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Comprehensive Biology Glossary: Key Terms and Definitions, Exams of Biology

A glossary of biological terms covering cellular processes to ecological concepts. Definitions include dipeptide, endocytosis, exchange surface, family, fermenter, gamete, gene pool, glycosidic bond, habitat, haem, haemoglobinic acid, haemolysis, health, histone, hormone, hydrocarbon chain, immune response, immunological memory, incidence, induced fit, interferon, intracellular, ion, ionic bond, keratin, leucocytes, lipids, lock-and-key hypothesis, lumen, lymphocyte, lysosomes, macrophages, magnification, messenger rna, microtubule motors, mitosis, monoculture, monocyte, monomer, monosaccharide, morbidity, mortality, mucus, mutation, mycelium, natural selection, niche, non-competitive inhibitor, nuclear envelope, nucleotide, nucleus, nutrition, oestrogen, omnivore, opportunistic infection, organ, organelle, organic base, oxygen tension, oxygenated, oxyhaemoglobin, pandemic, parenchyma, partial pressure, partially permeable membrane, passive immunity, pathogen, peptide, peptide bond, pe

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Dipeptide - ansA molecule consisting of two amino acids joined by a peptide bond.
Endocytosis - ansThe process of taking materials into a cell by surrounding them with plasma
membrane, which pinches off to form a vesicle inside the cell. This is an active process
requiring ATP.
Exchange surface - ansA specialised area adapted to make it easier for molecules to cross
from one side of the surface to the other.
Family - ansTaxonomic group used in the classification of living organisms. Contains related
genera.
Fermenter - ansA vessel used to grow microorganisms in large numbers.
Gamete - ansSex cells, usually haploid (one set of chromosomes). Fuse during sexual
reproduction to form zygotes (diploid).
Gene pool - ansThe sum total and variety of all the genes in a population or species at a given
time.
Glycosidic bond - ansThe covalent bond formed when carbohydrate molecules are joined
together in condensation reactions.
Habitat - ansThe place where an organism or population lives. It includes the climatic,
topographic and edaphic factors as well as the plants and animals that live there.
Haem - ansThe iron-containing prosthetic group found in haemoglobin.
Haemoglobinic acid - ansThe acid produced when haemoglobin takes up hydrogen ions.
Haemolysis - ansThe rupturing of animal cell surface membranes, and subsequent release of
their contents, when cells placed in a solution of higher water potential and water enters by
osmosis.
Health - ansComplete mental, physical and social wellbeing.
Histone - ansType of protein associated with DNA in eukaryotes. DNA is wound around
them to form chromatin.
Hormone - ansChemicals made in endocrine glands that are carried in the blood to target
cells/tissues/organs. They act as chemical messengers.
Hydrocarbon chain - ansA chain of carbon atoms bonded together with hydrogen atoms
bonded onto the carbons.
Immune response - ansA response to an antigen, which involves the activation of
lymphocytes.
Immunological memory - ansAbility of the immune system to respond very quickly to
antigens that it recognises as they have entered the body before.
Incidence - ansThe number of new cases of a disease in a certain time period.
Induced fit (hypothesis) - ansThe theory of enzyme action in which the enzyme molecule
changes shape to fit the substrate molecule more closely as it binds to it.
Interferon - ansA group of factors with non-specific antiviral activity. They also affect the
immune system.
Intracellular - ansInside the cell.
Ion - ansAn atom (or group of atoms) carrying a positive or a negative charge.
Ionic bond - ansAttraction between oppositely charged ions.
Keratin - ansFibrous protein found in skin, hair and nails.
Leucocytes - ansWhite blood cells.
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Dipeptide - ansA molecule consisting of two amino acids joined by a peptide bond. Endocytosis - ansThe process of taking materials into a cell by surrounding them with plasma membrane, which pinches off to form a vesicle inside the cell. This is an active process requiring ATP. Exchange surface - ansA specialised area adapted to make it easier for molecules to cross from one side of the surface to the other. Family - ansTaxonomic group used in the classification of living organisms. Contains related genera. Fermenter - ansA vessel used to grow microorganisms in large numbers. Gamete - ansSex cells, usually haploid (one set of chromosomes). Fuse during sexual reproduction to form zygotes (diploid). Gene pool - ansThe sum total and variety of all the genes in a population or species at a given time. Glycosidic bond - ansThe covalent bond formed when carbohydrate molecules are joined together in condensation reactions. Habitat - ansThe place where an organism or population lives. It includes the climatic, topographic and edaphic factors as well as the plants and animals that live there. Haem - ansThe iron-containing prosthetic group found in haemoglobin. Haemoglobinic acid - ansThe acid produced when haemoglobin takes up hydrogen ions. Haemolysis - ansThe rupturing of animal cell surface membranes, and subsequent release of their contents, when cells placed in a solution of higher water potential and water enters by osmosis. Health - ansComplete mental, physical and social wellbeing. Histone - ansType of protein associated with DNA in eukaryotes. DNA is wound around them to form chromatin. Hormone - ansChemicals made in endocrine glands that are carried in the blood to target cells/tissues/organs. They act as chemical messengers. Hydrocarbon chain - ansA chain of carbon atoms bonded together with hydrogen atoms bonded onto the carbons. Immune response - ansA response to an antigen, which involves the activation of lymphocytes. Immunological memory - ansAbility of the immune system to respond very quickly to antigens that it recognises as they have entered the body before. Incidence - ansThe number of new cases of a disease in a certain time period. Induced fit (hypothesis) - ansThe theory of enzyme action in which the enzyme molecule changes shape to fit the substrate molecule more closely as it binds to it. Interferon - ansA group of factors with non-specific antiviral activity. They also affect the immune system. Intracellular - ansInside the cell. Ion - ansAn atom (or group of atoms) carrying a positive or a negative charge. Ionic bond - ansAttraction between oppositely charged ions. Keratin - ansFibrous protein found in skin, hair and nails. Leucocytes - ansWhite blood cells.

