organisms respond to changes in their internal and external environments Flashcards
1
Q
What is a stimulus?
A
Detectable change in the internal/external environment of an organism that leads to a response.
2
Q
What is the role of a receptor?
A
Detects stimulus, specific to one type of stimulus.
3
Q
What does a coordinator do?
A
Formulates a suitable response to a stimulus, e.g., nervous system / hormonal system.
4
Q
What is an effector?
A
Produces response to a stimulus, e.g., muscles / glands.
5
Q
Define taxis.
A
A simple, directional response determined by the direction of the stimulus.
6
Q
What is positive taxis?
A
Movement towards a favourable stimulus.
7
Q
What is negative taxis?
A
Movement away from an unfavourable stimulus.
8
Q
Give an example of positive phototaxis.
A
Single-celled algae move towards light.
9
Q
Give an example of negative phototaxis.
A
Earthworms move away from light.
10
Q
What is a kinesis?
A
A non-directional simple response used by mobile organisms that change speed or direction in response to a non-directional stimulus.
11
Q
How does an organism respond to negative stimuli in kinesis?
A
The rate of turning increases to change directions more to return to more favourable conditions quicker
12
Q
Define tropism.
A
The growth of part of a plant in response to a directional stimulus.
13
Q
What is positive phototropism?
A
Growth towards light.
14
Q
What is negative gravitropism?
A
Growth away from gravity.
15
Q
What is hydrotropism?
A
Growth of plant roots towards water.
16
Q
What are plant growth factors?
A
Hormone-like substances that influence growth.
17
Q
What is indoleacetic acid (IAA)?
A
A type of auxin that controls cell elongation in shoots.
18
Q
What is the acid growth hypothesis?
A
It explains how IAA increases the plasticity of cells by active transport of hydrogen ions.
19
Q
What does IAA do in roots?
A
Inhibits the elongation of cells.
20
Q
What is the role of IAA in phototropism for young shoots?
A
IAA accumulates on the shaded side, causing that side to elongate more.
21
Q
What is a reflex?
A
Involuntary, rapid response to a sensory stimulus.
22
Q
What is a reflex arc?
A
The pathway of neurons involved in a reflex.
23
Q
What are the components of a spinal reflex?
A
- Stimulus
- Receptor
- Sensory neuron
- Coordinator (intermediate neuron)
- Motor neurone
- Effector
- Response
24
Q
True or False: Reflex arcs require brain involvement.
A
False.
25
What is the function of receptors?
Sensory reception.
26
What is the resting potential?
The potential difference across the membrane when a cell is at rest.
27
What is a generator potential?
Change in potential difference when a stimulus is detected.
28
What is an action potential?
Electrical impulse along a neurone triggered by a sufficient generator potential.
29
What are Pacinian corpuscles?
Mechanoreceptors that detect mechanical stimuli such as pressure and vibrations.
30
Where are Pacinian corpuscles found?
Deep in the skin, especially on fingers, soles of feet, and external genitalia.
31
How do Pacinian corpuscles function?
Pressure deforms the corpuscle, widening sodium channels, allowing sodium ions to enter and create a generator potential.
32
What is the fovea?
Area of the retina with a high concentration of photoreceptors.
33
What does the optic nerve do?
Carries nerve impulses from photoreceptors to the brain.
34
What changes occur to the membrane potential when sodium ions diffuse into the sensory neurone?
The membrane becomes depolarised, producing a generator potential.
35
What does the generator potential create?
An action potential (nerve impulse).
36
What is the function of the optic nerve?
Carries nerve impulses from photoreceptor cells to the brain.
37
What is the blind spot?
The point where the optic nerve leaves the eye, with no photoreceptors present.
38
What type of neuron connects photoreceptors to the optic nerve?
Bipolar neuron.
39
What are rod cells and where are they found?
Photoreceptors found at the edge of the retina, sensitive to low light and monochromatic.
