324 terms

OCR GCE Biology A2 Glossary

Complete glossary of terms for OCR GCE Biology A2
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Alpha cells
Cells in the islets of Langerhans that release glucagon in response to low blood glucose levels.
Acetylcholine
A neurotransmitter (transmitter substance) found in cholinergic synapses.
Acetylcholinesterase
An enzyme in the synaptic cleft that breaks down the transmitter substance acetylcholine.
Actin
A protein found in muscle cells. It is the main component of the thin filaments.
Action potential
A brief reversal of the resting potential across the cell surface membrane of a neurone. Gives a value of +40 mV.
Adenyl cyclase
The enzyme found inside cells, associated with hormone receptors, that converts ATP to cAMP.
Afferent
Incoming or leading towards.
Allele
An alternative version of a gene.
All or nothing
Refers to the fact that a neurone either conducts an action potential or it does not.
Allotransplantation
Transplantation of organs between individuals of the same species, for example transplantation of a human heart into another human.
Amplification (DNA)
The making of multiple copies of the same short section of DNA. The process of PCR is used in automatic amplification of DNA sections.
Anabolic steroids
Drugs that mimic the action of steroid hormones and increase muscle growth.
Anabolism
Type of metabolism: biochemical reactions that synthesise large molecules from smaller molecules. This requires energy/ATP.
Antagonistic
Working against each other in a pair.
Annealing
The term used to describe hydrogen-bond formation between complementary base pairs when sections of single-stranded DNA or RNA join together. Also seen when complementary sticky ends join and where DNA probes attach to a complementary DNA section.
Antidiuretic hormone (ADH)
The hormone made in the hypothalamus and released from the pituitary gland that acts on the collecting ducts in the kidneys to increase the reabsorption of water into the blood.
Apical dominance
The growing apical bud at the tip of the shoot inhibits growth of lateral buds further down the shoot.
Apoptosis
Programmed cell death. An orderly process by which cells die after they have undergone the maximum number of divisions.
Ascending limb
The limb of the loop of Henle that carries fluid from the medulla towards the cortex of the kidney.
Asepsis
Literally means without contamination. In biotechnology, this refers to lack of contamination by foreign, unwanted microorganisms.
Aseptic techniques
Any techniques/manipulations of equipment or materials that are designed to prevent contamination by foreign and unwanted microorganisms.
Association area
A region of the cerebral cortex where the information in the form of impulses from sensory areas is made sense of by comparison with previous experience.
ATP
Molecule (nucleotide derivative) found in all living cells and involved in energy transfer. When it is hydrolysed energy is released.
ATP synthase
Enzyme associated with stalked particles in mitochondria and chloroplasts. It catalyses the joining of ADP and inorganic phosphate to make ATP.
Audus microburette
Alternative name for a photosynthometer.
Autonomic nervous system
The system of motor neurones that controls the non-conscious actions of the body. The autonomic system controls the actions of involuntary muscles and glands
Autotroph
Organism that makes its own food using simple inorganic molecules, such as carbon dioxide and water, and energy. Photoautotrophs (plants, some protoctists and some bacteria) use light as the source of energy. Chemoautotrophs (some bacteria) use chemical energy.
Beta cells
Cells in the islets of Langerhans that release insulin in response to high blood glucose levels.
Basement membrane
A layer of connective tissue - mostly collagen - that holds an epithelium in place.
Batch culture
A culture of microorganisms that takes place in a single fermentation. Products are separated from the mixture at the end of the fermentation process.
Bilirubin
One of the waste products produced from breaking down haemoglobin.
Biodiversity
The number and variety of living things to be found in the world, an ecosystem or habitat.
Biofortified
Any food substance in which a particularly valuable nutrient is in higher than usual levels. Golden Rice(tm) is biofortified with the accumulation of vitamin A.
Bioremediation
Use of microorganisms to remove waste products from a location or substance. The most important example is waste water (sewage) treatment.
Biotechnology
Use of microorganisms or biochemical reactions to generate useful products.
Bivalent
Pair of synapsed (joined) homologous chromosomes during prophase and metaphase of meiosis I.
Bowman's capsule
The cup-shaped end of a nephron tubule.
Callus
A mass of undifferentiated plant cells formed by meristem tissue extracted from the plant and grown in tissue culture.
Cardiovascular centre
Region in the medulla oblongata of the brain that controls heart rate.
Carrying capacity
The maximum population size that can be maintained over a period of time in a particular habitat.
Catabolism
Type of metabolism: biochemical reactions that produce small molecules by hydrolysis of larger molecules.
Cell metabolism
The result of all the chemical reactions taking place in the cell cytoplasm.
Central nervous system
The brain and spinal cord. It has overall control over the coordination of the nervous system.
Chemiosmosis
The flow of hydrogen ions (protons) through ATP synthase enzymes. The force of this flow allows the production of ATP. Occurs across the thylakoid membranes during the light-dependent stage of photosynthesis. Also occurs across the inner mitochondrial membrane during oxidative phosphorylation (in respiration).
Chemoautotrophs
Organism that can make its own food using energy obtained by redox reaction using simple inorganic compounds.
Chiasmata
The points where non-sister chromatids within a bivalent join, where they cross over.
Chi-squared test
Statistical test that can be carried out on data that are in categories. It enables the investigator to determine how closely an observed set of data corresponds to the expected data.
Chloroplasts
Organelles, in plant and some protoctist cells, where photosynthesis occurs.
