Biology A Level > Key Words > Flashcards

Key Words Flashcards

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1
Q

Acetylcholine

A

A type of neurotransmitter that is used for communication between neurones.

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2
Q

Actin:

A

A type of protein filament found in myofibrils. It forms thin filaments consisting of two
long twisted chains.

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3
Q

Actinomyosin bridge:

A

The cross-bridge formed when a myosin head attaches to the myosin binding site on an actin filament.

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4
Q

Action potential:

A

The temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse.

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5
Q

Adenylate cyclase

A

An enzyme that catalyses the conversion of ATP to cAMP.

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6
Q

Adrenaline:

A

A hormone that is secreted by the adrenal glands under stressful conditions. It
increases blood glucose concentration by activating enzymes involved in glycogenolysis.

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7
Q

Afferent arteriole:

A

The blood vessel that stems from the renal artery and supplies blood to
the nephron. It has a larger diameter than the efferent arteriole and divides into a complex
system of capillaries, the glomerulus.

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8
Q

All-or-nothing:

A

A principle that states that all stimuli above a certain threshold value will
generate the same size of action potential, regardless of the strength of the stimulus.

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9
Q

Anisotropic (A) bands:

A

The darker bands in a myofibril, which consist of overlapping actin
and myosin filaments.

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10
Q

Antagonistic muscles:

A

Pairs of muscles that work in opposite directions.

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11
Q

Antidiuretic hormone (ADH):

A

A hormone made by the hypothalamus and secreted by the posterior pituitary gland in response to a fall in blood water potential. It increases the
permeability to water of the distal convoluted tubule and the collecting duct, allowing more
water to be reabsorbed into the blood.

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12
Q

Ascending limb:

A

The limb of the loop of Henle that rises into the cortex. It is wider in diameter than the ascending limb and its walls are impermeable to water. Sodium ions are
moved out of the ascending limb by active transport.

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13
Q

Atrioventricular node (AVN):

A

A group of cells located between the atria that slow down the wave of excitation and pass it between the ventricles, along the bundle of His.

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14
Q

Atrioventricular septum:

A

A layer of non-conductive tissue between the right atrium and left
ventricle of the mammalian heart.

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15
Q

Autonomic nervous system:

A

A branch of the motor nervous system that carries nerve
impulses to muscles and glands. It controls involuntary activities and has two divisions: the
sympathetic nervous system and the parasympathetic nervous system.

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16
Q

Auxins:

A

A class of plant hormones that control cell elongation.

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17
Q

Axon:

A

A long fibre that conducts nerve impulses away from the cell body.

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18
Q

Bundle of His:

A

A collection of Purkyne fibres which run from the AVN down to the apex of
the ventricles.

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19
Q

Cell body:

A

The region of the neurone that contains the organelles, notably the nucleus and
the rough endoplasmic reticulum.

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20
Q

Central nervous system (CNS):

A

The brain and spinal cord.

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21
Q

Chemoreceptor:

A

A type of receptor found in the walls of the carotid arteries that detects changes in blood pH and transmits nerve impulses to the medulla oblongata. For example, if
blood pH decreases, chemoreceptors increase the frequency of nerve impulses to the
medulla oblongata.

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22
Q

Cholinergic synapse:

A

An excitatory or inhibitory synapse formed between neurones or
neurones and other effector organs. It uses the neurotransmitter, acetylcholine.

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23
Q

Collecting duct:

A

The final region of the nephron that collects urine from the distal convoluted
tubules and empties it into the renal pelvis. Its permeability to water is altered by ADH.

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24
Q

Cone cells:

A

A type of light receptor cell that transduces light energy into a generator
potential. Cone cells are concentrated in the fovea, detect light of high intensity, and lead to
colour images. One cone cell forms a synapse with a single bipolar cell, giving high visual
acuity.

