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Biology > Module 5.1 - Homeostasis and Communication > Flashcards

Module 5.1 - Homeostasis and Communication Flashcards

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1
Q

What is homeostasis? (2)

A
  • Maintenance of constant internal environment
  • Metabolic processes that respond to changes in an organism’s external and internal environment
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2
Q

Why does homeostasis occur? (1)

A
  • To increase the chances of survival by avoiding harmful environments
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3
Q

What is the change in the internal/ external environment called? (1)

A
  • Stimulus
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4
Q

Receptors? (3)

A
  • Detect stimuli
  • Specific to one type of stimulus
  • Can be cells or cell membrane proteins
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5
Q

Effectors? (2)

A
  • Cells that respond to stimulus
  • Muscles or glands
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6
Q

What is cell signalling? (4)

A
  • Cells communicated with other cells to produce a response
  • Nervous system communicate via secreting neurotransmitters
  • Hormonal system release hormones
  • Cell-surface receptors recognise these chemicals secreted
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7
Q

Why is homeostasis important? (2)

A
  • Controls internal environment to allow optimum functioning for cells
  • Controls temperature, pH and concentration of ions
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8
Q

Why is homeostasis important for enzyme control? (3)

A
  • Enzymes control the rate of metabolic reactions
  • If body temperature is too high, enzymes can become denatured leading to low metabolic activity
  • If body temperature is too low, metabolic rate & activity becomes slow
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9
Q

How do enzymes become denatured? (4)

A
  • Enzyme’s molecules vibrate too much
  • Hydrogen bonds break changing tertiary structure
  • Enzyme can no longer work as an efficient catalyst
  • Metabolic reactions are less efficient
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10
Q

What is negative feedback? (4)

A
  • Effectors responding to stimulus
  • To counteract a change where internal environment has been shifted away from the norm
  • Negative feedback may not work if change is too big
  • e.g. Huge drop in body temperature due to prolonged exposure to the cold
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11
Q

What is positive feedback? (4)

A
  • Effectors responding to stimulus to rapidly activate something
  • e.g. blood clot
  • To amplify a change to push internal environment away from its norm
  • Positive feedback isn’t apart of homeostasis
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12
Q

Describe the feedback process of a blood clot (4)

A
  • Platelets activated and chemical cascade begin
  • The increase in activating platelets is the positive feedback
  • Blood clot forms
  • Negative feedback begins to stop
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13
Q

What are the types of neurones? (3)

A
  • Sensory
  • Relay
  • Motor
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14
Q

Structure of a neurone generally? (3)

A
  • Cell body with nucleus
  • Dendrites and dendrons
  • Axon
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15
Q

Structure of myelin sheath? (2)

A
  • Made of Schwann cells
  • Between Schwann cells are nodes of Ranvier
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16
Q

Sensory neurone? (5)

A
  • Transmit impulses from receptors to CNS
  • Myelinated
  • Short dendrites
  • One long dendron
  • Short axon
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17
Q

Relay neurone? (3)

A
  • Transmit impulses between sensory and motor neurones
  • Non-myelinated
  • Many short dendrites
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18
Q

Motor neurone? (4)

A
  • Transmit impulses from CNS to effectors
  • Myelinated
  • Many short dendrites
  • Long axon
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19
Q

Steps in neuronal communications: (6)

A
  • Stimulus
  • Receptors detect
  • Impulses sent through the sensory neurone to CNS
  • CNS processes information and coordinates response
  • Impulses sent through the motor neurone to effectors
  • Effectors respond to stimulus
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20
Q

Why are sensory receptors known as transducers? (2)

A
  • They convert different forms of energy into electrical energy
  • Electrical energy = nerve impulses
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21
Q

Resting potential? (4)

A
  • Potential difference at rest = resting potential
  • Membrane is polarised at -70mV
  • Outside of membrane is relatively positively charged compared to inside membrane
  • As there are more positive ions outside of cell
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22
Q

Generator potential? (3)

A
  • Stimulus detected
  • Cell membrane excited
  • Difference in charge inside and outside cell = change in potential difference = generator potential
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23
Q

Action potential? (3)

A
  • The bigger the stimulus; the bigger the movement of ions; the bigger the change in potential difference
  • If potential difference is big enough it’ll trigger an action potential
  • Weak stimulus = weak generator potential = no action potential
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24
Q

Threshold level (1)

