Chapter 6- Response to change in environment Flashcards
Response
1
Q
What is a stimulus
A
A stimulus is a detectable change in the environment that can be detected by receptors
2
Q
Define Taxes
A
Taxes is a simple response in which an organism will move it’s entire body to a favourable stimulus or away from an unfavourable stimulus
3
Q
What is positive taxis
A
Positive taxis is when organism’s move towards a stimulus
4
Q
What is negative taxis
A
Negative taxis is when organism’s move away from a stimulus.
5
Q
Define kinesis
A
Kinesis is when an organism changes the speed of movement and rate it changes direction in response to stimuli. It is non-directional
6
Q
What is a plant growth factor and where is it produced
A
IAA (indoleactic acid) and it is produced in the shoot/root tips
7
Q
What is a tropism
A
A tropism is the term given to when plants respond via growth to stimuli
8
Q
Describe positive phototropism in shoots
A
Shoots need light for the light dependent reaction in photosynthesis, which is why plants grow towards the light.
1. The IAA will diffuse into the shaded side of the shoot, which results in a high concentration there
2. The IAA causes the cells on the shaded side to elongate more and this causes the plant to bend towards the light source.
9
Q
Describe negative phototropism in roots
A
Roots do not photosynthesis and do not require light and are more able to anchor the plant if they are in deep soil, away from light.
1. In roots a high concentration of IAA inhibits cell elongation causing root cells to elongate more on the lighter side and so the root bends away from light.
(Negative phototropism)
10
Q
Describe negative gravitropism in shoots
A
- IAA will diffuse from the upper side to the lower side of a shoot. If a plant is vertical, this causes the plant cells to elongate and the plant grows upwards (against gravity). If a plant is on its side, it will cause the shoot to bend upwards
(negative gravitropism)
11
Q
Describe positive gravitropism in roots
A
- IAA will diffuse to the lower side of the roots to inhibit growth, so that the upper side elongates and the root bends down towards gravity and anchors the plant in the soil.
12
Q
What is a stimulus
A
A stimulus is a detectable change in environment that can be detected by receptors
13
Q
Describe the response triggered by a stimulus
A
- Stimulus
- Receptor
- Coordinator
- Effector
- Response
14
Q
What is the nervous system made up from
A
The nervous system is made up from the peripheral nervous system (which includes the receptors, sensory and motor neurones)
and the central nervous system (which includes the brain and spinal cord)
15
Q
Name 3 receptors and what they detect
A
- Pacinian corpuscle (a barroreceptor)- detects pressure changes
- Rods (light)
- Cones (light)
16
Q
Describe the pacinian corpuscle structure and function
A
The pacinian corpuscle responds to pressure changes, these receptors occur deep in the skin, mainly in the fingers and feet
- It consists of a single sensory neurone wrapped with layers of tissues separated by gel
- The sensory neurone has special channel proteins in its plasma membrane called Stretch-mediated sodium channels: These channels open and allow sodium ions to enter the senosry neurone only when they are stretched and deformed
17
Q
Describe the resting state of the pacinian corpuscle
A
In the resting state, there are no deformed layers (caused by pressure being applied), and therefore sodium channels are too narrow for sodium to diffuse into the sensory neurone, therefore the resting potential is maintained
18
Q
Describe when pressure is applied to the pacinian corpuscle
A
When pressure is applied, it deforms the neurone plasma membrane, which stretches and widens the sodium channels so sodium ions diffuse in which leads to the establishment of a generator potential.
19
Q
Describe the cell body of a neurone
A
The cell body of the neurone contains the organelles found in a typical animal cell, including the nucleus, proteins and neurotransmitter.
20
Q
Describe features of a neurone
A
Dendrites: Carry action potentials to surrounding cells
Axon: Is the conductive, long fibre that carries the nervous impulse along the motor neurone
Schwann cells: Wrap around the axon to form the myelin sheath, which is a lipid and therefore does not allow charged ions to pass through it
Nodes of ranvier: Gaps between the myelin sheath
21
Q
Describe the resting potential
A
In the resting potential, there are more positive ions (sodium and potassium) outside in comparison to inside the axon. Therefore, inside of the axon is more negative at around -70mV/-65mV
22
Q
How is the resting potential maintained
A
The resting potential is maintained by a sodium potassium pump, involving active transport (ATP). The pump moves in 2 potassium ions inside the axon for every 3 sodium ions pumped out.