Cholinergic synapse
A junction between neurones that uses acetylcholine as the neurotransmitter.
Chorionic gonadotrophin
A hormone released by the cells of an embryo.
Chromatogram
A chart produced when substances are separated by movement of a solvent along a permeable material such as paper or gel.
Chromosome mutation
Random change to the structure of a chromosome. There are different types: inversion (a section of chromosome turns through 180°); deletion (a part is lost); translocation (a piece of one chromosome becomes attached to another); non-disjunction (homologous chromosomes fail to separate properly at meiosis 1 or chromatids fail to separate at meiosis 2; if this happens to a whole set of chromosomes, polyploidy results). The shuffling of alleles in prophase 1 is not an example of mutation.
Clade
A monophyletic taxonomic group; that is, a single ancestor and all its descendants.
Cladistics
A method of classifying living organisms based on their evolutionary ancestry.
Classical conditioning
A form of learning in which two unrelated stimuli are applied to an animal, one a 'normal response' (for example salivation in the presence of food) another unrelated (for example the ringing of a bell). After repeated exposure to both stimuli together the animal will eventually respond with the normal response to the unrelated stimulus.
Closed culture
A culture of microorganisms set up in a reaction vessel and then allowed to grow without the addition of nutrients or the removal of products or wastes.
Codominant
A characteristic where both alleles contribute to the phenotype.
Coenzyme A
A coenzyme that carries acetate from the link reaction of respiration to Krebs cycle.
Coenzymes
Molecules that help enzymes carry out oxidation or reduction reactions. They work like shuttles, carrying atoms or molecules from one enzyme-controlled reaction to another. Many important coenzymes are involved in respiration and photosynthesis. In respiration, many coenzymes are concerned with removing hydrogen atoms from substrates.
Community
All the populations of different species that live in the same place at the same time, and who can interact with each other.
Comparative genome mapping
The comparison of DNA sequences coding for the production of proteins/polypeptides and regulatory sequences in the genomes of different organisms of different species. Comparisons include the search for sequences that make some organisms pathogenic whilst related organisms are not.
Competition
A struggle between individuals for resources (like food or water) that are not present in amounts adequate to satisfy the needs of all the individuals who depend on those resources.
Complementary genes
Genes that interact together to govern the expression of a single characteristic.
Conjugation (in bacteria)
Bacterial cells can join together and pass plasmid DNA from one bacterial cell to another. This process can take place between bacteria of different species and is of concern in terms of passing plasmid-located genes for antibiotic resistance.
Conservation
Maintenance of biodiversity, including diversity between species, genetic diversity within species, and maintenance of a variety of habitats and ecosystems.
Consumers
Living organisms that feed on other living organisms.
Continuous culture
A culture of microorganisms set up in a reaction vessel to which substrates are added and from which products are removed as the fermentation process continues.
Continuous variation
Genetic variation, also called quantitative variation, where there is a wide range of phenotypic variation within the population. There are no distinct categories. It is controlled by many genes. Examples include height in humans.
Coppicing
Cutting a tree trunk close to the ground to encourage new growth.
Co-transporter proteins
Proteins in the cell surface membrane that allow the facilitated diffusion of simple ions to be accompanied by transport of a larger molecule such as glucose.
Cotyledons
Food store in seeds of dicotyledonous plants. In some plants, these appear above the soil after germination and act as the first leaves.
Cross-bridge
In voluntary muscle, the joining of a myosin head group to an actin thin filament in the presence of calcium ions.
Crossing over
Where non-sister chromatids exchange alleles during prophase I of meiosis.
Cytokines
Cell-signalling molecules.
Deamination
The removal of the amine group from an amino acid to produce ammonia.
Decomposers
Organisms that feed on dead organic matter, releasing molecules, minerals and energy that then become available to other living organisms in that ecosystem.
Dehydrogenation
Removal of hydrogen atoms from a substrate molecule.
Depolarisation
The loss of polarisation across a membrane - when the membrane loses its resting potential.
Descending limb
The limb of the loop of Henle that carries fluid from the cortex towards the medulla of the kidney.
Detoxification
Conversion of toxic substances, such as alcohol, to less toxic substances.
Diabetes mellitus
A condition in which the patient is unable to control blood glucose levels.
Dialysis
Treatment for patients with kidney failure, in which metabolic wastes and excess salts and water are removed from the blood.
Dialysis fluid
The fluid used in dialysis; it consists of a complex solution that matches the composition of body fluids.
Dialysis membrane
A partially permeable membrane that separates the dialysis fluid from the patient's blood in a dialysis machine.
Diffusion
Movement of molecules down their concentration gradient. It may be through a partially permeable membrane.
Digest
Hydrolyse a large molecule to smaller molecules.
Diploid
Having two sets of chromosomes (eukaryotic cell or organism). Denoted by 2n.
Discontinuous variation
Also called qualitative variation. Genetic variation where there are distinct phenotypic categories. Usually controlled by one gene. Examples include cystic fibrosis, shape of earlobes in humans and height in pea plants.
Distal convoluted tubule
The coiled portion of the nephron between the loop of Henle and the collecting duct.
DNA ligase
An enzyme capable of catalysing a condensation reaction between the phosphate group of one nucleotide and the sugar group of another. This results in DNA backbone molecules being joined together and is an essential part of recombinant DNA procedures.
DNA mutation
A change to the DNA structure. May be substitution of one base pair for another; inversion of a base triplet; deletion of a base pair or triplet of bases (on both strands); addition of a base pair or triplet of bases (on both strands); or a triple nucleotide repeat - a stutter.