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Lipids - ansA diverse group of chemicals that includes triglycerides, fatty acids and cholesterol. Lock-and-key hypothesis - ansThe simple theory of enzyme action where the active site is directly complementary to the substrate molecule. Lumen - ansA cavity surrounded by a cell wall in cells, such as xylem vessels, which have lost their cell contents. Also used for the central cavities of blood vessels. Lymphocyte - ansA type of white blood cell activated as part of the immune response. Lysosomes - ansMembrane-bound vesicles made by pinching off from the Golgi body. They usually contain digestive enzymes. Macrophages - ansLarge, phagocytic, amoeba-like white blood cells that engulf, ingest and destroy bacteria, damaged cells and worn-out red blood cells. Magnification - ansThe number of time greater an image is than the object. Messenger RNA (mRNA) - ansA type of RNA polynucleotide involved in protein synthesis. Carries the information coding for a polypeptide from the nucleus to the ribosomes in the cytoplasm. Microtubule motors - ansProteins associated with microtubules. The proteins can move along microtubules. Kinesin moves towards the (+) end of the microtubules and dynein moves towards the (-) end. Mitosis - ansNuclear division that results in the formation of cells that are genetically identical to the parent cell. Monoculture - ansA crop of plants of a single species bred to be very similar. Monocyte - ansLarge, phagocytic white blood cell. Monomer - ansA small molecule that is one of the units bonded together to form a polymer. Monosaccharide - ansA simple sugar molecule. The monomer of polysaccharides. Morbidity - ansThe proportion of people in a population who are ill with a particular disease at any one time. Mortality - ansThe number of people who die from a disease in a certain time period. Mucus - ansA slimy substance secreted by goblet cells in animal epithelial tissues. It is made up mostly of glycoproteins and protects and/or lubricates the surface on to which it is secreted. Mutation - ansA change in the structure of DNA, or in the structure and number of chromosomes. Mycelium - ansThe mass of filaments (hyphae) that make up the body of a fungus. Natural selection - ansThe mechanism for evolution in which the best-adapted organisms in a population can outcompete those that are less well-adapted. Niche - ansThe exact role of an organism in the ecosystem - its use of the living and non- living components of the ecosystem. Non-competitive inhibitor - ansAn inhibitor of an enzyme-controlled reaction that binds to the enzyme molecule in a region away from the active site. Nuclear envelope - ansThe double membrane structure surrounding the nucleus in eukaryotic cells. Nucleotide - ansThe monomer of nucleic acids consisting of a phosphate, a sugar and an organic base.

