10th Class Biology Important Definitions

10th Class Biology Important Definitions


Abiotic: The non-living components of the environment like water, sunlight, soil, heat etc.

Acid rain: The rain containing sulphuric acid and nitric acid; with pH range of 3 to 6

Acromegaly: Abnormal growth due to excessive production of growth hormone after growing age; the internal organs and body extremities alone grow large and affected persons have large hands, feet and jawbones.

Acrosome: Cap-like head of sperm cell which helps it in penetrating the egg cell.

Addictive drug: The drug which makes a person dependent on it, or addicted

Adrenal cortex: The outer portion of adrenal gland; secretes corticosteroids

Adrenal medulla: The inner portion of adrenal gland; secrets epinephrine or adrenaline

Adrenaline: Epinephrine; a hormone that prepares body to overcome emergency situations; a neurotransmitter produced by some nerve cells

Allele: The alternative form of a gene

Alternation of generations: In plants, the phenomenon in which the sporophyte and gametophyte generations alternate with each other

Alveolar duct: Fine tubules at the end of bronchioles; open into alveoli

Alveolus: A sac-like structure present next to the alveolar duct in lungs

Ammonification: The decomposition of protein of dead plants and animals, and nitrogenous wastes to ammonia by ammonifying bacteria

Analgesic: The medicines that reduce pain

Androecium: The male reproductive whorl of the flower; consists of stamens

Anther: The sac-like structure of a stamen in which pollen grains are produced

Antibiotics: The medicines which inhibit or kill bacteria

Antidiuretic hormone: The hormone of the posterior pituitary; promotes the reabsorption of water in renal tubules

Appendicular Skeleton: The division of the skeleton that includes arms, hands, legs, feet pectoral girdle and pelvic girdle

Aqueous humour: The fluid present in the anterior chamber of the eye i.e. between the cornea and the iris

Arthritis: Terms used for the inflammation in joints

Artificial selection: Selective breeding; intentional breeding between individuals for certain traits, or combination of traits

Aspirin: Acetaminophen; A pain-killer medicine

Asthma: An inflammation of the bronchi that causes swelling and narrowing of the airways

Atmospheric nitrogen fixation: The conversion of atmospheric gaseous nitrogen to nitrates by thunderstorms and lightning

Auditory canal: The part of the external ear; ends at ear drum

Autonomic Nervous System: Part of the peripheral nervous system; consists of motor neurons that send signals to the cardiac muscles, smooth muscle and glands; generally without conscious control

Axial skeleton: The division of the skeleton that includes the skull, vertebral column, ribs and breastbone

Axon: A long, thin fibre that carries nerve impulse away from the cell body of a neuron

Bactericidal: The antibiotics that work by killing bacteria

Bacteriophages: The viruses that attack bacteria

Bacteriostatic: The antibiotics that work by stopping bacteria multiplying

Ball-and-socket joint: The joint that allows movement in all directions e.g. hip and shoulder joints

Batch fermentation process: The discontinuous fermentation process, divided into batches

Biceps: A flexor muscle on the front of the upper arm bone

Binary fission: Division into two; the simplest method of asexual reproduction in prokaryotes and many unicellular eukaryotes

Biogeochemical Cycle: The cyclic pathway through which chemical elements move from environment to organisms and back to the environment

Biological nitrogen fixation: The conversion of gaseous nitrogen into nitrates by living organisms

Biosphere: The last level of ecological organization; all the ecosystems of the world together form the biosphere

Biotechnology: The use of living organisms in systems or processes for the manufacture of useful products or for services for humankind

Biotic: The living components of the environment; include producers, consumers and decomposers

Bone: Hard connective tissue; moves, supports and protects the various organs of the body

Bowman’s capsule: Part of nephron: cup-shaped structure enclosing the glomerulus

Breathing: The process through which animals take air in their bodies to get oxygen and then give out the air for getting rid of carbon dioxide

Breeds: The animals which are bred through artificial selection

Bronchioles: Fine tubules formed by the division of the bronchi

Bronchitis: Inflammation in the bronchi or bronchioles

Bronchus: The part of air passageway; formed by the division of the trachea

Budding: A type of asexual reproduction in which a bud develops as a small outgrowth on parent’s body and forms the new individual