40
What are cone cells and where are they primarily located?
Photoreceptors found in the fovea, less sensitive to light and trichromatic.
41
What is retinal convergence?
The process by which multiple photoreceptor cells send signals to a single bipolar cell.
42
How many rod cells are typically found in each eye?
Around 120 million.
43
What is the significance of retinal convergence for rod cells?
It increases the chance of exceeding the threshold value for generating a potential.
44
What pigment is found in rod cells?
Rhodopsin.
45
What happens when light intensity is low?
Rod cells can detect it and generate a potential.
46
What is the visual acuity of rod cells?
Low visual acuity due to convergence.
47
What types of colors can cone cells detect?
Red, green, and blue.
48
How many cone cells are typically found in each eye?
Around 6 million.
49
What is the visual acuity of cone cells?
High visual acuity due to individual connections to bipolar cells.
50
What neurotransmitter is secreted by the parasympathetic nervous system?
Acetylcholine.
51
What neurotransmitter is secreted by the sympathetic nervous system?
Noradrenaline.
52
What are the two divisions of the autonomic nervous system?
Sympathetic nervous system and parasympathetic nervous system.
53
What is the function of the sinoatrial node (SAN)?
It is the pacemaker that controls the rhythm of the heartbeat.
54
What does the atrioventricular node (AVN) do?
Receives electrical activity from the SAN and provides a delay for ventricles to fill.
55
What is myogenic contraction?
Self-stimulation of cardiac muscle from within rather than external signals.
56
What role do Purkyne fibres play in the heart?
They convey electrical activity to the apex of the heart.
57
What is the role of baroreceptors?
Detect changes in blood pressure.
58
What are the two main forms of coordination in animals?
Nervous system and hormonal system.
59
How does the nervous system communicate?
Through nerve impulses and neurotransmitters.
60
How does the hormonal system communicate?
By producing hormones transported in the blood.
61
What is the difference in transmission speed between nervous and hormonal communication?
Nervous communication is rapid, hormonal communication is slow.
62
What are sensory neurones responsible for?
Transmitting nerve impulses from receptors to intermediate or motor neurones.
63
What are motor neurones responsible for?
Transmitting nerve impulses to effectors.
64
What are neurones?
Nerve cells specially adapted to carry nerve impulses.
65
What are sensory neurones?
Transmit nerve impulses from a receptor to an intermediate or motor neurone.
66
What are motor neurones?
Transmit nerve impulses from an intermediate or relay neurone to an effector.
67
What are intermediate or relay neurones?
Transmit impulses between neurones, such as from sensory to motor neurones.
68
What is the function of Schwann cells?
Surround the axon, providing protection, electrical insulation, and aiding in nerve regeneration.
69
What is the myelin sheath?
A covering to the axon made up of Schwann cell membranes rich in myelin.
70
What is resting potential?
The difference in electrical charge inside and outside of a neurone when it is not conducting an impulse.
71
What maintains the resting potential?
Sodium-potassium pump and potassium ion channels.
72
Fill in the blank: The resting potential is typically around _______ mV.
-70 mV
73
What happens during depolarisation?
Sodium ion channels open, allowing Na+ to diffuse into the axon, reversing the membrane charge.
74
What is the threshold level for action potential?
-55 mV
75
What is hyperpolarisation?
A temporary overshoot of the electrical gradient where the inside of the axon becomes more negative than resting potential.
76
What is the refractory period?
A period after action potential where further action potentials cannot be generated due to inactivated Na+ channels.
77
True or False: All action potentials are the same size.
True
78
How does the brain perceive the size of a stimulus?
By the number of impulses passing in a given time and different neurons with different threshold values.
79
What is saltatory conduction?
The jumping of action potentials from node to node in myelinated axons.
80
What factors affect the speed of conductance?
Myelination, axon diameter, and temperature.
81
What happens to conduction speed as temperature increases?
