3.6 Organisms respond to changes in their internal and external environment Flashcards
1
Q
What is a taxis?
A
Movement towards or away from a environmental stimulus.
2
Q
What is a kineses?
A
A random and non-directional movement in response to a stimulus.
3
Q
What is the name of a taxis involving:
a) pressure
b) temperature
A
a) thigmotaxis
b) thermotaxis
4
Q
Why do woodlice prefer dark and damp conditions?
A
- Woodlice are crustaceans and have gills
- They need some water in order to get oxygen for respiration
- Being in the dark helps them to hide from predators
5
Q
What happens when an organism is in a beneficial environment (kineses)?
A
It turns less frequently and slows done so that it can remain in that environment
6
Q
What is the term for speed and rate of turning (kineses)?
A
Orthokinesis = speed
Klinokinesis = rate of turns
7
Q
What is a tropism?
A
Growth movement of a plant in response to a uni-directional stimulus
8
Q
Give one difference and one similarity between tropisms and taxis?
A
Similarity: both involve a directional movement in response to a stimulus
Difference: tropism is plants, taxis is animals (maggots, woodlice)
9
Q
What is IAA and where is it produced?
A
- Indoleacetic acid
- Produced in meristems
10
Q
Describe the action of IAA in phototropism in shoots.
A
IAA stimulates cell elongation in shoots:
- IAA produced in meristems and diffuses down plant
- IAA accumulates on shaded side of plant
- It binds to specific receptors on plasma membrane, causing prton channels to open
- Cells become more acidic, activating enzymes whcih weaken the cell wall
- More water enters cells, turgidity pressure increases and cells elongate
- Cells on one side elongate, causing plant to bend towards the light
11
Q
Describe the action of IAA in geotropism in the roots.
A
IAA inhibits cell elongation:
- IAA accumulates on the lower side of the root
- Upper side of root elongates, causing the root to bend downwards
12
Q
What are two benefits of geotropism?
A
- Gives the plant stabiltiy as roots can reach further down into the soil
- Gives the plant a better access to water found deep in the soil
13
Q
What happens to the growth of a plant root when the root tip is removed and why?
A
- Plant root continues to grow horizontally
- Root growth responds to gravity in the root tip
14
Q
Describe the path of a simple reflex.
A
- Stimulus
- Receptor
- Sensory neurone
- CNS (Relay neurone)
- Motor neurone
- Effector
- Response
15
Q
Why are simple reflexes important?
A
- Rapid and autonomic response that protects you from harm
- For example, if you were to touch a hot pan there would be a simple reflex. You would respond by lifting up your arm so that you aren’t burnt for longer.
16
Q
Describe how the pascian corpuscle responds to the stimulus of pressure.
A
- Stimulus distorts the lamella
- Causing some stretch-mediated Na+ channels to open, cations diffuse in
- This increases the potential of the axon, once the action potential threshold is met the voltage-gated Na+ channels open
- Depolarisation down the nuerone
- The larger the pressure stimulus the more Na+ that diffuse in
17
Q
What are the differences between rod and cone cells?
think: colour, location, acuity, sensitivity in low light
A
- Rod cells only produce black/white image, cone cells produce coloured image due to red/blue/green sensitive cones
- Rod found in periphery of retina, cone in fovea
- Rod cells have hgiher sensitivity in low light
- Cone cells have higher acuity
18
Q
What is acuity and why is it higher in cone cells?
A
Acuity = the ability to distinguish detail
- Each cone cell is connected to one bipolar neurone
- This means the brain is able to distingush between two close points in an image as it has recieved a different impulse from each close point
19
Q
Why do rod cells have a better sensitivity in low light levels?
A
- Many rod cells connected to one bipolar neurone
- Collectively they have a large enough generator potential to trigger an action potential (spatial summation)
20
Q
What are the pigments found in rod and cone cells? What happens to them?
A
Rhodopsin = rod
Iodopsin = cone
- Pigments become bleached
21
Q
Describe the valves found in the heart.
A
Atrioventricular valves
Semi-lunar valves
22
Q
What is the function of the heart tendoms?
A
- Stop the heart valves from inverting the wrong way.
- Maintains the unidirectional flow of blood
23
Q
Describe the path of electrical impulses through the heart.