Bulbs: Underground vertical shoots which have modified leaves

CalyxThe outer whorl of flowers; consists of sepals

Carbon cycle: The biogeochemical cycle in which carbon flows between organisms and the environment

Cardiotonic: Medicines for giving strength to heart muscles

CarnivoresThe consumers which eat only animal flesh

Carpel: Part of the gynoecium of the flower; consists of stigma, style and ovary

CartilageThe connective tissue that makes part of the human skeleton

Cell bodyThe part of the nerve cell that contains nucleus

Central nervous systemThe part of the nervous system consisting of brain and spinal cord

Cephalosporin: A group of antibiotics; interfere with synthesis of the bacterial cell wall

Cerebellum: The part of the hindbrain; controls muscle movements

Cerebral hemispheresThe divisions of the cerebrum of the brain

Cerebrospinal fluidThe fluid in the ventricles of the brain and in the central canal of the spinal cord

Cerebrum: The largest part of the forebrain; controls many sensory and motor functions

Cervix: In female reproductive system, the part which separates uterus from the vagina

Chondrocyte: The cells present in the cartilage

Chromatin: The chemical material that make the structure of the chromosome

Cloning: Method of asexual reproduction in which identical offsprings are produced from a vegetative tissue or cell of the parent

Cochlea: The part of the inner ear; consists of three ducts wrapped in the form of a coiled tube; contains sound receptors

Co-dominance: The situation where two allele of a gene pair express their traits independently instead of showing a dominant-recessive relationship

Collecting duct: The tubes into which the renal tubules of nephrons open

Colour blindness: Genetic disorders in which person fails to recognize the basic colours

CommensalismA type of symbiosis in which one of the partners gets benefit while the other is neither benefited nor harmed

Compact bone: The hard outer layer of bones

Cones: The photosensitive cells in the retina of the eye; sensitive to bright light and so distinguish different colours

ConsumerThe part of the biotic components of the ecosystem that consists of animals

Continuous fermentation process: The fermentation in which substrate is added to the fermenter continuously, at a fixed rate

Corm: Short, swollen underground stem; has bud(s) at the top; gives rise to new plants by vegetative propagation

CorneaThe transparent part of sclera that forms in the front of the eye through which light enters

CorollaThe second whorl of flower, consisting of petals

Cotyledon: A modified leaf present in seeds; often gives nourishment to the developing seedling

Cowper’s glandAn accessory gland in rabbits male reproductive system; provides lubrication to the ducts

Cranial bones: The bone of the cranium

Cranial nervesNerves that arise from or lead to the brain

CultivarsThe plants which are bred through artificial selection

CuttingArtificial vegetative propagation in which cuttings are taken from stem or root of parent and are placed in soil

Decomposer: An organism which decomposes the dead bodies and dead matter

Deforestation: Clearing of forests by natural causes or by humans

Dendrites: Short, branched projections of neuron’s cell body; transmits nerve impulse towards cell body

Denitrification: The conversion of nitrites and nitrates into nitrogen gas

Diabetes mellitus: More than normal level of glucose in blood; a condition caused by insufficient concentration of insulin in blood

Dialysis: The cleaning of blood (removing nitrogenous wastes and extra water) by artificial ways

DialyzerThe apparatus used for haemodialysis

Diaphragm: The muscular structure that forms the floor of the chest cavity;

present below lungs

Dihybrid crossA genetic cross in which two pairs of contrasting traits are studied

Dominant traitThe trait that appears in the offspring of a cross between two homozygous individuals showing contrasting forms of the trait

DrugAny substance that, when absorbed into the body of a living organism, alters normal body function

Dwarfism: Less than normal body growth; a condition caused when growth hormone is insufficient during the growing age

Ear drumTympanic membrane; A membrane stretched across the inner end of the auditory canal of the ear

Ecological pyramid: A representation of the number of individuals or amount of biomass or energy present in various trophic levels of a food chain

EffectorsThe parts of the coordination system that respond when stimulated by nerve impulses or hormones

