A Level Biology Definitions Flashcards
action potential
A change in the electrical membrane potential which causes the transmission of a nerve impulse
activation energy
The energy that needs to be put in to cause a reaction. The activation energy is lowered by the presence of an enzyme (biological catalyst)
active immunity
A type of resistance developed in an organism through production of specific antibodies in response to an exposure to a pathogen (natural) or to a vaccine (artificial)
active site
A group of usually 3-12 amino acid R-groups that makes up a region on the surface of the enzyme into which a complementary substrate temporarily bonds to forming an enzyme-substrate complex
active transport
The movement of molecules from a region of low concentration to a region of high concentration against a concentration gradient requiring an input of ATP and involving transport proteins
acute disease
A disease that has a sudden onset and lasts a short time
adaptation
A trait that benefits an organism in its environment and increases its chances of survival and reproduction
adenosine triphosphate (ATP)
A phosphorylated nucleotide composed of a nitrogenous base (adenine), a pentose sugar, and three phosphate groups. The universal energy currency for cells
adhesion
The force of attraction between two different molecules e.g. water and molecule of lignin
adrenaline
A hormone secreted in response to stress
afferent
Leading towards or incoming (e.g. an afferent nerve or blood vessel is one that leads into a tissue or organ)
agglutination
The clumping together of antigen-bearing cells, microorganisms, or particles in the presence of specific antibodies
allele
A gene variant
alveoli
Small air sacs in the lungs which allow for rapid gaseous exchange
amino acid
An organic compound that has a central carbon atom to which an amine group (NH2) and carboxyl group (COOH) and variable residual group are attached. They are joined together by condensation reactions to form a polypeptide chain
amniocentesis
A procedure for sampling fetal cells from the amniotic fluid
anaphase
The stage of mitosis in which chromatids separate and are pulled towards opposite poles of the cell by the spindle
aneurysm
A localised bulge of an artery, vein, or the heart wall. The wall of the blood vessel or organ is weakened and may rupture
antenatal care
The care received by a pregnant woman
anther
The part of the plant that holds pollen
antibiotics
A substance produced by a living organism that kills or inhibits the growth of microorganisms, has no effect on viruses
antibodies
Globular protein molecules (immunoglobulins) produced by plasma cells (B lymphocytes) in response to stimulation by an antigen
anti-coagulant
A substance that prevents blood from clotting e.g. sodium citrate, heparin
anticodon
A sequence of three bases at the end of a tRNA molecule that allow complementary binding to a codon of the mRNA molecule being translated at the ribosome
antigen
A toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies
antiparallel
A feature of the two strands in a DNA molecule. The 5’ (5 prime) end of one strand is directly opposite the 3’ (3 prime) end of the parallel strand. The two strands run in opposite directions
aorta
The major artery of the body, supplying oxygenated blood to the circulatory system
apoplast pathway
The transport route taken by water and dissolved substances through the cell walls and intercellular spaces of plants
apoptosis
Programmed cell death
artery
A thick-walled vessel that carries blood away from the heart
aseptic techniques
Any techniques/manipulations of equipment or materials that are designed to prevent contamination by microorganisms
asthma
A respiratory condition characterised by the inflammation and narrowing of the bronchi
atrio-ventricular node (AV node)
A 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
atria
The upper chambers of the heart which receive blood returning from the organs and vessels of the body
autonomic nervous system
The branch of the motor nervous system that controls the non-conscious actions of the body. The autonomic system controls the actions of involuntary muscles and glands. Consists of two branches - the sympathetic and parasympathetic nervous systems
bacteriocidal
Describes a chemical substance that kills bacteria
bacteriostatic
Describes a chemical substance that prevents the reproduction of bacteria
Benedict’s test
A biochemical reaction to test for the presence of a reducing sugar, for example glucose. The test can be semi-quantitative of quantitative depending on the procedure used
benign
A tumour that stays in its original location and does not shed any cells into the blood plasma or lymph system
biodiversity
The variety of life, which can be measured on a genetic, species or ecosystem level
biosensor
A device which uses a living organism or biological molecules, especially enzymes or antibodies, to detect the presence of specific chemicals
biuret test
A biochemical reaction to test for the presence of proteins. It is qualitative test
blind trials
A clinical trial in which participants are unaware whether they are receiving a placebo or a medicinal drug
blood clot
A structure formed from fibrin fibres which traps red blood cells and platelets in response to the damage of a blood vessel
blood group
Also known as blood type - the classification of blood depending on which antigens are present on the plasma membrane of the erythrocytes
blood pressure
The force exerted by the blood against the walls of the blood vessels
B lymphocyte
A specialised leucocyte that is produced in the bone marrow and matures in the bone marrow. It forms plasma cells after contact with a specific antigen and produces antibodies
Bohr effect
Haemoglobin’s oxygen binding affinity is inversely related to the concentration of carbon dioxide and hence the acidity of the blood
- an increase in blood CO2 concentration causes a decrease in blood pH which results in oxyhaemoglobin releasing oxygen