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Photosynthesis - ansProcess by which plants, some bacteria and some protoctists make food using carbon dioxide, water and sunlight energy. Phylogeny - ansThe evolutionary relationships between organisms. Phylum - ansA taxonomic group used in classification of living organisms. Contains similar classes. Pinocytocis - ansThe process of endocytosis involving the bulk movement of liquids into a cell. Pits (or bordered pits) - ansThin areas in the lignified walls of xylem tissue cells that allow communication between adjacent cells. Plaque - ansFatty material built up under the endothelium of an artery. Plasma cells - ansMature B-lymphocytes (white blood cells) that secrete a specific kind of antibody. Plasma proteins - ansProteins made in the liver that are found in the non-cellular fraction of the blood. Plasmid - ansSmall, circular piece of DNA present in some bacterial cells. May have genes for antibiotic resistance and can also be used as vectors in genetic engineering. Plasmodesma(ta) - ansA fine strand of cytoplasm that links the protoplasm of adjacent cells through a thin area of cell wall called a pit. Plasmolysis - ansDetachment of the plasma membrane from the cell wall as the cytoplasm shrinks when water is lost from a plant cell. Platelets - ansFragments of cells in the blood that play a part in blood clotting. Pluripotent - ansStem cells capable of differentiating to become a limited number of cell types found in the organism (e.g. cells of an early embryo). Polymer - ansA large molecule made up of many/repeating similar, smaller molecules (monomers) covalently bonded together. Polynucleotide - ansA polymer consisting of many nucleotide monomers covalently bonded together (DNA and RNA are examples). Polypeptide - ansA polymer consisting of many amino acid monomers covalently bonded together. Polysaccharide - ansA polymer consisting of many monosaccharide monomers covalently bonded together. Potometer - ansApparatus used to measure water uptake in a leafy shoot and so to estimate rate of transpiration. Precipitate - ansA suspension of small solid particles in a liquid, produced by a chemical reaction. Prevalence - ansThe number of people with a particular disease at a certain time. Primary defences - ansThe defences that prevent the entry of a pathogen into the body. Primary structure - ansThe sequence of amino acids found in a protein molecule. Prokaryote - ansAn organism with cells that do not contain a true nucleus. Prophase - ansThe phase of mitosis where the chromosomes become visible as a pair of sister chromatids joined at the centromere. Prosthetic group - ansA non-protein organic molecule that forms a permanent part of a functioning protein molecule.

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Protease - ansAn enzyme capable of digesting proteins. Protein - ansA polymer consisting of many amino acid monomers covalently bonded together. Pulmonary circulation - ansThe circulation of the blood through the lungs. Pulmonary vein - ansThe vein carrying oxygenated blood from the lungs to the left atrium of the heart. Purine - ansAdenine and guanine - nitrogenous bases consisting of a double ring structure. Purkyne tissue (Purkinje tissue) - ansSpecialised tissue (muscle fibres) in the septum of the heart that conducts the electrical stimulus from the sinoatrial node to the ventricles. Pyrimidine - ansThymine, cytosine and uracil - nitrogenous bases consisting of a single ring structure. Quadrat - ansA square frame used for sampling in field work. Qualitative - ansA study is that does not involve quantity (numbers). For example, simple observations to see if a particular species lives in a selected area. Quantitative - ansA study involving quantity (numbers). For example, if you count the number of individuals of a species in a selected area. Quaternary structure - ansProtein structure where a protein consists of more than one polypeptide chain e.g. Haemoglobin and insulin. Receptor sites - ansProtein or glycoprotein molecules on cell surfaces, used for attachment of specific substances such as hormones or viruses. Reducing sugar - ansA carbohydrate monomer or dimer that gives a positive result in Benedict's test because it is able chemically to reduce copper sulfate in solution. Reduction - ansChemical reaction involving the gain of electrons or the addition of hydrogen. Resolution - ansThe ability to distinguish two separate points as distinct from each other. Respiration - ansThe process in which energy is released from complex molecules, such as glucose, within cells and transferred to molecules of ATP. Ribose - ansThe 5-carbon (pentose) sugar found in RNA nucleotides. Ribosomal RNA (rRNA) - ansThe nucleic acid found in ribosomes. Ribosome - ansThe organelle on which proteins are synthesised inside the cell. Risk factor - ansA factor that increases the chance that you may develop a particular disease. RNA - ansA single-stranded polynucleotide molecule that exists in three forms. Each form plays a part in the synthesis of proteins within cells. Root hair cells - ansCells in the epithelium of roots that have long extensions to increase surface area for the absorption of water and minerals. Secondary defences - ansDefences that attempt to kill or inactivate pathogens that have already invaded the body. Secondary structure - ansThe local coiling or folding parts of a protein molecule due to the formation of hydrogen bonds formed as the protein is synthesised. E.g. a-helix and b-pleated sheets. Secretion - ansThe release of a substance made inside the cell using the process of exocytosis. Selection pressure - ansAn external pressure that drives evolution in a particular direction. Semi-conservative replication - ansThe replication of a DNA strand where the replicated double helix consists of one old strand and one newly synthesised strand.