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25
Control mechanism:
A self-regulating system consisting of five features: optimum point, receptor, coordinator, effector, and feedback mechanism.
26
Coordinator:
Coordinates information from the receptors and sends instructions to the effectors.
27
Cyclic AMP (cAMP):
A ‘second messenger’ involved in the action of adrenaline that activates protein kinase.
28
Dendrites:
Short, branched extensions of the cell body that receive nerve impulses from other neurones.
29
Dendrons
Extensions of the cell body which branch into smaller fibres, dendrites.
30
Depolarisation:
A sudden, temporary change in the membrane potential of a neurone in response to the transmission of a nerve impulse. The inside of the axon is less negative than the outside.
31
Descending limb:
The limb of the loop of Henle that dips down into the medulla. It is smaller in diameter than the ascending limb. The walls of the descending limb are permeable to water, so the filtrate loses water as it moves down.
32
Diabetes:
A disorder of metabolism in which blood glucose concentration is not regulated properly. There are two forms: Type I and Type II diabetes.
33
Distal convoluted tubule:
The twisted region of the nephron between the loop of Henle and the collecting duct. It controls blood pH by reabsorbing ions and alters the concentration of water and salts reabsorbed. Its permeability to water is altered by ADH.
34
Effector:
An organ, tissue, or cell that produces a response to a stimulus.
35
Efferent arteriole:
The blood vessel that carries blood away from the glomerulus and sub-divides to form a network of capillaries. Its diameter is smaller than the afferent arteriole, creating a build up of hydrostatic pressure in the glomerulus.
36
Z-line:
The line in the centre of each I band
37
Visual acuity:
The clarity of vision.
38
Unidirectionality
Describes synaptic transmission; synapses can only transmit information in a single direction, from the presynaptic neurone to the postsynaptic neurone.
39
Type I diabetes:
A form of diabetes (insulin-dependent) in which the body cannot produce insulin. It has an early, rapid onset and is treated using insulin injections.
40
Type II diabetes:
A form of diabetes (insulin-independent) in which the body does not respond to insulin due to the loss of or unresponsiveness of glycoprotein receptors. In some cases, the body may not produce enough insulin. It has a late, slow onset and is controlled by managing diet and exercise.
41
Tropism:
The growth response of a plant to a directional stimulus.
42
Tropomyosin:
A protein found in muscles that forms a fibrous strand wrapped around an actin filament
43
Transducer cells
Cells that convert one form of energy into an electrical signal.
44
Threshold value:
A certain size of stimulus that is required to generate an action potential.
45
Taxis:
A response to a stimulus that is directional, i.e. the movement of an organism towards or away from a stimulus
46
Target cells:
Cells with specific receptor proteins on their cell surface membranes, complementary to the shape of a particular hormone.
47
Synaptic vesicles:
Secretory vesicles located in the presynaptic neurone that store neurotransmitters. Upon fusion with the presynaptic membrane, their contents are released into the synaptic cleft.
48
Synaptic cleft:
A small gap between neurones across which a nerve impulse is transmitted via neurotransmitters.
49
Sympathetic nervous system:
A branch of the autonomic nervous system that is active | under stressful conditions. It stimulates effectors, speeding up activity.
50
Summation:
The build-up of neurotransmitters in the synaptic cleft, allowing low-frequency action potentials to trigger a new action potential in the postsynaptic neurone. There are two forms of summation: spatial and temporal.
51
Stretch-mediated sodium channel:
A type of sodium channel whose permeability to sodium changes upon distortion (e.g. pressure changes, stretching). They are found in the plasma membrane of the sensory neurone ending at the centre of the Pacinian corpuscle.
52
Stimulus:
A change in an organism’s internal or external environment that can be detected.
53
Rod cells:
A type of light receptor cell that transduces light energy into a generator potential. They are located at the periphery of the retina, detect light of low intensity and lead to black and white images. Many rod cells form a synapse with a single bipolar cell, giving low visual acuity.
54
Saltatory conduction:
The process by which a nerve impulse is propagated along a myelinated neurone. Depolarisation occurs at the nodes of Ranvier and action potentials jump from node to node, speeding up transmission.
55
Sarcomere:
Each repeating unit of striations between adjacent Z-lines
56
Sarcoplasm
The cytoplasm shared by muscle fibres. It consists of a high concentration of mitochondria and endoplasmic reticulum
57
Schwann cells:
Cells that wrap around the axon. They have a range of roles including electrical insulation, axon protection, nerve regeneration and phagocytosis.
58
Second messenger model:
The mechanism by which a hormone (e.g. adrenaline or glucagon) has an effect inside a cell by triggering the production of a second messenger such as cAMP.
59
Sensory neurone:
: A neurone that carries nerve impulses from the receptors to the CNS.