- a decrease in carbon dioxide causes an increase in pH which results in haemoglobin picking up more oxygen
boosters
An additional dose of an immunising agent, such as a vaccine, given at a time after the initial dose to sustain the immune response elicited by the previous dose of the same agent
bradycardia
A slowness of the heartbeat, usually under 60 beats per minute in adults
broad-spectrum antibiotics
Antibiotics that are effective against a large variety of organisms
bronchi
The two main branches from the trachea that go into the lungs
bronchioles
One of the smaller subdivisions of the branched bronchial tree that connects the trachea to the alveoli
buffer
A chemical solution which has the ability to absorb or donate hydrogen ions (protons) to maintain the pH of the solution
bundle of His
Specialised cardiac muscle fibres that run from the atrioventricular node to the base of the heart
Calvin cycle
The reactions of the light-independent stage of photosynthesis
cancer
A disease usually caused by a mutation that causes uncontrolled cell division and the subsequent formation of a tumour. Some of these (primary tumour) cells may break away and be transported in the plasma or lymph system to form a secondary tumour in a different location
capillaries
Very small blood vessels where water, solutes, and respiratory gases are exchanged with body tissues
capsid
The outer protein coat of a virus
cardiac output
The amount of blood the heart pumps through the circulatory system in a minute
carcinogen
A chemical or form of radiation that causes cancer
cardiac monitor
A device for the continuous observation of cardiac function
carrier protein
Protein found within a cell membrane that carries a specific molecule or ion across the membrane by active transport
casparian strip
A band of impermeable suberin found in the walls of endodermal cells in plant roots
catalyst
A substance that speeds up the rate of the reaction without itself being altered or used up in the chemical reaction
cell cycle
The series of event that take place in a cell leading to its division to produce two daughter cells
cell surface membrane
The phospholipid bilayer that forms the membrane surrounding the outside of a cell - sometimes known as the plasma membrane
cellulose
A polysaccharide made from the condensation of many β-glucose molecules to form fribrils. It is used to form plant cell walls
cell wall
A freely permeable structure lying outside of the cell surface membrane of plant, fungal, and bacterial cells
centrifugation
The process of separating molecules and organelles on the basis of their density by spinning them at different speeds in a centrifuge
centriole(s)
Two cylinders composed of microtubules which are involved in the process of mitosis and cell division in some eurykaryotic cells
centromere
The region of a chromosome that joins two sister chromatids and attaches to spindle fibres during mitosis
cerebellum
A structure located at the back of the brain in vertebrates, which coordinates and regulates muscle activity
cerebrum
The largest part of the brain which is formed as two hemispheres
channel protein
A protein pore that spans a cell membrane to enable water soluble molecules and small ions to passively cross the membrane
chemotherapy
Destroying cancerous cells using drugs that affect cancerous cells more than other cells in the body
chiasmata
The points at which crossing over occurs between homologous chromosomes
chi-squared test
A statistical test that enables an investigator to determine whether differences exist between two sets of data
chloroplast
The organelle in which photosynthesis occurs
chordae tendinae
Also known as the heart strings, they are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart
chorionic villus sampling
A procedure for sampling fetal cells from the placenta
chromatid
A DNA molecule; during prophase and metaphase of mitosis, a chromosome consists of two identical chromatids from the replication of DNA in S phase
chromatography
A technique used to separate substances in a mixture according to differences in their solubility
chromosome
A single DNA molecule, linear, and associated with proteins such as histones in eukaryotic cells
chromosome mutation
A random change to the structure or number of chromosomes due to translocation or non-disjunction
chronic disease
A disease that lasts a long time and has symptoms that worsen over time
classification
The organisation of organisms into groups based on similarities in biochemistry, anatomy, behaviour and embryology
climax community
The stable community of species that exists at the end of ecological succession
clinical trials
A series of controlled studies in which a new medicinal drug is tested
codominant
Alleles at a gene locus that are both expressed and therefore both contribute to the phenotype
coenzyme
An organic non-protein molecule that binds temporarily with the substrate to the active site in order for an enzyme to function
codon
A sequence of three bases on the template strand of the DNA or the mRNA that codes for one amino acid
cofactor
A molecule or ion which aids the function of an enzymes - it can be an inorganic ion or a coenzyme
cohesion
The attraction between water molecules due to hydrogen bonding
cohesion-tension theory
A theory of intermolecular attraction that explains the process of water flow upwards (against the force of gravity) through the xylem of plants
colony morphology
The characteristic of a bacterial colony, in cultures, in terms of shape, colour, edge and elevation
colorimeter
A device that measures the absorbance of particular wavelengths of light by a specific solution, most commonly used to determine the concentration of a known solute in a given solution
communicable
A disease or infection caused by microorganisms capable of being communicated or transmitted to another organism
companion cells