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Sustainable development - ansDevelopment that does not cause excessive harm to the surrounding environment. The local biodiversity and people can continue to live and operate alongside the development. Sympatric - ansSpeciation that occurs within one area - some factor other than geographical separation has prevented free interbreeding between members of the species. Symplast pathway - ansThe route taken by water through the cytoplasm of cells in a plant. Systemic circulation - ansThe circulation that carries blood around the body, excluding the circulation to the lungs. Systole - ansThe stage of the heart cycle in which heart muscle contracts to pump blood. Taxon (pl: taxa) - ansA taxonomic group, such as a class or a family, used to aid classification. Taxonomy - ansThe study of the principles behind classification. Telophase - ansFinal phase of mitosis. Two new nuclear envelopes form around the two new nuclei. Tendinous cords - ansString-like tendons used to attach the atrioventricular valves of the heart to the sides of the ventricle wall. Sometimes called heart strings. Tertiary structure - ansThe overall three-dimensional shape of a protein molecule. Involves hydrogen bonding, disulfide bridges, ionic bonds and hydrophobic interactions. Testosterone - ansSteroid hormone made in the testes. Thrombus - ansA blood clot. Thylakoid - ansFlattened membrane sacs in chloroplasts, which hold the pigments used in photosynthesis and are the site of the light reactions. A stack of thylakoids forms a granum. Thymine - ansA nitrogen-containing organic base found in DNA. It pairs with adenine. Tissue - ansA group of similar cells that perform a particular function. Tissue fluid - ansThe fluid, derived from blood plasma, that surrounds the cells in a tissue. Totipotent - ansUndifferentiated cell that is capable of differentiating into any kind of specialised cell. Trachea - ansThe windpipe leading from the back of the mouth to the bronchi. Transcription - ansThe assembly of an mRNA molecule that is a copy of the DNA coding strand (and complementary to the template strand). Transect - ansA line through a habitat used to help take samples and study the habitat. Transfer RNA (tRNA) - ansA type of polynucleotide involved in protein synthesis. It transports amino acids to the ribosomes to be added to the growing polypeptide chain. Transgenic - ansOrganism that has genetic material from another organism, usually by genetic engineering. Translocation - ansThe movement of sucrose and other substances up and down a plant. Transmission - ansThe way in which a microorganism or other pathogen travels from one host to another. Transpiration - ansThe loss of water vapour from the aerial parts of a plant due to evaporation. Triglyceride - ansA molecule consisting of a glycerol molecule and three fatty acid molecules covalently bonded together.