A
  • Level of generator potential needed for action potential
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25
How is resting potential maintained? (2)
- Membrane permeability - Sodium-potassium pumps
26
Membrane permeability: (4)
- Membrane isn't permeable to Na+ - Na+ can't diffuse back in - Creates sodium ion electrochemical gradient - Membrane is permeable to K+
27
Sodium-potassium pumps? (3)
- 3 Na+ ions move out of neurone for every 2 K+ that move in - K+ move through K+ channels on membranes - ATP is used for this process
28
What is the cell membrane when it is stimulated? (1)
- Depolarised
29
Sequence in action potential: (5)
- Stimulus - Depolarisation - Repolarisation - Hyperpolarisation - Resting potential
30
What happens to the cell membrane when a stimulus is detected? (5)
- Stimulus excites membrane - Na+ channels open - Membrane become permeable to Na+ - Na+ diffuse in down Na+ electrochemical gradient - Inside of neurone becomes less negative
31
What happens to the cell membrane at depolarisation? (3)
- Potential difference raised from -70mV to -55mV - More Na+ ions diffuse in - Positive feedback
32
What happens to the cell membrane at repolarisation? (5)
- Potential difference raised from -55mV to +30mV - Na+ channels close - Voltage-gated K+ channels open - K+ diffuse out down K+ electrochemical gradient - Negative feedback as restoration to resting potential begins
33
What happens to the cell membrane at hyperpolarisation? (3)
- K+ channels are slow to close - Overshoot of K+ diffusing out of membrane - Potential difference becomes more negative than resting potential
34
What happens to the cell membrane at resting potential? (2)
- Ion channels are reset - Refractory period finishes
35
Refractory period? (3)
- Period of cell membrane recovery - Na+ channels close during repolarisation - K+ channels close during hyperpolarisation
36
How does action potential move down the neurone? (4)
- As a wave of depolarisation - Cell 1 depolarises and initiates cell 2 to depolarise - Cell 2 depolarises - Cell 1 enters refractory period
37
The "all or nothing" principle? (4)
- When threshold is reached an action potential will fire - With the same change in voltage - No matter how big the stimulus is - Bigger stimulus do increase frequency of action potentials
38
Action potential in myelinated neurones? (6)
- Saltatory conduction - Myelin sheath = electrical insulator - Schwann cells prevent impulse passing - Impulse needs to jump at node of Ranvier - Node of Ranvier can become depolarised - Faster
39
Action potential in non-myelinated neurones? (2)
- Impulses travel down whole length of axon membrane - Slower than saltatory conduction
40
What is a synapse? (1)
- A junction between a neurone and another neurone or a cell
41
What happens at the presynaptic neurone? (6)
- Action potential reaches synaptic knob - Triggers Ca2+ influx - Causes voltage-gates Ca2+ channels to open - Ca2+ diffuse into synaptic knob - Cause neurotransmitters vesicles to fuse with presynaptic membrane - Neurotransmitters leave via exocytosis
42
What happens at the synaptic cleft? (4)
- Neurotransmitters released into synaptic cleft - Diffuse across to postsynaptic membrane - Bind to specific receptors - Triggers action potential in the postsynaptic neurone
43
What happens at the postsynaptic neurone? (2)
- Action potential triggers opening of sodium channels - Influx in Na+ causes depolarisation
44
What happens to the neurotransmitters after an impulse passes through the synapse? (2)
- Neurotransmitters are removed from cleft and broken down by enzyme - They return to the synaptic knob to be reused
45
What is an excitatory synapse? (1)
- Depolarises postsynaptic neurone to trigger action potential
46
What is an inhibitory synapse? (2)
- Hyperpolarised postsynaptic neurone - Prevents an action potential
47
What is an synaptic divergence? (2)
- One neurone connect to many neurones - Information can be dispersed to many parts of the body
48
What is an synaptic convergence? (2)
- Many neurones connect to one neurone - Information can be amplified
49
What is summation? (2)
- Neurotransmitters combine to excite the postsynaptic neurone to meet the action potential threshold - Happens when the stimulus is weak
50
Types of summation? (2)
- Spatial - Temporal
51
Spatial summation? (3)
- Synaptic convergence - Many impulses can be coordinated into one amplified impulse - Increases chance of action potential threshold to be met
52
Temporal summation? (3)
- Two or more impulses arrive in quick succession from the same presynaptic neurone - Shortens frequency of impulses arriving - Increases chance of action potential threshold to be met
53
Why are receptors only on the postsynaptic neurone? (1)
- To ensure impulse only moves in one direction
54
Hormonal system? (1)
- Made of endocrine glands and hormones
55
Endocrine glands? (1)
- Secretes hormones
56
Hormones? (3)
- First messengers - Chemical messengers that travel through the bloodstream - Bind to specific receptors called target cells
57
What happens when a first messenger binds to a target cell? (2)
- Triggers an enzyme in the cell membrane - Which catalyse the production of second messengers
58
What are second messengers? (2)
- Signalling molecules - Activate a cascade inside cell
59
Adrenaline? (3)
- First messengers that binds to receptors and activate enzyme adenylyl cyclase - Activated adenylyl cyclase catalyses the production of cyclic AMP (cAMP) from ATP - cAMP activates a cascade for Glycogenolysis
60
How can glands be stimulated? (2)