EmphysemaA disease in which the walls of the alveoli are destroyed

Endocrine glandA ductless gland; produces and secretes hormones

Endosperm nucleus: In the female gametophyte, the triploid nucleus formed by the fusion of sperm and the fusion nucleus

Endosperm tissue: The tissues that develops from endosperm nucleus; often serves as a food supply for developing embryo

EndosporeThe spore formed inside the bacterial cell

Environment: The sum total of physical (abiotic) and biotic conditions which influence the organism

EpicotylThe embryonic stem above the point of attachment of the cotyledon(s)

Epididimys: A storage area for sperms on the upper part of the testes

Epigeal germination: A type of seed germination in which the hypocotyl elongates and forms a hook, pulling the cotyledons above the ground

Epilepsy: A nervous disorder characterized by recurrent unprovoked seizures (convulsions)

EpinephrineSee Adrenaline

EstrogenA hormone secreted by the ovaries; promotes development of female secondary sex characteristics and regulates the reproductive cycle

Eustachian tube: The tube between middle ear and the nasal cavity that equalizes the pressure on both sides of the ear drum

Eutrophication: The enrichment of water with inorganic nutrients; the nutrients promote the growth of algae and it leads to increase in the number of the decomposers and depletion of oxygen

Excretion: The process by which the metabolic wastes are removed from the body

Exhalation: The phase of breathing in which air is expelled from the lungs

Exocrine gland: A gland that discharges its secretion into a duct

Extensor: A muscle that extends a joint.

Fallopian tube: a part of the female reproductive system; receives egg cell discharged from the ovary

Feedback mechanisms: The mechanisms to control certain functions; one of the products of a pathway are used, usually the end product, to control the activity of the pathway

Fermentation: The process in which there is incomplete oxidation-reduction of the organic substrate (glucose)

Fermenter: A device that provides optimum environment in which organisms can grow to produce biomass and to form the product.

FertilizationThe fusion of male and female gametes to form a zygote

Fibrous cartilageThe cartilage that has large number of fibres in the matrix e.g. the cartilage in intervertebral disc

Flexor: A muscle that bends a joint

FollicleA structure in the ovary in which the mature egg develops

Food chainThe series of organisms in an ecosystem, in which an organism eats the preceding one and is eaten by the next one

Food webA network of interconnected food chains; has a number of feeding connections amongst different organisms of a community

ForebrainThe part of the brain; includes cerebrum, thalamus and hypothalamus

FragmentationA type of asexual reproduction in which the animal breaks up into many pieces and each piece develops into a mature animal

Fusion nucleusA part of the female gametophyte in plants; formed by the fusion of two nuclei; gives rise to endosperm nucleus when fertilized by a sperm

GametogenesisThe process of the formation of gametes

Gametophyte: The haploid generation in plant life cycle; produces gametes

GanglionThe aggregation of the cell bodies of neurons

Gaseous exchange: Taking in and giving out of gas (oxygen and carbon dioxide) by organism

Gene: Unit of inheritance; consists of the length of DNA that contains specific instructions for the synthesis of a protein molecule

Genetically Modified Organism: The organism in which DNA (gene) from some other organism has been transferred

GenotypeThe specific combination of genes in an individual; may be homozygous or heterozygous

GerminationThe process by which a seed embryo develops into a seedling

GigantismThe condition due to excessively production of growth hormone during the growing age; leads to very tall and overweight persons

Global Warming: Increase in the temperature of the Earth; due to the addition of greenhouse gases in atmosphere, which do not allow solar radiations to reflect back into the space

Glomerular filtrateThe material that passes from glomerulus into the Bowman’s capsule

Glomerulus: The network of capillaries in the nephron of kidney

GlucagonThe hormone secreted by the islets of Langerhan; increases the blood glucose level

GoutA type of arthritis; characterised by the accumulation of uric acid crystals in the moveable joints

Grey matter: The nervous tissue containing cell bodies and non-myelinated processes of the neurons

GuttationAppearance of drops of xylem sap on the tips or edges of leaves

HallucinogenDrug that causes changes in perception, thought, emotion and consciousness

Haemodialysis: The dialysis in which patient’s blood is pumped through the apparatus called dialyzer for cleaning

Heroin: A commonly abused narcotic; derived from morphine; affects the central nervous system and causes drowsiness, disorientation, hypotension etc.