A
- Electrical impulse arrives at sinoatrial node (SAN), causing the atria to contract
- Non-conductive tissue between the atria and ventricles stops the ventricles from contracting at the same time
- Then impulses travel to atrioventricular node (AVN)
- Impulses travel down Bundle of His
- Then impulses travel up the ventricle wall from the bottom to the top by the Purkyne fibres
- Ventricles contract
24
Q
What happens when chemoreceptors detect a low pH in the blood? Suggest why there would be a low pH as well?
A
- Exercise has lowered blood pH due to increased carbon dioixde and carbonic acid in blood
- Chemoreceptors in carotid artery wall detect change and send impulse to medulla oblongata in the brain
- Impulse from brain to SAN via the sympathetic NS
- This increases heart rate and so blood is pumped aorund the body more quickly and carbon dioxide pumped to lungs and removed more quickly
25
What happens when barorecptors detect high/low blood pressure?
- Baroreceptors in carotid artery wall detect change in bp and send impulse to medulla oblongata (brain)
- Impulse from brain to SAN via symapthetic NS (low bp) or parasympathetic NS (high bp)
- This will increase heart rate (sympathetic) or decrease heart rate (parasympathetic) which will change the blood pressure
26
What are the parasympathetic and symapthetic nervous system?
Parasympathetic = inhibits effectors, rest and digest
Sympathetic = stimulates effectors, flight or flight
27
What are the nuerotransmitters associated with the following nervous systems:
a) parasympathetic
b) sympathetic
a) acetylcholine
b) noradrenaline
28
What is a neurone?
A specialised cell that transmits nerve impulses in the form of action potentials
29
Describe the structures of the following neurones:
a) sensory
b) relay
c) motor
a) nucleus in the middle, long myelinated axon
b) short non-myelinated axon
c) long myelinated axon
30
Describe the all-or-nothing principle.
- Generator potential must reach the threshold value in order to produce an action potential
- All action potentials are the same size
31
What is the myeline sheath?
How does it help increase the nerve impulse speed?
- Membrane wrapped around Schwann cells along the axon
- Myelin sheath is an insulator, action potential cannot travel through so jump between the Nodes of Ranvier
- Elongates the local currents
32
Name the structures of a neurone.
- Dendrons, dendrites
- Nucleus
- Axon, Schwann cells, Nodes of Ranvier
- Terminal braches, synaptic terminal
33
Describe how the axon membrane potential changes when a stimulus is applied.
1. Resting potential- no net moevement of ions (-65mV)
2. Generator potential- stimulus causes some Na+ channels to open, cations diffuse in, membrane potential increases
3. Action potential and depolarisation- threshold value reached (-55mV) and voltage-gated Na+ channels open, influx of Na+, large increase in potential
4. Repolarisation- potential reaches +40mV, voltage-gated Na+ channels shut, K+ channels open, efflux of K+ down electrochemical gradient and membrane potential decreases
5. Hyperpolarisation- repolarisation overshoots, K+/Na+ pump helps membrane potential return to resting potential
34
Explain how the resting potential in a neurone is maintained when no pressure is applied.
- Membrane becomes more permeable to potassium ions and less permeable to sodium ions
- Na+ pumped out, K+ pumped in
35
How does an impulse propagate down a neurone?
- Na+ diffuse sideaways along axon, down electrochemical gradient
- Stimulate threshold (action potential) and voltage-gated Na+ channels open
- Localised electrical current is created
36
How does a body reognise a larger stimulus if all action potentials are the same size?
The frequency of action potentials
37
Explain 3 factors that increase the speed of conduction.
1. Wider axon diameter- less leakage of ions
2. Myelinated axon- saltatory conduction
3. High temeprature- increased KE
38
Why do nerve impulses only travel in one direction?
Refractory period
- Axon membrane potential more -ve than resting potential
- Voltage-gated Na+ channels remain closed for a small period of time
39
Why are synapses described as unidirectional?
- Only presynaptic knob has vesicles containing neurotransmitters
- Only the postsynaptic membrane has the specific receptors for these neurotransmitters
40
Describe the two types of summation.