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Turgid - ansDescribes a cell that is full of water as a result of entry of water due to osmosis such that pressure of the cell wall prevents more water entering. Ultrastructure - ansThe detailed structure of the internal components of cells as revealed by the electron microscope rather than by the light microscope. Uracil - ansA nitrogen-containing organic base found in RNA. Pairs with adenine. Urea - ansChemical made in the liver from amine groups from deaminated amino acids and carbon dioxide. It is toxic and is removed from the body in urine. Vaccine - ansA preparation of antigens given to provide artificial immunity. Vacuolar pathway - ansThe pathway taken by water in plants as it passes from cell to cell via the cell cytoplasm and vacuole. Variable - ansCondition in an experimental investigation. Can be independent (altered by the experimenter) or dependent (respond to changes in the independent variable). Variation - ansThe differences between individuals. Vascular tissue / bundle - ansThe transport tissue in a plant - usually found as a bundle containing both xylem and phloem. Vector - ansAn organism that carries a disease-causing organism (pathogen) from one host to another. Also describes an agent (such as a plasmid) that can transfer genetic material. Vena cava - ansEither of two large veins that carry deoxygenated blood from the body back to the heart. Ventilation - ansBreathing - movement of diaphragm and rib cage that bring air into and out of the lungs. Ventricles - ansThe lower chambers in the heart. Vesicle - ansA membrane-bound sac found in cells and used to transport materials around the cell. Villi - ansFolds in the wall of an organ or tissue that increase surface area. Vitamin - ansChemical needed in small amounts for healthy metabolism. Some organisms can make them, some organisms have to obtain them in the diet. Water potential (Y) - ansA measure of the ability of water molecules to move freely in solution. Decreased by the presence of solutes. Water vapour potential - ansThe potential energy of water vapour in a gas - it is used to indicate how much water vapour is present. Xerophyte - ansA plant specially adapted to living in dry areas. Xylem - ansA plant tissue containing vessels (and other cells) that are used to transport water in a plant and provide support. Zygote - ansDiploid cell made from fusion of male and female gametes. Abundance - ansThe frequency of occurrence of plants in a sampled area, such as a quadrat. Activation energy - ansThe level of energy required to enable a reaction to take place. Enzymes reduce the amount of energy required to allow a reaction to proceed. Active immunity - ansImmunity that is acquired by activation of immune system. Active site - ansThe area on an enzyme molecule to which the substrate binds. Adhesion - ansForce of attraction between molecules of two different substances. a-helix - ansA protein secondary structure - a right-handed spiral held in place by hydrogen bonds between adjacent C=O and NH groups.

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Carrier protein - ansA protein found in membranes, which is capable of carrying a specific molecule or ion through the membrane by active transport. Calibration - ansTo use known concentrations of a substance in a solution to make a standard curve on a graph. This can be used to determine the amount of that substance in solutions of unknown concentration. Centromere - ansThe region of a chromosome where two sister chromatids are joined together, and where the spindle fibre attaches during cell division. Cellulose - ansA carbohydrate polymer (of b-glucose) that forms plant cell walls. Atrioventricular node (AVN) - ansA patch of tissue in the septum of the heart that conducts the electrical stimulus from the atria in the heart through to the Purkyne fibres. Cartilage ring - ansA flexible ring of cartilage that holds the airways open. Chromatin - ansMaterial staining dark red in the nucleus during interphase. It consists of nucleic acids and proteins. Condenses into chromosomes during prophase of nucler division. Benedict's test - ansTest for reducing sugars. Sample is heated to 80ÂșC with reagent. If a reducing sugar is present, the reagent changes from blue to red precipitate. Cardiac cycle - ansThe sequence of events making up one heartbeat. Anomalous - ansDescribes a result/data point that does not appear to fit the pattern of the other results. Clones - ansGenetically identical cells or individuals. Chloride shift - ansThe movement of chloride ions into red blood cells to balance the loss of hydrogencarbonate ions. Adaptation - ansFeature of a living organism that increases its chances of survival, for example thick fur on an animal that lives in a cold habitat. Centriole - ansAn organelle from which the spindle fibres develop during cell division in animal cells. Antigen - ansA foreign molecule (which may be protein or glycoprotein) that can provoke an immune response. Artificial selection - ansAlso called selective breeding - the process of improving a variety of crop plant or domesticated animal by breeding from individuals with desired characteristics. Cohesion - ansThe attraction between water molecules due to hydrogen bonding. Cambium - ansPlant tissue in the stem and root that contains dividing cells. Anaphase - ansIn mitosis, the stage when the newly separated chromatids are pulled towards opposite poles of the nuclear spindle. Carnivore - ansAn animal that eats meat. Cell surface membrane - ansAlso known as the Plasma membrane. Cartilage - ansA flexible, slightly elastic connective tissue. Cytokines - ansHormone-like proteins produced by vertebrates, which are used for communication between cells, allowing some cells to regulate the activities of others. Cytoskeleton - ansThe network of protein fibres and microtubules found within the cell that gives structure to the cell and is responsible for the movement of many materials within it. Cholesterol - ansA lipid molecule (not a triglyceride) found in all cell membranes and involved in the synthesis of steroid hormones.