Heterozygous: The genotype that has two different alleles of a trait

HilumA scar on the seed coat; the point where the seed is attached to the ovary wall

Hilus: A depression near the centre of the concave area of the kidney; the area through which the ureter, blood and lymphatic vessels and nerves enter/leave the kidney

HindbrainThe part of the brain consisting of cerebellum, medulla oblongata and pons

Hinge joint: A joint that permits movement of bones in one plane e.g. elbow and knee joints

Histone: The protein present in the structure of chromosome

Homeostasis: The maintenance of a constant internal environment in response to environmental changes

HormoneA substance that is secreted by an endocrine gland directly into blood and that produces a specific effect on a particular tissue

Hyaline cartilage: The cartilage that has collagen fibres in its matrix; found covering the ends of the long bones, in the nose, larynx, trachea and bronchial tubes

Hyoid boneThe bone present in neck

Hypermetropia: The condition in which a person is not able to see near objects clearly; happens when the eyeball shortens and image is formed behind the retina

Hyperthyroidism: The over-production

of thyroxin; result in increase in energy production, increased heart-beat, frequent sweating and shivering of hands

HypocotylThe embryonic stem below the point of attachment of cotyledon

Hypogeal germination: A type of seed germination in which the epicotyl elongates and forms the hook while the cotyledons stay underground

Hypothalamus: The part of the forebrain below the thalamus; controls body temperature, blood pressure and emotion

Hypothyroidism: The under-production of thyroxin; results in low energy production and slowing down of heart-beat

Incomplete dominance: A type of inheritance in which neither of the pair of contrasting alleles is dominant over the other and the heterozygous individual is intermediate in phenotype

Inhalation: The phase of breathing in which air is drawn into the lungs

InheritanceThe transmission of characteristics from parents to offspring

Insertion: The end of the muscle that is attached with a moveable bone

Insulin: The hormone produced by the Islets of Langerhans; lowers the blood glucose level

Interneurons: The neurons present in the brain and spinal cord

Interspecific interactions: Interactions between the members of the different species

Intraspecific interactionsInteractions between the members of the same species

IodopsinA pigment present in the cones of the retina

Islets of Langerhans: Groups of endocrine cells present in pancreas;secrete hormones insulin and glucagon

IrisA muscular ring formed by the bending of the choroid behind the cornea of the eye

Kidney failure: A complete or near complete failure of the kidneys to excrete wastes and to regulate water and salts

Kidney stoneThe deposits of large chemicals such as calcium oxalate, calcium and ammonium phosphate, uric acid, cystine etc. present in kidneys, ureter or bladder; cannot pass in the urine

LacunaThe fluid filled space in bone and cartilage, where their cells are present

Larynx: The part of the air passageway between pharynx and the trachea

LenticelsPores in the bark of wooding stems and mature roots

LigamentStrong but flexible connective tissue that joins one bone to bone at the joints

LithotripsyTreatment for removing kidney stones; non-electrical shock waves are bombarded on the stones to break them

LocusPlural Loci; The locations or positions of genes on chromosomes

Loop of Henle: The U-shaped portion of the renal tubule of nephron

Macrospore: Haploid cell produced in the ovule; divides mitotically and produces the female gametophyte

Marijuana: A hallucinogen and addictive drug; obtained from the flowers, stems, and leaves of the marijuana plant

Medicinal drugAny chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease

Medulla oblongata: Part of the hindbrain; on the top of the spinal cord; controls breathing, heart rate, blood of the retina

Narcotics: Strong painkiller drugs; also used as addictive drugs; commonly abused narcotics include heroin, morphine, methadone etc

Nasal cavityHollow space in the nose; opens to the outside through nostrils; divided into two portions by a wall

Natural resourcesThe resources on Earth, which provide everything that humans use or consume

