A2 glossary of key terms

alpha cells

Cells in the islets of Langerhans that release glucagon in response to low blood glucose levels

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Acetylcholine

A neurotransmitter found in cholinergic synapses.

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Acetylcholinesterase

An enzyme in the synaptic cleft that breaks down the transmitter substance acetylcholine

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Actin

A protein found in the muscle cells. It is the main component of the thin filaments

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Action potential

A brief reversal of the resting potential across the cell surface membrane of a neurone. All action potential have a value of +40mV

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Adenyl cyclase

the enzyme found inside cells, associated with hormone receptors, that converts ATP to cAMP

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Allele

An alternative version of a gene

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Amplification

The making of multiple copies of the same short section of DNA. The process of PCR is used in automatic amplification of DNA sections.

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Anabolic steroids

Drugs that mimic the action of steroids and increase muscle growth

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Anabolism

Type of metabolism, a biochemical reaction which synthesises large molecules from smaller molecules, this requires ATP

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Antagonistic

Working against each other in a pair of muscles

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Antidiuretic hormone (ADH)

Hormone made in the hypothalamus and released from the pituitary gland that acts on the collecting ducts in the kidneys to increase reabsorption of water in the blood

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Apoptosios

Programmed cell death. They die after they have performed their maximum number of divisions.

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Association area

A region of the cerebral cortex where information in the form of impulses from sensory areas is made sense of by comparison with previous experiences

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ATP

Found in all living cells, involved in energy transfer. When it is hydrolysed energy is released

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ATP synthase

Enzyme associated with stalked particles in mitochondria and chloroplasts. It catalyses the joining of ADP and inorganic phosphate to make ATP

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Autonomic nervous system

The system of motor neurones that controls non conscious action n the body. For example, the heart.

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Autotroph

Organism that makes its own food using simple inorganic molecules, such as CO2 and H20

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Beta cells

Cells in the islets of Langerhans that release insulin in response to high blood glucose levels.

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Basement membrane

A layer of connective tissue - mostly collagen-that holds epithelium in place.

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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.

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Biodiversity

The number and variety of living things to be found in the world, an ecosystem or a habitat.

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Bioremediation

Any use of a microorganisms to remove waste products from a location such as a sewage plant.

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Biotechnology

Use of biotechnology to generate useful products, such as beer.

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Bowman's capsule

The cup shaped end of a nephron tubule

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Callus

A mass of undifferentiated plant cells formed by meristem tissue extracted from the plant and grown in tissue culture

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Cardiovascular centre

The region of the brain in which controls the heart rate

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Carrying capacity

The maximum population size that can be maintained over a period of time in a particular habitat

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Catabolism

Type of metabolism, biochemical reactions that produce small molecules by hydrolysis of larger molecules

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Cell metabolism

The result of all the chemical reactions taking place in the cell cytoplasm

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Central nervous system (CNS)

The brain and spinal chord. It has control over the coordination of the nervous system

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Chemiosmosis

The flow of hydrogen ions through ATP synthase enzymes.The force of this flow allows production of ATP.This occurs across the thylakoid membrane during the light-dependent stage of photosynthesis. Also occurs across the inner mitochondrial membrane.

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Chemoautotrophs

Use chemical energy to make its own food

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Chi squared test

Statistical test that can be carried out on data in categories. It enables the investigator to determine how closely an observed set of data corresponds to the expected data

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Chloroplasts

Organelles, in plant and some protoctist cells, where photosynthesis occurs

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Cholinergic synapse

A junction between neurones that uses acetylcholine as the neurotransmitters

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Chromatogram

A chart produced when substances are separated by movement of a solvent along a permeable material such as paper or gel

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Chromosome mutation

Random change to the structure of a chromosome

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Cladistics

A method of classifying living organisms based on their evolutionary ancestry

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Classical conditioning

a learning process that occurs when two stimuli are repeatedly paired until the behaviour becomes learned

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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 such as waste.

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Codominant

A characteristic where both alleles contribute to the phenotype

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Coenzyme A

A Coenzyme that carries acetate from the link reaction of respiration to the krebs cycle

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Coenzymes

Molecules that help enzymes carry out oxidation or reduction of reactions.

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Community

All the populations of different species that live in the same place at the same time, and who can interact with each other

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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

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Competition

A struggle between individuals for resources that are scarce but are still needed

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Complementary genes

Genes that interact together to govern the expression of a single characteristic

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Conjugation

Bacterial cells can join together and pass plasmid DNA from one bacterial cell to another. This a method that can occur between species and is a means of passing plasmid coating genes for antibiotic resistance

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Conservation

Maintenance of biodiversity, including diversity between species, genetic diversity with species and maintenance of a variety of habitats and ecosystems

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Consumers

Living organisms that feed on other living organisms.