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Casparian strip - ansA strip of waterproof material (suberin) in the cell walls of root endodermis cells. It blocks the apoplast pathway. Bronchioles - ansAirways in the lungs that lead from the bronchi to the alveoli. Buffer - ansA chemical system that resists changes in pH by maintaining a constant level of hydrogen ions in solution. Certain chemicals dissolved in the solution are responsible for this. Constrict - ansTo make narrow. For example, in the narrowing of blood vessels. Clonal expansion - ansThe division of selected cells by mitosis to increase their numbers. Clonal selection - ansThe selection of cells (of the immune system) with a specific receptor site. These cells will undergo expansion as part of the immune response. Cytokinesis - ansThe division of the cell, following nuclear division, to form two new cells. Chromosome - ansA linear DNA molecule wrapped around histone proteins found in the nucleus. Become visible in prophase of cell division. Crenation - ansState of animal cells when they have been immersed in a solution of lower water potential and have lost water by osmosis and become shrivelled. Catalyst - ansA substance that increases the rate of a reaction but does not take part in the reaction, and so is re-usable. Carcinogen - ansA substance that causes cancer. Cristae - ansThe folds found in the inner membrane of a mitochondrion. Stalked particles containing ATP synthase are found here. Binomial system - ansA system of naming living things using two Latin words - the genus name and the specific name. Continuous variation - ansVariation where there is a range of intermediates, such as height, hair colour and intelligence in humans. Affected by multiple genes and environment Electrocardiogram - ansTrace (graph) showing the electrical activity of the heart muscle (atria and ventricles) during a cycle. Ciliated epithelium - ansLining cells that have cilia on their cell surface. Domain - ansClassification level introduced by Carl Woese dividing the kingdom Prokaryotae into two and placing all Eukaryotes into a third. Connective tissue - ansA type of tissue that consists of separate cells held together by a ground substance (matrix). Cofactor - ansA molecule or ion that helps an enzyme to work. It may be an inorganic ion or an enzyme. Enzyme - ansA protein molecule that acts as a biological catalyst. Discontinuous variation - ansVariation between living organisms within a species, where there are discrete categories and no intermediates, e.g. blood groups A, B, AB or O in humans. Disease - ansA departure from full health. Covalent bond - ansA chemical bond formed by the sharing of one or more electrons between two atoms. Bohr shift / Bohr effect - ansThe effect of carbon dioxide concentration on the affinity of haemoglobin for oxygen. Disaccharide - ansA molecule consisting of two monosaccharide sugars joined by a glycosidic bond.

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Diaphragm - ansA sheet of muscular and fibrous tissue separating the chest cavity from the abdominal cavity. Cell signalling - ansProcesses that lead to communication and coordination between cells. Hormones binding to their receptors on the cell surface membrane are an example. Deoxygenated - ansBlood with haemoglobin that carries no or little oxygen. Cytosine - ansA nitrogen-containing organic base found in nucleic acids. It pairs with guanine in DNA. Condensation - ansA type of chemical reaction in which two molecules are joined together by means of a covalent bond to form a larger molecule, and at the same time a water molecule is released. Dilate - ansTo make wider. For example, when the lumens of blood vessels become wider. Dissociation - ansThe separation of a molecule into two molecules, atoms or ions without breakage of a covalent bond. For example, the release of oxygen from oxyhaemoglobin. Conservation ex situ - ansConservation in areas other than the natural habitat. Cotransporter - ansA protein in a cell membrane that allows movement of one molecule when linked to the movement of another molecule in the same direction by active transport. Emulsion - ansA suspension of one material in another as droplets, because it does not dissolve. For example, fat droplets dispersed in water. Endodermis - ansA ring of cells between the cortex of a root and the area housing the xylem and phloem. DNA - ansA polymer of nucleotide molecules that form the instructions for the synthesis of proteins found within organisms. These nucleotides contain the 5-carbon sugar deoxyribose. Epidemiology - ansThe study of patterns of disease and the factors that influence their spread. Enzyme-substrate complex - ansThe intermediate structure formed when a substrate molecule binds to an enzyme molecule. Deamination - ansRemoval of amine (NH2) group from an amino acid Endothelium - ansA tissue that lines the inside of a structure, such as a blood vessel. Evolution - ansProcess by which the present diversity of living organisms arose from simple primitive organisms, with new species arising by natural selection. Diastole - ansThe period when the heart muscle in the ventricles is relaxing and blood pressure is at its lowest. Elastic tissue - ansTissue containing the protein elastin, which is able to stretch and recoil. Coenzyme - ansAn organic non-protein molecule that binds temporarily with substrate to an enzyme active site. It is essential for enzyme activity. Calibration - ansTo determine the value of intervals of a scale on an instrument, such as a thermometer. Chloroplast - ansAn organelle found in plants, which contains chlorophyll and is responsible for photosynthetic activity in the plant. Classification - ansThe organisation of living organisms (or other items) into groups according to their shared similarities. Collagen - ansA structural fibrous protein found in connective tissue, bones, skin and cartilage. It accounts for 30% of body protein.