Natural selectionThe process in which organisms with favourable variations survive and produce more offspring than less well-adapted organisms

NephronThe functional unit of kidneys

NerveThe union of several axons that are enveloped by a covering made of lipid

Neuron: Nerve cell; the unit of the nervous system; able to conduct nerve impulses

Nitrification: The oxidation of ammonia to nitrites and nitrates by the nitrifying bacteria

Nitrogen cycleThe flow of nitrogen between environment and the organisms

Nitrogen fixation: Conversion of nitrogen into nitrates

Nodes of RanvierThe non-myelinated points between the areas of myelin on the axons of neurons

Non-renewable resource: A resource that is formed over very long periods; the rate of formation is extremely slow so cannot be replaced; e.g. minerals and fossil fuels

NostrilThe openings of the nasal cavity

NucleosomeThe structure formed by the wrapping of DNA around histone proteins

Olfactory bulbsThe anterior parts of the cerebral hemispheres; receive impulses from the olfactory nerves and create the sensation of smell

Oogenesis: The formation of ovum (egg cell)

Oogonium: (Plural Oogonia): The diplod cells in the follicles of the ovary; produce diploid primary oocytes during oogenesis

Optic disc: Blind spot; a point on the retina of the eye where the optic nerve enters the retina; no photosensitive cells exist at this point

Organic evolution: Biological evolution: The modification of characteristics in the species or populations of organisms during their descent, generation by generation

Origin: The end of the muscle that is attached with a immoveable bone

Osmoregulation: The regulation of water content in body fluids

Osteoarthritis: Inflammation in joints due to degeneration in the cartilage present at the joints or due to decreased lubricant production at the joints

Osteocyte: The mature bone cells

OsteoporosisA bone disease in adults, especially in old age; there is a decrease in the density of bones due to loss of calcium and phosphorus

Oval windowThe membrane which separates the middle ear from the inner ear

OvaryThe female gonad; produces egg cells and female sex hormones

Overpopulation: Increase in population beyond the carrying capacity of an area or environment

Ovule: In seed plants, a structure present in the ovary; contains macrospore that develops into female gametophyte; ovule develops into seed after fertilization

Ozone: The O3 gas; also present in theupper layer of the atmosphere where it absorbs the ultraviolet rays present in the sun’s radiation

OxytocinThe hormone secreted by the posterior pituitary; stimulates the contraction of uterus walls in females for child birth; necessary

for ejection of milk from the breasts

Papillary ducts: The ducts formed by the joining of many collecting ducts; open into renal pelvis

ParalysisComplete loss of function by one or more muscle groups due to damage in the nervous system

Parasitism: A type of interspecific interaction in which smaller partner (parasite) derives food and shelter from the body of larger partner (host) and harms the host

Parasympathetic nervous system: Part of the autonomic nervous system; works when there is little or no stress and slows down the overall activity of the body

Parathormone: Hormone of the parathyroid glands; increases the level of calcium ions in the blood

ParathyroidThe endocrine glands located on the posterior sides of the thyroid gland; secrete parathormone

ParthenocarpyThe process in which ovaries develop into fruit without the fertilization in the ovules present in them; results in seedless fruits e.g. bananas

ParthenogenesisA form of asexual reproduction in which an unfertilized egg develops into new offspring

Peripheral nervous system: A division of the nervous system that consists of nerves and ganglia

Peritoneal dialysis: The dialysis in which the dialysis fluid is pumped into the abdominal peritoneal cavity; the wastes from the blood vessels of the peritoneum diffuse into the dialysis fluid which is then drained out

Pharmaceutical drug: See medicinal drug

PharmacologyThe study of drug composition and properties and medical applications

Phenotype: The expression of the genotype in the form of trait

PhytoplanktonPhotosynthetic organisms that float on the surface of water

PituitaryThe endocrine gland attached to the hypothalamus that controls many other endocrine glands in the body

PlumuleThe part of the plant embryo that develops into new shoot

Pneumonia: The infection of one or both lungs; caused by specific bacteria, viruses or fungi; the infected part of the lung becomes filled with fluid and pus