Speed of conduction increases until around 40°C, after which proteins begin to denature.
82
What is the role of the sodium-potassium pump?
Transport sodium ions out and potassium ions into the neurone to maintain resting potential.
83
Fill in the blank: The electrical gradient preventing K+ from moving out is reversed during _______.
Repolarisation
84
What is the significance of the all-or-nothing principle?
If depolarisation reaches the threshold, an action potential is triggered; otherwise, nothing happens.
85
What is the structure of a synapse?
The gap/junction where one neurone communicates with another.
86
What are nodes of Ranvier?
Gaps between adjacent Schwann cells where depolarisation can occur.
87
What happens during repolarisation?
K+ ions diffuse out of the axon, restoring the negative charge inside.
88
What makes membrane potentials harder to maintain in a large axon?
Leakage
89
How does temperature affect the speed of conduction in neurons?
Increases as temperature increases up to around 40°C
90
What happens to proteins when the temperature exceeds 40°C?
They begin to denature and impulses fail to be conducted at all
91
What provides ATP for active transport in neurons?
Respiration controlled by enzymes
92
What is a synapse?
The gap/junction where one neurone communicates with another or with an effector
93
What is the synaptic cleft?
The gap between the cells where neurotransmitters diffuse across
94
What does the pre-synaptic neurone do?
Releases neurotransmitters after action potential travels along it
95
What is the role of the post-synaptic neurone?
Integrates signals to determine if it fires an action potential
96
What is contained in the synaptic knob?
Synaptic vesicles, mitochondria, and endoplasmic reticulum
97
What are neurotransmitters?
Chemicals that diffuse across the synaptic cleft and may trigger an action potential
98
What do synapses allow regarding impulses?
Transmit information from one neurone to another
99
True or False: A single impulse can initiate new impulses in multiple neurones at a synapse.
True
100
What is the process by which a neurotransmitter is released?
Action potential reaches the synaptic knob, causing vesicles to fuse with the membrane and release neurotransmitter
101
What is an excitatory synapse?
A synapse that produces new action potentials
102
What happens when an action potential reaches the synaptic knob?
Depolarization stimulates voltage-gated calcium ion channels to open
103
What causes synaptic vesicles to move to the presynaptic membrane?
Influx of calcium ions
104
What neurotransmitter is released at cholinergic synapses?
Acetylcholine (ACh)
105
What happens to acetylcholine after it binds to receptors?
It opens sodium ion channels, causing depolarization in the postsynaptic neurone
106
What enzyme hydrolyzes acetylcholine in the synaptic cleft?
Acetylcholinesterase (AChE)
107
What is the purpose of degradation of neurotransmitters like ACh?
Prevents continuous generation of a new action potential
108
What is unidirectionality in synapses?
Information only travels from pre-synaptic to post-synaptic neurone
109
What is spatial summation?
Many presynaptic neurones connect to one postsynaptic neurone and release neurotransmitters together
110
What is temporal summation?
A single presynaptic neurone releases neurotransmitter multiple times in quick succession
111
What is the effect of inhibitory synapses?
Induce hyperpolarization, making action potential less likely
112
What ions move into the postsynaptic neurone during inhibition?
Chloride ions (Cl-)
113
What ions move out of the postsynaptic neurone during inhibition?
Potassium ions (K+)
114
What type of neurotransmitter depolarizes the postsynaptic membrane?
Excitatory neurotransmitters
115
What type of neurotransmitter hyperpolarizes the postsynaptic membrane?
Inhibitory neurotransmitters
116
What determines whether acetylcholine is excitatory or inhibitory?
The location and type of receptor
117
What is a neuromuscular junction?
A synapse between a motor neurone and a skeletal muscle fibre.
118
Why are there many neuromuscular junctions along a muscle?
To ensure rapid and powerful muscle contraction when stimulated by action potentials.
119
What is a motor unit?
All muscle fibres supplied by a single motor neurone that act together as a single functional unit.