Dominant
Characteristic in which the allele responsible is expressed in the phenotype even in those with heterozygous genotypes.
DRD4
Gene that codes for a dopamine receptor molecule.
Ecosystem
All the living organisms and all the non-living components in a specific habitat, and their interactions.
Ectotherms
Organisms that rely on external sources of heat and behavioural activities to regulate their body temperature.
Efferent
Outgoing or leading away from.
Electron acceptors
Chemicals that accept electrons from another compound. They are reduced while acting as oxidising agents.
Electron carriers
Molecules that transfer electrons.
Electrophoresis
A method used to separate molecules in a mixture based on their size. The method relies on the substances within the mixture having a charge. When a current is applied, charged molecules are attracted to the oppositely charged electrode. The smallest molecules travel fastest through the stationary phase (a gel-based medium) and in a fixed period of time will travel furthest, so the molecules separate out by size. The method is particularly important in separating DNA fragments of different sizes in DNA sequencing and profiling (fingerprinting) procedures.
Endocrine gland
A gland that secretes hormones directly into blood capillaries.
Endocytosis
The transport of large molecules or fluids into the cytoplasm of the cell, by the invagination (folding inwards) of the cell surface membrane to form a vesicle.
Endothelium
The tissue which lines the inside of a blood vessel or nephron.
Endotherms
Organisms that can control production and loss of heat to maintain their body temperature.
Energy
The ability to do work. From the Greek energos, meaning active work.
Envelope
Double membrane. Double lipid bilayer.
Environmental resistance
The combined action of biotic and abiotic factors that limits the growth of a population.
Epistasis
The interaction of genes concerned with the expression of one characteristic. One gene may mask the expression of another gene.
Epithelium
The tissue that covers the outside of a structure.
Eukaryotes
Organisms with eukaryotic cells - protoctists, fungi, plants and animals.
Evolution
The process of gradual change in the inherited traits passed from one generation to the next within a population. It results in the formation of new species.
Excretion
The removal of metabolic waste (waste from the reactions inside cells) from the body.
Exergonic
Chemical or biochemical reaction that releases heat energy.
Exocrine gland
A gland that secretes substances into a duct.
Exocytosis
A mechanism of secretion from a cell involving vesicles that fuse to the cell surface membrane and release their contents to the outside. It uses ATP.
Explant
A piece of tissue taken from a particular plant (which includes meristematic tissue) then sterilised in order to grow a callus in tissue culture micropropagation.
Facilitated diffusion
Diffusion that is enhanced by the action of protein channels or carriers in the cell membrane.
Fermentation
(1) The process of anaerobic respiration in microorganisms, used to yield specific products. For example, the anaerobic respiration of yeast is used in the fermentation of grapes to produce wine.
Fermentation
(2) The process of culturing any microorganism in order to generate a specific product, either aerobically or anaerobically. All industrial biotechnological processes using whole microorganisms are referred to as fermentation.
Fertilisation
Fusion of male and female gamete nuclei.
Fight or flight response
The set of responses in an animal that accompany the perception of threat. The response is driven by the sympathetic nervous system and sets the body at a higher level of capacity to respond to the threat; for example increased respiration rate in muscles and increased blood flow to muscles to prepare for explosive muscle action necessary to fight or run away.
First messenger
A hormone that acts as a message in the bloodstream.
Gametes
Specialised sex cells. In many organisms the gametes are haploid and are produced by meiosis.
Gas chromatography
A technique used to separate substances in a gaseous state.
Gene
A length of DNA that codes for one (or more) polypeptides/proteins. Some genes code for RNA and regulate other genes.
Gene pool
Total genetic information possessed by the reproductive members within a population of organisms.
Gene therapy
In humans, any therapeutic technique where the functioning allele of a particular gene is placed in the cells of an individual lacking functioning alleles of that particular gene. Can be used to treat some recessive conditions but not dominant conditions such as Huntington disease.
Generator potential
A small depolarisation of the membrane in a receptor cell.
Genetic drift
Also called allelic drift. The change in allele frequency in a population, as some alleles pass to the next generation and some disappear. This causes some phenotypic traits to become rarer or more common.
Genetic engineering
The branch of biotechnology characterised by the obtaining of a particular gene, either by removal from a donor organism's genome using restriction enzymes or by manufacture, usually from mRNA transcript using reverse transcriptase enzyme. Once obtained, the gene is inserted into the genome of a recipient organism - often of a different species from the donor organism. The inserted gene is transcribed into protein, so giving the recipient organism a characteristic/capacity that it did not have previously. Such organisms are referred to as being transgenic or genetically modified.
Genetic fingerprinting (genetic profiling)
The use of DNA fragmentation and electrophoresis gives banding patterns that are unique to each individual. Samples of DNA, for example from crime scenes, are fragmented using a range of restriction enzymes, and, because each individual's DNA has differences, the number and size of fragments produced is slightly different. Electrophoresis and staining of the DNA gives a banded pattern that can be compared with other samples of DNA treated with the same set of restriction enzymes.
Genetic markers
Antibiotic resistance genes held on bacterial plasmids are used as genetic markers to identify the bacteria that have taken up the required gene. The gene is inserted into a plasmid that carries a resistance to a particular antibiotic. If a bacterium can grow on the particular antibiotic, then the plasmid, and so the required gene, is present in the bacterium.
Genetic variation
Variation of genetic information in a gene pool.