Pollen tubeA tube formed by the tube nucleus of the pollen grain; carries sperms to the ovule

Pollen-sac: The part of the anther where microspore (pollen grains) are produced

Pollination: The transfer of pollen grains from flower’s anther to stigma

PollutantThe substance that causes pollution

Pollution: Undesirable change in the physical, chemical or biological characteristics of air, water and land that may harmfully affect living organisms and other resources

Pons: Part of the hindbrain; present on top of the medulla; assists the medulla in controlling breathing and serves as a connection between the cerebellum and the spinal cord

Predation: An interaction between animals of two species or any plant and an animal, in which the predator attacks, kills and feeds on the smaller animal called prey

Pressure filtration: The first step in urine formation; the process in which most of the water, salts, glucose and urea of the blood is forced out of the glomerulus and passed into Bowman’s capsule

Producer: An organism that produces organic compounds from inorganic compounds; an autotroph

Progesterone: A hormone secreted by the ovaries that maintains the uterus during pregnancy

Prostate glandAn accessory gland in the male reproductive system; produces a secretion that neutralizes the acidity

Proximal convoluted tubule: The part of the nephron between Bowman’s capsule and the loop of Henle

Pupil: The opening in the centre of the iris of the eye

Pyramid of Biomass: The graphic representation of biomass present per unit area at different trophic levels in an ecosystem

Pyramid of NumbersThe graphic representation of the number of individuals per unit area at various trophic levels in an ecosystem

RadicleThe part of the plant embryo that develops into new root

Receptors: The organs, tissues or cells which detect particular type of stimuli

Recessive trait: The trait which is masked in the offspring of a cross between two homozygous individuals showing contrasting forms of the trait

Recombinant DNA: The vector DNA and the attached gene of interest

Reflex ActionThe involuntary and immediate response to a stimulus

Reflex arc: The nerve pathway over which the nerve impulses travel in a reflex action

Renal corpuscle: The collective name for the glomerulus and Bowman’s capsule of the nephron

Renal pelvisThe funnel-shaped cavity into which the renal pyramids of kidney project

Renal pyramids: Cone-shaped areas in the renal medulla

Renal tubuleThe part of the nephron after the Bowman’s capsule; consists of proximal convoluted tubule, loop of Henle and distal convoluted tubule

Renewable resources: The resources which are replenished or reproduced easily e.g. sunlight, air, wind etc.

Reproduction: The process by which organisms produce new organisms of their own kind

Restriction endonucleases: Enzymes used to cut the gene from the total DNA of the organism

RetinaThe innermost and the sensitive layer in the eye

Rheumatoid arthritis: Painful inflammation of the membranes at the joints

Rhizomes: Horizontal underground stems; have scale leaves with buds; shoots of the new plant develop and grow form buds (vegetative propagation)

Rhodopsin: A pigment present in the rods of the retina

Rods: The photosensitive cells present in the retina of the eye; sensitive to dim light

Saltatory conduction: Fast nerve impulses; jump over the areas of myelin going from node to node

Schwann cellsThe supporting cells around neurons; form the myelin sheath

Scrotum: A sac of skin outside the body wall in which the testes of the male are located

SedativesTypes of drugs that interact with the central nervous system to depress its activities; make a person calm or drowsy

Seed coat: Testa: Outer covering of a seed; develops from the integument of the ovule; protects the embryo from mechanical injury and from drying out.

Seed dormancy: A period, during which there is no growth in the seed; seeds in dormancy are ripe seeds but do not germinate; under favourable conditions, the seeds break dormancy and begin to germinate

Selective re-absorption: The second step in urine formation; in it about 99% of the glomerular filtrate is reabsorbed into the blood capillaries surrounding the renal tubule

Semen: The material containing sperms in a fluid

Semicircular canals: The three bony canals present posterior to the vestibule in the inner ear

Seminal vesicle: The associated gland in male reproductive system; produces secretions having nutrients for the sperms

Seminiferous tubuleThe coiled tubes present in testes; sperms are formed in these tubules

Sensory nervesThe nerves which contain only the axons of sensory neurons

Single-Cell Protein: The protein content extracted from pure or mixed cultures of algae, yeasts, fungi or bacteria; the micro-organisms are grown in fermenters where they produce a high yield of protein