2. This creates an electrochemical gradient, which causes potassium to diffuse out and sodium ions to diffuse in. (HOWEVER AS THE MEMBRANE IS MORE PERMEABLE TO POTASSIUM IONS, MORE ARE MOVED OUT which results in the -70mV.)
3. Therefore, the inside of the axon is negatively charged in comparison to the outside
23
Q
Describe an action potential
A
An action potential is when the neurones voltage increases beyond a set point from the resting potential (which generates a nervous impulse)
An increase in voltage and depolarisation is due to the neurone membrane becoming more permeable to sodium ions
Once an action potential has been generated, it moves a long the axon across nodes of ranvier (because the myelin sheath is non-conductive)
24
Q
In what order does the action potential occur
A
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Refractory period
25
Describe depolarisation
1. A stimulus provides enough energy for voltage gated sodium ion channels in the axon membrane to open
2. Sodium ions then diffuse into axon and potassium diffuse out
-Depolarisation triggers all of the voltage gated sodium ion channels to open, which allows more sodium ions to diffuse into the axon
3. As the potential difference reaches -55mV (this is the threshold value), more channels open which allows the axon to reach +40mV.
4. An action potential is generated and peaks at +40mV, which then causes voltage gated sodium ion channels to close
26
Describe repolarisation
1. After an action potential has been generated, voltage gated sodium ion channels close and voltage gated potassium ion channels open, which allows potassium ions to diffuse out of the axon
2. This decreases the voltage, which means the inside of the axon becomes more negatively
3. This returns the potential difference back to -70mV
27
Describe hyperpolarisation
1. Voltage gated potassium ion channels remain open, allowing more potassium to diffuse out of the axon
2. This continues to happen for a brief period of time, which means the potential exceeds the resting potential and is about -80mV
28
Describe the refractory period
1. After an action potential has been generated, the membrane enters a refractory period when it cannot be stimulated because sodium channels are recovering and can't be opened
29
Describe the importance of refractory periods
1. Refractory periods ensure that discrete impulses are produced, meaning that an action potential cannot be generated immediately after another one to make sure that each is separate from another.
2. It ensures that action potentials travel in one direction. It stops the action potential from spreading out in 2 directions which would prevent a response.
3. It limits the number of impulse transmission. This is important to prevent over reaction to a stimulus and therefore overwhelming the senses
30
Describe synaptic transmission for a cholinergic synapse
1. An action potential arrives at the presynaptic membrane, which causes depolarisation of the membrane
2. This stimulates voltage-gated calcium ion channels to open
3. Calcium ions diffuse down an electrochemical gradient (from the tissue surrounding the synapse) into the cytoplasm of the presynaptic knob
3. This stimulates acetylcholine containing vesicles to fuse with the presynaptic membrane, which releases acetylcholine as a neurotransmitter across the synaptic cleft
4. Acetylcholine bind to a receptor binding site on voltage gated sodium ion channels, which allows sodium ions to diffuse into the postsynaptic knob
5. These sodium ions cause depolarisation of the postsynaptic membrane, which generates an action potential
6. The enzyme acetycholinesterase catalyses the hydrolysis of the Ach molecules into acetate and choline
7. Choline is reabsorbed back into the presynaptic membrane and reacts with acetyl coenzyme A
31
What are the 2 types of summation
1. Temporal summation- Only one neurone release neurotransmitter repeatedly over a short period of time to add up enough to exceed the threshold value
2. Spatial summation- Multiple impulses arriving simultaneously at different synaptic knobs stimulating the same cell body
32
List some drugs that have an impact on synapses
1. Dopamine
2. Morphine
3. Cocaine
4. Cannabinoids
5. MDMA
33
Describe dopamine's affect on synapses
Dopamine is a neurotransmitter that is involved in muscle control.