Genome
All the genetic information within an organism/cell.
Genome sequencing
The technique used to give the base sequence of DNA of a particular organism. The sequencing reaction can only identify up to around 1000 base pairs of sequence in a fragment. In order to sequence the whole genome, overlapping fragments are sequenced, then reassembled by computer software in order to generate the original sequence detail.
Genomics
The study of the whole set of genetic information in the form of the DNA base sequences that occur in the cells of organisms of a particular species.
Genotype
Alleles present within cells of an individual, for a particular trait/characteristic.
Germ line gene therapy
This involves placing the gene into embryonic cells. This technique is not currently legal and is deemed unethical.
Glomerulus
A small network of capillaries found inside the Bowman's capsule.
Glucagon
A hormone released by the _ cells in the islets of Langerhans in the pancreas - it causes the blood glucose level to rise by converting glycogen in liver cells to glucose.
Glycerate-3-phosphate (GP)
Intermediate compound produced during the Calvin cycle in the light-independent stage of photosynthesis.
Glycolysis
Metabolic pathway. The first stage of respiration. It is anaerobic and occurs in the cytosol (cytoplasm). Although anaerobic, it involves oxidation as substrate molecules are dehydrogenated.
Golden Rice
A variety of rice that is genetically engineered to carry large amounts of the vitamin A precursor beta-carotene. The rice appears golden brown, unlike its non-engineered relative, which is white in colour.
Grana (s. granum)
Stacks of thylakoid membranes, found in a chloroplast.
Habitat
The place where an organism or population of organisms lives.
Haemodialysis
A form of treatment for kidney patients in which blood is taken from a vein and passed through a dialysis machine so that exchange can occur across an artificial partially permeable membrane.
Hairpin countercurrent multiplier
An arrangement of a tubule or blood vessel involving a 180° bend so that the fluid in one end of the tubule flows back past the fluid at the other end. This arrangement facilitates the exchange of materials by ensuring that there is a concentration gradient all along the tubule.
Half-life
The time taken for the concentration of a substance to drop to half its original value.
Haploid
Eukaryotic cell or organism having only one set of chromosomes. Denoted by n.
Hardy-Weinberg principle
The concept that both genotype frequencies and gene frequencies will stay constant from generation to generation, within a large interbreeding population where mating is random, there is no mutation and no selection or migration.
Hayflick constant
The number of times that a normal body cell divides before undergoing apoptosis. The number of divisions is about 50.
Hemizygous
Cell or individual having only one allele for a particular gene.
Hepatic portal vein
An unusual blood vessel that has capillaries at both ends - it carries blood from the digestive system to the liver.
Hepatocytes
Liver cells.
Heterotroph
Organism that gains its nutrients from complex organic molecules. It digests them to simpler, soluble molecules and then respires some of them to obtain energy, or uses the products of digestion to synthesise the organic molecules it needs. Heterotrophs are consumers in food chains. Parasites and saprotrophs are also heterotrophs. Animals, some bacteria and some protoctists are heterotrophs.
Heterozygous
Eukaryotic cell or organism that has two different alleles for a specific gene.
Hierarchy (social)
Within a group individuals have a place in the order of importance within the group. This is often shown by individuals higher up in the hierarchy receiving more food or having rights of access to mate with other individuals.
Homeobox genes
Genes that control the development of the body plan of an organism.
Homeostasis
The maintenance of a constant internal environment despite external changes.
Homeotic selector genes
These direct the development of individual body segments. They are master genes that control other regulatory genes.
Homozygous
Eukaryotic cell or organism that has two identical alleles for a specific gene.
Hormone
A molecule released into the blood that acts as a chemical messenger.
Hox clusters
Groups of homeobox genes. More complex organisms have more Hox clusters. This is probably due to a mutation that duplicated the Hox clusters.
Human chorionic gonadotrophin (hCG)
A hormone released by the human embryo. Its presence in a pregnant woman's urine can be detected to confirm pregnancy.
Hydrolysis
Splitting of large molecules into smaller molecules with addition of water.
Hyperglycaemia
A high blood glucose concentration.
Hyperpolarised
The condition of a membrane that is more highly polarised than the usual resting state. The resting potential is lower than usual.
Hypertension
A condition in which the resting blood pressure (particularly the diastolic pressure) is raised for prolonged periods.
Hypoglycaemia
A low blood glucose concentration.
Hypostasis
Where two alleles interact to control the expression of one characteristic one is epistatic and one is hypostatic. Where a homozygous recessive allele at the first locus (place on a chromosome) prevents the expression of another allele at a second locus, the alleles at the first locus are epistatic and the alleles at the second locus are hypostatic.
Hypothalamus
A portion of the brain that contains various receptors that monitor the blood. Also involved in controlling the autonomic nervous system.
Innate behaviour
A behaviour that an animal is capable of from birth without any learning or practice. Such behaviours appear to be very inflexible in their operation although they may often be slightly modified in individuals by some elements of learning.
Insulin
A hormone released by the _ cells in the islets of Langerhans in the pancreas - it causes the blood glucose level to fall.
Islets of Langerhans
Patches of endocrine tissue in the pancreas - they consist of _ and _ cells.
Isolating mechanism
Mechanism that divides populations of organisms into subgroups.
Kangaroo mother care
The term used to describe a method of human infant care which involves extended skin-to-skin contact and breastfeeding on demand.
Krebs cycle
Third stage of respiration. It is aerobic and in eukaryotes it occurs in the matrix of the mitochondria.
