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GLOSSARY
A comprehensive, exam-ready reference of essential biology terms with clear, in-depth explanations. Designed to support students in mastering concepts, reinforcing revision, and building confidence for success.
Organized alphabetically for easy navigation, this glossary ensures quick access to definitions during study sessions.
Each entry is crafted to connect theory with practical understanding, making biology both accessible and engaging.
A
Absorption – The process by which digested food molecules pass into the blood or lymph from the small intestine.
Active Transport – Movement of molecules across a membrane using energy (ATP), often against a concentration gradient.
Adaptation – Structural, behavioral, or physiological traits that improve an organism’s survival in its environment.
Aerobic Respiration – Cellular process using oxygen to release energy from glucose, producing carbon dioxide and water.
Allele – Alternative form of a gene found at the same locus on homologous chromosomes.
Amino Acids – Building blocks of proteins, containing an amino group, carboxyl group, and variable side chain.
Anaphase – Stage of mitosis/meiosis where sister chromatids or homologous chromosomes separate to opposite poles.
Antibody – Protein produced by B-lymphocytes that binds specifically to antigens to neutralize pathogens.
Antigen – Foreign molecule (often protein) that triggers an immune response.
Autotroph – Organism that produces its own food, usually through photosynthesis or chemosynthesis.
B
Bacteria – Single-celled prokaryotes lacking a nucleus, some beneficial, others pathogenic.
Balanced Diet – Nutritional intake providing all essential nutrients in correct proportions for health.
Binary Fission – Asexual reproduction in prokaryotes where one cell divides into two identical cells.
Biomass – Total mass of living organisms in a given area, often used in energy flow studies.
Biotic Factors – Living components of an ecosystem (plants, animals, microbes).
Blood Plasma – Liquid portion of blood carrying nutrients, hormones, and waste products.
Bronchi – Two main branches of the trachea leading into the lungs.
Bryophytes – Non-vascular plants like mosses, dependent on water for reproduction.
Buffer Systems – Chemical systems that maintain pH stability in biological fluids.
Biodiversity – Variety of life forms within a habitat, ecosystem, or the planet.
C
Capillaries – Smallest blood vessels where exchange of gases, nutrients, and wastes occurs.
Carbohydrates – Organic compounds (sugars, starches, cellulose) providing energy and structural support.
Carnivores – Animals that feed primarily on other animals.
Catalyst – Substance that speeds up chemical reactions without being consumed; enzymes are biological catalysts.
Cell Membrane – Semi-permeable barrier controlling entry and exit of substances in cells.
Cell Wall – Rigid outer layer in plant, fungal, and bacterial cells providing support and protection.
Chlorophyll – Green pigment in chloroplasts that absorbs light energy for photosynthesis.
Chromosomes – Thread-like structures of DNA and protein carrying genetic information.
Cloning – Production of genetically identical organisms or cells.
Community – All populations of different species living and interacting in a given area.
D
Decomposer – Organism (like fungi or bacteria) that breaks down dead organic matter, recycling nutrients into ecosystems.
Denaturation – Structural change in proteins (often due to heat or pH) that causes loss of biological function.
Diffusion – Passive movement of molecules from high to low concentration until equilibrium is reached.
Diploid – Cells containing two sets of chromosomes (one from each parent).
DNA (Deoxyribonucleic Acid) – Molecule carrying genetic instructions for growth, development, and reproduction.
Dominant Allele – Gene variant that expresses its trait even when only one copy is present.
Dormancy – Period of suspended growth or activity in organisms, often to survive unfavorable conditions.
Double Circulation – Blood passes through the heart twice in one complete circuit (systemic + pulmonary).
Drug Resistance – Ability of pathogens to withstand effects of drugs, often due to genetic mutations.
Drought Stress – Physiological strain on plants caused by lack of water, affecting photosynthesis and growth.
E
Ecology – Study of interactions between organisms and their environment.
Ecosystem – Community of organisms interacting with each other and their physical environment.
Effector – Organ or cell that responds to a stimulus (e.g., muscles contracting, glands secreting).