1. Temporal - high frequency of action potentials from a single neurone
2. Spatial- many presynaptic neurones to one postsynaptic neurone
41
Describe the sequence of events that occur at a synapse.
- Action potenetial eneters presynaptic knob
- This causes the voltage-gated Ca2+ channels to open, influx of calcium ions
- Calcium ions cause vesicles of neurotransmitters the move closer to presynaptic membrane and then fuse to release neurotransmitters into synpatic cleft
- Nuerotransmitter diffuses down concentration gradeitn across synaptic cleft and binds to specific receptors on postsynaptic membrane
- Ligand-gated Na+ channels open, influx of Na+ into postsynaptic neurone
- Possibly stimulating an action potential
- Remaiing neurotransmitters in synaptic cleft are broken down by enzymes or there is a reuptake back into presynatic neurone
42
Name and describe the work of an inhibitory transmitter.
GABA
- Binds to receptors on ligand-gated Cl- channels, influx of Cl- into postsynaptic neurone
- Opens K+ channels, efflux of K+ out of postsynaptic neurone
- Neurone becomes more negative, harder to reach threshold for action potential
43
What is different about a neuromuscular junction?
- Only neurotransmitter is acetycholine
- Motor neurone to muscle
- Only excitatory, never inhibitory
44
How do neurones and their synapses orevent over-stimulation?
Acclimitisation
45
Give 3 ways a drug can interfer with a synapse.
1. Inhibit the action of enzymes used to break dwon excess neurotransmitters in synaptic cleft
2. Block the neurotransmitter receptor on postsynaptic membrane
3. Block the Ca2+ channels so vesicles cannot release neurotransmitter into synaptic cleft
46
Describe the structure of muscle fibres.
- Muscle fibre made up of many myofibrils (organelles)
- Myofibril made up of repeating unit of sarcomeres
- Sarcomeres made up of myofilaments: actin and myosin
47
Describe the structure of actin and myosij.
Actin = thin filament, tropomysoin + troponin
Myosin = thick filament, bulbous head
48
Describe the structure of actin and myosij.
Actin = thin filament, tropomysoin + troponin
Myosin = thick filament, bulbous head
49
Describe the main structures of a sarcomere.
Sarcolemma = cell surface membrane
Sarcoplasm = cytoplasm
Sarcoplasmic reticulum
T-tubules = cytoplasm projections
50
What is the function of t-tubules and the sarcasplasmic reticulum in the sarcomere?
- T-tubules act as cytoplasm projections which action potentials to the SR
- SR contains the Ca2+ ions for muscle contraction
51
Through which part of the nervous system does the skeletal muscle contract?
Somatic NS
52
Describe the key details on a diagram of a sarcomere.
- Z lines
- M line
- H zone = only myosin filaments
- Light band = isotropic, just actin
- Dark band = anisotrpic, actin + myosin overlap
53
Describe the differences between slow and fast twitch fibres.
- Slow exhibit more aerobic respiration, fast are anaerobic
- Slow twitch fibres appear more red than fast due to the myoglobin store of oxygen, fast twitch are pale
- Slow twitch fibres have more continuos and slow contractions, fast twitch fibres contract more rapidly
54
What is the advantage of slow twitch muscle fibres during exercise?
- Increase indurance
- Delay onset of anaerobic respiration and muscle fatigue (lactate build up)
55
What happens when an action potential reaches the sarcoplasmic reticulum?
- Voltage-gated Ca2+ channels open
- Influx of calcium ions into sarcoplasm
56
What are the two roles of Ca2+ ions in muscle contraction?
- Activate ATPase to hydrolyse ATP, releasing the energy required to re-cock the mysoin head into the correct orientation for binding to actin
- Cause a conformational change in tropomyosin, exposing the binding site for myosin on actin
57
Describe the sliding filament mechanism.
- Ca2+ ions bind to tropomyosin, causing a conformational shape change in actin to expose the binding site for myosin
- Myosin and actin form cross-bridge
- ADP and Pi leave myosin head, causing the myosin head to tilt and enter a low energy state
- This causes a power-stroke, where actin slides towards the M-line
- The cross-bridge breaks as ATP binds to myosin head
- Ca2+ ions activate ATPase to hydrolyse ATP, this releases the enrgy required to re-cock the myosin head into the correct orientation for binding to actin
- Cross-bridge reforms
58
How does a mucle relax?