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Competitive inhibitor - ansA substance that reduces the rate of an enzyme-controlled reaction by binding to the enzyme's active site. Diffusion - ansThe net movement of molecules or ions in a gas or liquid from an area of high concentration to an area where they are less concentrated. Channel protein - ansA protein pore that spans a membrane, through which very small ions and water soluble molecules may pass. Dissociation curve - ansThe curve on a graph showing the proportion of haemoglobin that is saturated with oxygen at different oxygen tensions. Division of labour - ansAny system where different parts perform specialised functions, each contributing to the functioning of the whole. Double circulatory system - ansA transport system in which blood travels twice through the heart for each complete circulation of the body. Conservation in situ - ansConservation in the natural habitat. Diploid - ansCells or organisms that have two copies of each chromosome in their nuclei. End-product inhibition - ansThe regulation of metabolic pathways where the last product in a sequence of enzyme-controlled reactions becomes an inhibitor of one of the enzymes earlier in the sequence. Environmental impact assessment - ansAn assessment of the damage that may be caused to the (local) environment by a proposed development. Double helix - ansDescribes the structure of DNA, a twisted helix of two strands with bases joining the strands. Ester bond - ansThe bond formed when fatty acid molecules are joined to glycerol molecules in condensation reactions. Erythrocytes - ansRed blood cells. Differentiation - ansThe development and changes seen in cells as they mature to form specialised cells. Extinction - ansThe death of the last individual in a species. Endoplasmic reticulum (ER) - ansA series of membrane-bound, flattened sacs extending from the outer nuclear membrane through the cytoplasm. Comes in rough and smooth forms. Epithelium - ansA tissue that covers the outside of a structure. Extracellular - ansOutside the cell - for example describes enzymes that work outside the cell. Diffusion gradient - ansThe difference in molecular concentration that allows diffusion to occur. Exocytosis - ansThe process of removing materials from the cell by fusing vesicles containing the material with the plasma membrane. Eukaryote - ansAn organism having cells with a nucleus and membrane-bound organelles. Enzyme-product complex - ansThe intermediate structure in which product molecules are bound to an enzyme molecule. Fertiliser - ansA substance added to soil to enhance the growth of plants. Flaccid - ansA term used to describe plant tissue where the cells have lost turgor and are not firm. Epidemic - ansDescribes a disease that spreads to many people quickly and affects a large proportion of the population.