Endocytosis – Process where cells engulf substances into vesicles for transport inside.
Endoplasmic Reticulum (ER) – Organelle involved in protein and lipid synthesis; rough ER has ribosomes, smooth ER does not.
Enzyme – Biological catalyst that speeds up chemical reactions by lowering activation energy.
Epidermis – Outer protective layer of cells in plants and animals.
Erythrocytes – Red blood cells that transport oxygen using hemoglobin.
Excretion – Removal of metabolic waste products (like urea, carbon dioxide) from the body.
Extinction – Permanent loss of a species from Earth.
F
Facilitated Diffusion – Passive transport of molecules across membranes via carrier proteins.
Fats (Lipids) – Organic compounds used for energy storage, insulation, and cell membrane structure.
Fermentation – Anaerobic breakdown of glucose producing energy, ethanol/lactic acid, and carbon dioxide.
Fertilization – Fusion of male and female gametes to form a zygote.
Flagella – Whip-like structures enabling movement in certain cells (e.g., sperm, bacteria).
Flora – Plant life of a particular region or ecosystem.
Food Chain – Linear sequence showing energy transfer from producers to consumers.
Food Web – Complex network of interconnected food chains in an ecosystem.
Fructose – Simple sugar found in fruits, metabolized for energy.
Fungi – Kingdom of organisms including molds, yeasts, and mushrooms; many act as decomposers.
G
Gamete – Specialized sex cell (sperm or egg) carrying half the genetic material (haploid) for reproduction.
Gene – Segment of DNA coding for a specific protein or trait.
Genetic Drift – Random changes in allele frequencies in small populations, leading to evolutionary change.
Genotype – Genetic makeup of an organism, determining potential traits.
Germination – Process by which a seed develops into a seedling under suitable conditions.
Glucose – Simple sugar that is a primary energy source for cells.
Golgi Apparatus – Organelle that modifies, packages, and distributes proteins and lipids.
Growth Hormone – Hormone stimulating growth and cell reproduction in animals.
Guard Cells – Specialized cells controlling the opening and closing of stomata in plant leaves.
Guttation – Exudation of water droplets from leaf edges due to root pressure.
H
Habitat – Natural environment where an organism lives and thrives.
Haemoglobin – Iron-containing protein in red blood cells that binds and transports oxygen.
Haploid – Cells containing a single set of chromosomes (e.g., gametes).
Herbivores – Animals that feed primarily on plants.
Heterozygous – Having two different alleles for a particular gene.
Homeostasis – Maintenance of stable internal conditions despite external changes.
Hormones – Chemical messengers regulating physiological processes in organisms.
Hybrid – Offspring resulting from the cross of two different species or varieties.
Hydrolysis – Chemical breakdown of compounds using water.
Hypothesis – Testable explanation or prediction based on observations.
I
Immune System – Body’s defense system against pathogens, involving cells, tissues, and organs.
Immunity – Ability to resist infection, either naturally or through vaccination.
Ingestion – Process of taking in food or drink into the body.
Insect Pollination – Transfer of pollen by insects, aiding plant reproduction.
Insulin – Hormone produced by the pancreas that regulates blood glucose levels.
Interphase – Stage of the cell cycle where the cell grows, replicates DNA, and prepares for division.
Invertebrates – Animals lacking a backbone (e.g., insects, mollusks).
Ion – Atom or molecule with an electrical charge due to loss or gain of electrons.
Isotonic Solution – Solution with equal solute concentration as the cell, causing no net water movement.
Isolation Mechanisms – Biological barriers preventing interbreeding between species, maintaining distinct populations.
J
Joint – Point where two bones meet, allowing movement and flexibility.
Jugular Vein – Major vein in the neck returning blood from the head to the heart.
Juvenile Stage – Developmental phase between infancy and adulthood in organisms.
Joule – SI unit of energy, relevant in biological processes like respiration.
Jellyfish – Simple invertebrate with radial symmetry, part of the phylum Cnidaria.
Jaundice – Condition caused by excess bilirubin, leading to yellowing of skin and eyes.