Kupffer cells
Specialised macrophages that move around in the sinusoids and are involved in the breakdown and recycling of old red blood cells.
Lamellae
A pair of membranes that contain chlorophyll. Intergranal lamellae in the chloroplasts link the thylakoids of one granum with the thylakoids of another granum.
Light-dependent stage
First stage of photosynthesis. Occurs in the thylakoid membranes of the chloroplasts. It involves using light energy to make ATP. Other products are reduced NADP and oxygen.
Light-independent stage
Second stage of photosynthesis. Occurs in the stroma of the chloroplasts. Involves using ATP, reduced NADP and carbon dioxide to make organic molecules.
Light intensity
A measure of the amount of energy associated with light. The relative light intensity of a source can be calculated using the formula I = 1/d2 where d is the distance between source and object receiving the light.
Limiting factor
A variable that limits the rate of a particular process. If the factor is increased then the process will take place at a faster rate. Where the rate of a natural process is affected by a number of factors, the limiting factor is the one whose magnitude limits the rate of the process.
Linkage
Genes for different characteristics that are present at different loci on the same chromosome are linked.
Link reaction
Stage of aerobic respiration that links glycolysis with the Krebs cycle. In eukaryote cells it occurs in the mitochondrial matrix.
Local currents
Movements of ions along a neurone close to the cell surface membrane, caused by influx or efflux of ions through the membrane.
Locus
Specific position on a chromosome, occupied by a specific gene.
Maternal chromosome
Member of a homologous pair of chromosomes that originally came from the female gamete.
Medulla oblongata
A portion of the brain (the brain stem) that contains centres for the control of various unconscious bodily functions and via the autonomic nervous system.
Meiosis
Type of nuclear division. A reduction division. The chromosome number is halved. It involves two divisions. It produces cells that are genetically different from each other and from the parent cell.
Meristem
Growth points in a plant where immature cells are still capable of dividing.
Metabolic waste
Waste substances that may be toxic or are produced in excess by the chemical reactions inside cells.
Micropropagation
A form of artificial vegetative propagation using sterile explant tissue grown to form a callus culture from which many new plants are grown by separation and growth of small parts of the callus. Particularly useful in generating vast numbers of genetically identical plants following the genetic engineering of a particular gene into the callus.
Microvilli
Microscopic folds of the cell surface membrane that increase the surface area of the cell.
Monoclonal antibodies
Antibodies that are identical because they have been produced by cells that are clones of one original cell.
Monogenic
Characteristic coded for by one gene.
Monophyletic
A monophyletic group is one that includes an ancestral organism and all its descendent species.
Morphogen
A substance that controls the pattern of tissue development. It is produced in a particular region of a developing organism. It diffuses to other cells, which then enter a specific developmental pathway.
Motor area
An area of the cerebral cortex within which the neurones are responsible for driving motor functions.
Motor unit
Refers to the innervation of a cluster of muscle fibres by a single motor neurone. The number of muscle fibres within a motor unit is governed by the level of manipulation required in the muscle. Muscles responsible for very fine motor functions have as few as three muscle fibres in a motor unit. Muscles requiring less fine motor control may have over 200 muscle fibres in a motor unit.
Mutation
Structural change to genetic material - either to a gene or to a chromosome.
Mutualism
A relationship between two organisms from which both benefit.
Myelin
A fatty sheath around a neurone that consists of many layers of the plasma membranes of Schwann cells.
Myogenic
Contraction of the muscle is generated from within the muscle itself. The term is used to describe the contraction of the heart, which is controlled by the action of the sinoatrial node.
Myosin
The protein that forms the thick filament in muscle cells. This protein has head groups that form the cross-bridges associated with muscular contraction.
NAD
Coenzyme involved in respiration. It removes hydrogen atoms from substrates. It becomes reduced NAD, which carries hydrogen atoms (protons and electrons).
NADP
Coenzyme involved in photosynthesis. It accepts hydrogen atoms from photolysis of water during the light-dependent stage and carries them to the light-independent stage.
Natural selection
Mechanism for evolution. Organisms that are well adapted to their environment are more likely to survive and reproduce, passing on the alleles for the favourable characteristics.
Necrosis
Disorderly, often accidental cell death.
Negative feedback
A process in which any change in a parameter brings about the reversal of that change so the parameter is kept fairly constant.
Nephrons
Tubules in the kidney that are used to produce urine.
Neurosecretory cells
Cells in the hypothalamus that are similar to neurones but release a hormone into the blood instead of a transmitter substance into a synapse.
Neurotransmitter
A transmitter substance - a chemical that is released from the presynaptic membrane of one neurone to pass a signal to another neurone.
Niche
The role that a species plays in an ecosystem.
Nitrogen fixation
Conversion of nitrogen gas into a form which is usable by plants, such as nitrate or ammonium ions.
Non-disjunction
Failure of members of a homologous pair of chromosomes, or of a pair of chromatids, to separate during nuclear division.
Non-reproductive cloning
Also known as therapeutic cloning. The use of stem cells in order to generate replacement cells, tissue or organs, which may be used to treat particular diseases or conditions of humans. For example, the use of stem cells to generate replacement heart cells in patients suffering from myocardial infarction (heart attack).
Operant conditioning
Also known as trial-and-error learning. The term is used to describe learning that takes place in animals given punishment or reward to reinforce the performance of a particular operation. Most famously, this type of learning is seen in rats and pigeons in a 'Skinner box', where operation of a lever rewards the animal with a food pellet.
