the moss or fern capsule that splits and allows liberation of spores.

antenna (pl. antennae)
Usually one of a pair of many-jointed, whip-like structures present on the head of many arthropods, particularly insects (first appendage on head) and crustaceans(second appendage). Antennae have a sensory function, though in some crustaceans they are used for attachment or swimming.

antennule
The foremost of two pairs of antennae that occurs in some crustaceans. Most antennae in other arthropods are homologous with the antennules of crustaceans.

anther
The terminal pollen sac of a stamen, inside which pollen grains with male gametes form in the flower of an angiosperm.

antheridium (pl. antheridia)
The male sex organ or gametangium, within which male gametes are formed, in algae, fungi, bryophytes (mosses, liverworts, etc.), and pteridophytes (ferns).

antipodal
The three haploid nuclei which are formed during megasporogenesis in plants. They are all located opposite the micropyle end of an ovule.

anus
The terminal opening of the gut; the solid residues of digestion are eliminated through the anus.

aorta
The major artery of vertebrate systemic blood circulation. It carries oxygenated blood from the left ventricle of the heart around the trunk, giving rise to several branches to individual body organs.

aortic arch
one of up to six paired arteries that join the ventral and dorsal aorta in vertebrates or their embryos.

apical meristem
A group of plant cells that are found at the growing tip of a root or a stem. These cells are capable of dividing indefinitely and their main function is the production of new growth.

Apicomplexa
members of this phylum were formerly called sporozoans, and are parasites of animals, some of which cause dangerous human diseases. Most apicomplexans have intricate life cycles with both sexual and asexual stages, often requiring two or more different host species for completion.

aponeurosis
A tough, flat sheet of connective tissue that distributes the tension of a muscle.

Arachnida
the class contains scorpions, spiders, ticks, mites, and king crabs. They lack antennae, usually have four pairs of walking legs and with the exception of the king crab, Limulus, are air-breathing.

archegonium (pl. archegonia)
The female sex organ of liverworts, mosses, ferns, and most gymnosperms. It is usually a flask-shaped organ, comprising a swollen base or venter containing a single egg-cell and a slender elongated neck containing one or more layers of cells.

archenteron
The endoderm-lined cavity formed during the gastrulation process that develops into the digestive tract of an animal.

arterial system
Blood vessels that carry oxygenated blood to tissues from the heart , forming part of the blood circulatory system.

Ascaris
a genus of parasitic roundworm, phylum Nematoda, that occasionally inhabit the small intestine of man.

Ascomycotina
a subdivision of fungi in which sexually produced spores are contained within asci and are called ascospores.

asexual reproduction
A type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts.

ATP
(Adenosine TriPhosphate) A molecule consisting of adenosine (adenine plus a ribose sugar) and three phosphate groups. The last two phosphates are joined by high energy bonds which provide energy used in chemical reactions such as respiration and glycolysis. In plants, ATP is formed in the chlorplasts during photosynthesis.

atrium
A chamber in the heart which receives blood from the body.

autotrophs
An organism able to build all the complex organic molecules that it requires as its own food source, using only simple inorganic compounds. Plants, and some bacteria are autotrophs.

axon
a typically long outgrowth, or process, from a neuron that carries nerve impulses away from the cell body toward target cells.

B

Bacillus
a bacterial cell that is rod-shaped (i.e. longer than it is wide).

bacteriophages
a type of virus that infects bacteria. Infection with a bacteriophage may or may not lead to the death of the bacterium, depending on the phage and sometimes on conditions. Each bacteriophage is specific to one form of bacterium.

bark
The living tissue outside the vascular cambium in a woody stem. It is composed of phloem tissues, which occur as living inner and dead outer zones.

basidium
a reproductive appendage that produces sexual spores on the gills of mushrooms. The fungal division Basidiomycota is named for this structure.

belly
The central portion of a muscle.

biceps
A group of muscles present in the upper forelimb of tetrapods, which are flexors of the elbow joint. In the hind limb, the biceps femoris is a flexor of the knee and an elevator of the femur.

bilateral symmetry
An animal body structure in which the right and left halves of an organism are approximately mirror images of each other. Most higher invertebrates and all vertebrates have members which are bilaterally symmetrical.

bile
a mixture of substances containing bile salts, which emulsify fats and aid in their digestion and absorption.

binary fission
the type of cell divisions by which prokaryotes reproduce; each dividing daughter cell receives a copy of the single parental chromosome.

blastema
An undifferentiated mass of animal cells that later forms a structure or organ either embryologically if through regeneration, for example the head of a flatworm.

blastocoel
The central cavity of the blastula stage of vertebrate embryos.

blastoderm
The layer of cells formed by cleavage of the fertilized egg in the presence of large amounts of yolk.

blastomeres
Any cell that occurs in the blastula.

blastopore
The opening of the gastrula that develops into the mouth in protostomes and the anus in deuterostomes.

blastula
The hollow ball of cells marking the end stage of cleavage during early embryonic development.

blood vascular system
the mechanism by which blood is moved through the body. This includes the arteries, veins, capillaries, and heart.

bone cell
Also referred to as an Osteoblast.

Bowman's Capsule
Found at the end of a kidney nephron, it contains the glomerulus and functions in filtration.

brachial
of or relating to the arm or to an arm-like structure.

bract
A modified leaf with a single flower growing in its axil.

branch primordia
A lateral stem that is in its earliest stage of differentiation.

branchial chamber
A chamber or cavity containing the gills of fish.

brush border
Formed by epithelial cells with microscopic projections called microvilli, that extend into the intestinal lumen

buccal cavity
Mouth cavity.

bud
An immature shoot, which the stems, leaves, or flowers may develop from.

budding
A method of asexual reproduction common in some lower animal groups in which part of the body wall bulges outward and eventually forms a new individual, which becomes detached from the parent. Budding can also occur in single-celled organisms such as yeast.

C

caecum (pl. caeca)
a blind-ending sac in the digestive system, which occurs in mammals at the junction of the small and large intestines. In herbivores the caecum contains bacteria that produce cellulase, enabling breakdown of cellulose cell walls.

calcareous algae
algae that contains calcium carbonate.

calyx
A collective term for all the sepals of a flower.

canines
Four pointed teeth present in the jaw between the incisors and the premolars in mammals, being particularly prominent in the Carnivora and having a stabbing function.

cannibalistic
The act of an animal feeding on its own kind.

cap (also pileus)
The fleshy or leathery structure upon which the spore-bearing structures occurs in a fungal fruit body.

capillaries
One of the many minute blood vessels that connect arterioles and venules in vertebrate tissues, allowing a high level of exchange of materials between blood and tissues via the interstitial fluid.

capitulum
In animals it is the rounded rib head that articulates with the centrum of the vertebra. In plants it is a head of flowers.

capsid
the protein shell that encloses the viral genome; rod-shaped, polyhedral, or more completely shaped.

capsule
a containing structure with a strong outer covering, found in many different groups.

carapace
The part of a Crustacean that spreads over the head and thorax.

carbohydrate
A family of organic molecules with the general formula (CH20)x, ranging from simple sugars, such as glucose and fructose, to complex molecules, such as starch and cellulose.

cardiac muscle
A type of muscle that forms the contractile wall of the heart; its cells are joined by intercalated discs that relay each heartbeat.
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cardiac portion
Of or relating to the heart.

cardiac stomach
Front portion of the stomach.

carpel
The female reproductive organ of a flower, consisting of the stigma, style and ovary.

catabolism
A type of metabolism in which biochemical processes taking place in a cell result in the breaking down of complex compounds into simpler ones to release energy.

catalase
An enzyme found in tissues, such as the liver, whose function is to catalyze the breakdown of toxic hydrogen peroxide into water and oxygen.

caudal
Relating to or in the position of the tail.

cell membrane
the outer boundary of cells, the structure of which is visible only under the electron microscope.

cellulose
A type of unbranched polysaccharide carbohydrate that is composed of glucose sugars.

cell vacuole
a membrane-bound sac that is found in many cells, normally acting as a storage organ of various types. A large central vacuole is a particular feature of many plant cells, where it can occupy 80-90% of the total cell volume.

cell wall
Unique to plant cells, a wall formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and the primary constituent of wood.

cellular respiration
the most prevalent and efficient catabolic pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel

central cell
Found in the central region of the megagametophyte, it contains two polar nuclei.

centriole
One of two structures in the center of animal cells, composed of cylinders of nine triplet microtubules in a ring. Centrioles help organize microtubule assembly during cell division.

centromere
The centralized region joining two sister chromatids.

cephalic
Pertaining to the head.

cephalization
The evolution of a head (anterior) end with sensory structures and a highly specialized brain to process sensory input; a feature of bilaterally symmetric animals, especially the vertebrates.

cephalothorax
The fused head and thorax occurring in many Arthropods, particularly Crustaceans.

cerebellum
part of the vertebrate hind-brain (rhombencephalon) located dorsally; it is responsible for unconscious coordination of movement and balance.

cerebrum
the dorsal portion, composed of right and left hemispheres, of the vertebrate forebrain; the integrating center for memory, learning, emotions, and other highly complex functions of the central nervous system.

cervical
Referring to the neck.