- Ca2+ is actively transported into the sarcoplasmic reticulum
- This returns the shape of tropomyosin + troponin to normal, myosin binding site no longer exposed
- Antagonistic muscle pair contracts, seperating actin and myosin
59
What is the role of phosphocreatine?
- Extra supply of Pi
ADP + cPi → ATP
60
What is homeostasis?
The maintenance of a constant internal environment within narrow limits despite changes in the external and internal environments.
61
What 4 features of the tissue fluid affect the activities of the cell?
1. Temperature (KE)
2. Glucose concentration (osmosis)
3. pH (OH- and H+)
4. Water balance of the body (osmosis)
62
What is the role of tissue fluid?
- Bathes the cells and helps supply them with nutrients as well as remove waste products.
- Creates a stable environment for the survival and function of cells.
63
What is negative feedback?
- Deviation from the norm detected by receptors
- Receptors initiate a response at the effectors, reversing any changes
- Maintains the optimum state
64
What is positive feedback?
- The reinforcement of the change detected by receptors
- This pushes the parameter further and further away from the optimum
- Destabilizes the system and does not return the system to the optimum state
65
Suggest why effective homeostasis depends on negative rather than positive feedback systems.
- Homeostasis seeks to maintain the optimum state of a system by dynamic equilibrium, returning them to the optimum state when they deviate
- Negative feedback does this
- Positive feedback, however, pushes the parameter further and further away from the optimum
66
Discuss the principles of homeostasis.
- *Definition of homeostasis*
- The change is detected by a receptor which is signalled to other parts of the body by the endocrine/nervous sytem
- Coordinator sends intructions to effector
- Negative feedback mechanism returns ssystem to optimum
- Required as cel/enzyme function impacted by conditions like temperature
- Increase in temperature causes enzymes to denature, enzyme activity slows
67
What is an endotherm?
Mammal, birds
Animals which derive their heat from metabolic activities, they maintain their internal body temperature independent of the external environment.
68
What is an ectotherm?
Reptiles, amphibians, fish, insects
Animals which gain heat energy from the external environment, therefore the environments they can survive in are limited.
69
What behavioural adaptions to ectotherms have?
- Hide in burrows (shade)
- Change body shape (SA for radiation from Sun)
- Change orientation of body towards/away from Sun
- Increase breathing movements (water vapour)
- Move into cooler mud/water (high heat capacity of water)
70
What mechanisms do endotherms have to cool down?
- Sweating (evaporative cooling)
- Hairs are lowered
- Vasodilation
71
What mechanisms do endotherms have to maintain and release heat energy?
- Shivering
- Increased metabolic activity
- Vasoconstriction
- Hairs stick up
- Decreased sweating (evaporative cooling)
72
Describe and explain how vasodilation/vasoconstriction impacts the body?
Vasoconstriction = blood vessels constrict, decreased blood flow to skins surface, less radiaition of heat energy
Vasodilation = blood vessels dilate, greater blood flow to skins surface, increased radiation of heat energy
73
What is evaporative heat loss?
Heat lost as water evaporates from the skin's surface.
Energy used to change water from a liquid to gas has a cooling effect on the body.
(panting, sweating)
74
How does an endotherm detect a change in internal body temperature and respond to this change?
- Hypothalamas detects chnage in blood temperature
- Skin receptors detect change in external temperature
- Nerve impulse sent to effectors which carry out mechanisms (sweating etc.) to help retur the body temperature to the optimum (37° in humans)
75
What ar two positives of endothermy compared to exothermy?
1. Enzymes at optimum temperatures
2. Endotherm is more independent of environment and can survive in a larger range of environments
76
What are the differences between the nervous system and endocrine system?
- Endocrine system is chemical (hormones), NS is electrical (impulses)
- Endocrine system has a slower speed of transmission
- Message travels through bloodstream in endocrine system but through neurones in NS
- Endocrine response is more permanent/irreversible, nervous system response is temporary/reversible
- The target area of the endocrine system is non-specific, NS is specific
77
What are the two types of glands, what is the function of each one?
