All Definition Of Biology For Class 9th [A to Z]

All Definition Of Biology For Class 9th [A to Z]

Acquired Diseases: These diseases develop after birth and are not inherited.

Acute Diseases: Diseases which last for a short period of time, e.g., common cold.

Aerenchyma: Parenchyma having large air cavities present in hydrophytes to give buoyancy to the plant.

Antibody: Protein molecule which is produced by an organism to counteract a foreign substance in the tissue or blood.

Antibiotic: A chemical substance obtained from some microbes (bacteria and fungi), which inhibit the growth of other microbes.

Antigen: A foreign substance or toxin which when introduced into the body of an organism stimulates the production of specific antibody.

Atmosphere: The air that covers the whole of the earth like a blanket.

Autotroph: An organism that synthesises its food by itself.

Balanced Diet: A diet that contains all the nutrients in adequate properties to maintain health.

Biocide: Any chemical that kills living organisms.

Biodiversity: The diversity of life forms found in a region.

Biosphere: Life-supporting zone of the earth, where the atmosphere, the hydrosphere and the lithosphere interact and make life possible.

Bone: A strong and non-flexible specialised connective tissue that supports the body.

Cambium: Thin ring of meristematic cells surrounding the circumference of woody plants responsible for the growth in width.

Cell: A cell is the fundamental structural and functional unit of life.

Chemotherapy: The treatment of infectious diseases with chemicals that kill the microbes without harming the patient.

Chitin: An insoluble polysaccharide bound to protein to form a glycoprotein.

Chromatid: One of the two identical longitudinal halves of a chromosome.

Chromatin: A thread-like structure found in initial stage of cell division made up of deoxyribonucleoprotein.

Chromatophore: This is the term used for photosynthetic plastids of algae other than green.

Chronic Diseases: The diseases which are long-lasting, i.e., persistent, e.g., elephantiasis.

Coelom: Body cavity of triploblastic animals lying within mesoderm and lined by it.

Dendrite: Dendrite is the short branched fibre of neuron which receives nerve impulses.

Diffusion: Movement of molecules of any substance from a region of higher concentration to lower concentration.

Diploblastic: Animal having a body made of two germ layers of cells is called diploblastic.

Diploid: An individual or cell with two complete sets of chromosome, symbolised as 2n, characteristics of somatic cells.

Domestication: Adapting wild plants or animals for human cultivation and use is called domestication.

Endocytosis: Bulk intake of solid particle by formation of vesicles from part of a plasma membrane, bringing these materials into the cell.

Endoskeleton: The bony and cartilaginous supporting structure within the animal body.

Epidermis: The outermost single cell layer of an organism.

Eukaryote: Organisms having a well-defined nucleus enclosed in a nuclear envelope and one or more membrane-bound organelles in their cells.

Eutely: The phenomenon of having a constant and genetically fixed number of cells.

Exoskeleton: Calcareous, chitinous, or other hard material covering the body surface and providing protection and support.

Fossils: The remains of ancient animals in rocks strata.

Genome: Haploid set of chromosome along with all its genes.

Gland: A group of cells which produces and secretes special chemicals to be used in th body.

Hermaphrodite: An individual who possesses both female and male reproductive organs.

Homocercal: Homocercal can be define as; Pertaining to the caudal fin of certain fish which has almost equal lobes, with the vertebral column terminating near the middle of the base.

Humus: Complex organic matter valuable for plant growth, resulting from decomposition of plant and animal tissues.

Hybridisation: Process in which a crossbreed is obtained by crossing two genetically dissimilar plants.

Impulse: The passage of electrical activity along the axon of a nerve cell.

Immunisation: Immunisation is the technique to strengthen defence mechanism of the body against infections.

Infection: Invasion of the body by a foreign pathogen.

Involuntary Muscle: The muscles which do not work at our will.

Leucocytes: White blood cells which provide resistance against infections.

Ligament: A flexible, dense, fibrous connective tissue joining the bones to each other.

Lignin: Lignin is a complex polymer which hardens and makes the cell wall impermeable.

Lymph: Lymph is a colourless fluid that has filtered out of the blood capillaries.