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Haploid - ansA cell or organism that has one set of chromosomes/one copy of each chromosome. Glycolipid - ansA lipid with carbohydrate molecules attached. Fluid mosaic (model) - ansThe model of cell membrane structure proposed by Singer and Nicholson - a phospholipid bilayer with proteins 'floating' in it. Food tests - ansSimple procedures that show the presence of various biological molecules in samples or structures. Interleukin - ansCell-signalling chemicals. Some are involved in activating cells of the immune system. A type of cytokine. Hydrogen bond - ansA weak bond formed between partially charged atoms. It is seen in water molecules, and is important in the secondary and tertiary structure of proteins. Hydrolysis - ansA reaction in which a molecule is broken down into two smaller molecules by the addition of a water molecule and the breaking of a covalent bond. Lacteal - ansA blind-ending branch of the lymph system found in each villus of the small intestine. Heterotroph - ansOrganism that gains nutrients from complex organic molecules. These molecules are digested by enzymes to simple soluble molecules. Kinetic energy - ansEnergy of movement. Glycoprotein - ansA protein with carbohydrate molecules attached. Genetic erosion - ansThe loss of genetic variation due to (artificial) selection. Kingdom - ansTaxonomic group. Living organisms are grouped into one of five: Prokaryotae, Protoctista, Fungi, Plantae and Animalia. Fat - ansMixture of lipids, mainly triglycerides with saturated fatty acids, that is solid at body temperature. Act as an energy store, insulation, waterproofing and may give buoyancy. Interphase - ansThe phase of the cell cycle where synthesis of new DNA and organelles takes place. Monokines - ansChemical produced by monocytes to signal to other cells. Also called lymphokines. Homologous - ansChromosomes in diploid organisms that have the same genes at the same loci and that pair up during meiosis. Can also refer to structures that have a common evolutionary origin. Microtubules - ansComponents of the cell cytoskeleton. Involved in mitosis, cytokinesis and movement of vesicles within cells. Initial reaction rate - ansRate of reaction at the beginning before a significant amount of product has been formed or reactant used up. Hydrostatic pressure - ansPressure created by a fluid pushing against the sides of a container. Myogenic - ansDescribes muscle tissue (heart muscle) that generates its own contractions. Meiosis - ansNuclear division that results in the formation of cells containing half the number of chromosomes of the adult cell. Memory cells - ansB and T cells that remain in the body after an immune response. Their presence enables a much faster and greater second immune response. Keratinocytes - ansCells that make keratin.

Biology AS - Comprehensive Questions & 100%

Correct Answers for Your A+ Journey.

Latest Updated current Guide 2025/2026.

Fibrous protein - ansA protein with a relatively long, thin structure, which is insoluble in water and metabolically inactive, often having a structural role within the organism. Marker-assisted selection - ansUsed by animal and plant breeders to help select individuals with the desired genotype. The desired gene is linked to a section of DNA that is easy to identify in a young individual. Monophyletic - ansA group of organisms that share a common ancestor and therefore belong to the same classification group. Omnipotent - ansAnother word for totipotent. Nucleic acid - ansA polymer of nucleotide molecules. Diversity - ansTerm used to describe a large range of species in an area or a population of organisms that have significant genetic variation. Metabolism - ansAll the chemical reactions that take place in an organism. Osmosis - ansThe movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane. Lymphatic system - ansA system of lymph nodes and lacteals with lymph fluid. Myoglobin - ansA respiratory pigment (protein) with a higher affinity for oxygen than haemoglobin. Metaphase - ansThe phase of mitosis where the chromosomes line up at the equator of the spindle. Microvilli - ansFolds in the membrane of a cell that increase its surface area. Maltose - ansA disaccharide molecule consisting of two a-glucose molecules bonded together. Limiting factor - ansA variable that limits the rate of a process. If it is increased, then the rate of the process will increase. Macromolecule - ansA very large molecule. Intercostal muscles - ansMuscles between the ribs, responsible for moving the rib cage during breathing. Fibrillation - ansA state in which the chambers in the heart contract out of rhythm. Inhibition/inhibitor - ansThe slowing of an enzyme-controlled reaction by a molecule that slows down or prevents the formation of enzyme-substrate complexes. Plasma membrane or cell surface membrane - ansThe membrane that surrounds every cell, forming the selectively permeable boundary between the cell and its environment. Gene - ansA length of DNA that carries the code for the synthesis of one (or more) specific polypeptide(s). Mitochondrion - ansThe organelle found in cells in which most of the ATP synthesis occurs. It is the site of aerobic respiration. Meristem cells - ansUndifferentiated plant cells capable of rapid cell division. Natural immunity - ansImmunity acquired through exposure to disease during the normal course of life. Hydrophobic - ansWater-repelling (water-hating). Neutrophils - ansPhagocytic white blood cells. They engulf and digest bacteria. They have a many-lobed nucleus, and a granular cytoplasm due to the large numbers of lysosomes present.