Excitatory neurotransmitter result in the production of an action potential
Inhibitory neurotransmitter prevent the production of an action potential. They do this by causing potassium ions to leave the postsynaptic membrane
Dopamine agonist- Produces the same affect as dopamine by binding to the same receptors
Dopamine precursor- Can be used to synthesise dopamine in the neurones
34
Describe morphine's affect on synapses
Chemicals called endorphins which are produced in the brain can stimulate the release of dopamine
1) The endorphins attach to opioid receptors found on presynaptic neurones that release dopamine molecules
2) Morphine is a chemical very similiar to the structure of endorphins and so it can provide pain relief by stimulating the release of dopamine
35
Describe cocaine's affect on synapses
36
Describe cannabinoids affect on synapses
37
Describe MDMA's affect on synapses
38
What is the all or nothing principle
The all or nothing principle is if the depolarisation does not exceed -55mV, then an action potential and the impulse is not produced.
-Any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage. Bigger stimuli instead increase the frequency of action potentials
This is important as it makes sure animals only respond to large enough stimuli, rather than every slight change in the environment.
39
What is an inhibitory synapse
Inhibitory synapses causde chloride ions to move into the postsynaptic neurone and potassium ions to move out.
The combined effect of negative ions moving in and positive ions moving out, makes the membrane potential to decrease to -80mV (hyperpolarisation), and therefore an action potential is highly unlikely.
40
Describe the neuromuscular junction and its function
This is a synapse between a motor neurone and a muscle and is very similar to a synaptic junction. However, instead of triggering an action potential, it triggers the muscle to contract.
41
Outline the differences and similiarities between a neuromuscular junction and a cholinergic synapse
1. Both are un-directional due to the neurotransmitter only being the presynaptic membrane
2. The neuromuscular junction is excitatory, whereas the cholinergic synapse can be excitatory or inhibitory
3. The neuromuscular junction connects motor neurones to muscles, whereas the cholinergic synapse connects 2 neurones which could be sensory, relay, or motor
4. Acetylcholine binds to receptors on muscle fibres, and for cholinergic synapses acetylcholine binds to receptors on the post synaptic membrane of a neurone
42
What does myogenic mean
Myogenic means that the heart can contract and relax without a stimulus
43
Where is the sinoatrial node found
The sinoatrial node is located in the right atrium and is known as the pacemaker (it is a group of cells/tissue)
44
Where is the atrioventricular node found
The atrioventricular node is located between the atria and ventricle (right and left ventricle, however within the the atria still)
45
Where is the bundle of His located
The bundle of His (conductive tissue) runs through the septum and up the walls of the ventricles
46
Describe the control of heart rate
1. The SAN release a wave of depolarisation across the atria, causing it to contract (atrial systole)
2. The AVN releases another wave of depolarisation when the first reaches it. However, there is non-conductive tissue/layer between the atria and ventricles which will prevent the wave of depolarisation travelling down to the ventricles
3. Instead, the bundle of His, running through the septum can conduct and pass the wave of depolarisation down the septum and to the Purkyne fibres up the walls of the ventricles
4. As a result, the apex (tip) and then walls of the ventricles contract. There is a short delay before this happens, whilst the AVN transmits the second waves of depolarisation.
5. This allows enough time for the atria to pump all the blood into the ventricles. Finally, the cells repolarise and the cardiac muscle relaxes
47
Describe the medulla oblongata and its function in relation to control of heart rate
The medulla oblongata is located in the brain, and controls the heart rate via the autonomic nervous system
48
What are the 2 parts of the autonomic nervous system in relation to the control of heart rate
1. A centre linked to the SAN that increases heart rate via the sympathetic nervous system
2. Another centre linked to to the SAN that decreases heart rate via the parasympathetic nervous system
49
Define the term homeostasis
Homeostasis is the maintenance of a constant internal environment.
50
Discuss homeostasis in relation to response to pressure
High blood pressures may be caused by diet, stress and anxiety. If the blood pressure is too high, it can cause damage to the walls of the arteries (which causes blood clots and strokes)
Therefore, it is important mechanisms are put into place to reduce blood pressure.
However, if blood pressure is too low, there may be an insufficient supply of oxygenated blood to respiring cells and removal of waste, such as carbon dioxide to the alveoli.