Exocrine = secrete chemicals (enzymes) into a duct
Endocrine = secrete hormones
78
What is a hormone?
- Chemical messengers secreted by endocrine glands
- Carry information via the blood stream to a specific target organ or tissue
79
How does a steroid hormone act?
- Lipid soluble so can diffuse into cell across plasma membrane
- Binds to specific receptor in cytoplasm to form a hormone-receptor complex
- Complex can then enter the nucelus, binding to the DNA promoter region as a transcription factor or inhibiting the transcription of the gene
80
How does a non-steroid hormone act?
Second messenger model:
- Hormones derived from amino acids/proteins are water soluble, these can't pass the cell membrane
- Hormone is the first messenger and binds to a specific receptor on the membrane of a target cell
- This causes a cascade effect, and causes a conformational change is protein shapes down the membrane. This activates a 2nd messenger (cyclic AMP)
- This messenger brings about the particular reaction
81
Describe the tissue in the pancreas.
Exocrine, Islets of Langerhans:
- Alpha cells (glucagon)
- Beta cells (insulin)
- Blood capillaries
Endocrine, Acinar cells
Cells have many ribosomes, RER, golgi apparatus, mitchondria
82
What hormones do the following glands secrete:
a) Pituitary
b) Thyroid
c) Adrenal
d) Pancreas
e) Ovaries
f) Testes
a) FSH, ADH, LH, TSH
b) Thyroxine
c) Adrenaline
d) Insulin, glucagon
e) Oestrogen, progesterone
f) Testostrogen
83
Why is it important to maintain blood glucose levels?
Falls too low:
- Less glucose for respiration, cells deprived of energy and die
- Hypotonic solution, water moves into cells by osmosis, swell and burst
Too high:
- Hypertonic solution (low water potential in blood and tissue fluid), water moves out of cells by osmosis, cells shrivel and cytolysis/crenation
84
What do the following terms means:
a) Glycogenesis
b) Glycogenolysis
c) Gluconeogenesis
Include the role of insulin and glucagon in these reactions.
a) Conversion of glucose into glycogen (insulin)
b) Breakdown of glycogen into glucose (glucagon)
c) Production of glucose from sources other than carbohydrates (glucagon)
85
Describe the mechanism of decreasing blood glucose levels.
- Receptors on beta cells detect high blood glucose levels and secrete insulin into the blood
- Insulin acts on all cells (apart from red blood cells), binding to the glycoprotein receptors on the target cell
- Increases the number of glucose transport proteins (GLUT 4) on cell membranes through the fusion of vesicles containing GLUT 4 with the membrane
- More GLUT 4 so more glucose transported into cells by facilitated diffusion
- This activates enzymes that convert glucose to glycogen (glycogenesis)
86
Describe the mechanism of increasing blood glucose levels.
- Receptors on alpha cells detect high blood glucose levels and secrete glucagon into the blood
- Glucagon binds to glycoprotein receptors on the cell membrane on liver cells
- This activates enzymes that hydrolyse glycogen to glucose (glycogenolysis), glucose moves out the cell by facilitated diffusion
- Activation of enzymes involved in the production of glucose from other substances (gluconeogenesis), more fatty acids are used in respiration instead of glucose
87
What is the role of adrenaline in blood glucose concentration?
Adrenaline causes
88
What are adrenaline, insulin and glucagon an example of?
What molecule is involved in this?
Second messenger model and the cascade effect
Cyclic AMP
89
Describe the role of adrenaline.
Increases blood glucose concentration in times of stress/excitement:
- Adrenaline is the 1st messenger, binds to receptor in cell surface membrane of a liver cell
- Causes conformational shape change in protein, activating enzyme (adenyl cyclase) which converts ATP to cyclic AMP
- Cyclic AMP is a 2nd messenger which binds to another enzyme (protein kinase) which hydrolyses glycgon to glucose
- Glucose enters bloodstream by facilitated diffusion
90
Describe the structure of the kidneys and surrounding system.