- Change in concentration of a substance - Electrical impulses
61
Structure of adrenal gland? (3)
- Outer part called cortex - Inner part called medulla - Both structures are involved in the response to stress
62
Cortex? (2)
- Secrete steroid hormones - Cortisol and aldosterone
63
Roles of cortisol and aldosterone? (3)
- Triggers gluconeogenesis to increase amount of energy available so body can respond to situation - Increasing blood volume and pressure by up taking sodium ions and water by kidneys - Supress the immune system
64
Medulla? (2)
- Secretes catecholamine hormones (modified amino acids) - Secretes adrenaline and noradrenaline
65
Roles of adrenaline and noradrenaline? (3)
- Make energy by increasing heart and breathing rate - Glycogenolysis - Constricts blood vessels so that blood is diverted to the brain and muscle
66
Ectotherms? (5)
- Internal temperature is dependent on external temperature - Cannot regulate internal temperature through homeostasis - Rely on changing their behaviour - Metabolic rates are higher at higher temperatures - Generate little heat
67
Endotherms? (3)
- Internal temperature is not dependent on external temperature - Regulate internal temperature through homeostasis - Have high metabolic rates and generate a lot of heat
68
Mechanisms to reduce body temperature: (3)
- Sweating - Hair lie flat - Vasodilation
69
Sweating? (1)
- Water in sweat evaporates from the surface of the hot skin cooling the body down
70
Hair lie flat? (3)
- Erector pili muscles relax and hair lie flat - Less air is trapped in hairy insulating layer - Heat can be lost easier
71
Vasodilation? (2)
- Arterioles near skin dilate for more blood in the capillary - More heat is loss through radiation
72
Mechanisms to increase body temperature: (5)
- Shivering - Less sweat - Hair stands up - Vasoconstriction - Hormones
73
Shivering? (2)
- Muscles contract in spasms - Makes body shiver to produce more heat through increased respiration
74
Less sweat? (1)
- Less sweat is secreted to reduce heat loss via evaporation
75
Hairs stand up? (3)
- Erector pili muscles contract - Trapping more air within the hairy insulating layer - Reduces heat loss
76
Vasoconstriction? (2)
- Arterioles near skin constrict for less blood in the capillary - Less heat is loss through radiation
77
Hormones? (2)
- Adrenaline and thyroxine are released - Increase metabolism so more heat is produces
78
What is role of the hypothalamus in controlling body temperature? (1)
- Hypothalamus receives information from thermoreceptors and coordinates a response to increase or reduce temperature
79
Types of thermoreceptors: (2)
- Thermoreceptors in hypothalamus detects change in internal temperature (through blood temperature) - Thermoreceptors in the skin (peripheral temperature receptors) detect external temperature
80
How are the levels of glucose controlled? (1)
- Through the hormonal system with the help of insulin and glucagon
81
From where are insulin and glucagon secreted from? (3)
- From a cluster of cells called the Islets of Langerhans - Alpha cells secrete glucagon - Beta cells secrete insulin
82
Role of insulin and glucagon: (2)
- Insulin lowers blood-glucose concentration - Glucagon increases blood-glucose concentration
83
How does insulin work? (3)
- Binds to receptors on liver and muscles cell membranes which increases its permeability to glucose so that more glucose is taken up by cells - Activates enzymes involved in glycogenesis - Increases the rate of respiration of glucose
84
How does glucagon work? (2)
- Binds to receptors on liver cell membranes and activates enzymes involved in glycogenolysis and gluconeogenesis - Decreases the rate of respiration of glucose
85
When do beta cells secrete insulin? (1)
- When cells are depolarised
86
How do beta cells secrete insulin? (5)
- Glucose enters cell by facilitated diffusion - More glucose in beta cell causes the rate of respiration to increase - More ATP is produced which triggers K+ ion channels to close - This causes a build-up of K+ ions inside the cell and the cell become depolarised - Depolarisation triggers Ca2+ channels to aid insulin-stored-vesicles to leave the cell via exocytosis
87
When does diabetes occur? (1)
- When blood glucose concentration is not controlled
88
Type 1 diabetes? (6)
- Auto-immune disease where body attacks beta cells - No insulin is produced - So when blood glucose concentrations rises it remains high - Glucose can't be absorbed by the kidney and is excreted through urine - Develops in children or young adults - Can be hereditary
89
How do you treat Type 1 diabetes? (3)
- Insulin therapy through insulin injections or insulin pumps - Islet cell transplantation - Lifestyle changes such as monitoring diet and increased physical activity
90
Type 2 diabetes? (3)
- Beta cells don't produce enough insulin or insulin receptors are faulty - Develops later on in life - Linked to obesity
91
How do you treat Type 2 diabetes? (3)
- Lifestyle changes such as eating a balanced diet, regular exercise and loosing weight - Medication such as metformin, sulfonylureas and thiazolidinediones - Insulin therapy
92
Why is using genetically modified bacteria to produce insulin a good alternative to animal pancreas extractions? (5)
- Cheaper - Larger quantities - GM bacteria makes human insulin which more effective than using pig or cattle insulin - Less likely to trigger and immune response - May be ethically and religiously preferred
93
How can stem cells be used to cure diabetes? (1)
- Can be grown in beta cells for transplantation

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