51
Discuss homeostasis in relation to response to pH
The pH of the blood will decrease during times of high respiratory rate due to the production of carbon dioxide or lactic acid.
Therefore, excess acid must be removed from the blood rapidly to prevent enzymes denaturing
This is achieved by increasing the heart rate, so carbon dioxide can diffuse out into the alveoli more rapidly.
52
What happens when blood pressure is increased
1) Stimulus: Increased pressure
2) Pressure receptors (barroreceptors) in the walls of arteries and aorta are stretched if the blood pressure is high
3) Coordination: More electrical impulses sent to the medulla oblongata and then impulses sent via parasympathetic nervous system to SAN to decrease the frequency of electrical impulses
4) Effector- Cardiac muscle (SAN tissues)
5) Response- Reduced heart rate and blood pressure
53
What happens when blood pressure is decreased
1) Stimulus: Decreased pressure
2) Receptor: Pressure receptors in wall of aorta and carotid artery are not stretched if low blood pressure
3) Coordination: More electrical impulses sent to medulla oblongata and then impulses sent via sympathetic nervous system to SAN to increase the frequency of electrical impulses
4) Effector: Cardiac muscle- SAN tissues
5) Response: Increased heart rate and blood pressure increases
54
What happens if pH is decreased
1) Stimulus: Decreased pH
2) Receptor: Chemoreceptor on wall of aorta and carotid artery
3) Coordination: More electrical impulses sent to medulla oblongata and then impulses sent via sympathetic nervous system to increase frequency of electrical impulses
4) Effector: Cardiac muscle - SAN tissues
5) Response: Increased heart rate to delivery of blood to lungs to rapidly remove carbon dioxide.
55
What is negative feedback
Negative feedback mechanism is when any deviation from the normal values are restored back to their original level. This involves the nervous system and often the hormone system too.
56
What is positive feedback
Positive feedback is when the change is increased, such as the dilation of the cervix increasing during childbirth
57
What does the concentration of blood glucose depend on
The concentration of blood glucose depends on food intake and will fall following excercise or if an individual has not eaten
58
What organ detects change in blood glucose levels
The pancreas detects changes in the blood glucose levels. It contains endocrine cells in the Iselts of Langerhans which release the hormones insulin and glucagon to bring glucose levels back to normal
59
How is adrenaline released
Adrenaline is released by adrenal glands when your body anticipates danger, and this results in more glucose being released from stores of glycogen in the liver
60
What is glycogenesis
This is the process of excess glucose being converted to glycogen when blood glucose levels are higher than normal, this occurs mainly in the liver
61
What is glycogenolysis
Glycogenolysis is the hydrolysis of glycogen back into glucose in the liver. This occurs when blood glucose levels are lower than normal
62
What is gluconeogenesis
Gluconeogenesis is the process of creating glucose from a non-carbohydrate store in the liver. This occurs if all of the glycogen has been hydrolysed into glucose and your body still needs more glucose
63
Describe the action of insulin
Beta cells on the islets of Langerhans detect when blood glucose levels are too high and secrete insulin in response to this. Insulin will decrease blood glucose in the following ways.
1. Insulin attaches to the receptors on the surfaces of target cells (liver cells). This changes the tertiary structure of the channel protiens and widening them, resulting in more glucose being absorbed by facilitated diffusion
2. There are more protein channels fusing and incorporating into the cell surface membrane, so creates a larger surface area so that more glucose is absorbed from the blood into cells
3. Activating enzymes that catalyse the conversion of glucose into glycogen (which results in glycogenesis in the liver)
64
Describe the action of glucagon
Alpha cells in the islets of Langerhans detect when blood glucose levels are too low and will secrete glucagon in response to this. Glucagon will:
1. Attach to receptors on the surfaces of target cells (liver cells)
2. When glucagon binds, it causes a protein to be activated into adenylate cyclase and to convert ATP into a molecule called cyclic AMP . cAMP activates the enzyme kinase, that can hydrolyse glycogen into glucose
3. Activation of enzymes involved in the conversion of glycerol and amino acids into glucose (gluconeogenesis)
65
What is the second messenger model
1) Glucagon binds to glucagon receptors on liver cells
2) Once bound, it causes a change in shape to the enzyme adenyl cyclase, which activates it
3) Activated adenyl cyclase enzymes converts ATP into cyclic AMP (cAMP)
4) cAMP activates inactive protein kinase to active kinase
5) Kinase catalyses glycogen to glucose.