Operon
A unit consisting of genes that work together under the control of an operator gene. An example is the lac operon, which consists of two structural genes and an operator gene. Operons were first discovered in prokaryotes but later found in eukaryotes.
Organelles
Structures within cells. Each carries out a specific function.
Ornithine cycle
A process that occurs inside liver cells to convert ammonia to urea.
Osmoreceptors
Receptor cells that monitor the water potential of the blood and detect any changes.
Osmoregulation
The control and regulation of the water potential of the blood and body fluids.
Oxidation
Chemical reaction involving loss of electrons, gain of oxygen or loss of hydrogen atoms.
Oxidative phosphorylation
The formation of ATP, in the presence of oxygen, by chemiosmosis.
Oxytocin
A hormone released by the posterior pituitary gland to facilitate birth and breastfeeding.
Pancreas
A small organ in the abdomen that secretes digestive fluids and hormones.
Pancreatic duct
A duct leading from the pancreas to carry digestive juices to the small intestine.
Paraphyletic group
A classification group for living organisms that includes the most recent ancestor but not all of the descendants.
Partially permeable membrane
A membrane that is permeable to certain substances, such as water, but is not permeable to other substances.
Paternal chromosome
Member of a pair of homologous chromosomes that originally came from the male gamete.
Peripheral nervous system
The sensory and motor neurones connecting the central nervous system to the sensors and effectors around the body.
Peritoneal dialysis
A form of treatment for kidney patients in which dialysis fluid is pumped into the body cavity so that exchange can occur across the peritoneal membrane.
Phagocytosis
Endocytosis of large solid molecules into a cell.
Phenotype
Observable characteristics of an organism.
Photoautotroph
Organism that can make its own food using energy obtained from light.
Photolysis
Enzyme-catalysed reaction where water molecules are split, using light energy. It occurs in photosystem II, during the light-dependent stage of photosynthesis.
Photophosphorylation
Formation of ATP in the presence of light energy. It takes place in thylakoid membranes of chloroplasts, during the light-dependent stage of photosynthesis. There are two types: cyclic photophosphorylation and non-cyclic photophosphorylation.
Photosynthetic pigments
Chemicals that absorb light energy. Found in thylakoid membranes, in photosystems. Each pigment absorbs energy associated with light of a specific wavelength. Examples include chlorophyll a, chlorophyll b, carotenoids and xanthophylls.
Photosynthometer
Apparatus to measure rate of photosynthesis by collecting and measuring the volume of oxygen produced in a certain time.
Photosystems
Group of photosynthetic pigments in the thylakoid membrane. Consists of a primary reaction centre and accessory pigments.
Phylogenetic group
Group of organisms that share evolutionary ancestry.
Podocyte
A specialised cell that makes up the lining (endothelium) of the Bowman's capsule. Podocytes have finger-like processes. They aid ultrafilitration as fluid entering the renal capsule from the blood goes through the gaps in these processes, making ultrafiltration more efficient as the podocytes do not provide a barrier to filtration.
Polarised
Membrane with a potential difference across it.
Polygenic
Characteristic coded for by many genes. Examples include height and intelligence in humans. Polygenic characteristics are more influenced by environmental factors than are monogenic characteristics.
Polypeptide
Large polymer molecule made of many amino acids joined by peptide bonds.
Polyploid
Eukaryotic organisms or cell with more than two sets of chromosomes.
Population
All of the organisms of one species, who live in the same place at the same time, and who can breed together.
Population genetics
The study of the gene pools and the allele and genotype frequencies of populations of organisms.
Positive feedback
A process in which any change in a parameter brings about an increase in that change.
Posterior pituitary gland
The hind part of the pituitary gland, which releases ADH.
Power stroke
The term describes the action of the myosin head in muscular contraction. The head group attached to the actin filament tilts backwards, pulling the thick filament to overlap further with the thin filament. Energy from ATP is used up in the power stroke.
Precursor
Literally means 'coming before'. In biology, a precursor molecule is one which is used in order to form another more useful molecule. For example, beta-carotene is the precursor molecule for vitamin A.
Primary metabolite
Any metabolite which is formed as part of the normal growth of a microorganism. During growth the lipids, proteins, carbohydrates and waste products generated by the microorganism in order to grow in numbers are described as primary metabolites.
Primary pigment reaction centre
The primary photosynthetic pigments in a photosystem act as reaction centres. In PSI the primary pigment reaction centre is a molecule of chlorophyll a that has a peak absorption of 680_nm. This means that its greatest absorption is of light with a wavelength of 680_nm. In PSII the primary pigment reaction centre is a molecule of another type of chlorophyll a that has an absorption peak of 700_nm.
Primer (DNA)
Short single-stranded sequences of DNA, around 10 bases in length. They are needed, in sequencing reactions and polymerase chain reactions, to bind to a section of DNA because the DNA polymerase enzymes cannot bind directly to single-stranded DNA fragments.
Producers
Autotrophic organisms (plants, some protoctists and some bacteria) that convert light energy to chemical energy, which they then supply to consumers.
Productivity
Primary productivity is the rate of production of new biomass by producers. It is the energy captured by their chlorophyll and used to synthesise organic molecules. This minus the energy released via their respiration is the net primary productivity - the energy available to heterotrophs through consumption of producers' biomass.
Programmed cell death
Apoptosis. An orderly process by which cells die after they have undergone the maximum number of cell divisions.