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Continuos 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

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Continuos variation

When there is a wide range of phenotypic variation within a population. For example height in humans

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Coppicing

cutting a tree trunk close to the ground to encourage new growth

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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

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Cross bridge

In voluntary muscle, the joining of a myosin head group to an actin thin filament in the presence of calcium ions

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Crossing over

Where non-sister chromatids exchange alleles during prophases 1 of meiosis

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Cytokines

Cell signalling molecules

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Deamination

The removal of the amine group from an amino acid to produce ammonia

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Decomposers

Organisms that feed on dead organic matter, releasing molecules,mineral and energy

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Dehydrogenation

Removal of hydrogen atoms from a substrate molecule

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Depolarisation

The loss of polarisation across a membrane- when the membrane loses its resting potential

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Detoxification

Coversion of toxic substances, such as alcohol, to less toxic substances

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Diabetes mellitus

A condition in which metabolic wastes and excess salts and water a removed from the blood

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Dialysis

Treatment for patients with kidney failure, in which metabolic wastes and excess salts and water are removed from the blood

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Dialysis membrane

A partially permeable membrane that separates the dialysis fluid from the patients blood in a dialysis machine

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Diffusion

Movement of molecules down their concentration gradient. It may be through a partially permeable membrane

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Digest

Hydrolyse a large molecule to smaller molecules

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Diploid

Having two sets of chromosomes

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Discontinuos variation

Genetic variation where there are distinct phenotypic categories

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DNA ligase

An enzyme capable of catalysing a condensation reaction between the phosphate group of one nucleotide and the sugar group of another

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DNA mutation

A change to a DNA structure

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Dominant

Characteristic in which the allele responsible is expressed in the phenotype even in those with heterozygous genotypes

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Ecosystem

All the living organisms and all the non living components in a specific habitat, and their interactions

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Ectotherms

Organisms that rely on external sources of heat and behavioural activities to regulate body temperature

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Electron acceptors

Chemicas that accept electrons from another compound. They are reduced while acting as oxidising agents

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Endocrine gland

A gland that secrets hormones directly into the blood capillaries

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Endocytosis

The transport of large molecules or fluids into the cytoplasm of the cell by invagination of the cell membrane

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Endothelium

The tissue which lines the inside of a blood vessel or nephron

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Endotherms

Organisms that control production and loss of heat to maintain their body temperature

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Environmental resistance

The combined action of biotic and abiotic factors that limits the growth of a population

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Epistasis

The interaction of genes concerned with the expression of one characteristic. One gene may mask the expression of another gene

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Epithelium

The tissue that covers the outside of a structure

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Eukaryotes

Organisms with eukaryotic cells- protoctists,fungi,plants and animals

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Evolution

The process of gradual change in the inherited traits passed from one generation to the next within a population

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Excretion

The removal of metabolic waste from the body

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Exocrine gland

A gland that secretes substances into a duct

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Exocytosis

A mechanism of secretion from a cel involving vesicles that fuse to the cel surface membrane and release their contents outside, it uses ATP

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Facilitated diffusion

Diffusion that is enhanced by the action of protein channels or carriers in the cell membrane

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Fermentation

The process of anaerobic respiration in microorganisms, used to yield specific products

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Fertilisation

Fusion of male and female gamete nuclei

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Fight or flight response

The set of responses in an animal that accompany the perception of threat, through the reaction of the sympathetic nervous system

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First messenger

A hormone that acts as a message in the bloodstream

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Gametes

Specialised sex cells. In many organisms the gametes are haploid and are produced by meiosis

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Gene

A section of DNA that codes for proteins

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Gene pool

Total genetic information possessed by the reproductive members within a population of organisms

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Generator potential

A small depolarisation of the membrane in a receptor cell

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Genetic drift

The change in allele frequency in a population, as some alleles pass to the next generation and some disappear

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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

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Genetic markers

Variation of genetic information in a gene pool

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Genome

All the genetic information within an organism/cell

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Genome sequencing

The technique used to give the base sequence of DNA of a particular organism

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Genotype

Alleles present within cells of an individual, for a particular trait/characteristic

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Grana

Stacks of thylakoid membranes, found in a chloroplast

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Habitat

The place where an organism or population of organisms lives

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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

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Half life

The time taken for the concentration of a substance to drop to half its original value

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Haploid

Eukaryotic cell or organism having only one set of chromosomes

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Hayflick constant

The number of times that a normal body cell divides before undergoing apoptosis

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Hemizygous

Cell or individual having only one allele for a particular gene

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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

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Heterozygous

Eukaryotic cell or organism that has two different alleles for a specific gene

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Hierachy

Within a group individuals have a place in the order of importance within the group

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Homeobox genes

Genes that control the development of the body plan of an organism

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Homeostasis

The maintenance of a constant internal environment despite external changes

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Islets of Langerhans

Patches of endocrine tissue in the pancreas – they consist of α and β cells

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Isolating mechanism

Mechanism that divides populations of organisms into subgroups

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Kupfer cells

Specialised macrophages that move around in the sinusoids and are involved in the breakdown and recycling of old red blood cells

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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

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Light intensity

A measure of the amount of energy associated with light

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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

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Linkage

Genes for different characteristics that are present at different loci on the same chromosome are linked

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Locus

Specific position on a chromosome, occupied by a specific gene

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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

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Meristem

Growth points in a plant where immature cells are still capable of dividing

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Microvilli

Microscopic folds of the cell surface membrane that increase the surface area of the cell

