Paper 2 done properly easter Flashcards
What are stimuli?
- Stimuli are internal or external changes to the environment.
What are 3 responses to stimuli?
1) Tropisms
2) Taxis and Kinesis
3) Simple reflexes
What is a tropism?
- Tropism is a growth response of a plant to a directional stimulus.
How are tropisms controlled?
- Controlled by growth factors
Where are growth factors produced?
- Growing regions such as shoot tips, they move to areas which require growth.
What is the main growth factor?
- Auxin
What is phototropism?
- The movement towards or away from LIGHT.
Outline phototropism in a shoot?
1) In shoots, IAA causes cell elongation.
2) In shoots, light is detected by photoreceptors
3) IAA diffuses to the darker side.
4) IAA increases on the darker side.
5) IAA causes cells on the darker side to elongate, and the shoots bend towards the light.
How does phototropism happen in roots?
- Roots detect light and IAA will diffuse to the darker side and inhibit cell elongation, so the roots will bend downwards.
Outline Gravitropism in shoots?
- Gravitropism in shoots sees IAA diffuse to the lower side of the shoot.
- IAA concentration increases on the lower side.
- IAA causes cells on the lower side to elongate and bend upwards.
Outline gravitropism in roots?
- IAA diffuses to the lower side of the root.
- More inhibition of cell elongation causes the roots to bend downwards.
What is taxis and kinesis?
- Simple responses which maintain a mobile organism in a favourable environment.
What is a taxis response?
- The organism moves towards or away from a directional stimulus.
What is a kinesis response?
- The organisms movement is affected by a non directional stimulus so the rate of turning increases as an organism gets closer to the stimulus.
What are the 3 neurones involved in simple reflexes
1) Sensory
2) Relay
3) Motor
Outline the process of a simple reflex?
Receptor detects stimulus
Sensory neurone carries the impulse from the receptor to the relay neurone in the central nervous system.
The Relay neurone carries impulse directly from the sensory to motor neurone.
The motor neurone carries impulse from the relay neurone to the effector.
The effector carries out a response which may be a muscle contraction of a gland secreting a hormone.
Why are reflex arcs so important?
They result in fast responses, as they don’t involve the conscious part of the brain because the impulse is carried directly from a sensory neurone to a motor neurone via a relay neurone.
They are also fast as they travel along neurones.
The responses are localised, meaning that the neurotransmitters are secreted directly onto target cells.
Responses are shortlived, because the re-uptake of neurotransmitters is rapid.
How do simple reflexes aid survival?
Helps protect the body from tissue damage
Pressure/balance
Escape from predators
Involuntary response meaning there is no overriding.
Outline the role of 3 types of receptors?
- Mechanoreceptors detect pressure.
- Chemoreceptors detect certain chemicals
- Photoreceptors detect light.
What does the Pacinian corpuscle consist of?
- Contains a sensory neurone ending that is wrapped around lamellae.
How does a Pacinian corpuscle work?
Pressure causes the lamellae to be deformed and press on the sensory neurone ending.
This increase in pressure deforms the stretch mediated sodium ion channels.
Sodium ion channels open and sodium ions diffuse into the sensory neurone endings.
This depolarises the cell, creating a generator potential.
When the generator potential.
When the generator potential reaches the threshold an action potential is triggered.
How does the action potential get generated?
Potential difference between inside and outside of the cell is called a resting potential.
When a stimulus is detected, the membrane becomes more permeable so ions will diffuse across and the potential difference increases.
If the generator potential is large enough, there is triggering of an action potential.
How does the retina detect changes in light?
Light is detected by photoreceptors.
Light pigments absorb the light, light bleaches the pigments, altering the membrane permeability to sodium ions.
A generator potential is created.
If it is large enough and over the threshold, an action potential is created.
Bipolar neurones connects to optic nerves, which takes impulses to the brain.
Why do rods have a higher sensitivity to light?
- Rods have a high sensitivity to light, because many rods connect to 1 bipolar neurone so many weak generator potentials combine to reach the threshold.
Why do cones have lower sensitivity to light?
- Cones have low sensitivity to light, because only 1 cone connects to a bipolar neurone so it takes more light to reach the threshold and generates an action potential.
What does myogenic mean for the cardiac muscle?
- the contraction is initiated by the muscle itself without any contraction.
What is the role of the SAN?
- Found in the right atrium, the SAN sets the frequency at which the cardiac muscle cell contracts.
How does a contraction occur?
SAN generates an electrical impulse.
The electrical impulse spreads from SAN across both atria, causing them to contract simultaneously.
Septum prevents the impulse from crossing to ventricles.
Impulse reaches the AVN
After a short delay, the AVN passes on the impulse to the Bundle of His fibres, which conduct the impulse down to the Purkyne fibres.
Impulse reaches the Purkyne fibres at the heart apex, which carry the impulse up the walls of the ventricles, causing them to contract from bottom up.
Why is there a short delay between the impulse being passed from SAN to AVN?
- Short delay allows the atria to be empties before the ventricles contract.
How do we control heart rate?
Autonomic nervous system.
The rate at which the SAN generates impulses is controlled by the Medulla Oblangata in the brain.
Heart rate is changed in response to internal stimuli.
What stimuli cause change in blood pressure?
Changes include change in blood pressure, change in chemical composition in the blood, detected by baroreceptors and chemoreceptors.
What neurotransmitters are released at the sympathetic/parasympathetic nervous system?
- Parasympathetic - Acetylcholine
- Sympathetic - Noradrenaline
Outline the pathway if the stimuli is high blood pressure or high blood O2 conc?
Chemoreceptors/baroreceptors detect the stimulus and send more impulses to the medulla.
Medulla processes information and sends impulses down the parasympatheitc neurone.