Jawbone (Mandible) – Largest and strongest bone of the face, crucial for chewing.
Jejunum – Middle section of the small intestine where absorption of nutrients occurs.
Juxtaglomerular Apparatus – Kidney structure regulating blood pressure and filtration rate.
J-shaped Growth Curve – Population growth pattern showing exponential increase without limiting factors.
K
Kidney – Organ responsible for filtering blood, removing waste, and regulating water balance.
Keratin – Structural protein in hair, nails, and skin, providing strength and protection.
Kinesis – Non-directional movement response of organisms to stimuli (e.g., humidity, light).
Krebs Cycle – Series of reactions in cellular respiration producing ATP, NADH, and FADH₂.
Karyotype – Visual display of an organism’s chromosomes, used to detect abnormalities.
Keystone Species – Species with a disproportionately large impact on ecosystem stability.
Kingdom – Highest taxonomic rank grouping organisms (e.g., Animalia, Plantae, Fungi).
Kinase – Enzyme that transfers phosphate groups, important in cell signaling.
Krill – Small crustaceans forming a crucial part of marine food webs.
K-strategists – Species producing fewer offspring with high parental investment (e.g., elephants).
L
Lactase – Enzyme breaking down lactose into glucose and galactose.
Lactic Acid – Byproduct of anaerobic respiration in muscle cells.
Larynx – Voice box containing vocal cords, essential for sound production.
Leaf – Plant organ specialized for photosynthesis and gas exchange.
Ligament – Tough connective tissue linking bones at joints.
Light-dependent Reactions – Photosynthesis stage converting light energy into chemical energy (ATP, NADPH).
Lipid Bilayer – Structural foundation of cell membranes, composed of phospholipids.
Lymph – Fluid in lymphatic system transporting immune cells and waste.
Lysosome – Organelle containing digestive enzymes to break down waste and damaged organelles.
Lymphocytes – White blood cells (B and T cells) central to immune responses.
M
Meiosis – Type of cell division producing gametes with half the chromosome number, ensuring genetic variation.
Mitochondria – Organelles known as the “powerhouses” of the cell, generating ATP through respiration.
Mutation – Permanent change in DNA sequence that may alter traits or cause disease.
Mycelium – Network of fungal hyphae that absorbs nutrients from the environment.
Myelin Sheath – Fatty covering around nerve axons that speeds up impulse transmission.
Microorganism – Microscopic living organism such as bacteria, fungi, or protozoa.
Monohybrid Cross – Genetic cross involving one trait, used to study inheritance patterns.
Morphology – Study of the form and structure of organisms.
Muscle Fibers – Specialized cells capable of contraction, enabling movement.
Mutualism – Symbiotic relationship where both organisms benefit (e.g., bees and flowers)
N
Nervous System – Network of nerves and cells transmitting signals between body parts.
Nephrons – Functional units of the kidney that filter blood and form urine.
Niche – Role or position of an organism in its ecosystem.
Nitrogen Cycle – Biogeochemical cycle recycling nitrogen through ecosystems.
Nucleolus – Structure within the nucleus that produces ribosomes.
Nucleotide – Building block of DNA and RNA, consisting of sugar, phosphate, and base.
Nutrition – Process of obtaining and using food for growth and energy.
Non-renewable Resources – Natural resources that cannot be replenished quickly (e.g., fossil fuels).
Nuclear Division – Separation of genetic material during mitosis or meiosis.
Neurotransmitter – Chemical messenger transmitting signals across synapses between neurons.
O
Osmosis – Movement of water molecules across a semi-permeable membrane from low to high solute concentration.
Ovary – Female reproductive organ producing eggs and hormones.
Oviduct (Fallopian Tube) – Tube carrying eggs from ovary to uterus; site of fertilization.
Omnivores – Animals that eat both plants and animals.
Organelles – Specialized structures within cells performing distinct functions.
Organism – Individual living entity capable of growth, reproduction, and response to stimuli.
Oxidation – Chemical reaction involving loss of electrons, often in respiration.
Oxygen Debt – Temporary shortage of oxygen in muscles during intense activity, repaid after exercise.