Cestoda
a phylum of Platyhelminthes containing the parasitic tapeworms, the adults of which are intestinal parasites of vertebrates.

chalazae
ZOOLOGICAL - Either of two spiral bands in the white of a bird's egg that extend from the yolk and attach to opposite ends of the lining membrane.
BOTANICAL - the basal part of a plant ovule where the nucellus is fused to the surrounding integument and to which the funiculus is usually attached.

cheliped (aka chelicerae)
Clawlike feeding appendages characteristic of the chelicerate group.

chitin
A structural polysaccharide of an amino sugar found in many fungi and in the exoskeletons of all Arthropods.

chloragogue cells
Yellow cells which surround the gut of earthworms. These cells break loose into the coelom and absorb wastes.

chlorenchyma
plant parenchyma cells that contain chloroplasts in their cytoplasm.

Chlorophyta
the green algae, which constitute the largest division of algae. They are terrestrial, found in damp places, such as tree trunks, in fresh water, and in the marine environment.

chloroplast
A subcellular organelle which contains chlorophyll and enzymes necessary to perform photosynthesis. Has an inner and outer membrane, as well as a third membrane bound sac, the thylakoid. Stacks of thylakoids are called grana, where the Light Reaction occurs. The cytoplasm of the chlorplast is called the stroma, and the Light Independant Reaction (carbon fixation) occurs here.

chordate
a member of a diverse phylum of animals that possess a notochord; a dorsal, hollow nerve cord; pharyngeal gill slits; and a postanal tail as embryos.

chromatid
One of a pair of duplicated chromosomes produced during the S phase of the cell cycle, which are joined together at the centromere.

chromatin
the aggregate mass of dispersed genetic material formed of DNA and protein and observed between periods of cell division in eukaryotic cells.

chromosome
a long, threadlike association of genes in the nucleus of all eukaryotic cells and most visible during mitosis and meiosis. Chromosomes consist of DNA and protein.

cilium (plural, cilia)
A short cellular appendage specialized for locomotion.

Ciliophora
a very large subphylum of Protozoans, including the Ciliata and Suctoria, that at some time during the life cycle possess cilia and usually a micro- and meganucleus.

circular muscle fiber
The layer of muscles found just below the epidermis.

cleavage
The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane; also, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells.

cloaca
A common opening for the digestive, urinary, and reproductive tracts in all vertebrates except most mammals.
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clone
A lineage of genetically identical individuals.

closed circulatory system
A type of internal transport in which blood is confined to vessels.

coarse adjustment knob
knob located on the arm of a microscope used to obtain an approximate focus

coelom
The main body cavity, which is lined with mesoderm, and found in annelids, molluscs, arthropods, echinoderms, and chordates.
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collateral
a minor side branch of a blood vessel or nerve.

collecting tubules
That part of the renal tubule in a kidney in which water absorption takes place under the control of ADH, producing urine of variable concentration depending on overall water levels in the body.

collenchyma
A supporting plant tissue similar to parenchyma cells, but have cellulose wall thickenings.

colon
A part of the large intestine in mammals which functions in the reabsorption of water from feces.

columella
The sterile central column in the sporangia of mosses and liverworts.

columnar epithelial cells
A layer of covering cells that is normally one cell thick and usually covers connective tissue embryologically derived from the ectoderm. Columnar refers to their shape.

companion cells
A type of plant cell that is connected to a sieve-tube member, making up the phloem tissue.

complete metamorphosis
The change in an organism from larval to adult from where the larval stages look entirely different from the adult stage.

compound eye
a type of multi-faceted eye in insects and crustaceans consisting of up to several thousand light-detecting, focusing ommatidia; especially good at detecting movement.

compound pistil
Made up of several pistils to form one structure

conaliculi
Fine passages that radiate from the lacunae of the lamellae.

condenser
concentrates light from the illuminator below.

conjugation
A recombination mechanism that results in the transfer of genetic, material between two cells that are temporarily joined.

conjugation tube
Connecting tube that allows two individuals to fuse together temporarily in order to exchange micronuclear material.

contractile vacuole
An organelle that pumps excess water out of many freshwater protist cells.

cork cambium
A cylinder of meristematic tissue in plants that produces cork cells to replace the epidermis during secondary growth.

cork cell
A secondary tissue produced by the cork cambium, and forms the outer part of the periderm in a woody plant.

corolla
A collective term for all the petals of a flower. The petals are often brightly coloured and attract pollinating animals. The corolla encloses the reproductive organs, and is itself protected by the sepal.

corpus luteum
Formed from a follicle that has ruptured due to hormonal regulation. The corpus luteum secretes progesterone, which prepares the reproductive organs for pregnanacy and maintains the uterine lining. If the egg is fertilized the corpus luteum will persist during pregnancy, otherwise it will degenerate.

cortex
The region of the root between the stele and epidermis filled with ground tissue.

cortex
The outer zone of an organ, ex. kidney.

cotyledons
The one (monocot) or two (dicot) seed leaves of an angiosperm embryo.

cranium
The skull of vertebrates.

crista (plural, cristae)
An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzymes catalyzing the synthesis of ATP.

crop
In vertebrates, it is an expanded part of the esophagus where food is stored while in invertebrates it is an expansion of the anterior part of the gut system where food is either digested or stored.

crossing over
the reciprocal exchange of genetic material between non-sister chromatids during synapsis of meiosis I.

Crustacea
class in the phylum Arthropoda. Most members of this class are aquatic, although a few are terrestrial.

cuboidal epithelial cells
a layer of covering cells that is normally one cell thick and usually covers connective tissue embryologically derived from the ectoderm. Cuboidal refers to their shape.

cutaneous maximus
Muscle that originates in the region of the armpit and the outer surface of the latissumus dorsi muscle. The cutaneous maximus muscle inserts on the skin and it is used for shaking the skin.

cuticle
(1) a waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants. (2) the exoskeleton of an arthropod, consisting of layers of protein and chitin that are variously modified for different functions.
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cyanobacteria
a large and varied group of bacteria which possess chlorophyll a and which carry out photosynthesis in the presence of light and air with concomitant production of oxygen.

cytokinesis
the division of the cytoplasm to form two separate daughter cells immediately after mitosis.

cytoplasm
the entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.

D

dehiscent
will spontaneously burst open to release it's contents, usually spores or seeds.

dendrite
one of usually numerous, short, highly branched processes of a neuron that conveys nerve impulses toward the cell body.

depressors
muscles which produce the down stroke in birds flight and run from the humerus to the sternum.

determinate growth
A type of growth characteristic of animals, in which the organism stops growing after it reaches a certain size.

deuterostome
An evolutionary line of coelomates (ex. echinoderms and chordates) that are characterized by radial, indeterminate cleavage and development of the anus from the blastopore.

diaphragm
A sheet of muscle that forms the bottom wall of the thoracic cavity in mammals; active in ventilating the lungs.

diastema
A gap between teeth.

dicot
A subdivision of flowering plants whose members possess two embryonic seed leaves, or cotyledons. Dicots also differ from monocots in terms of structure of the roots and shoots.

differentiation
Divergence in structure and function of cells as they become specialized during a multicellular organism's development; depends on the control of gene expression (cell differentiation).

digitigrade
Walking on the toes or fingers, as in most fast-running animals, such as dogs and cats.

digit
Any part of the pentadactyl limb of vertebrates that contains a linear group of phalanges. A primate finger or toe.

dimorphism
An occurance of an organism in two forms. Sexual dimorphism refers to males and females. Dimorphism may occur in, for example, body form or colour.

dioecious
Possesses male and female flowers or other reproductive organs on separate, unisexual, individual plants.

diploid
Refers to a cell nucleus containing two of each type of chromosome. Refers to an organism in the main life stage having cell nuclei having two of each type of chromosome, written as 2N.
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distal
Farthest from the body in any structure, or farthest from the center of the system concerned. For example, the finger is at the distal end of the human arm.

dorsal
Referring to the top (or back) half of a bilaterally symmetric animal.

dorsal aorta
an artery of the mammalian blood circulatory system that carries oxygenated blood from the heart down the length of the trunk, giving rise to several branches to individual body organs.

dorsal horn of gray matter
the gray matter of the spinal cord that is internally arranged in an H shape in cross section.

dorsal lip
The upper edge of the blastopore produced by invagination during gastrula formation in amphibian embryos; the site toward which surface cells of the gastrula converge and migrate inward along the roof of the blastocoel in the process of involution.

dorsal root ganglion
a nerve trunk containing only sensory axons that enters the spinal cord near the dorsal surface.

dorsoventrally flattened
Flattened along the length of it's back ex. platyhelminths.

double circulation
A circulation scheme with separate pulmonary and systemic circuits, which ensures vigorous blood flow to all organs.

double stranded
two adjacent strands. For example DNA has two adjacent polynucleotide strands wound into a spiral shape.

duodenum
Part of the small intestine connecting the stomach to the ileum.
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E

ectoderm
The outermost of the three primary germ layers in animal embryos; gives rise to the outer covering and, in some phyla, to the nervous system, inner ear, and lens of the eye.

ectotherm
An animal, such as a reptile, fish, or amphibian, that must use environmental energy and behavioral adaptations to regulate its body temperature.

effector cell
A muscle cell or gland cell that performs the body's responses to stimuli; responds to signals from the brain or other processing center of the nervous system.

elevators
muscles which produce the upstroke for flight and are attached to the upper surface of the humerus by a tendon that runs through the pectoral girdle to the sternum.

embryo sac
The female gametophyte of angiosperms, formed from the growth and division of the megaspore into a multicellular structure with eight haploid nuclei.

endoderm
The innermost of the three primary germ layers in animal embryos; lines the archenteron and gives rise to the liver, pancreas, lungs, and the lining of the digestive tract.

endodermis
The innermost layer of the plant cortex which surrounds the stele in plants. It functions in controlling the transport of substances within the plant.

endoplasmic reticulum
a series of interconnected, flattened cavities lined with a membrane about 4 nm thick, which is continuous with the nuclear membrane.

endosperm
A nutrient-rich tissue formed by union of a sperm cell with two polar nuclei during double fertilization, which provides nourishment to the developing embryo in angiosperm seeds.

endotherm
An animal that uses metabolic energy to maintain a constant body temperature, such as a bird or mammal.

enteron
The tubular passage that extends from mouth to anus.

epidermis
(1) the dermal tissue system in plants. (2) the outer covering of animals.

epididymis
The long, coiled narrow tube running from the testis to the vas deferens in the higher vertebrates. It functions to store sperm.

epiglottis
A thin flexible structure, made of cartilage with a leaf-like shape, which guards the entrance to the larynx (the glottis) and prevents food material from entering the trachea during swallowing.

erythrocyte
A red blood cell; contains hemoglobin, which functions in transporting oxygen in the circulatory system. These are the most common cell type of the blood.

esophagus
The part of the alimentary canal of vertebrates that lies between the pharynx and the stomach.
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eukaryotes
Any member of a group of organisms that contains all plants and animals apart form bacteria and blue-green algae. Their cells possess a membrane-bound nucleus containing the genetic material.