Malpighian Tubules: The long, slender, tubular excretory organs attached to the gut of many terrestrial arthropods such as spiders and insects.

Malnutrition: Deficiency of one or more nutrients is called malnutrition.

Manure: An organic substance that is added to the soil, to increase its fertility, is called manure.

Mesoglea: A gelatinous matrix located between the epidermis and gastrodermis of coelenterates.

Mesophyll: Chloroplast containing parenchymatous cells of leaf below the upper epidermis.

Micronutrients: Essential elements required by plants in relatively small quantity.

Monoculture: Agricultural practice of growing large number of a single species of plants together.

Nematocyst: A minute stinging structure found on coelenterates or cnidarians and used for anchorage, for defence and for the capture of prey is known as nematocyst.

Nephridium: A tubular excretory organ of many invertebrates.

Notochord: A dorsal gelatinous stiff rod present in all chordates at some stage of life, vertebral column is laid down around it.

Nucleus: A membrane-bound centred structure containing genetic material of inheritance and controlling the metabolic activities of the cell.

Neurons: Nerve cells are functional unit of the nervous system, specialised to respond to Stimuli by electrical impulses that are rapidly conducted along the axon of the neuron to reach other cells with which the axon synapses.

Osmosis: Movement of solvent/water from a region of high concentration to a region of low concentration through a semi-permeable membrane.

Ostia: Core or holes leading to a canal system in sponges.

Oviparous: Egg-laying animals.

Palaeontology: The study of fossils.

Parapodia: Paired fleshy appendages extending laterally from each segment of polychaete worms and bearing setae.

Parasitism: A type of heterotrophic nutrition in which one organism is benefitted and other is harmed.

Parenchyma: Thin-walled living cells, with intercellular spaces present in many parts of the plant.

Pesticide: Chemical which kills pests.

Phagocytosis: Transport of solid matter like food, pathogens and foreign matter across the membrane by forming detachable vesicles.

Phloem: The vascular tissue of plants consisting of sieve tubes and companion cells that specialises in nutrient transport.

Pinocytosis: Intake of droplets of extracellular fluid along with sub-microscopic particles.

Polymorphism: Occurrence of several forms among the members of a species.

Probocis: Any tubular process of the head or snout of an animal, usually used in feeding.

Prokaryote: Organisms lacking nuclear membrane and membrane-bound organelles in their cell.

Pseudocoelom: Body cavity or area between body wall and gut not lined with cells of mesodermal origin.

Pseudopodium (False Feet): Temporary cytoplasmic protrusion of an amoeboid cell used in amoeboid locomotion and feeding.

Regeneration: Regrowth of a lost or injured tissue or part of an organism.

Sarcoplasm: Cytoplasm of a muscle fibre or cell.

Sebaceous Glands: The cutaneous glands on skin that secrete oily substances for lubricating hair and skin.

Setae: Bristle-like chitinous projections of the body surface.

Soil erosion: The removal of the top layer of the soil by wind and rainfall.

Sporophyte: Diploid plant which produces spores.

Symbiotic: A relationship between two organisms in which both the organisms get benefits from each other.

Taxonomy: Arranging organisms into various groups on the basis of similarities and differences.

Tendon: Band of connective tissue connecting a bone to muscle.

Thorax: The region of body between the head and abdomen of some animal.

Tissue: A group of similar cells working together to achieve a particular function and have common origin.

Totipotency: The ability of giving rise to all the various cell types of the body of an organism.

Triploblastic: Animals having a body made 'or' composed of three germ layers: ectoderm, mesoderm and endoderm.

Vaccination: The administration of vaccine to stimulate the immune system against microbes.

Vector: An organism which carries germs from a sick person to other persons.

Virus: An organism, sub-microscopic cellular that consist of either RNA or DNA in a protein coat.

Voluntary Muscle: The muscles which work at our will.

Warm-blooded: Condition in which the internal temperature of an animal is dependent upon its metabolic processes and held at a relatively high and constant level.

Weed: A herbaceous plant or shrub that grows wildly and hinders growth of cultivated plants.

Xylem: Water conducting and supporting vascular tissue in plants.

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