60
Sinoatrial node (SAN):
A group of cells in the wall of the right atrium that generate electrical activity. The SAN is often referred to as the heart’s pacemaker.
61
Skeletal muscle:
: A voluntary muscle responsible for movement. It makes up the majority of body muscle and is attached to the skeleton by tendons.
62
Sliding filament theory:
The mechanism by which a muscle contracts. During contraction, myosin filaments pull actin filaments to the centre of the sarcomere. The actin filaments slide along the myosin filaments. The sarcomere is shortened and the muscle length is reduced.
63
Slow-twitch muscle fibres:
A type of muscle fibre that contracts more slowly, with less power, over a greater period. They are adapted for aerobic respiration and enable endurance.
64
Sodium-potassium pump:
A carrier protein found in the plasma membrane of an axon. It actively transports three sodium ions (Na+ ) out of the axon for every two potassium ions (K+ ) that it pumps into the axon.
65
Spatial summation:
A type of summation involving the release of neurotransmitters from multiple presynaptic neurones. The concentration of neurotransmitter exceeds the threshold value and triggers an action potential in the postsynaptic neurone.
66
Presynaptic neurone:
The neurone before the synapse which releases neurotransmitters from synaptic vesicles into the synaptic cleft.
67
Protein kinase:
An enzyme that catalyses the conversion of glycogen to glucose.
68
Proximal convoluted tubule:
The twisted portion of the nephron between the renal capsule and the loop of Henle. Its walls consist of epithelial cells that are adapted for the reabsorption of glucose and water into the blood.
69
Purkyne tissue:
Specialised cardiac muscle fibres which conduct the wave of excitation from the AVN down to the apex of the ventricles.
70
Receptor:
Specialised structure that detects a specific type of stimulus
71
Reflex:
A rapid, automatic response to a sensory stimulus by the body. It serves as a protective mechanism.
72
Refractory period:
The time period after an action potential during which further action potentials are prevented. This ensures that action potentials can only be propagated in one direction. It limits the frequency of action potentials and ensures nervous impulses are discrete.
73
Renal (Bowman’s) capsule:
: The cup-like structure at the start of a nephron that surrounds the glomerulus. The inner layer of the capsule, through which filtration of the blood takes place, is composed of podocytes.
74
Repolarisation:
The re-establishment of the resting potential (-65mV)
75
Response:
A change in an organism as a result of a stimulus.
76
Resting potential:
An electrical potential difference of -65 mV across the membrane of an axon. The inside of the axon is more negative than the outside. The membrane is described as polarised.
77
Retina:
The inner layer of the mammalian eye. It consists of light receptor cells that act as transducers, converting light energy into electrical energy.
78
Rhodopsin:
The pigment found in rod cells which is broken down to create a generator potential
79
Distal convoluted tubule
The twisted region of the nephron between the loop of Henle and the collecting duct. It controls blood pH by reabsorbing ions and alters the concentration of water and salts reabsorbed. Its permeability to water is altered by ADH.
80
Effector:
: An organ, tissue, or cell that produces a response to a stimulus.
81
Efferent arteriole:
The blood vessel that carries blood away from the glomerulus and sub-divides to form a network of capillaries. Its diameter is smaller than the afferent arteriole, creating a build up of hydrostatic pressure in the glomerulus.
82
Excitatory synapse:
A synapse that produces new action potentials when neurotransmitters bind with receptor proteins on the postsynaptic neurone
83
Fast-twitch muscle fibres:
A type of muscle fibre that contracts more rapidly, with more power, over a shorter period. They are adapted for anaerobic respiration and intense activity.
84
Feedback mechanism:
The mechanism by which the change to a system, brought about by the effector, is detected by the receptor.
85
Fovea:
The point on the retina, opposite the pupil, that receives the highest intensity of light. It contains the greatest concentration of cone cells but no rod cells.
86
Generator potential:
Depolarisation of the membrane of a sensory receptor cell that occurs in response to a stimulus.
87
Glomerular filtrate:
The fluid produced by ultrafiltration of the blood into the renal capsule. It contains water, glucose, mineral ions and urea.
88
Glomerulus:
A bundle of capillaries located in the renal capsule which are adapted for the filtration of blood. They later merge to form the efferent arteriole.
89
Glucagon:
A hormone that is produced by α cells of the islets of Langerhans. It increases blood glucose concentration by activating enzymes involved in gluconeogenesis and the conversion of glycogen to glucose.
90
Gluconeogenesis:
The formation of glucose from sources that are not carbohydrate, e.g. amino acids and glycerol.
91
Glycogenesis:
The formation of glycogen from glucose in the liver.
92
Gravitropism:
A plant’s growth response to gravity.
93
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Biology A Level
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