Eustachian tubes
A tube passing from the pharynx to the middle ear in higher vertebrates, serving to equalize pressure on either side of the tympanic membrane.

exoskeleton
A skeleton present on the outside of an organism, as in Arthropods or Mollusks.

exponential phase
Rapid increase resulting in a J-shaped curve through time.

extensor
a muscle that extends of straightens a limb.

external nares
An external opening of the nose leading into the nasal cavity.

external oblique
Muscle that inserts on the linea alba and border of the pubis and its action is to constrict the abdominal region.

eye-piece
or ocular, one of the magnifying elements of a microscope.

eyespots
a light-sensitive organelle present in unicellular organisms, green algae, zoospores, and some gametes.

F

Fallopian Tube
upper part of the oviduct in mammals, which is ciliated and where the egg passes from the coelom.

fascia
sheets of connective tissue.

fat (triacylglycerol)
a biological compound consisting of three fatty acids linked to one glycerol molecule.

femur
The thigh bone of tetrapods.

fermentation
a catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end-product, such as ethyl alcohol or lactic acid.

fiber cell
A type of plant cell which has a thickened cell wall that performs a structural role. (ex. cortex, phloem, and xylem.)

fibroblast
a type of cell in loose connective tissue that secretes the protein ingredients of the extracellular fibers.

fibula
A bone present in the posterior limb of tetrapods lying slightly posterior to and parallel with the tibia.

flagellum (pl. flagella)
A long cellular appendage specialized for locomotion, ensheathed in an extension of plasma membrane.
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flame cell
A cell specialized for excretion found in platyhelminths.

flexor
any muscle that brings about the bending of a limb.

flower
A structure involved in sexual reproduction. It consists of the androecium (male organs) and gynoecium (female organs), surrounded by a corolla and a calyx. The male and female parts may or may not be in the same flower.

foliose
Leaf-like; made up of thin flat lobes, as are the thalli of certain types of lichen.

follicles
Microscopic structures in the ovary that contain developing ova and secrete estrogens.

foot
The molluscian organ of locomotion.

frond
A big compound leaf applied to those of palms and ferns.

fructose
a simple carbohydrate (monosaccharide) that is a structural isomer of glucose and considered to be an atypical ketose.

funiculus
The stalk by which a developing angiosperm ovule attaches to the carpel wall.

G

gametangium (pl. gametangia)
The reproductive organ of bryophytes, consisting of the male antheridium and female archegonium; a multichambered jacket of sterile cells in which gametes are formed.

gametes
Haploid egg or sperm cells that unite during sexual reproduction to produce a diploid zygote.

gametogenesis
The process where haploid gametes are produced from diploid cells via meiosis. In animals the two processes are spermatogenesis and oogenesis.

gametophyte
The part of the life cycle of plants having haploid nuclei and giving rise to the sex cells that on fusing produce a diploid stage, usually the sporophyte.

ganglion (plural, ganglia)
A cluster (functional group) of nerve cell bodies in a centralized nervous system.

gastric
of or relating to the stomach.

gastric caeca
Out pockets of the gut. For example they are found in starfish.

gastrulation
The formation of a gastrula from a blastula.

generative cell
One of two haploid nuclei found within pollen grains of flowering plants, which enters the pollen tube when it is produced, divides by mitosis, and becomes the male gamete nucleus that fuses with the female egg cell at fertilization.

gene
one of many discrete units of hereditary information located on the chromosomes and consisting of DNA.

germinal disc
A small mass of active protoplasm found directly under the vitelline membrane.

gill
The respiratory organ of aquatic animals.

glomerulus
A ball of capillaries surrounded by the Bowman's capsule in the nephron and serving as the site of filtration in the vertebrate kidney.

glottis
Opening of the larynx (windpipe).

glucose
(C6H12O6) An important monosaccharide (simple carbohydrate) that acts as a primary energy supply for both plant and animal cells.

glycolysis
The splitting of glucose into pyruvate. Glycolysis is the one metabolic pathway that occurs in all living cells, serving as the starting point for fermentation or aerobic respiration.

glycogen
An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.

goblet cells
a wineglass-shaped cell, which is present in the columnar epithelium of the mammalian intestine and secretes mucin.

Golgi apparatus
An organelle in eukaryotic cells consisting of stacks of membranes that modify, store, and route products to the endoplasmic reticulum.

gonads
The male and female sex organs; the gamete-producing organs in most animals.

granum (plural, grana)
A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.

granulocyte
A type of white blood cell (leucocyte) that possesses granules in the cytoplasm and is formed in the bone marrow. Granulocytes form about 70% of all leucocytes.

guard cell
A specialized epidermal plant cell that forms the boundaries of the stomata.

gymnosperm
A vascular plant that bears naked seeds not enclosed in any specialized chambers.

gynoecium
The female reproductive organs of a flower, consisting of one or more carpels.

H

habituation
a simple kind of learning involving loss of sensitivity to unimportant stimuli, allowing an animal to conserve time and energy.

haemocoel
The body cavity of invertebrates, arthropods, and mollusks. As to the coelom, the haemocoel never opens to the exterior and it does not contain germ cells.

haploid
Referring to a cell nucleus it contains one of each type of chromosome. Referring to an organism it is one in which the main life stage has cell nuclei with one of each type of chromosome, written as n.

haploid gametophyte
The part of the life cycle of plants having haploid nuclei and giving rise to the sex cells that on fusing produce a diploid stage, usually the sporophyte.

Haversian canal
One of many channels formed within bone by the development of osteoblasts in concentric rings around them, and whose function is to facilitate linking of the living parts.

heart
The muscular pump of the blood circulatory system.

hepatic caeca
A blind-ending sac in the digestive system, which occurs in mammals at the junction of the small and large intestines. In herbivores the cecum contains bacteria that produce cellulase, enabling breakdown of cellulose cell walls.

hepatic portal system
The part of the blood circulatory system of vertebrates in which blood from the alimentary canal is taken through capillaries in the liver before transport to the heart.
Covered in:

hepatic portal vein
A vein which enables some materials absorbed from the gut to be stored or filtered out during passage through the liver.

hepatocytes
A liver cell.

hermaphrodite
Plants which possess both stamens and carpels in the same flower, while in animals it is organisms which possess both male and female sex organs

heterocyst
A specialized cell that engages in nitrogen fixation on some filamentous cyanobacteria.

heterodont
Possessing teeth of different kinds, such as incisors or molars.

heterosporous
The formation of more than one sort of spore, usually microspores and megaspores in ferns and seed plants, giving rise to distinct male and female gametophyte generations.

heterotroph
An organism dependent on obtaining organic food from the environment because it is unable to synthesize organic material. They (animals, fungi, many bacteria, and a few flowering plants) obtain almost all their organic material either directly or indirectly from the activity of autotrophs.

homeothermic
Any warm-blooded animal (mammal or bird that can maintain its body temperature within a narrow range, usually above that of its surroundings despite large variations in environmental temperature. It may be maintained continually or for limited periods only.

homologous chromosomes
chromosome pairs of the same length centromere position, and staining pattern that possess genes for the same traits at corresponding loci. One homologous chromosome is inherited from the organism's father, the other from the mother.

homology
similarity in characteristics resulting from a shared ancestry.

homospory
The possession of only one form of spore. This gives rise to a single gametophyte generation carrying both male and female reproductive organs.

humerus
The bone of the vertebrate forelimb, or arm, nearest to the body, to which it is attached at the shoulder. It is attached distally to the radius and ulna at the elbow.

hypha (plural, hyphae)
A filament that collectively makes up the body of a fungus.