66
Describe the role of adrenaline
Adrenaline will increase blood glucose in the following ways:
- Adrenaline attaches to receptors on the surface of target cells. This causes a protein (G-protein) to be activated and to convert ATP to cAMP
- cAMP activates an enzyme that can hydrolyse glycogen into glucose (glycogenolysis)
- This is known as the second messenger model of adrenaline and glucagon action because the process results in the formation of cAMP, which acts as a second messenger
67
Describe the structure of muscle fibres
Muscle fibres are made of millions of myofibrils which collectively bring about the force to cause movement. Myofibril are made up of two types of protein:
1) Myosin- Thick filament
2) Actin- Thin filament
In combination, these form a sarcomere
H-zone is only myosin
I-band is only actin
68
Explain the sliding filament theory
1) When an action potential reaches a muscle, it stimulates a response
Calcium ions enter and cause the protein tropomyosin (that blocks binding sites for myosin head of actin), to move an uncover the binding sites)
The binding sites become exposed, therefore myosin heads can attach, this is happening whilst ADP is attached to the myosin head
It can bind to the binding site on the actin to form a cross bridge
The angle created on this cross-bridge creates tension and as a result, the actin filament is pulled and slides along the myosin.
In doing so, ADP molecules are released
2) A new ATP molecule can bind to the myosin head and causes it to change shape slightly, as a result it detaches from the actin (due to it not being complementary to actin binding site)
Within the sarcoplasm, there is an enzyme ATPase which is activated by calcium ions, to hydrolyse the ATP on the myosin head into ADP and releases enough energy for the myosin head to return to its original position
This entire process repeats continually whilst the calcium remains high, and therefore whilst the muscle remains stimulated by the nervous system
69
Describe phosphocreatine relation to muscle contraction
In times where aerobic respiration cannot create enough ATP to meet this demand, anaerobic respiration occurs.
The chemical phosphocreatine, which is stored in muscles, assists this by providing phosphate to regenerate ATP from ADP
70
Identify the sarcomere bands and structure
I band- Labelling where the actin is by itself with no overlap of myosin (Decreases when muscle contracts)
A band- Total width of myosin, which does overlap with actin (stays constant when muscle contracts)
H-zone- The part of the band which only consists of myosin (Decreases when muscles contract)
M-line- Marks the middle of myosin
Z-line- Start and end of sarcomere
71
Describe the structure, location and general properties of slow twitch fibres
Structure- Contains a large store of myoglobin (so stores lots of oxygen), a rich supply of blood and many mitochondria for aerobic respiration
Location- Back, lower legs, calf)
General properties: Contract slower and can respire aerobically for longer periods of time due to the rich blood supply and myoglobin
These muscles are adapted for endurance like marathons
72
Describe the structure, location and general properties of fast twitch fibres
Structure- Thicker and more myosin fliaments, a large store of glycogen, a store of phosphocreatine to help make ATP from ADP, a high concentration of enzymes involved in anaerobic respiration
Location- Biceps, eyes
General properties- Contract faster to provide short bursts of powerful contraction. These are adapted for intense exercises such as sprinting or weight lifting
73
Describe rods structure and function
- Rod like in shape
- They cannot distinguish different wavelengths of light and processes images in black and white
- Rods can detect light of very slow intensity as many rod cells are connected to one sensory neurone
74
How is a generator potential achieved for rod cells
To create a generator potential, the pigment of rod cells (rhodopsin) must be broken down by light energy. There is enough energy from low-intensity light to cause the breakdown. Enough pigment has to be broken down for the threshold to be met in the bipolar cell
The threshold can be reached even in low light because there are so many rod cells that are connected to a single bipolar cell (summation)
However, this retinal convergence means that the brain cannot distinguish between the separate sources of light that stimulated it
Two light sources close together cannot b seen as separate- Rod cells give low visual acuity
75
Describe cone cells structure and function
There are three types of cone cells with the only difference being the type of iodopsin pigment it has (red, green, blue) which all absorbs different wavelengths of light
Depending on the proportion of each cone cell that is stimulated we perceived coloured images
Iodopsin is only broken down if there is a high light intensity, so action potentials can only be generated with enough light
76
How can be generator potential be generated in cone cells
Iodopsin is only broken down if there is a high light intensity, so action potentials can only be generated with enough light.