Ozone Layer – Atmospheric layer protecting Earth from harmful UV radiation.
Oogenesis – Formation and development of female gametes (ova).
P
Photosynthesis – Process in plants converting light energy, carbon dioxide, and water into glucose and oxygen.
Phloem – Vascular tissue transporting sugars and nutrients throughout plants.
Phenotype – Observable traits of an organism, influenced by genotype and environment.
Phagocytosis – Process where cells engulf and digest foreign particles or pathogens.
Placenta – Organ in mammals that nourishes the developing fetus and removes waste.
Plasma Membrane – Semi-permeable barrier controlling entry and exit of substances in cells.
Plasmid – Small circular DNA molecule in bacteria, often carrying useful genes like antibiotic resistance.
Pollination – Transfer of pollen from anther to stigma, enabling fertilization in plants.
Population – Group of individuals of the same species living in a given area.
Protein Synthesis – Cellular process of building proteins from amino acids, directed by DNA and RNA.
Q
Quarantine – Isolation of individuals to prevent spread of disease.
Quaternary Structure – Level of protein organization involving multiple polypeptide chains.
Quercetin – Plant flavonoid with antioxidant properties.
Quadriceps – Large muscle group in the thigh responsible for leg extension.
Quorum Sensing – Communication among bacteria to coordinate behavior based on population density.
Quaternary Consumers – Organisms at the top of food chains, feeding on tertiary consumers.
Quiescence – State of inactivity or dormancy in cells or organisms.
Quinolones – Class of antibiotics targeting bacterial DNA replication.
Quill – Stiff feather structure in birds, important for flight.
Quercus – Genus of oak trees, ecologically significant in many forests
R
Respiration – Process of breaking down glucose to release energy, either aerobically or anaerobically.
Ribosome – Organelle where protein synthesis occurs.
RNA (Ribonucleic Acid) – Molecule involved in protein synthesis and gene regulation.
Recessive Allele – Gene variant expressed only when two copies are present.
Reproduction – Biological process of producing offspring, sexually or asexually.
Root Hair – Extension of root epidermal cells increasing surface area for water absorption.
Reflex Action – Rapid, automatic response to stimuli, protecting the body from harm.
Regeneration – Ability of organisms to regrow lost or damaged body parts.
Rumen – Specialized stomach chamber in ruminants where microbial digestion of cellulose occurs.
Runoff – Movement of water across land surfaces, often carrying nutrients or pollutants into ecosystems.
S
Saprophytes – Organisms (like fungi) that feed on decaying organic matter.
Secondary Consumers – Animals that feed on primary consumers (herbivores).
Segregation (Genetics) – Separation of alleles during gamete formation in meiosis.
Sexual Reproduction – Process involving fusion of gametes to produce genetically diverse offspring.
Species – Group of organisms capable of interbreeding and producing fertile offspring.
Spindle Fibers – Structures that help separate chromosomes during cell division.
Stomata – Pores on plant leaves controlling gas exchange and water loss.
Symbiosis – Close relationship between two species, which may be mutualistic, commensal, or parasitic.
Synapse – Junction between two neurons where neurotransmitters transmit signals.
Systemic Circulation – Pathway carrying oxygenated blood from the heart to the body and back.
T
Tissue – Group of similar cells performing a specific function.
Transpiration – Loss of water vapor from plant leaves through stomata.
Trophic Level – Position of an organism in a food chain (producer, consumer, etc.).
Tuberculosis (TB) – Infectious disease caused by Mycobacterium tuberculosis, affecting lungs.
Tundra – Cold biome with limited vegetation, found in polar regions.
Turgor Pressure – Pressure of water inside plant cells keeping them rigid.
Thylakoid – Membrane-bound structure in chloroplasts where light-dependent reactions occur.
Toxin – Poisonous substance produced by organisms, often harmful to others.
Tropism – Growth response of plants toward or away from stimuli (light, gravity, etc.).
Trachea – Windpipe carrying air to and from the lungs.
U
Ultrastructure – Detailed structure of cells revealed by electron microscopy.