I

ileum
The part of the intestine lying between the duodenum and the colon, where digestion is completed by enzymes that break down carbohydrates, fates, and proteins. Absorption of food also occurs here.

iliac artery
Arise at the posterior end of the abdominal cavity, where they form the two major terminal branches off the aorta supplying the legs with oxygenated blood.

iliolumbar artery
arise form the aorta posterior to the genital arteries and send branches to the dorsal musculature of the body wall.

illuminator
light source found at the base of the microscope.

imprinting
an aspect of learning in which there is rapid development of a response to a particular stimulus at an early stage of development. Young animals recognize the first object they see, such as a mother figure, and they can be imprinted on objects other that their own species.

incisor
A front, chisel-shaped tooth in mammals, normally used for cutting or gnawing. In some species incisors continue to grow throughout life.

incomplete metamorphosis
The change in an organism from larval to adult form where there is a gradual development of a nymph to an adult.

indehiscent
Will not spontaneously burst open to release it's contents, usually spores or seeds.

independent assortment
the random arrangement and separation of chromosomes during meiosis, giving all possible combinations in equal frequency. This process explains the random distribution in the gametes of genes or homologous chromosomes.

indeterminate cleavage
Characteristic of deuterostomes, each cell produced by early cleavages retains the ability to develop into a complete embryo.

inferior vena cava
Drains blood from the abdominal region and brings it back to the heart via the right atrium.

inflorescence
A specialized branching stem bearing more than a single flower, for example, a male catkin.

infundibulum
the part of the pituitary gland that is produced by a down growth of the posterior region of the forebrain.

innominate artery
A short artery arising from the aorta that gives rise to the subclavian and carotid arteries.

Insecta
class of organisms that are small air-breathing arthropods. This class contains organisms that in the adult normally have six legs, three distinct regions to the body (head, thorax, and abdomen), one pair of antennae, and one or two pairs of wings.

insertion
A mutation involving the addition of one or more nucleotide pairs to a gene.

insertion
The more movable attachment point of a muscle.

integument
The outermost layer or layers of tissue that serve in protection.

intercalated disc
A specialized region in cardiac muscle which allows the action potential to spread to all cardiac muscle cells, causing the whole heart to contract.

intercostal muscles
The muscles lying between the ribs of vertebrates that, with the ribs, form the walls of the thorax.

internal nares
two small openings in the roof of the buccal cavity.

internal oblique
Muscle that inserts on the linea alba and its action is to compress the abdominal region.

internode
The segment of a plant stem between the points where leaves are attached.

interphase
A stage of growth in the cell cycle in which metabolism occurs without visible evidence of nuclear division. Interphase is the phase between divisions (meiosis and mitosis).

interstitial cells
Cells scattered among the seminiferous tubules of the vertebrate testis that secrete testosterone and other androgens, the male sex hormones.

intestinal villi
folds and projections on the internal surface if the intestine that greatly increases the surface area for digestion and absorption.

intestine
The part of the alimentary canal that lies between the stomach and anus. It is usually coiled, and the internal surface is greatly increased by the presence of folds and projections (villi) to enable efficient digestion and absorption.

iris diaphragm control
small lever that allows the size of the opening to change in order to regulate the amount of light passing through it.

J

jejunum
Found in the small intestine, it is located between the duodenum and the ileum.

jointed appendages
Where the bones that make up the appendage have contacts between them

K

karyokinesis
the division of the cell nucleus.

kidney
Paired vertebrate organs that regulate fluid balance in the body and filter out wastes from the blood in the form of urine. The functional unit of the kidney is the nephron. Wastes are filtered from the blood by nephrons, which drain into the ureters (muscular tubes that connect each kidney to the bladder).

L

labium
The lower lip of insects, found immediately behind the maxillae.

labrum
A cuticular plate at the front of the insect head, forming an upper lip.

lacunae
One of many small cavities uniformly spaced along the lamellae of bones. In living bone, each lacuna contains one bone cell known as an osteocyte. Small canals (canaliculi) radiate from the lacunae and in these are small protoplasmic processes that conn ect with the osteoblast in other lacunae.

lag phase
The stage of growth of microbial cells in which nucleic acids and proteins are synthesized, but in which there is no cell division.

lamellae
(a) the sheet-like membrane that occurs within the chloroplast, each of which consists of a pair of membranes with a narrow space between. (b) the gills of a basidiomycete fungus that radiate out from the stalk beneath the cap of the fruit and bear the spores.

larynx
(the voice box) A dilation of the upper part of the trachea (windpipe) of tetrapods (Adam's apple in humans), occurring in the front part of the neck containing the vocal cords

lateral
At the side of

lateral meristem
Consisting of the vascular cambium and the cork cambium, it produces the secondary tissues which make up the secondary plant body.

lateral (secondary) roots
The branches that develop from deep inside the plant root. This type of branching is initiated by the plant hormone, auxin.

latissimus dorsi muscle
This muscle originates on the thoracic and lumbar vertebrate and inserts on the shaft of the humerus. Its action is to pull the arm backward and upward.

leaf
A thin organ arising from the node on the stem of a plant. The main site of phtosynthesis.
Covered in:

leaflets
the "leaves" that make up a compound leaf.

leaf primordia
The early, precursor cells of a leaf.

lenticel
A small pore found on the surface of stems and roots in higher plants through which gas exchange can take place.

leucocyte
A white blood cell; typically functions in immunity, such as phagocytosis or antibody production.

limb
An articulated (jointed) projection from the body of an animal that is used for locomotion, such as a leg or wing.

linea alba
A narrow, longitudinal, whitish band of tendonous tissue found along the mid-ventral line.

lipid
One of a family of compounds, including fats, phospholipids, and steroids, that are insoluble in water.

liver
The largest organ in the vertebrate body, performing such functions as producing bile, preparing nitrogenous wastes for disposal, and detoxifying poisonous chemicals in the blood.

liverworts
Belong to the class Bryophyta and are found in damp and wet conditions.

lobule
One of several lobes or divisions of the liver.

locus (pl. loci)
a particular place along the length of a certain chromosome where a given gene is located.

log (logarithmic) phase
The exponential phase of growth in a bacterial culture.

longitudinal axis
a lengthwise axis from head to tail end of an animal.

longitudinal muscle fiber
Arranged in a feather-like pattern, this thick layer of muscles is found below the circular muscle fibers.

loop of Henle
The long hairpin turn, with a descending and ascending limb, of the renal tubule in the vertebrate kidney; functions in water and salt reabsorption.

lower epidermis
the tissue in plants, usually one cell thick, that is on the bottom of the leaves.

lumbar
Vertebrae present between the thoracic vertebrae and the sacral vertebrae, in the region of the waist in mammals.

lumen
Any cavity enclosed within a cell or structure, such as the lumen of the gut.

lung
The organ that enables an animal to breathe air. In mammals the paired lungs are each supplied by a bronchus that divides, treelike, into bronchioles. Each bronchiole ends in an atrium from which arise numerous alveoli that contact a vast capillary system.

lymphatic system
A system of tubules in vertebrates that drains excess tissue fluid (lymph) from the tissue spaces to the blood system. Lymph are blind-ending in the tissue spaces, gradually joining up to larger and larger vessels with two major lymphatic ducts entering the venous system in the upper thoracic cavity. Lymph is moved by the action of skeletal muscles.

lysosome
a membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.

M

macromere
A large cell from the vegetative pole of a developing egg. Such a cell contains yolk and gives rise to the endoderm of the embryo.

macronucleus
The larger of two nuclei found in some Protozoans and concerned with cell division. It appears to have mainly vegetative functions.

madreporite
The porous opening to the hydrocele in echinoderms.

Malpighian tubule
A unique excretory organ of insects that empties into the digestive tract, removes nitrogenous wastes from the blood, and functions in osmoregulation.

mammary gland
A gland present in female mammals that produces milk used to suckle the young. It probably evolved from a modified sweat gland and at least two are normally present, although in many mammals more than two are developed, usually concentrated on the underbelly beneath the pelvic girdle. In most mammals the size of the gland is determined by the state of the estrous cycle.

mandibles
The mouthparts of an animal that does most of the crushing of food materials. In vertebrates, the term usually denotes the lower jaw.

mandibular abductor muscle
Muscle in the crayfish that pulls up the mandible.

mantle
The part of the epidermis of a mollusk that secretes the shell and covers the dorsal and lateral surfaces.

masseter
Large muscle that elevates the jaw.

mature ovum
a functional egg cell of an animal.

maxilla
In vertebrates it is the bone of the upper jaw, carrying all teeth except the incisors. In invertebrates (arthropods) it is part of the mouthparts lying behind the jaws.

maxillipede
Any limb modified for feeding, normally found immediately in front of the legs, particularly in crustaceans.

median
describing a location along the line of bilateral symmetry (median plane).

medulla
The central part of an organ. Ex. kidney.

medulla oblongata
The lowest part of the vertebrate brain; a swelling of the hind-brain dorsal to the anterior spinal cord that controls autonomic, homeostatic functions, including breathing, heart and blood vessel activity, swallowing, digestion, and vomiting.

medusa
the floating, flattened, mouth-down version of the cnidarian body plan. The alternate form is the polyp.

megagametophyte
Female gametophyte in seed plants.

megasporangium
The organ in which megaspores are formed.

megaspore
The larger of two types of spores produced by many ferns and seed plants. The megaspore gives rise to a female gametophyte in ferns and in seed plants, and in flowering plants becomes the embryo sac.

megasporocyte
Special cell of the megasporangium called the megaspore mother cell.

meiosis
A type of nuclear division associated with sexual reproduction, producing four haploid cells from a single diploid cell, the process involving two cycles of division.

meristem
A region of a plant in which active cell division occurs, the cells of the meristem being undifferentiated into a specialized form. Meristematic tissues occur at the root and shoot tips giving growth in length.

mesentery
The layers of peritoneum that attach the gut system and its associated organs, for example, the spleen, to the dorsal surface of the peritoneal cavity in mammals.