- Cortex- outer, lighter region (renal capsules, convoluted tubules, blood vessels)
- Medulla- inner, darker region (loop of Henle, collecting ducts, blood vessels)
- Pelvis- collects urine into the ureter
- Renal artery- transports unflitered blood from aorta to kidneys
- Renal vein- transports filtered blood from kidney to vena cava
- Ureter- trasnports urine to bladder
- Bladder- stores urine
- Urethra- releases urine
91
Describe the path of the nephron.
1. Afferent arterioles
2. Renal capsule
3. Efferent arterioles
4. Proximal convoluted tubules
5. Loops of Henle (ascending/descending limb)
6. Distal convoluted tubules
7. Collecting duct
92
What are the blood capillaries and cells lining the renal capsule known as?
Glomerulus = capillaries
Podocytes = cells
93
What are the 4 steps of osmoregulation?
1. Ultrafiltration
2. Reabsorption
3. Maintaining gradient of Na+ ions
4. Reabsorption of water
94
What substances are/are not filtered out of the blood during ultrafiltration?
Are: amino acids, glucose, water, urea, ions
Are **not**: proteins, blood cells (too large to pass from basement membrane)
95
How does glomerular filtrate form?
- Afferent arteriole has wider diameter than efferent arteriole
- Large difference in blood pressure in either one
- High hydrostatic pressure in renal capsule, so substances are forced out of blood
96
What is the movement of the glomerular filtrate resisted by?
1. The endothelial cells of the blood capillary
2. The epithelial cells of the renal capsule (podocytes)
3. The basement membrane resistance
4. The high hydrostatic pressure of the renal capsule
5. The high water potential inside the renal capsule, or the low water potential in the glomerulus
97
What 2 ways does the renal capsule overcome the resitance faced during ultrafiltration?
1. Podocytes: highly branched cells which have gaps between the branches, offering a lower resitance pathway where substances don't have to pass through the cells
2. Glomerulus endothelium cells: circular pores which offer lower resistance path
98
How is the PCT adapted for reabsorption of substances back into the blood?
1. Many mitochondria
2. Microvilli
3. Infolding at base
99
Describe how each substance is reabsorbed:
a) glucose
b) amino acids
c) ions
d) urea
e) water
a) co-transport
b) co-transport
c) active transport
d) simple diffusion, lipid soluble
e) osmosis, water potential decreases in blood as substances are reabsorbed
100
What is the main role of the loop of henle?
Create and maintain a Na+ ion concentration gradient in the medulla, enabling the collecting duct to reabsorb water.
101
Explain how the loop of henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct.
What is the mechanism known as.
Counter-current multiplier
- In the ascending limb, Na+ ions are actively transported out. Decreases water potential in the medulla tissue fluid.
- Water moves out of descending limb by osmosis, increase in filtrate concentration down the limb
- Hair pin has lowest water potential, Na+ ions leave ascending limb by facilitated diffusion and then active transport further up
102
How does the collecting duct reabsorb water?
- Collecting duct is permeable to water
- As the filtrate moves down the collecting duct, water can be withdrawn the entire length as a water potential gradient is always maintained
- The water is carried away by the blood capillaries
103
What kidney adaptions do desert animals have and why?
Deeper medullas and longer loops of Henle
- More Na+ ions are actively transported out of the ascending limb enabling a larger water potential gradient to be established throughout the medulla
- More water can be reabsorbed by osmosis from the collecting ducts
- More concentrated urine, retains more water in dry conditions
104
What is the role of the distal convoluting tubule?
- Reaborbs ions and some water
- Controls blood pH by selectively reabsorbing ions
- Permeability controlled by ADH
105
What is the role of osmoreceptors and where are they found?
- Found in the hypothalamas
- Respond to water levels (osmosis), shrink at low water potential in blood and swell at high water potential.
- Shrinking causes the osmoreceptor to synthesise ADH which then passes along the axon in a vesicle to the lower end of the pituitary gland
- Increased frequency of impulses results in ADH being secreted into blood
106
Describe the effect ADH has on the collecting duct wall.
- ADH binds to specific receptors on the collecting duct wall
- This activates polymerase which causes vesicles containing aquaporon to move closer to the cell membrane and fuse with it
- Increase in the number of aquaporon channel proteins, so permeability of collecting duct wall increases
- Decrease in water potential of filtrate, increase in concentration of urine
- Thirst receptors triggered to tell the individual to seek out water