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Monogenic

Characteristic coded for by one gene

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Mutation

Structural change to genetic material – either to a gene or to a chromosome

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Myogenic

Contraction of the muscle is generated from within the muscle itself

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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

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NAD

The coenzyme that removes hydrogen atoms from substrates, NADH carries hydrogen atoms

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Natural selection

Organisms that are well adapted to their environment are more likely to survive and reproduce

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Necrosis

Disorderly, often accidental cell death

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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

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Nephrons

Tubules in the kidney that are used to produce urine

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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

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Niche

The role that a species plays in an ecosystem

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Nitrogen fixation

Conversion of nitrogen gas into a form which is usable by plants, such as nitrate or ammonium ions

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Operant conditoning

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

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Operon

A unit consisting of genes that work together under the control of an operator gene

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Organelles

Structures within cells. Each carries out a specific function

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Osmoreceptors

Receptor cells that monitor the water potential of the blood and detect any changes

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Osmoregulation

The control and regulation of the water potential of the blood and body fluids

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Oxidation

hemical reaction involving loss of electrons, gain of oxygen or loss of hydrogen atoms

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Oxytocin

A hormone released by the posterior pituitary gland to facilitate birth and breastfeeding

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Peripheral nervous system

The sensory and motor neurones connecting the central nervous system to the sensors and effectors around the body

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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

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Phenotype

Observable characteristics of an organism

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Photolysis

Enzyme-catalysed reaction where water molecules are split, using light energy. It occurs in photosystem II, during the light-dependent stage of photosynthesis

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Photosynthetic pigments

Chemicals that absorb light energy

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Polarised

Membrane with a potential difference across it

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Polypeptide

Large polymer molecule made of many amino acids joined by peptide bonds

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Polyploid

Eukaryotic organisms or cell with more than two sets of chromosomes

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Population

All of the organisms of one species, who live in the same place at the same time, and who can breed together

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Protein

A macromolecule. A polymer of many amino acids joined by peptide bonds. May also be called a polypeptide

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Protoctist

It includes algae, protozoa and slime moulds. Some members of this phylum are photosynthetic. Some have undulipodia and some have cilia

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Recessive

Characteristic in which the allele responsible is only expressed in the phenotype if there is no dominant allele present

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Refractory period

The short period of time after firing during which it is more difficult to stimulate a neurone

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Resting potential

The potential difference or voltage across the neurone cell membrane while the neurone is at rest

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Restriction enzyme

The enzymes catalyse a hydrolysis reaction that breaks the phosphate–sugar backbone of the DNA double helix

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Reverse transcriptase

The enzyme catalyses the construction of a DNA strand using an mRNA strand as a template. Effectively the reverse of transcription.

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RuBP

5-carbon compound, present in small amounts in stroma of chloroplasts. It is a carbon dioxide acceptor. It is regenerated from triose phosphate

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RUBISCO

Enzyme that catalyses the carboxylation (addition of carbon dioxide) to ribulose bisphosphate

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Saltatory

Refers to way in which the action potential appears to jump from node to node

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Saprotrophs

Organisms (like bacteria and fungi) that feed by secreting enzymes onto food, and absorbing digested nutrients across their outer walls

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Sarcomere

The sarcomere is the smallest unit of contraction of voluntary muscle, consisting of the thick and thin filaments responsible for muscular contraction

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Secondary messenger

A chemical inside the cell released in response to a hormone binding to the cell surface membrane, e.g. cAMP

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Selection pressure

Environmental factor that confers greater chances of surviving and reproducing on some members of the population than on others

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selective reabsorbtion

The absorption of certain selected molecules back into the blood from the fluid in the nephron tubule

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Sensory area

An area of the cerebral cortex within which the neurones associated with receiving sensory information from the receptors are found

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Sex linkage

Gene with its locus on one of the sex chromosomes, X or Y

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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

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Somatic cell gene therapy

nvolves 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

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Species

The biological species concept is a group of similar organisms that can interbreed and produce fertile offspring

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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

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Stroma

Fluid-filled matrix of chloroplasts. This is where the light-independent stage of photosynthesis takes place

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Succession

A directional change in a community of organisms over time

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Summation

A directional change in a community of organisms over time

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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

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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

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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.

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Thylakoid

Inner membrane in chloroplast. Site of photosystems and ATP synthase

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Tissue culture

Also called micropropagation. The cloning of isolated cells or small pieces of plant tissue in special culture solutions, under controlled aseptic conditions

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Totipotent stem cells

Stem cells that can differentiate into any type of specialised cells found in organisms of that species

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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

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Transformation

Bacteria that take up DNA from their surroundings (e.g. from dead bacteria) are transformed

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Translation

Stage of protein/polypeptide synthesis in which the amino acids are assembled at ribosomes

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Trophic level

The level at which an organism feeds in a food chain

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Tropism

A directional growth response in which the direction of the response is determined by the direction of the external stimulus

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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

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Urea

An excretory product formed from the breakdown of excess amino acids

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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

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Xenotransplantation

The transplantation of cells or organs from one species into the body of an organism of another species

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Zygote

Cell formed, during sexual reproduction, from the fusion of two gametes

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A2 glossary of key terms

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