A cell in the phloem tissue involved in actively loading sucrose into sieve tube elements. The companion cell is closely associated with the phloem sieve element, to which it is linked by many plasmodesmata
compartmentalisation
The use of intracellular membranes to separate metabolic processes within the cell e.g. the nuclear envelope around the nucleus
compensation point
The light intensity at which the rate of photosynthesis matches the rate of respiration
competitive inhibitor
A molecule that has a similar shape to the natural substrate and which competes for the active site on the enzyme preventing the formation of enzymes substrate complexes and instead forming enzyme-inhibitor complexes
complementary therapy
Treatments that involve procedures that are not part of mainstream medicine e.g. acupuncture, aromatherapy
computed tomography (CT)
A radiographic technique that produces an image of a detailed cross section of tissue
condensation reaction
A chemical process in which two molecules are combined to form a more complex molecule with the removal of a molecule of water to form a covalent bond
correlation
The relationship between two variables e.g. a linear relationship
co-transporter
Proteins in the cell surface membrane that allows movement of one molecule when linked to the movement of another molecule by active transport
cotyledon
In seeds, the part of a plant embryo that becomes the first leaf
countercurrent multiplier
Any mechanism that uses energy and countercurrent flow to establish concentration gradients
cristae
Fold in inner membrane of mitochondria
crossing over
The process in which homologous chromosomes exchange alleles during prophase I of meiosis
cytokines
Cell signalling molecules which are used for communication between cells, allowing some cells to regulate the activity of others
cytokinesis
The division of a cell to form two new cells
cytoskeleton
A network of microtubules and microfilaments that give the cell shape and maintain its structure. They can attach to organelles and move organelles within the cytosol
deamination
The removal of the amino group from an amino acid
defibrillator
An apparatus used to control heart filbrillation by application of an electric current to the chest wall or heart
deflection succession
The changes resulting from human activities (such as farming) that produce a stable community called a plagioclimax. A plagioclimax community and a climax community formed by natural, unimpeded succession have different compositions
degenerate code
Situation where more than one codon codes for the same amino acid
denaturation
Usually permanent change to the tertiary structure of a protein resulting in the loss of function. This can be caused by large changes in pH or high temperatures
denitrification
The production of nitrogen gas from nitrates in the soil
deoxyribonucleic acid (DNA)
The molecule responsible for the storage of genetic information
depolarisation
The loss of the difference in charge between the inside and the outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior
diabetes mellitus
A condition in which a person cannot control blood glucose levels
diaphragm
A sheet of muscular and fibrous tissue separating the chest cavity from the abdominal cavity. Plays an important role in ventilation
diastole
Period of relaxation and repolarisation of the cardiac muscle when the chambers fill with blood
dicotyledons
A plant that produces flowers and has two cotyledons (seed leaf) inside the seed, which develops wide leaves with veins
differential staining
Staining processes that use more than one chemical stain, for example multiple stains can be used to distinguish between different microorganisms or structures/cellular components of a single organism
differentiation
The development of unspecialised cells to form specialised cells
diffusion
The movement of molecules down their concentration gradient as a result of random motion. In cells, diffusion may occur passively directly across the plasma membrane (simple) or via membrane proteins (facilicated)
diploid
Cells that have two copies of each chromosome
disaccharide
A dimer made from the condensation of two monosaccharides joined by a glucosidic bond
disulfide bond
A S-S chemical bond between two sulfur atoms in the R group of two cysteine amino acids
dominant
An allele that is expressed in the phenotype, the presence of which prevents a recessive allele from being expressed
dopamine
Dopamine is a neurotransmitter (or chemical in the brain) that either increases or reduces the activity of neurons (nerve cells). A precursor to both adrenaline and noradrenaline
double-blind trials
A clinical trial in which neither participants nor scientists are aware whether a placebo or medicinal drug has been issued
double circulatory system
A type of blood circulation system in which the blood flows through the heart twice for each full circuit of the body
ecosystem
The organisms and non-living components of a specific area, and their interactions
efferent
Leading away from or outgoing (e.g. an efferent nerve or blood vessel is one that leads away from a tissue or organ
electrocardiogram (ECG)
A graph showing the electrical activity in the heart during the cardiac cycle (heartbeat)
electroencephalogram (EEG)
Technique where electrodes attached to the scalp detect small electrical impulses transmitted between brain cells. Impulses are recorded and monitored for abnormal readings
electrolytes
Ions such as sodium, potassium, and chloride dissolved in water
electron microscopes
A microscope that uses a beam of electrons to view a magnified image of an object giving it a greater resolution than a light microscope. There are two main types - scanning and transmission electron microscopes
electron transport chain
A series of compounds that can transfer electrons from electron donors to electron acceptors via a series of redox reactions resulting in the transfer of protons (H+ ions) across a membrane and the generation an electrochemical proton gradient. This gradient drives the formation of ATP