mesoderm
The middle primary germ layer of an early embryo that develops into the notochord, the lining of the coelom, muscles, skeleton, gonads, kidneys, and most of the circulatory system.

mesophyll
The ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis.

metabolism
The totality of an organism's chemical processes, consisting of catabolic and anabolic pathways.

metaphase
a stage of nuclear division in eukaryote cells, occurring once in mitosis and twice in meiosis. This phase begins when all of the centromeres line up at the equatorial plane.

microgametophyte
Pollen grains.

micromere
Any of the small blastomeres formed at the animal pole of a developing egg. These eventually give rise to the ectoderm.

micronucleus
The smaller of the two nuclei found in some Protozoans that is concerned with cell division.

micropyle
A small canal in the integument surrounding the ovule of a flowering plant, through which the pollen tube usually enters the ovule on the way to the embryo sac. Water enters the seed via the micropyle prior to germination.

microsporangium
The sporangium from which the microspores are formed, which in higher plants is the pollen sac.

microspore
The smaller of the two types of spore produced by ferns and higher plants, giving rise to the male gametophyte. In Tracheophytes the microspore is the pollen grain.

microsporocytes
Thousands of cells (pollen mother cells) found within a young microsporangium.

microvillus (plural, microvilli)
collectively, fine, finger-like projections of the epithelial cells in the lumen of the small intestine that increase its surface area.

mictic egg
A thin shelled haploid egg. If not fertilized, they will produce males by parthenogenesis. If fertilized, they will accumulate a large amount of yolk and secrete a heavier, resistant shell. These eggs are now dormant and can survive harsher environmental conditions until they develop into a diploid amictic female.

mitochondrion (plural, mitochondria)
An organelle in eukaryotic cells that serves as the site of cellular respiration.

mitosis
A process of cell division in eukaryotic cells conventionally divided into the growth period (interphase) and four stages: prophase, metaphase, anaphase, and telophase. The stages conserve chromosome number by equally allocating replicated chromosomes to each of the daughter cells.

mitospores
Spores resulting from meiosis.

molar teeth
The crushing teeth that occur at the back of the jaw of mammals. Each molar has a complicated pattern of cusps and ridges and several roots. The molars have no preceding milk teeth.

monocot
A subdivision of flowering plants whose members possess one embryonic seed leaf, or cotyledon. The grasses are a classic example of monocots.

monoecious
Referring to a plant species that has both staminate and carpellate flowers on the same individual.

morphogenesis
The development of body shape and organization during ontogeny.

moss
Any bryophyte of the class Musci. Usually these are small plants (less than 5 cm high) attached to moist or wet substrates by rhizoids; this is the sporophyte generation. The sexual organs are borne on a gametophyte generation, and the antheridia and archegonia are on separate leaf rosettes.

mouth
The anterior opening of the alimentary canal of animals through which food is taken into the body. It is often surrounded by mouthparts or tentacles that facilitate feeding.

mucosa
Any epithelium that secretes mucus, such as the mucous membrane lining the alimentary canal.

Mullerian duct
The duct from the embryonic pronephros, which in later development in mammals becomes the oviduct in females and disappears in males.

muscularis
The fleshy part of any animal that consists of tissue made up of highly contractile cells serving to move parts of the body relative to each other.

mushroom gills
A tissue of radiating strips found on the lower surface of the mushroom cap.

mycelium
The densely branched network of hyphae in a fungus.

myelin
a sheath of fatty substance associated with protein that surrounds larger nerve fibers of vertebrates. The sheath permits a greater current flow and thus speeds transmission of nerve impulses.

myofibrils
Fibrils arranged in longitudinal bundles in muscle cells (fibers); composed of thin filaments of actin and a regulatory protein and thick filaments of myosin.

myotome
A muscle block that is repeated in each metameric segment.

N

nare
An external opening of the nose that leads into the nasal cavity.

nasal cavity
A system of chambers above the hard palate of mammals through which air passes from the nostrils to the pharynx and on to the lungs. During inspiration, air is filtered, warmed, moistened, and smelled.

nasal septum
A dividing wall of partition that occurs between the nasal cavities.

naso-pharynx
Above the palate where the nasal cavities open into.

nectary (pl. nectaries)
An area in the tissue in a flower that secretes sugary nectar, serving as an attraction for visiting insects. Nectaries are frequently deep inside the corolla so that the pollinator both deposits and carries off pollen.

neoblast
Are undifferentiated cells arising from the parenchyma, which are rich in RNA. Thse cells form the blastema, which preceeds regeneration of planarians.

nephridium
(pl. nephridia) A primitive excretory organ present in many invertebrates, for example, the earthworm, in the form of a tube that opens at one end to the exterior. The other end may open into the coelom or may terminate in a flame cell.

nephron
The functional unit of the vertebrate kidney.

neural
Relating to the nerves or to the nervous system.

neuron
(nerve cell) the structural unit of the nervous system, usually consisting of the cell body and cytoplasmic extensions.

neurula
The stage of a vertebrate embryo when gastrulation is largely finished and a neural plate is forming, ending with formation of the neural tube.

nictitating membrane
A third eyelid that occurs in birds, reptiles, sharks, amphibians, and some mammals. It is transparent and flicks over the eyeball without shutting out the light.

nodes
A point along the stem of a plant at which leaves are attached.

nodes of Ranvier
the small gaps in the myelin sheath between successive ganglia cells along the axon of a neuron; also, the site of high concentration of voltage-sensitive ion channels.

Nostoc
a blue-green algae.

nostril
(nares) An external opening of the nose leading into the nasal cavity.

notochord
A longitudinal, flexible rod formed from dorsal mesoderm and located between the gut and the nerve cord in all chordate embryos.

nucleolus (plural, nucleoli)
A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.

nucleus
An organelle of eukaryotic cells that is bounded by a nuclear membrane and contains the chromosomes whose genes control the structure of proteins within the cell.

O

objective
A magnifying element found on the revolving nosepiece of a microscope.

ocelli
A type of eye found in threes in insects that detects light and dark, used primarily in flight.

ocular
the eye-piece of a microscope which serves to magnify the object.

olfactory bulb
a projection of the frontal lobe of a cerebral hemisphere that is well developed in most vertebrates, but reduced in humans, from which arises the olfactory nerve. It is associated with the sense of smell.

olfactory nerve
arises from the olfactory bulb and is associated with receiving and transmitting signals concerning the sense of smell.

omentum (pl. omenta)
A membrane that joins one internal organ to another.

oogenesis
The process in the ovary that results in the production of female gametes.

ootid
(ovum) Produced when a haploid secondary ooctye undergoes meiosis.

operculum
(1) the lid of a moss capsule. (2) the hard bony flap covering the gills of fishes. (3) the plate of exoskeletal material on the foot of a gastropod mollusk with which it closes off the entrance to the shell.

opposite arrangement
leaves located at the same height on the plant but at opposite sides of the stem.

optic chiasma
a point under the hypothalamus of the brain where the two optic nerves meet and cross over, so that a stimulus from either eye is interpreted in the optic lobe of the opposite side of the brain.

optic lobes
one of a pair of lobes found as swellings on the dorsal side of the midbrain of some lower vertebrates. The lobes integrate sensory information from the eyes and certain auditory reflexes.

oral groove
A depression leading to the mouth in some invertebrates.

organ
any multicellular structural or functional unit of an animal of plant, often composed of different tissues that perform specific roles, such as the liver and leaf.

organogenesis
An early period of rapid embryonic development in which the organs take form from the primary germ layers.

origin
The less movable attachment point of a muscle.

origin of life
the process by which biomolecules, subcellular structures, and living cells have come into existence.

oro-pharynx
Part of the pharynx found behind the buccal cavity and is shared by the respiratory and digestive systems

Oscillatoria
blue-green algae without any heterocysts.

osteocyte
A cell located in lacunae of vertebrate bone, that deposits a matrix of collagen and calcium phosphate that forms a mineralized connective tissue.

ostia
An opening in the heart where blood enters. Found in open circulatory systems.

ostium
Any of numerous openings present in sponges through which water is drawn in.

ovarian artery
Arise from the abdominal aorta just posterior to the kidneys and supplies the ovaries with oxygenated blood.

ovary
(1) in flowers, the portion of a carpel in which the egg-containing ovules develop. (2) in animals, the structure that produces female gametes and reproductive hormones.
Covered in:

oviduct
A tube passing from the ovary to the vagina in invertebrates or to the uterus in vertebrates.

ovule
A structure found in higher plants that contains an egg cell and develops into a seed after fertilization.

ovuliferous scales
A spiral series of overlapping scales making up the female or ovulate cone with each scale producing two ovules on the upper surface.

ovum (pl. ova)
A functional egg cell of an animal, produced by gametogenesis. Ova are frequently packed with nutritive yolk granules and are usually immobile.
Covered in:

oxidation
A chemical process in which either electrons are lost from an atom, or oxygen is added to a molecule. Oxidation may also occur without the addition of oxygen if hydrogen is removed (dehydrogenation.)

oxygen
A colourless, tasteless gas forming about 21% of Earth's atmosphere and capable of combining with all other elements except the inert gases.

oxygenated blood
blood that has become enriched with oxygen as it exchanges with the lungs.