120
How does the number of motor units stimulated affect muscle force?
Fewer units are stimulated for slight force; more units are stimulated for greater force.
121
What happens when a nerve impulse reaches the neuromuscular junction?
Calcium ion channels open, causing synaptic vesicles to release acetylcholine.
122
What is the role of acetylcholine in muscle contraction?
It binds to nicotinic cholinergic receptors, altering membrane permeability to sodium ions.
123
What does acetylcholinesterase do?
Breaks down acetylcholine to prevent over-stimulation of the muscle.
124
What are the similarities between cholinergic synapses and neuromuscular junctions?
Both are unidirectional, have neurotransmitters transported by diffusion, and use sodium-potassium pumps.
125
How do stimulatory drugs affect synapses?
They create more action potentials in postsynaptic neurones.
126
What is an agonist in the context of synaptic transmission?
A substance that mimics a neurotransmitter and stimulates receptor activation.
127
What is an antagonist in the context of synaptic transmission?
A substance that blocks receptors, preventing neurotransmitter activation.
128
What are the three types of muscle in the body?
* Smooth * Cardiac * Skeletal
129
What is the role of antagonistic muscles?
Pairs of skeletal muscles contract and relax to move bones at a joint.
130
What is the sarcolemma?
The cell membrane of muscle fibre cells.
131
What is the function of transverse (T) tubules?
Spread electrical impulses throughout the sarcoplasm to reach all parts of the muscle fibre.
132
What is the sarcoplasmic reticulum?
A network of internal membranes that store and release calcium ions needed for muscle contractions.
133
What are myofibrils?
Long, cylindrical organelles made of proteins, specialized for contraction.
134
What are the two types of myofilaments?
* Thick myofilaments (myosin) * Thin myofilaments (actin)
135
What are I-bands and A-bands in myofibrils?
* I-bands: Light bands containing only thin actin filaments * A-bands: Dark bands containing thick myosin filaments
136
What are sarcomeres?
Short units that make up myofibrils, marked by Z-lines.
137
What is the sliding filament mechanism?
The process through which myosin and actin filaments slide over each other to contract sarcomeres.
138
What initiates muscle contraction?
The action potential causes depolarization in the sarcolemma and releases calcium ions.
139
What is the role of ATP in muscle contraction?
Provides energy for myosin heads to pull actin filaments along.
140
How does muscle relaxation occur?
Calcium ions are actively transported back into the sarcoplasmic reticulum, allowing tropomyosin to block binding sites.
141
What is the function of tropomyosin in muscle contraction?
Blocks the actin-myosin binding site in resting muscle.
142
What happens when nervous stimulation ceases?
Calcium ions are reabsorbed, tropomyosin blocks binding sites, and muscles relax.
143
What is actively transported back into the sarcoplasmic reticulum using energy from ATP hydrolysis?
Calcium ions
144
What does tropomyosin block to prevent myosin heads from binding?
Actin-myosin binding sites
145
What happens to the actin filaments when calcium ions are reabsorbed?
They slide back to their relaxed position
146
What visual evidence supports the sliding-filament mechanism?
Myofibrils appear darker where actin and myosin filaments overlap
147
What change occurs to the I-band during muscle contraction?
It becomes narrower
148
What remains the same width during muscle contraction?
A-band
149
What is the main energy source for muscle contraction?
Hydrolysis of ATP
150
List the three main ways ATP is regenerated.
* Aerobic respiration
* Anaerobic respiration
* ATP-phosphocreatine system
151
What type of muscle fiber has a large store of myoglobin?
Slow twitch
152
What is the contraction speed of fast-twitch muscle fibers?
Faster and more powerful
153
What type of respiration do slow twitch fibers mainly use?
Aerobic
154
What is homeostasis?
The maintenance of a constant internal environment within restricted limits
155
What surrounds the cells in the internal environment of an organism?
