A Level Biology Definitions Flashcards
(143 cards)
1
Q
action potential
A
A change in the electrical membrane potential which causes the transmission of a nerve impulse
2
Q
activation energy
A
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)
3
Q
active immunity
A
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)
4
Q
active site
A
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
5
Q
active transport
A
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
6
Q
acute disease
A
A disease that has a sudden onset and lasts a short time
7
Q
adaptation
A
A trait that benefits an organism in its environment and increases its chances of survival and reproduction
8
Q
adenosine triphosphate (ATP)
A
A phosphorylated nucleotide composed of a nitrogenous base (adenine), a pentose sugar, and three phosphate groups. The universal energy currency for cells
9
Q
adhesion
A
The force of attraction between two different molecules e.g. water and molecule of lignin
10
Q
adrenaline
A
A hormone secreted in response to stress
11
Q
afferent
A
Leading towards or incoming (e.g. an afferent nerve or blood vessel is one that leads into a tissue or organ)
12
Q
agglutination
A
The clumping together of antigen-bearing cells, microorganisms, or particles in the presence of specific antibodies
13
Q
allele
A
A gene variant
14
Q
alveoli
A
Small air sacs in the lungs which allow for rapid gaseous exchange
15
Q
amino acid
A
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
16
Q
amniocentesis
A
A procedure for sampling fetal cells from the amniotic fluid
17
Q
anaphase
A
The stage of mitosis in which chromatids separate and are pulled towards opposite poles of the cell by the spindle
18
Q
aneurysm
A
A localised bulge of an artery, vein, or the heart wall. The wall of the blood vessel or organ is weakened and may rupture
19
Q
antenatal care
A
The care received by a pregnant woman
20
Q
anther
A
The part of the plant that holds pollen
21
Q
antibiotics
A
A substance produced by a living organism that kills or inhibits the growth of microorganisms, has no effect on viruses
22
Q
antibodies
A
Globular protein molecules (immunoglobulins) produced by plasma cells (B lymphocytes) in response to stimulation by an antigen
23
Q
anti-coagulant
A
A substance that prevents blood from clotting e.g. sodium citrate, heparin
24
Q
anticodon
A
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
25
antigen
A toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies
26
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
27
aorta
The major artery of the body, supplying oxygenated blood to the circulatory system
28
apoplast pathway
The transport route taken by water and dissolved substances through the cell walls and intercellular spaces of plants
29
apoptosis
Programmed cell death
30
artery
A thick-walled vessel that carries blood away from the heart
31
aseptic techniques
Any techniques/manipulations of equipment or materials that are designed to prevent contamination by microorganisms
32
asthma
A respiratory condition characterised by the inflammation and narrowing of the bronchi
33
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
34
atria
The upper chambers of the heart which receive blood returning from the organs and vessels of the body
35
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
36
bacteriocidal
Describes a chemical substance that kills bacteria
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bacteriostatic
Describes a chemical substance that prevents the reproduction of bacteria
38
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
39
benign
A tumour that stays in its original location and does not shed any cells into the blood plasma or lymph system
40
biodiversity
The variety of life, which can be measured on a genetic, species or ecosystem level
41
biosensor
A device which uses a living organism or biological molecules, especially enzymes or antibodies, to detect the presence of specific chemicals
42
biuret test
A biochemical reaction to test for the presence of proteins. It is qualitative test
43
blind trials
A clinical trial in which participants are unaware whether they are receiving a placebo or a medicinal drug
44
blood clot
A structure formed from fibrin fibres which traps red blood cells and platelets in response to the damage of a blood vessel
45
blood group
Also known as blood type - the classification of blood depending on which antigens are present on the plasma membrane of the erythrocytes
46
blood pressure
The force exerted by the blood against the walls of the blood vessels
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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
48
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
49
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
50
bradycardia
A slowness of the heartbeat, usually under 60 beats per minute in adults
51
broad-spectrum antibiotics
Antibiotics that are effective against a large variety of organisms
52
bronchi
The two main branches from the trachea that go into the lungs
53
bronchioles
One of the smaller subdivisions of the branched bronchial tree that connects the trachea to the alveoli
54
buffer
A chemical solution which has the ability to absorb or donate hydrogen ions (protons) to maintain the pH of the solution
55
bundle of His
Specialised cardiac muscle fibres that run from the atrioventricular node to the base of the heart
56
Calvin cycle
The reactions of the light-independent stage of photosynthesis
57
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
58
capillaries
Very small blood vessels where water, solutes, and respiratory gases are exchanged with body tissues
59
capsid
The outer protein coat of a virus
60
cardiac output
The amount of blood the heart pumps through the circulatory system in a minute
61
carcinogen
A chemical or form of radiation that causes cancer
62
cardiac monitor
A device for the continuous observation of cardiac function
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carrier protein
Protein found within a cell membrane that carries a specific molecule or ion across the membrane by active transport
64
casparian strip
A band of impermeable suberin found in the walls of endodermal cells in plant roots
65
catalyst
A substance that speeds up the rate of the reaction without itself being altered or used up in the chemical reaction
66
cell cycle
The series of event that take place in a cell leading to its division to produce two daughter cells
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cell surface membrane
The phospholipid bilayer that forms the membrane surrounding the outside of a cell - sometimes known as the plasma membrane
68
cellulose
A polysaccharide made from the condensation of many β-glucose molecules to form fribrils. It is used to form plant cell walls
69
cell wall
A freely permeable structure lying outside of the cell surface membrane of plant, fungal, and bacterial cells
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centrifugation
The process of separating molecules and organelles on the basis of their density by spinning them at different speeds in a centrifuge
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centriole(s)