P

palate
The roof of the mouth in vertebrates formed anteriorly by a bony projection of the upper jaw and posteriorly by the fold of connecitve tissue (soft palate).

palisade chlorenchyma
the upper internal tissue of a plant leaf which are stacked side by side and contain chloroplasts for photosynthesis. The chloroplasts lie close to the edge of the cell in order to gain maximum light and gas supply.

palisdae mesophyll
the upper internal tissue of a plant leaf which are stacked side by side resembling columns.

pancreas (Frog, Rat)
A gland situated in the mesentery of the duodenum of jawed vertebrates that has both an exocrine and an endocrine function.

papilla (pl. papillae)
A projection from the surface of a structure, such as tongue papillae, which carry the taste buds.

Paramecium
a genus of freshwater protozoan, having an oval body covered with cilia and a ventral ciliated groove for feeding.

paramylum
A starch-like substance that occurs as a food reserve in flagellate Protozoans and algae, such as Euglena.

parasite
An organism that absorbs nutrients from the body fluids of living hosts.

parenchyma cells
A relatively unspecialized plant cell type that carries on most of the metabolism synthesizes and stores organic products, and develops into more differentiated cell types.

parietal peritonium
A thin layer of connective tissue which originated from the mesoderm. It lines the abdominal cavity, as opposed to the internal organs.

parthenogenesis
The development from an egg without fertilization by a sperm. The egg cell may be haploid or diploid.

pectoral girdle
The skeletal support for the anterior limbs of vertebrates that transmits power from limbs to the body and also serves to protect and support the organs in the thorax.

pectoralis major
A muscle that originates on the sternum and inserts on the humerus.

pelvic girdle
The skeletal support for posterior limbs of vertebrates that transmits power in locomotion from the hind limbs to the body.

pentadactyl
Bearing five digits (fingers or toes), which is present in amphibia, reptiles, birds, and mammals.

pereiopod
The walking legs of a crayfish.

pericardial cavity
The part of the coelom surrounding the heart in vertebrates or the part of the hemocoel surrounding the heart in arthropods.

pericardial sinus
A cavity which contains the heart.

pericardial membrane
The membrane surrounding the heart.

pericardium
A sac-like envelope surrounding the vertebrate heart and the pericardial cavity in arthropods and mollusks.

pericycle
A layer of cells just inside the endodermis of a root that may become meristematic and begin dividing again.

periderm
The protective coat that replaces the epidermis in plants during secondary growth, formed of the cork and cork cambium.

peripheral
of or relating to the outside or extreme edge of a structure.

peripheral nervous system
The sensory and motor neurons that connect to the central nervous system.

peritoneum
The thin membrane of meosdermal origin that lines the body cavity, covers the heart, and forms mesenteries.

petal
Any of the separate parts of the corolla of a flower. Often brightly colored, the petal is a modified leaf and is important in flowers pollinated by insects.

petiole
the stalk of a leaf, which joins the leaf to a node of the stem.

Phaeophyta
a division of algae, comprising the brown algae.

phagocytosis
A type of endocytosis involving large, particulate substances.

pharynx
An area in the vertebrate throat where air and food passages cross; in flatworms, the muscular tube that protrudes from the ventral side of the worm and ends in the mouth.

phloem
The portion of the vascular system in plants consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.

photosynthesis
The conversion of light energy into chemical energy that is stored in glucose or other organic compounds; occurs in plants, algae, and certain procaryotes.

photoautotroph
A type of autotroph that uses light as an energy source to synthesize organic compounds from inorganic materials. Green plants are photoautotrophs.

pileus
the cap of certain groups of fungi.
See also Cap

pinna
1. the primary division of a leaf. 2. a wing or fin. 3. the projecting part of the external ear of mammals.

pistil
The flask-shaped female reproductive unit of a flower, composed of ovary, style, and stigma.

pith
The core of a dicotyledon stem, containing parenchyma cells that have a storage function.

pituitary gland
An endocrine gland at the base of the hypothalamus; consists of a posterior lobe (neurohypophysis), which stores and releases two hormones produced by the hypothalamus, and an anterior lobe (adenohypophysis), which produces and secretes many hormones that regulate diverse body functions.

plantigrade
Walking on the entire sole of the foot, as in humans and bears.

plaque
A clear area in a lawn of a bacterial colony, where the bacteria have undergone lysis due to bacteriophage infection.

plasma membrane
The outer boundary of cells which is only visible with an electron microscope.

plasmalemma
the cell membrane that also lines the connecting plamsodesmata between living cells.

plateau
A period or level at which something is stabilized for a time, represented on a graph as a horizontal line.

pleopod
A biramous (forked) abdominal appendage of the crayfish. They may be used for swimming or carrying eggs, in the females case. In the male, the first two pairs are modified for copulation.

pleura
The membrane that covers the lung and lines the innermost wall of the thorax.

poikilothermic
(Ectotherm) Any animal whose body temperature follows that of the surrounding environment.

polar body
A small haploid cell, produced during oogenesis in female animals, that does not develop into a functional ovum. A similar situation arises in the development of the egg cell of higher plants, in which only one fertile gamete is produced from meiosis.

polar nuclei
The two nuclei that are formed at each pole of the angiosperm embryo sac. They will fuse with a male nucleus to form a primary endosperm nucleus.

pollen grain
A small structure of higher plants that contains haploid male gamete nuclei and is surrounded by a double wall, the exine and intine. Pollen grains are transported from the male stamen to the female stigma in a process called pollination.

pollen tube
A slender structure produced from a pollen grain after pollination.

polyp
The asexual reproducing, normally sedentary form of coelenterates such as the sea anemone.

polysaccharide
A large carbohydrate molecule with a chainlike or branched structrure composed of many monosaccharides. Functions in storage (ex. starch, insulin, glycogen) or structre (ex. cellulose, chitin.)

posterior
situated behind; back; hind.

premolars
The cheek teeth in mammals that occur between the molars and the canines. They have a grinding function.

primary growth
Growth that takes place relatively close to the tips of roots and stems. It is intiated by the apical meristems, and primarily involves extending the length of the plant body.

primary oocyte
A diploid cell formed after a diploid oogonium underwent mitosis. The primary oocyte is arrested in Prophase of Meiosis I. It will complete meiosis to form a haploid primary oocyte and the haploid first polar body.

primary root
The first root of the plant. It develops in continuation from the root tip.

primary spermatocyte
A diploid cell formed after a diploid spermatogonium underwent mitosis. The primary spermatocyte is arrested in Prophase of Meiosis I. It will complete meiosis to form two haploid secondary spermatocytes.

primitive streak
A line of cells in the center of the embryonic disk of reptiles, birds, and mammals that forms the future axis of the embryo.

proboscis
The elongated mouthparts of some insects and other invertibrates.

prokaryotes
an organism that is either a bacterium or a blue-green alga, its main characteristic being prokaryotic cells lacking a membrane-bound nucleus and no mitosis or meiosis.

proglottid
A reproductive division of a tapeworm.

prostate gland
a gland of male animals that produces substances that are added to the semen.

protein
A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids.

Protozoan (plural, protozoa)
A protist that lives primarily by ingesting food, an animal-like mode of nutrition.

proximal
Pertaining to the region near the body.

pubic symphysis
Joint where the pubic bones come together.

pulmonary veins
Veins that carry the oxygenated blood from the lungs back to the heart.

pyloric portion
Of or relating to the end of the vertebrate stomach that opens into the intestine.

pyloric sphincter
A ring of smooth muscle surrounding the opening of the pyloric portion of the stomach into the intestine. The sphincter prevents premature escape of food from the stomach into the intestine before the food is properly digested.

pyrenoid
A region of starch formation found in the chloroplasts of various algae, for example, Chlamydomonas.

pyruvic acid
An important 3-carbon molecule formed from glucose and glycerol in glycolysis.

R

radial canal
Part of the water vascular system, it extends into each arm of the starfish and ends in a small external tentacale at the tip of each arm.

radial symmetry
Characterizing a body shaped like a pie or barrel, with many equal parts radiating outward like the spokes of a wheel; present in cnidarians and echinoderms.

radius
The anterior bone in the lower part of the forelimb of vertebrates.

receptacle
1. in flowering plants, the end of the stalk becoming the flower parts. 2. in ferns, the mass of tissue that becomes the sporangium. 3. in liverworts, the cup containing a gemma. 4. in algae, the swollen tip of a branch carrying the reproductive organs.

rectum
The terminal part of the intestine of an animal, opening into the anus or cloaca.

rectus abdominis
Muscle that originates on the pelvic girdle (pubis) and inserts on the cartilage of the first and second ribs.

reducing agent
any substance capable of removing oxygen from a molecule or of adding hydrogen, that is, it is capable of contributing electrons to a process.

renal
Pertaining to the kidneys.

renal portal system
The system of veins in fish and amphibians taking blood from the region of the tail or hind limbs directly to the kidneys.

replication
the production of exact copies of complex molecules during the growth of living organisms.

respiration
A process by which gaseous exchange -oxygen and carbon dioxide-takes place between an organism and the surrounding medium.

rhizoid
A hair-like structure that functions as a root in lower organisms, such as certain fungi and mosses. Rhizoids are important in penetrating a substance, giving anchorage and absorbing nutrients.

rhizome
A horizontal underground stem, with leaves and buds, that serves as a storage organ and a means of vegetative propagation.

Rhizopoda
subclass which includes the amebiod protozoans that feed by means of pseudopodia and lack cilia or flagella.