Blood and tissue fluid
156
What do fluctuations in internal and external conditions affect?
Homeostasis
157
What happens to enzymes if the temperature is too high?
They become denatured
158
What is the optimum temperature for enzyme activity in humans?
37°C
159
What occurs when blood glucose is too high?
Water potential of blood is reduced
160
What are the components of a self-regulating homeostatic system?
* Receptors
* Coordinator
* Effectors
161
What type of feedback mechanism counteracts changes to maintain stability?
Negative feedback
162
What is positive feedback?
Amplifies the effect of a change, enhancing it further away from the normal level
163
How do ectotherms control their body temperature?
By adapting their behavior to changes in external temperature
164
What physiological mechanisms do endotherms use to maintain body temperature?
* Vasoconstriction
* Shivering
* Hair raising
* Increased metabolic rate
165
What is the danger of blood glucose being too low?
Cells will be deprived of energy and can die
166
What hormones are involved in regulating blood glucose?
* Insulin
* Glucagon
167
What is glycogenolysis?
The hydrolysis of glycogen to glucose
168
What is gluconeogenesis?
The production of glucose from sources other than carbohydrate
169
What is the normal concentration of blood glucose?
5 mmol/dm³
170
What are the three sources of blood glucose?
1. Directly from the diet in the form of glucose
2. From glycogenolysis stored in the liver and muscle cells
3. From gluconeogenesis
171
What happens to blood glucose levels after eating?
Blood glucose levels increase after eating food containing carbohydrates
172
What causes blood glucose levels to decrease?
Not eating and after exercise
173
What enzymes does the pancreas produce for digestion?
Protease, amylase, and lipase
174
What hormones does the pancreas produce for regulating blood glucose concentration?
Insulin and glucagon
175
What are the islets of Langerhans?
Groups of hormone-producing cells in the pancreas
176
What do ɑ-cells in the islets of Langerhans produce?
Glucagon
177
What do ꞵ-cells in the islets of Langerhans produce?
Insulin
178
What is the first step in the negative feedback cycle when blood glucose is too high?
Receptors on ꞵ-cells in the pancreas detect high blood glucose concentration
179
What happens when blood glucose concentration is too low?
Receptors on ɑ-cells in the pancreas detect low blood glucose concentration
180
What is glycogenesis?
The conversion of glucose into glycogen
181
What is glycogenolysis?
The breakdown of glycogen to glucose
182
What is gluconeogenesis?
The production of glucose from non-carbohydrate sources
183
How does insulin lower blood glucose concentration?
1. Attaches to receptors on liver and muscle cells
2. Increases cell permeability to glucose
3. Activates glycogenesis
4. Increases the rate of respiration
184
What is GLUT4?
A glucose transporter channel protein stored in vesicles when insulin is low
185
What is the action of glucagon?
Raises blood glucose concentration
186
What happens when glucagon binds to liver cell receptors?
1. Activates glycogenolysis
2. Activates gluconeogenesis
3. Decreases the rate of respiration
187
What is the second messenger model?
The process by which hormones activate glycogenolysis inside a cell despite binding to receptors on the outside
188
What is Type I Diabetes Mellitus?
A disease where the body is unable to produce its own insulin
189
What causes Type I Diabetes?
An autoimmune response attacking beta-cells in the islets of Langerhans
190
What is a common treatment for Type I Diabetes?
Insulin therapy
191
What is Type II Diabetes Mellitus?
A condition where beta-cells do not produce enough insulin or body cells do not respond properly to insulin
192
What are common causes of Type II Diabetes?
Obesity, lack of exercise, age, and poor diet
193
What is a treatment method for Type II Diabetes?
Diet control, exercise, and medications like metformin
194
What is osmoregulation?
The homeostatic control of the water potential of the blood
195
What is the nephron?
The structure in the kidney where blood is filtered and useful substances are reabsorbed
196
What substances are typically found in urine?