Umbilical Cord – Structure connecting fetus to placenta, transporting nutrients and wastes.
Unicellular Organisms – Living beings made up of a single cell (e.g., bacteria, amoeba).
Urinary System – Organ system removing waste and maintaining water balance.
Urea – Nitrogenous waste product formed in the liver and excreted in urine.
Uracil – Nitrogenous base found in RNA, replacing thymine.
Uterus – Female reproductive organ where embryo develops.
Ultraviolet Radiation – High-energy light that can damage DNA but also aids vitamin D production.
Upwelling – Ocean process bringing nutrient-rich water to the surface, supporting marine life.
Uptake (Nutrients) – Absorption of minerals and water by plant roots.
V
Vaccination – Introduction of antigens to stimulate immunity against specific diseases.
Vacuole – Membrane-bound sac in cells storing water, nutrients, and waste.
Variation – Differences among individuals in a population, essential for evolution.
Vector – Organism that transmits pathogens (e.g., mosquito carrying malaria).
Veins – Blood vessels carrying blood toward the heart.
Venation – Pattern of veins in plant leaves.
Vertebrates – Animals with a backbone (fish, amphibians, reptiles, birds, mammals).
Virus – Non-cellular infectious agent requiring host cells to replicate.
Vitamin – Organic compound essential in small amounts for normal metabolism.
Villi – Finger-like projections in the small intestine increasing surface area for absorption.
W
Water Cycle – Continuous movement of water through evaporation, condensation, and precipitation.
White Blood Cells – Immune cells defending the body against pathogens.
Worms (Helminths) – Parasitic organisms affecting humans and animals.
Wavelength – Distance between successive peaks of a wave, important in photosynthesis.
Wildlife – Collective term for animals living in natural habitats.
Winds – Air movements influencing climate and dispersal of seeds/pollen.
Womb – Another term for uterus, where embryo develops.
Wood – Plant tissue composed of xylem, providing support and transport.
Waste Products – Substances excreted after metabolism (e.g., carbon dioxide, urea).
Water Potential – Measure of the tendency of water to move, crucial in osmosis.
X
Xylem – Vascular tissue transporting water and minerals from roots to shoots.
Xanthophyll – Yellow pigment in plants aiding photosynthesis.
Xerophytes – Plants adapted to dry environments (e.g., cacti).
X-chromosome – Sex chromosome determining female characteristics when paired (XX).
Xenobiotics – Foreign chemical substances not naturally produced in organisms.
Xenotransplantation – Transplanting organs/tissues between different species.
Xanthoma – Fatty growth under skin linked to lipid metabolism disorders.
Xenon – Inert gas sometimes used in medical imaging.
Xerosis – Abnormal dryness of skin or mucous membranes.
Xenophyophore – Large deep-sea protists important in marine ecosystems.
Y
Yeast – Single-celled fungi used in fermentation and baking.
Yolk – Nutrient-rich portion of an egg supporting embryo development.
Y-chromosome – Sex chromosome determining male characteristics (XY).
Yield – Amount of crop produced per unit area.
Yellow Fever – Viral disease transmitted by mosquitoes.
Yolk Sac – Embryonic structure providing nutrients in early development.
Yersinia pestis – Bacterium causing plague.
Yolk Proteins – Nutrient proteins stored in eggs.
Yolk Plug – Embryonic structure in amphibians during gastrulation.
Yolk Granules – Nutrient storage bodies in eggs.
Z
Zygote – Fertilized egg cell formed by fusion of gametes.
Zoology – Scientific study of animals.
Zonation – Distribution of organisms in distinct zones within ecosystems.
Zymase – Enzyme complex in yeast catalyzing fermentation.
Zooplankton – Microscopic animals drifting in aquatic environments.
Zygomycota – Fungal group producing zygospores during reproduction.
Zygomatic Bone – Cheekbone in vertebrates.
Zygomorphy – Bilateral symmetry in flowers.
Zoonosis – Disease transmitted from animals to humans.
Zygospore – Thick-walled spore formed by fungi during sexual reproduction.