Rhodophyta
members of the Thallophyta division Rhodophyta, in which the chlorophyll is masked by phytocoerythrin. Rhodophytes vary from filamentous forms to those with an extensive thallus and have non-motile gametes.

ribosome
a cell organelle constructed in the nucleolus, consisting of two subunits and functioning as the site of protein synthesis in the cytoplasm.

root
The part of a plant that usually grows below ground. The root provides anchorage for aerial parts, absorbs water and mineral salts from the soil, conducts water and nutrients to other parts of the plant, and often stores food materials over winter.

root apical meristem
A group of plant cells found at the growing end of a root which are capable of dividing indefinetly. Their main function is the production of new root.

root cap
A structure found at the apex of roots, except those of many water plants, produced by the apical meristem. As the root pushes its way through the soil, the outer (older) cells of the root cap are sloughed off and replaced by new cells from the meristem.

rosette arrangement
an arrangement in which the structures (leaves, petals, etc.) are spread in a horizontal plane from a short axis at ground level.

rostrum
Anterior point of Arthropod head.

rough endoplasmic reticulum
Endoplasmic reticulum when it is covered with ribosomes is referred to as rough ER.

rumin
A branch of the esophagus where unchewed food is temporarily stored until it is regurgitated tothe mouth for chewing.

S

sagittal section
a longitudinal section through the median vertical plane.

saprophytes
Any plant of microorganism that obtains its nutrition from dead or decaying organic materials in the form of organic substances in solution. Such organisms are important in breaking down dead organic material.

sarcolemma
The thin connective tissue sheath that occurs around a muscle fiber and extends and contracts with the contractile material enclosed.

sarcoplasm
The cytoplasm of a muscle cell.

scale
Any plate-like outgrowth of the integument, each in the form of a flat calcified or horny structure on the surface of the skin.

scapula
The shoulder blade.

Schwann cells
a chain of supporting cells enclosing the axons of many neurons and forming an insulating layer called the myelin sheath.

sciatic nerve
composed of spinal nerves VII, VIII, IX united to send impulses to the hind leg.

sciatic plexus
the uniting of spinal nerves VII, VIII, IX to form the sciatic nerve to the hind leg.

scolex
The head of a tapeworm, found at the anterior end. It has hooks and suckers for attachment to it's host.

scrotum
a sac containing the testes of male mammals that is situated outside the posteriorly ventral part of the abdomen. The external location ensures that the testes are cooled to below body temperature, since heat can adversely affect development of sperm.

secondary growth
The increase in girth of the stems and roots of many plants, especially woody, perennial dicots.

secondary oocyte
A haploid cell whose chromosome number was reduced when a diploid primary oocyte underwent meiosis. A secondary oocyte will undergo a second round of meiosis to produce a haploid ovum and the haploid second polar body.

secondary spermatocyte
A haploid cell whose chromosome number was reduced when a diploid primary spermatocyte underwent meiosis. A secondary spermatocyte will undergo a second round of meiosis to produce two haploid spermatids.

secondary root
(Lateral root.) A root that arises from another, older primary root. Initiated by the plant hormone, auxin.

secondary phloem
Tissue produced by vascular cambium and composed of both sieve tubes and companion cells.

secondary xylem
Tissue produced by vascular cambium and composed of both tracheids and vessel elements.

secondary palate
the roof of the mouth in vertebrates formed anteriorly by a bony projection of the upper jaw forms the hard palate.

seed
Formed from a fertilized ovule, it is the body from which a new plant develops. It is comprised of an outer coat enclosing a food source (which may be stored in the cotyledon), and an embryo.

seed coat
A protective coat around the seed, formed from the integuments of the ovule.

seed plant
any plant that bears seeds. Most seed plants, have flowers and produce seeds in fruits; some, such as the pines, form seeds on cones.

segment
a division; a section.

segregation
the separation of homologous chromosomes during anaphase 1 of meiosis, producing gametes containing only one allele of each gene. Such an occurrence is the physical mechanism underlying the first law of Mendelian genetics and is particularly important when the two separated alleles are different.

seminal vesicles
Apart of the male reproductive tract that stores sperm in invertebrates and produces semen in vertebrates.

seminiferous tubules
Highly coiled tubes in the testes in which sperm are produced.

sepal
A whorl of modified leaves in angiosperms that encloses and protects the flower bud before it opens.

septum (plural, septa)
Any dividing wall or partition that occurs between structures or in a cavity.

serosa
A serous membrane such as the peritoneum that secretes a serum.

seta (plural, setae)
1. the erect aerial part of the spore-producing structure of mosses or liverworts. 2. a slender, straight prickle.

sex cells
gametes. In the male it is the sperm and in the female it is the egg.

sexual reproduction
A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the two parents.

shell
Any hard outer covering, such as the carapace of turtles and tortoises, the exoskeleton of crustaceans, the calcareous plates of echinoderms, the outermost membranes of an egg, the skeleton of Forminifera, and the mantle secretions of mollusks.

shell membrane
The membranes of an egg that surround the yolk (ovum).

shoot
The part of a vascular plant above the ground, consisting of stem and leaves.

sieve tubes
A series of long cells lying end to end and forming a tube, found in the phloem of Angiosperms.

simple eye (ocellus)
a single eye with a single lens found in insects and some other invertebrates.

sinus venosus
1. in lower vertebrates it is the chamber of the heart to which veins return blood. 2. in mammals it is a vessel of the embryonic heart, present in the transverse septum, into which open the vitelline, allantoic, and cardinal veins.

siphon
Found at the posterior margin in the mantle of Bivalves where fresh water enters the organism through the incurrent siphon, circulates through the mantle cavity and over the gills, and leaves through the excurrent siphon.

skeleton
any structure present in an organism that maintains its shape and supports structures associated with the body. It can take the form of an internal bony skeleton as in vertebrates, an external calcareous or chitinous exoskeleton as in arthropods, a hydrostatic skeleton as in jellyfish , or that of a subcellular system of support.

smooth endoplasmic reticulum
Endoplasmic reticulum that is not covered with ribosomes and gives rise to the Golgi Apparatus.

smooth muscle
A type of muscle lacking the striations of skeletal and cardiac muscle because of the uniform distribution of myosin filaments in the cell.

soft palate
the posterior section of the roof of the mouth that is characterized by a fold of connective tissue.

somatic cell
any of the cells of a plant or animal except the reproductive cells.

somite
A serial segment of the animal body.

sorus (pl. sori)
A group of sporangia developed on the underside of sporophylls (spore-bearing leaflets) of the sporophyte generation of a fern.

sperm
Spermatozoon; a small, usually motile male gamete.

spermatic artery
Arise from the abdominal aorta just posterior to the kidneys and supplies the testes with oxygenated blood.

spermatids
A haploid stage in male gametogenesis.

spermatogenesis
the continuous and prolific production of mature sperm cells in the testis via meiosis.

spermatogonium (plural, spermatagonia)
An early diploid stage of male gametogenesis.

spermatozoon (plural, spermatozoa)
The male gamete; a haploid, usually small, flagellated cell.

sphincter
a ring-like valve, consisting of modified muscles in a muscular tube, such as a digestive tract; closes off the tube like a drawstring.

spinal cord
A more or less uniform tube extending the full length of the body in vertebrates behind the head. It is enclosed in the backbone.

spinal nerve
any of numerous nerves that leave the spinal cord, one pair in each segment, each being connected with the cord by a dorsal and a ventral root.

spiracles
Minute pores distributed over the surface of an insect's body that serve as entrances to the tracheal system.

spleen (Frog, Rat)
An important part of the mononuclear phagocyte system, make up of lymphoid tissue. It stores excess red blood cells, destroys old cells, and is capable of acting as a reservoir holding 20-30% of all blood cells. It produces lymphocytes and serves to regulate the volume of blood cells elsewhere in the blood system.

spongy mesophyll
The internal tissue layer of a leaf found below the palisade mesophyll. Lacks a regular organization due to irregularly shaped cells and many air spaces.

sporangium (pl. sporangia)
A capsule in fungi and plants in which meiosis occurs and haploid spores develop.

sporangiophore
A fungal hypha bearing one or more sporangia.

spore
In the life cycle of a plant or alga undergoing alternation of generations, a meiotically produced haploid cell that divides mitotically, generating a multicellular individual, the gametophyte, without fusing with another cell.

sporophyte
The multicellular diploid form in organisms undergoing alternation of generations that results from a union of gametes and that meiotically produces haploid spores that grow into the gametophyte generation.

sporozoan
any parasitic protozoan of the class Sporozoa, such as the Malaria parasite.

stalk
Holds up the cap of mushrooms.

stamen
The pollen-producing male reproductive organ of a flower, consisting of an anther and filament.

stapes
The innermost of the three ear ossicles, which contacts the oval window of the ear. It is stirrup-shaped.

starch
A polysaccharide carbohydrate consisting of two forms of glucose units, amylose and amylopectin.

stele
The central vascular cylinder in roots where xylem and phloem are located.

stem
The part of the plant bearing the buds, leaves, and flowers. It forms the central axis of the plant, and provides mechanical support. If present below ground, it is usually called a rhizome.

sterile cell
A cell derived from the microgametophyte which does not divide further.

stigma
The part of the reproductive organs of flowers where pollen grains germinate.

stipe
The fruiting body of a fungus.

stipule
one of a pair of leaflets found at the base of a leaf where it joins the stem.

stolon
A long slender stem running along the surface of the ground, arising from the axil of a leaf, whose function is to enable rapid vegetative propagation in an area. Runners are found, for example, in strawberries and creeping buttercup.

stoma (pl. stomata)
A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.