Two cylinders composed of microtubules which are involved in the process of mitosis and cell division in some eurykaryotic cells
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centromere
The region of a chromosome that joins two sister chromatids and attaches to spindle fibres during mitosis
73
cerebellum
A structure located at the back of the brain in vertebrates, which coordinates and regulates muscle activity
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cerebrum
The largest part of the brain which is formed as two hemispheres
75
channel protein
A protein pore that spans a cell membrane to enable water soluble molecules and small ions to passively cross the membrane
76
chemotherapy
Destroying cancerous cells using drugs that affect cancerous cells more than other cells in the body
77
chiasmata
The points at which crossing over occurs between homologous chromosomes
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chi-squared test
A statistical test that enables an investigator to determine whether differences exist between two sets of data
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chloroplast
The organelle in which photosynthesis occurs
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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
81
chorionic villus sampling
A procedure for sampling fetal cells from the placenta
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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
83
chromatography
A technique used to separate substances in a mixture according to differences in their solubility
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chromosome
A single DNA molecule, linear, and associated with proteins such as histones in eukaryotic cells
85
chromosome mutation
A random change to the structure or number of chromosomes due to translocation or non-disjunction
86
chronic disease
A disease that lasts a long time and has symptoms that worsen over time
87
classification
The organisation of organisms into groups based on similarities in biochemistry, anatomy, behaviour and embryology
88
climax community
The stable community of species that exists at the end of ecological succession
89
clinical trials
A series of controlled studies in which a new medicinal drug is tested
90
codominant
Alleles at a gene locus that are both expressed and therefore both contribute to the phenotype
91
coenzyme
An organic non-protein molecule that binds temporarily with the substrate to the active site in order for an enzyme to function
92
codon
A sequence of three bases on the template strand of the DNA or the mRNA that codes for one amino acid
93
cofactor
A molecule or ion which aids the function of an enzymes - it can be an inorganic ion or a coenzyme
94
cohesion
The attraction between water molecules due to hydrogen bonding
95
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
96
colony morphology
The characteristic of a bacterial colony, in cultures, in terms of shape, colour, edge and elevation
97
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
98
communicable
A disease or infection caused by microorganisms capable of being communicated or transmitted to another organism
99
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
100
compartmentalisation
The use of intracellular membranes to separate metabolic processes within the cell e.g. the nuclear envelope around the nucleus
101
compensation point
The light intensity at which the rate of photosynthesis matches the rate of respiration
102
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
103
complementary therapy
Treatments that involve procedures that are not part of mainstream medicine e.g. acupuncture, aromatherapy
104
computed tomography (CT)
A radiographic technique that produces an image of a detailed cross section of tissue
105
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
106
correlation
The relationship between two variables e.g. a linear relationship
107
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
108
cotyledon
In seeds, the part of a plant embryo that becomes the first leaf
109
countercurrent multiplier
Any mechanism that uses energy and countercurrent flow to establish concentration gradients
110
cristae
Fold in inner membrane of mitochondria
111
crossing over
The process in which homologous chromosomes exchange alleles during prophase I of meiosis
112
cytokines
Cell signalling molecules which are used for communication between cells, allowing some cells to regulate the activity of others
113
cytokinesis
The division of a cell to form two new cells
114
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
115
deamination
The removal of the amino group from an amino acid
116
defibrillator
An apparatus used to control heart filbrillation by application of an electric current to the chest wall or heart
117
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
118
degenerate code
Situation where more than one codon codes for the same amino acid
119
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
120
denitrification
The production of nitrogen gas from nitrates in the soil
121
deoxyribonucleic acid (DNA)
The molecule responsible for the storage of genetic information
122
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
123
diabetes mellitus
A condition in which a person cannot control blood glucose levels
124
diaphragm
A sheet of muscular and fibrous tissue separating the chest cavity from the abdominal cavity. Plays an important role in ventilation
125
diastole
Period of relaxation and repolarisation of the cardiac muscle when the chambers fill with blood
126
dicotyledons
A plant that produces flowers and has two cotyledons (seed leaf) inside the seed, which develops wide leaves with veins
127
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
128
differentiation
The development of unspecialised cells to form specialised cells
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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)
130
diploid
Cells that have two copies of each chromosome
131
disaccharide
A dimer made from the condensation of two monosaccharides joined by a glucosidic bond
132
disulfide bond
A S-S chemical bond between two sulfur atoms in the R group of two cysteine amino acids
133
dominant
An allele that is expressed in the phenotype, the presence of which prevents a recessive allele from being expressed
134
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
135
double-blind trials
A clinical trial in which neither participants nor scientists are aware whether a placebo or medicinal drug has been issued
136
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
137
ecosystem
The organisms and non-living components of a specific area, and their interactions
138
efferent
Leading away from or outgoing (e.g. an efferent nerve or blood vessel is one that leads away from a tissue or organ
139
electrocardiogram (ECG)
A graph showing the electrical activity in the heart during the cardiac cycle (heartbeat)
140
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
141
electrolytes
Ions such as sodium, potassium, and chloride dissolved in water
142
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
143
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