SkeletonThe framework of hard, articulated structures that provide physical support, attachment for skeletal muscles, and protection for the bodies of animals

Somatic Nervous systemThe part of the motor pathway of the peripheral nervous system; gives voluntary control; includes all of the motor neurons that conduct impulses from the CNS to the skeletal muscles

Somatotrophin: Growth hormone: A hormone of the anterior pituitary;promotes the growth of the body

Sperm: The male gamete

Spermatid: The immature non-motile forms of sperms; are converted into sperms after many changes

SpermatogenesisThe formation of sperms

Spermatogonia: The diploid cells in semineferous tubules of the testes; divide mitotically and produce primary spermatocytes

Spinal nerves: The nerves which arise from the spinal cord

Spongy bone: The soft and porous interior of the bone; contains blood vessels and bone marrow

Sporophyte: The diploid generation in plant life cycle; produces spores

Stamen: The part of the androcium; consists of anther and filament

Sternum: The chest bone

StigmaThe upper part of the carpel

StyleThe middle portion of the carpel

Sulfonamides: Sulpha drugs: Synthetic antibiotics that contain the sulfonamide group; bacteriostatic in action

Suspensory ligamentThe ring that attaches the lens of the eye to the ciliary muscles

SymbiosisLong or short term relationship between members of different species; three forms are parasitism, commensalism and mutualism

Sympathetic nervous system: Part of the autonomic nervous system; prepares the body to deal with emergency situations

SynapseA junction between a neuron and another cell; transmits nerve impulse from one neuron to the next neuron or to effector’s cell

Tendon: Tough connective tissue that attaches muscles to bones

Testa : See Seed coat

Testis : The male gonads ; produces sperms and male sex hormones

TestosteroneThe male sex hormone secreted by testis; stimulates the development of male reproductive system and the male secondary sex characteristics

Tetracycline: Broad-spectrum bacteriostatic antibiotics; inhibit bacterial protein synthesis

ThalamusThe part of the forebrain; serves as a relay centre between various parts of the brain and spinal cord

ThyroidThe endocrine gland located in front of the trachea; secretes hormones thyroxin and calcitonin

Thyroxin: The hormone of the thyroid gland; increases the break down of food and release of energy; also responsible for the growth of body

Trachea: Windpipe: Part of the air passageway between larynx and bronchi

TraitThe characteristics which are controlled and transmitted to next generations through genes

Transgenic: Organisms with modified genome (genetic make-up)

Triceps: An extensor muscle on the back of the upper arm bone

True-breeding: The homozygous individual

TubersThe swollen ends of slender rhizomes (underground stem); new plants develop from buds on the stem tubers (vegetative propagation)

Tubular secretion: The third step in urine formation; different ions, creatinine, urea etc. are secreted from the blood into the filtrate in the renal tubule

TympanumTympanic membrane: See Ear drum

UreterA tube that carries urine from a kidney to the urinary bladder

Urethra: The tube that carries urine from urinary bladder to the outside of the body

Urinary system: The system responsible for the production and excretion of urine; includes kidneys, ureters, urinary bladder and urethra

Uterus hornThe two separate parts of the uterus in the female rabbit

Variation: A characteristic in an individual that differs from the typical characteristics of other individuals of the same species

Vas deferensThe tubes that carry sperms from each testis to the urethra

Vasopressin: Antidiuretic hormone; the hormones secreted by the posterior pituitary; responsible for the reabsorption of water from renal tubules of the nephron

Vector(in Biology) The DNA (plasmid) or bacteriophage etc. that transfers the isolated gene of interest to the host cell

Vegetative propagationA type of asexual reproduction in which the vegetative parts of the plants i.e. roots, stems or leaves produce new generation

Vestibule: Part of the inner ear; helps to maintain balance of the body

Vitreous humour: The fluid present in the posterior chamber of the eye i.e. between the iris and retina

Vocal cords: Two pairs of fibrous bands in the larynx; vibrate when the air passes through them and produce sounds.

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