stomach
The part of the vertebrate gut system that follows the esophagus. It is expanded to form a chamber, and its walls secrete pepsinogen, giving rise to pepsin, rennin, and hydrochloric acid. Gastric secretions also include mucin, which lubricates the food mass that is passed a little at a time to the small intestine via the pyloric sphincter.

storage material
any compound that accumulates naturally within a cell, for example, the starch grains of potato tubers and glycogen in liver cells.

striate
in plant structures, marked with parallel ridges or depressions.

striated muscle
Contractile tissue, in vertebrates consisting of fibrils with marked striations at right angles to the long axis. The muscle is concerned with movement of skeletal parts.

stroma
the fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

style
The slender, neck-like portion of the carpel that leads to the ovary.

suberin
A complex of fatty substances present in the wall of cork tissue that waterproofs it and makes it resistant to decay.

submucosa
Located below the mucosal layer.

subsidiary cells
secondary or auxiliary cells

superficial
on or near the surface, for example, of an artery, vein or ovule.

superior vena cava
Drains the anterior body regions, returning blood back to the heart via the right atrium.

synapse
the locus where one neuron communicates with another neuron in a neural pathway; a narrow gap between a synaptic terminal of an axon and a signal-receiving portion (dendrite or cell body) of another neuron or effector cell. Neurotransmitters released by synaptic terminals diffuse across the synapse, relaying messages to the dendrite or effector.

syncytium
A cellular structure containing many nuclei.

synergid
Either of two small cells present in the embryo sac of seed plants near the egg cell at the micropylar end.

syngamy
The process of cellular union during fertilization.

T

teat
Of female mammals, the nipple of a breast or udder, from which the young suck milk.

telson
The terminal appendage of the last abdominal segment of some arthropods.

tendon
A bunch of parallel collagen fibers making up a bank of connective tissue that serves to attach a muscle to a bone.

testis (plural, testes)
The male reproducitve organ, or gonad, in which sperm and reproductive hormones are produced.

tetrad
the four homologous chromatids that associate during prophase and metaphase of meiosis and are involved in crossing over. A tetrad is also the four haploid cells produced by one complete meiotic division.

tetrapod
Any vertebrate with two pairs of pentadactyl limbs. Ex. rats, frogs.

thallus
The vegetative part of simple plants, ranging from unicellular structures to large seaweeds. It shows no differentiation into root, stem, and leaves.

thoracic cavity
The space within the thorax.

thorax
1. in vertebrates it is the part of the body that contains the lungs and heart, and in mammals is divided from the abdomen by the diaphragm. 2. in arthropods it is the part of the body directly behind the head and in front of the abdomen. 3. in insects it is the three segments bearing the legs and wings.

thylakoid
a flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.

tibia
The anterior of the two long bones articulating in the hind limb. In humans, the tibia is the shinbone.

tissue
A large group of cells of similar structure in plants or animals that performs a specific function. (ex. muscle, phloem, etc.)

tongue
A muscular organ on the floor of the mouth in most higher vertebrates that carries taste buds and manipulates food. It may act as a tactile or prehensile organ in some species.

trachea (pl. tracheae)
1. the windpipe; that portion of the respiratory tube that has C-shaped cartilaginous rings and passes from the larynx to two bronchi. 2. tiny air tubes that ramify throughout the insect body for gas exchange. 3. in plants they make up part of the xylem tissue.

Tracheophyte
any plant of the division Tracheophyta, comprising all forms of vascular plants, Pteridophytes and Spermatophytes.

transverse
Lying or placed across or crosswise

traverse muscles
Fibers run ventrally and slightly posteriorly, originates from cartilage of the floating ribs, the lumbar vertebrae and the border of the ilium and inserts on the linea alba. Its action is to constrict the abdominal region.

trematode
any parasitic flatworm of the class Trematoda, including the flukes.

triceps muscle
Found on the back side of the arm, it is an antagonist to the biceps. It originates from the humerus and the scapula and inserts on the ulna. The triceps extends the forearm.

tripartite
Having three parts.

tube cell nucleus
one of two haploid nuclei within a developing pollen tube, whose function may be control of tube growth.

tube feet
The locomotory organs of Echinoderms, which are protruded from the body by, and are retracted by, fluid pressure from the water vascular system.

tunica
Any layer of tissue or membrane that encloses a structure or organ in either an animal or plant.

turbellarian
any aquatic free-swimming platyhelminth of the class Turbellaria, the body of which is covered with cilia.

tympanic membrane
The eardrum. A membrane situated at the end of the external auditory meatus at the junction of the outer and middle ears. Vibrations are set up in the membrane by sound waves, and these are transmitted by the ear ossicles to the oval window.

typhlosole
A dorsal unfolding of the earthworm's intestine along its entire length that increases its surface area for digestive purposes.

U

ulna
The posterior of two bones of the forearm of tetrapods. The ulna articulates proximally with the humerus and distally with the carpals.

umbo
The pointed centre of an oyster shell. It is the oldest part and surrounded by concentric lines of growth.

unicellular
made up of one cell.

upper epidermis
the tissue in plants, usually one cell thick, that is on the top surface of the leaf.

ureter
A duct leading from the kidney to the urinary bladder.

urethra
A tube that releases urine from the body near the vagina in females or through the penis in males; also serves in males as the exit tube for the reproductive system.

urinary bladder
An elastic, muscular sac located in the pelvic cavity, in which urine is collected before excretion.

uropod
The flattened, sixth pair of pleoplods that, together with the telson, forms the tail fin of crayfish.

uterus
The enlarged posterior portion of the oviduct in which the embryo implants a develops in viviparous species. It is also called the womb of female humans.

V

vacuole
A membrane-enclosed sac taking up most of the interior of a mature plant cell and containing a variety of substances important in plant reproduction, growth, and development.

vagina
A thin-walled chamber that forms the birth canal and is the repository for sperm during copulation.

vas deferens
The tube in the male reproductive system in which sperm travel from the epidiymis to the urethra.

vascular bundle
A structure of vascular plants that runs up through the roots, into the stems, and out into the leaves, and whose function is transport of water, ions and dissolved organic solutes within the plant.

vascular cambium
A continuous cylinder of meristematic cells surrounding the xylem and pith that produces secondary xylem and phloem.

vascular system
1. in animals the blood circulatory system and the water vascular system in echinoderms that manipulate the tube feet. 2. in plants the tissue that serves to conduct water throughout plants.

veins
Vessels which carry blood back to the heart from the tissues. Veins are thin walled and will collapse if empty. They have a series of one-way valves to prevent blood from flowing backwards.

vena cava
One of the major veins of the blood circulatory system.

venous system
The part of the blood circulatory system carrying blood back to the heart from the tissues.

venter
The swollen base of the archegonium that contains the egg cell.

ventral
Of or relating to the underside of an organism, or the side normally directed downward in the usual stance or resting position.

ventral root
any of the nerve roots issuing from the ventral side of the vertebrate brain or spinal cord, containing the motor nerves.

ventricle
(1) a chamber that pumps blood out of the vertebrate heart. (2) a space in the vertebrate brain filled with cerebrospinal fluid.

venules
Vessels into which capillaries converge and that empty into veins.

vertebral column
Spinal cord or backbone; the series of vertebrae surrounding the spinal cord.

vessel cell
An empty tube formed from longitudinal fusion of several cells with strong walls reinforced with lignin, whose function is mass transport of water for transpiration.

vestigial organ
any organ over the course of evolution had become reduced in function and usually in size.

vibrissa (plural, vibrissae)
Any of the stiff sensitive hairs found around the mouths of mammals; whiskers.

villus (plural, villi)
A finger-like outgrowth, as in the lining of the small intestine. Villi effectively increase the surface area of the gut wall

viriod
a plant pathogen composed of molecules of naked RNA only several hundred nucleotides long.

virus
the smallest organism known, ranging in size from about 0.025-0.25 um. Viruses infect cells of bacteria, plants , and animals, and while they carry out no metabolism themselves, they are able to control the metabolism of the infected cell.

viscera
The internal organs of the body cavity.

visceral peritonium
A thin layer of connective tissue which originated from the mesoderm. It lines the internal organs, as opposed to the abdominal cavity.

vital stains
the staining of cells while alive, which has been used particularly for studying the movements of parts of embryos.

vitelline membrane
Delicate membrane that surrounds the yolk of an egg.

vomerine teeth
found on the roof of the buccal cavity, medial to the internal nares, on either side of the midline in frogs.

W

walking legs
Pereiopods of Crustaceans. Posterior jointed, thoracic appendages.

whorled arrangement
a circular set (two or more) of leaves or sepals arising at the same level on the plant.

Wolffian duct
The duct from the mesonephros in vertebrates. In fish and amphibians, it forms the urinary duct in females and the genitourinary duct in males. In reptiles, birds, and mammals, it forms the vas deferens in males and it degenerates in females.

X

xylem
The tube-shaped, nonliving portion of the vascular system in plants that carries water and minerals from the roots to the rest of the plant.

Y

yolk
The food store in the eggs of the majority of animals, made up mainly of fat and protein granules. Where yolk is present in the egg, as in chickens, there is meroblastic cleavage, but where it is absent, or nearly so, cleavage is holoblastic, as in Amphioxus.

yolk plug
In amphibians, when the opening of the archenteron, the blastopore, is filled with yolk-rich cells, it is called the yolk plug.

Z

zygospore
A thick-walled resting spore that is formed from the union of similar gametes.

zygote
The diploid product of the union of haploid gametes in conception; a fertilized egg.


Copyright © Michael Shaw 2007 (Images and Text)

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