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

Calyx: The 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

Carnivores: The consumers which eat only animal flesh

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

Cartilage: The connective tissue that makes part of the human skeleton

Cell body: The part of the nerve cell that contains nucleus

Central nervous system: The 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 hemispheres: The divisions of the cerebrum of the brain

Cerebrospinal fluid: The 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

Commensalism: A 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

Consumer: The 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

Cornea: The transparent part of sclera that forms in the front of the eye through which light enters

Corolla: The second whorl of flower, consisting of petals

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

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

Cranial bones: The bone of the cranium

Cranial nerves: Nerves that arise from or lead to the brain

Cultivars: The plants which are bred through artificial selection

Cutting: Artificial 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

Dialyzer: The apparatus used for haemodialysis

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

present below lungs

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

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

Drug: Any 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 drum: Tympanic 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

Effectors: The parts of the coordination system that respond when stimulated by nerve impulses or hormones

Emphysema: A disease in which the walls of the alveoli are destroyed

Endocrine gland: A 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

Endospore: The spore formed inside the bacterial cell

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

Epicotyl: The 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)

Epinephrine: See Adrenaline

Estrogen: A 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.

Fertilization: The fusion of male and female gametes to form a zygote

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

Flexor: A muscle that bends a joint

Follicle: A structure in the ovary in which the mature egg develops

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

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

Forebrain: The part of the brain; includes cerebrum, thalamus and hypothalamus

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

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

Gametogenesis: The process of the formation of gametes

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

Ganglion: The 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

Genotype: The specific combination of genes in an individual; may be homozygous or heterozygous

Germination: The process by which a seed embryo develops into a seedling

Gigantism: The 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 filtrate: The material that passes from glomerulus into the Bowman’s capsule

Glomerulus: The network of capillaries in the nephron of kidney

Glucagon: The hormone secreted by the islets of Langerhan; increases the blood glucose level

Gout: A 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

Guttation: Appearance of drops of xylem sap on the tips or edges of leaves

Hallucinogen: Drug 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

Hilum: A 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

Hindbrain: The 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

Hormone: A 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 bone: The 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

Hypocotyl: The 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

Inheritance: The 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 interactions: Interactions between the members of the same species

Iodopsin: A pigment present in the cones of the retina

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

Iris: A 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 stone: The 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

Lacuna: The fluid filled space in bone and cartilage, where their cells are present

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

Lenticels: Pores in the bark of wooding stems and mature roots

Ligament: Strong but flexible connective tissue that joins one bone to bone at the joints

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

Locus: Plural 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 drug: Any 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 cavity: Hollow space in the nose; opens to the outside through nostrils; divided into two portions by a wall

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

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

Nephron: The functional unit of kidneys

Nerve: The 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 cycle: The flow of nitrogen between environment and the organisms

Nitrogen fixation: Conversion of nitrogen into nitrates

Nodes of Ranvier: The 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

Nostril: The openings of the nasal cavity

Nucleosome: The structure formed by the wrapping of DNA around histone proteins

Olfactory bulbs: The 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

Osteoporosis: A 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 window: The membrane which separates the middle ear from the inner ear

Ovary: The 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

Oxytocin: The 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

Paralysis: Complete 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

Parathyroid: The endocrine glands located on the posterior sides of the thyroid gland; secrete parathormone

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

Parthenogenesis: A 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

Pharmacology: The study of drug composition and properties and medical applications

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

Phytoplankton: Photosynthetic organisms that float on the surface of water

Pituitary: The endocrine gland attached to the hypothalamus that controls many other endocrine glands in the body

Plumule: The 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 tube: A 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

Pollutant: The 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 gland: An 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 Numbers: The graphic representation of the number of individuals per unit area at various trophic levels in an ecosystem

Radicle: The 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 Action: The 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 pelvis: The funnel-shaped cavity into which the renal pyramids of kidney project

Renal pyramids: Cone-shaped areas in the renal medulla

Renal tubule: The 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

Retina: The 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 cells: The 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

Sedatives: Types 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 tubule: The coiled tubes present in testes; sperms are formed in these tubules

Sensory nerves: The 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

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

Somatic Nervous system: The 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

Spermatogenesis: The 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

Stigma: The upper part of the carpel

Style: The middle portion of the carpel

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

Suspensory ligament: The ring that attaches the lens of the eye to the ciliary muscles

Symbiosis: Long 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

Synapse: A 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

Testosterone: The 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

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

Thyroid: The 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

Trait: The 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

Tubers: The 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

Tympanum: Tympanic membrane: See Ear drum

Ureter: A 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 horn: The 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 deferens: The 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 propagation: A 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.