Usually only one cone cell connects to a bipolar cell. Therefore, no spatial summation occurs and cones can only respond to high light intensity, which is why we can't see colour in the dark
As each cone cell is connected to one bipolar cell the brain can distinguish between separate sources of light detected by cone cells to give high visual acuity
77
Describe the distribution of rod and cone cells in the retina
The distribution of rods and cones in the retina is uneven. Light is focused by the lens on the part of the retina opposite the pupil, the fovea which will receive the highest light intensity.
Therefore more cone cells are located near the fovea as they require e/only respond to high light intensity and rod cells further away as these can respond at lower light intensity.
78
Identify the nephron structure and function
- Renal capsule with glomerulus
- Proximal convoluted tubule
- Loop of henle
- Distal convoluted tubule
- Collecting ducts
Its function is to filter the blood to remove waste and selectively reabsorb useful substances back into the blood
79
What does urine contain and not contain
1) Water
2) Dissolved salts
3) Urea
4) Other small substances like hormones and excess vitamins
Urine does not contain: Proteins, and blood cells are too large to leave the capillaries and glucose as all the glucose is reabsorbed out the reabsoprtion stage in the proximal convoluted tubule
80
How does filtering and reabsorption occur
Stage 1- Ultrafiltration occurs due to the high hydrostatic pressure, therefore water and small molecules are forced out of the glomerulus capillaries into the renal capsule
Stage 2- Filtrate is passed through the proximal convoluted tubule (PCT) and this is where selective reabsorption occurs
Stage 3+4- The loop of henle maintains a sodium ion graident so water can be reabsorbed into the blood
Stage 5+6- Water moves out of the distal convoluted tubule and collecting duct to return back to the blood
The collecting duct then carries the remaining liquid (urine) back to the ureter
81
Describe ultrafiltration in relation to the nephron
1. Blood enters through the afferent arterioles, this splits into lots of smaller capillaries which makes up the glomerulus. This creates a high hydrostatic pressure, as it is going from a wider lumen to small capillaries
2. Due to the high hydrostatic pressure, water and small molecules, such as glucose and mineral ions are forced out of the capillaries and form glomerulus filtrate
3. Large proteins and blood cells are too big to fit through the gaps in the capillary endothelium, therefore thye remain in the blood. This blood leaves via the efferent arteriole
82
Describe selective reabsorption
This occurs in the proximal convoluted tubule, here 85% of the glomerulus filtrate is reabsorbed back into the blood, leaving urea and excess mineral ions behind
1) The concentration of sodium in the proximal convoluted tubule cells is decreased as the sodium ions are actively transported out of the PCT cells into the blood in the capillaries.
2) Due to the concentration gradient, sodium diffuses down the gradient from the lumen of the PCT into the cells lining the PCT. This is an example of co-transport as the proteins which transport sodium carry glucose with it
3) The glucose can then diffuse from the PCT epithelial cell into the blood stream
4) This is how all the glucose is reabsorbed
83
How is a sodium ion gradient maintained by the loop of henle ;
The loop of henle has an ascending limb and a descending limb
1) Mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb of the loop of henle
2) The accumulation of sodium ions in the outside of the nephron in the medulla lowers the water potential
3) Therefore, water diffuses out by osmosis into the inerstitial space and then blood capillaries (water reabsorbed into the blood)
4) At the base of the ascending limb, some sodium are transported about by diffusion, as there is now very dilute solution due to all the water that has moved out
84
Describe the reabsorption of water at the distal convoluted tuble and collecting duct
-Due to all the sodium being actively transported out of the loop of Henle, when the filtrate reaches the DCT it is very dilute
- The filtrate moves into the DCT and collecting duct. This section of the medulla is very concentrated
-Therefore, even more water diffuses out of the DCT and collecting duct
- What remains is transported to form urine
85