Protein
A macromolecule. A polymer of many amino acids joined by peptide bonds. May also be called a polypeptide.
Protoctist
Eukaryotic organism classified as belonging to the kingdom Protoctista. This kingdom includes organisms that do not fit into/cannot be classified as belonging to the other four kingdoms. It includes algae, protozoa and slime moulds. Some members of this phylum are photosynthetic. Some have undulipodia and some have cilia.
Proton motive force
Force produced as hydrogen ions flow, through ATP synthase channels, down their concentration gradient. The force causes ADP and Pi to combine and form ATP.
Proto-oncogene
Gene that can undergo mutations to become an oncogene, which induces tumour formation (cancer).
Quadrat
A square frame used for sampling in fieldwork.
Recessive
Characteristic in which the allele responsible is only expressed in the phenotype if there is no dominant allele present.
Recombinant DNA
A section of DNA, often in the form of a plasmid, which is formed by joining DNA sections from two different sources.
Reduction
Chemical reaction involving the gain of electrons, gain of hydrogen atoms or loss of oxygen atoms.
Refractory period
The short period of time after firing during which it is more difficult to stimulate a neurone.
Replica plating
The process of growing bacteria on an agar plate, then transferring a replica of that growth to other plates using a sterile velvet pad. The replica plates usually contain different antibiotics. Analysis of growth patterns on the replica plates gives information about the genetic properties of the growing bacteria.
Response
The reaction to a stimulus.
Resting potential
The potential difference or voltage across the neurone cell membrane while the neurone is at rest.
Restriction enzyme
An enzyme originally derived from bacteria, in which it has a role in defence against infection by viruses. The enzymes catalyse a hydrolysis reaction that breaks the phosphate-sugar backbone of the DNA double helix. The two backbones are usually broken at slightly different points on the restriction site, leaving a staggered cut known as a sticky end. The restriction site for each restriction enzyme is unique.
Restriction site
The specific location on a stretch of DNA which is the target site of a restriction enzyme. Restriction sites are around eight bases long.
Reverse transcriptase
An enzyme originally derived from retroviruses. The enzyme catalyses the construction of a DNA strand using an mRNA strand as a template. Effectively the reverse of transcription.
Ribulose bisphosphate (RuBP)
5-carbon compound, present in small amounts in stroma of chloroplasts. It is a carbon dioxide acceptor. It is regenerated from triose phosphate.
Ribulose bisphosphate carboxylase (rubisco)
Enzyme that catalyses the carboxylation (addition of carbon dioxide) to ribulose bisphosphate.
RNA interference
Describes the process in which short fragments of single-stranded RNA bind to complementary regions on mRNA molecules and in doing so form sections of double-stranded mRNA which cannot be translated. The binding of the interfering RNA section often triggers cellular destruction of the mRNA. The term gene silencing is used to mean that RNA interference can prevent the formation of the product of a particular gene within a cell/organism. RNA interference has been shown to operate in natural regulation of gene expression as well as in the targeted silencing of genes in the laboratory.
Saltatory
Refers to way in which the action potential appears to jump from node to node.
Saprotrophs
Organisms (like bacteria and fungi) that feed by secreting enzymes onto food, and absorbing digested nutrients across their outer walls.
Sarcomere
In voluntary muscle, the span between one Z-line and the next Z-line. The Z-line is the central part of the I band, which alternates with the A band. The sarcomere is the smallest unit of contraction of voluntary muscle, consisting of the thick and thin filaments responsible for muscular contraction.
Second messenger
A chemical inside the cell released in response to a hormone binding to the cell surface membrane, e.g. cAMP.
Secondary metabolite
A metabolite produced by a microorganism, usually in the latter stages of growth as the culture ages. Secondary metabolites are not specifically required for the organism to grow. They usually have antibiotic properties.
Segmentation genes
Genes that control the development of polarity (which end is head and which end is tail) in organisms.
Selection pressure
Environmental factor that confers greater chances of surviving and reproducing on some members of the population than on others.
Selective reabsorption
The absorption of certain selected molecules back into the blood from the fluid in the nephron tubule.
Sensory area
An area of the cerebral cortex within which the neurones associated with receiving sensory information from the receptors are found. These neurones often pass information to association areas in order to make sense of the incoming information.
Sex linkage
Gene with its locus on one of the sex chromosomes, X or Y. As there are few genes on the Y chromosome, in humans, most sex-linked genes are on the X chromosome. However, there are some genes on the Y chromosome, notably the gene SRy that stimulates development of the testes and subsequent development of the embryo into a male. There is also a Y STR (short tandem repeat on the Y chromosome) used in genealogy DNA testing. (Note that in some organisms it is not the presence of a Y chromosome that controls development into a male. For example in Drosophila it is the number of X chromosomes, 1 for male and 2 for female. In turtles, sex is determined by incubation temperature of the eggs.) In birds, butterflies and moths, males are XX (or ZZ) and females are XY (ZW). In grasshoppers and crickets females are XX and males are XO (just one X chromosome). In bees and wasps, diploid individuals are female and haploid individuals are male. Earthworms and some snails are hermaphrodite (have both male and female anatomies). Some organisms, such as oysters and some fish, can change sex during their life cycle.
Sexual reproduction
Production of new organisms involving fusion of nuclei from male and female gametes, usually from unrelated individuals. Increases genetic variation in the population.