Urea, water, dissolved salts, and other small substances
197
What does not normally appear in urine?
Proteins, blood cells, and glucose
198
What are the main parts of the mammalian kidney?
Fibrous capsule, cortex, medulla, renal pelvis, ureter, renal artery, renal vein
199
What is the structure of the nephron?
Afferent arteriole, glomerulus, renal (Bowman's) capsule, efferent arteriole, blood capillaries, proximal convoluted tubule
200
What is the efferent arteriole?
A vessel that leaves the renal capsule, has a smaller diameter to increase blood pressure, and branches into blood capillaries.
201
What is the role of blood capillaries in the nephron?
They surround the loop of Henle and distal convoluted tubule, reabsorbing mineral salts, glucose, and water.
202
What is the proximal convoluted tubule (PCT)?
A series of loops surrounded by blood capillaries, with walls made of epithelial cells having microvilli to increase surface area for glucose diffusion.
203
What is the loop of Henle?
A long, hairpin loop that extends from the cortex into the medulla of the kidney, consisting of an ascending limb and a descending limb.
204
What is the distal convoluted tubule?
A series of loops following the loop of Henle, surrounded by fewer blood capillaries than the proximal tubule.
205
What is the collecting duct?
A tube into which distal convoluted tubules from several nephrons empty, lined by epithelial cells, increasing in width as it empties into the kidney pelvis.
206
What are the four main stages of nephron function in osmoregulation?
* Formation of glomerular filtrate by ultrafiltration
* Selective reabsorption of glucose and water
* Maintaining a gradient of sodium ions in the medulla
* Reabsorption of water
207
What is ultrafiltration?
The process where blood is filtered in the glomerulus, forming glomerular filtrate by allowing water, glucose, urea, and mineral ions to pass while retaining blood cells and proteins.
208
What assists ultrafiltration in the kidneys?
Podocytes and capillary endothelium with gaps between cells allow filtrate to pass through.
209
What is selective reabsorption?
The process where useful substances like sodium ions and glucose are reabsorbed from the glomerular filtrate back into the blood.
210
How do sodium ions move during selective reabsorption in the PCT?
Sodium ions are actively transported out of epithelial cells into blood capillaries, creating a concentration gradient.
211
What adaptations do PCT epithelial cells have for reabsorption?
* Microvilli for increased surface area
* Infoldings at bases for substance transfer
* High density of mitochondria for ATP production
212
What is the role of the loop of Henle in osmoregulation?
To maintain a sodium ion gradient in the medulla, enabling water reabsorption.
213
Describe the ascending limb of the loop of Henle.
Wider, thick walls that are impermeable to water and actively transport sodium ions out.
214
What occurs in the descending limb of the loop of Henle?
Narrow, thin walls that are highly permeable to water, allowing water to leave the filtrate by osmosis.
215
What is the final water absorption process in the nephron?
Filtrate moves into the distal convoluted tubule and collecting duct, where water is reabsorbed by osmosis into the blood.
216
What happens when blood has too low a water potential?
More water is reabsorbed from the nephron tubules, resulting in more concentrated urine.
217
What occurs when blood has too high a water potential?
Less water is reabsorbed from the nephron, leading to more dilute urine.
218
What is the role of osmoreceptors in the hypothalamus?
They detect changes in water potential and signal for the production of antidiuretic hormone (ADH).
219
What is the function of ADH?
Increases permeability of the collecting duct and distal convoluted tubules to water, promoting water reabsorption.
220
What triggers the release of ADH?
Detection of decreased water potential by osmoreceptors in the hypothalamus.
221
What is glucosuria?
The presence of glucose in urine, indicating possible diabetes mellitus or kidney dysfunction.
222
Fill in the blank: The nephron filters the blood to remove waste and selectively reabsorb _______.
[useful substances]
223
True or False: Blood cells and proteins can pass into the renal capsule during ultrafiltration.
False