Sinoatrial node (SAN) or sinus node
The region of the heart right atrial muscle wall, about 3_mm wide, 15_mm long and 1_mm deep, which consists of specialised muscle fibres (cells) that have no contractile filaments but connect directly to atrial muscle fibres. Any excitation (electrical activity) starting in the SAN spreads immediately to the rest of the atrial wall. Hence the pacemaker controls the synchronised rate of beating of the whole heart. (Artificial pacemakers are battery-powered devices, usually inserted under the skin and connected via wires in the subclavian vein and vena cava to the heart muscle.)
Social behaviour
Behaviour of organisms of a particular species living together in groups with relatively defined roles for each member of the group.
Sodium-potassium pumps
Protein carriers embedded in the membranes of some cells, which use energy from ATP to move sodium ions and potassium ions in opposite directions simultaneously, against their concentration gradients. They are chemically gated ion channels.
Somatic cell gene therapy
Involves the placing of the gene in adult differentiated cells. Examples include the placing of CFTR genes into the respiratory system cells of individuals with cystic fibrosis.
Somatic cell nuclear transfer
The technique of cloning organisms involving the removal of the nucleus from an adult, differentiated cell, which is then placed into the enucleated egg cell taken from a donor organism. The cell formed is placed into a surrogate mother in order to develop. The resulting organism is a clone of the organism which provided the adult, differentiated cell nucleus.
Species
The biological species concept is a group of similar organisms that can interbreed and produce fertile offspring. The phylogenetic species concept is a group of organisms with similar morphology, physiology, embryology and behaviour, and that all occupy the same ecological niche.
Stabilising selection
A type of natural selection in which the allele and genotype frequency within populations stays the same because the organisms are already well adapted to their environment.
Stem cells
Undifferentiated cells. Embryonic stem cells are totipotent and are able to differentiate into any type of specialised cell found in organisms of that species. Umbilical stem cells and adult stem cells may become specialised into a more limited range of cell types.
Stimulus
Any change in the environment of an organism that causes a response.
Stomata
Pores between guard cells in the epidermis of leaves.
Stroma
Fluid-filled matrix of chloroplasts. This is where the light-independent stage of photosynthesis takes place.
Substrate-level phosphorylation
Formation of ATP from ADP and Pi during glycolysis and the Krebs cycle.
Succession
A directional change in a community of organisms over time.
Summation
The way that several small potential changes can combine to produce one larger change in potential difference across a neurone membrane.
Synaptic knob
The swelling at the end of a neurone where it forms a junction (synapse) with another neurone.
Synovial joint
A type of joint in the skeleton characterised by the presence of a synovial membrane that produces synovial fluid to lubricate the joint. Synovial joints are found where a large movement range is required, such as the elbow and the hip.
Target cells
Cells that have receptors embedded in the plasma membrane that are complementary in shape to specific hormone molecules. Only these cells will respond to that specific hormone.
Taxon (pl. taxa)
Group of organisms used in a hierarchical classification. Examples are Kingdom, Phylum, Class, Order, Family.
Threshold potential
A potential difference (usually -50_mV) across the membrane. If the depolarisation of the membrane does not reach the threshold potential then no action potential is created. If the depolarisation reaches the threshold potential then more sodium ion channels open and an action potential is created.
Thylakoid
Inner membrane in chloroplast. Site of photosystems and ATP synthase.
Tissue
A group of cells, with a common origin and similar structures, which performs a particular function; for example, blood, bone, epithelium, muscle, nervous tissue, xylem and phloem.
Tissue culture
Also called micropropagation. The cloning of isolated cells or small pieces of plant tissue in special culture solutions, under controlled aseptic conditions.
Totipotent stem cells
Stem cells that can differentiate into any type of specialised cells found in organisms of that species.
Transcription
The formation of an RNA molecule, using a length of DNA as a template. Complementary base pairing is used. The enzyme RNA polymerase catalyses the reaction.
Transect
A line taken through a habitat, which helps with systematic sampling of changes across a habitat.
Transformation
Bacteria that take up DNA from their surroundings (e.g. from dead bacteria) are transformed.
Translation
Stage of protein/polypeptide synthesis in which the amino acids are assembled at ribosomes. The order in which the amino acids are joined together, by peptide bonds, is determined by the sequence of codons on the mRNA, which is itself determined by the sequence of nucleotide triplets on the coding strand of a length of DNA (gene). The genetic code is translated.
Triose phosphate (TP)
3-carbon compound formed when a molecule of glycerate phosphate is reduced, during the Calvin cycle in the light-independent stage of photosynthesis.
Trophic level
The level at which an organism feeds in a food chain.
Tropism
A directional growth response in which the direction of the response is determined by the direction of the external stimulus.
Ultrafiltration
Filtration at the molecular level in the glomerulus of kidneys. Some molecules are filtered out of the blood of the glomerulus into the renal capsule. Molecules with relative molecular masses above 69_000 are retained in the blood capillaries.
Urea
An excretory product formed from the breakdown of excess amino acids.
Vector
Carrier. In DNA technology, refers to the agent that carries a piece of DNA from one cell into another, e.g. a bacterial plasmid.
Vegetative propagation
Asexual reproduction in plants making use of specialised vegetative structures that grow to form new and separate individual organisms.
Voltage-gated channels
Channels in plasma membranes that allow the passage of ions. They respond to changes in potential difference (voltage) across a membrane and, as a result, open or close.
Xenotransplantation
The transplantation of cells or organs from one species into the body of an organism of another species.
Zygote
Cell formed, during sexual reproduction, from the fusion of two gametes.
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