THis releases the neurotransmitter acetylcholine, which binds to the SAN and sends impulses at a lower frequency.
Blood pressure/other factors will decrease.
Outline the pathway if there is a low blood pressure or low blood O2 conc?
Baroreceptors/chemoreceptors detect the stimulus and send more impulses to the medulla.
Medulla processes information and sends impulses down the sympathetic neurone.
This release the neurone noradrenaline, which binds to the SAN and sends impulses at a higher frequency.
Increases heart rate.
How is a resting potential established?
3 sodium ions are actively transported out of the axon in exchange for 2 potassium ions via a sodium-potassium pump.
Sodium ions build up outside the axon as the voltage gated sodium ion channels are closed so sodium ions cannot diffuse back.
Voltage gated potassium ion channels are also close.
What is the role of dendrites?
Dendrites recieve electrical impulses from neighbouring neurones.
What is the role of the myelin sheath?
Myelin sheath forms an electrically-insulating cover around the axon, made of layers of schwann cells wrapped around each other.
What is the role of synapses?
Synapses transmit impulses to neighbouring neurones.
What is the mV of the resting potential?
-70mv
Outline the depolarisation stage
A stimulus excites the membrane causing the cell surface membrane to become more permeable to sodium ions.
Voltage gated sodium ion channels open and sodium ions diffuse into the neurone.
Voltage gated potassium ion channels are closed.
Inside of membrane is more positive than outside
Outline the repolarisation stage
Voltage-gated sodium ion channels close
Voltage-gated potassium ion channels open
Potassium ions diffuse out of the neurone
Inside of the neurone become more negative
Voltage decreases to a normal level.
Outline the hyperpolarisation stage
Voltage-gated potassium ion channels remain open for a short time which means too many potassium ions diffuse out of the neurone and the voltage becomes more negative than the –70mV resting potential.
How is the resting potential reestablished after hyperpolarisation?
Voltage gated potassium ion channels close
The sodium/potassium pump restores the resting potential.
Outline the unmyelinated neurone pathway..
As one region depolarises, it acts as a stimulus for the depolarisation of the next region – Action potential is a travelling wave of depolarisation.
The previous region repolarises
What is the refractory period?
During the refractory period, ion channels cannot be opened so there is a time delay between one action potential and the next.
Why is the refractory period important?
The refractory period allows non-overlapping of APs, unidirectional APs and a time limit to the frequency at which nerve impulses can be transmitted.
Outline the pathway of a myelinated neurone
Myelin sheaths act as electrical insulates which prevent action potentials from occurring.
At regular intervals, there are breaks in the insulation called Nodes of Ranvier.
Action potentials only occur at Nodes of Ranvier.
Action potentials jump from one node to another during saltatory conduction.
AP passes along the neurone faster
Less energy from ATP hydrolysis is needed for the sodium/potassium pump.
What is the all or nothing principle?
An action potential only happens if the stimulus reaches the threshold value.
Action potentials are always the same size.
How is the size of a stimulus measured?
The size of a stimulus is determined by the frequency of impulses so larger stimulus means there is a higher frequency of impulses.
Neurones with different threshold values means the brain interprets the number and type of neurones where action potentials are triggered and so determines its size.
What factors affect the speed of a neurone impulse?
- Temperature because higher temperatures increase the amount of KE available.
- Myelination
- Diameter of the axon (Larger diameter means less resistance to the movement of ions)
What is a synapse?
A junction between two neurones or between a neurone and a muscle (neuromuscular junction)
Neuromuscular junctions are found at the ends of axons.
Most synapses use the neurotransmitter acetylcholine
Outline transmission at a cholinergic synapse..
Action potential arrives at the synpatic knob of the presynpatic neurone.
Stimulates voltage-gated calcium ion channels to open so calcium ions diffuse into the synapse.
Increase in calcium ions triggers synaptic vesicles to move to the presynaptic membrane and fuse with it, releasing acetylcholine into the synaptic cleft.
Acetylcholine diffuses across the synaptic cleft.
Acetylcholine binds to receptors on post synaptic membrane.
Causes sodium ion channels to open so sodium ions diffuses into postsynaptic neurone which causes depolarisation.
If the threshold is reached, a new action potential is triggered.
What is meant by nerve impulses being unidirectional?
- The impulse only travels in one direction because receptors are only found on the postsynpatic membrane.
What is summation?
- Low frequency action potentials cause insufficient amounts of neurotransmitter to be released to trigger a new action potential in the postsynaptic neurone.
What is spatial summation?
- When presynaptic neurones connect to a single post synaptic neurone, together they release enough neurotransmitter to exceed the threshold value in the postsynaptic neurone and trigger an action potential.
What is temporal summation?
-Single presynaptic neurone releases neurotransmitter many times over a short period of time.
What is inhibition?
-Some synapses make it less likely that a new action potential will be triggered in the post synaptic neurone.
-This happens when neurotransmitters may bind to chloride channels, causing them to open and allowing chloride ions to diffuse into the post synaptic neurone.
They may cause potassium ion channels to open causing potassium to diffuse out.
Overall, an even more negative membrane potential is established.
Hyperpolarisation
What is the neuromuscular junction?
Synapse between a motor neurone and a muscle.
There are many neuromuscular junctions along a muscle – all fibres contract simultaneously and rapidly.
What are some differences between cholingergic synapses and neuromuscular junctions?
Cholinergic – Neurone to neurone
Neuromuscular – Motor neurone to muscle
Cholinergic – Inhibitory or Excitatory
Neuromuscular – Only Excitatory
A new AP may be triggered at the postsynaptic neurone in cholinergic synapses, but the AP ends at neuromuscular junctions.
Post synpatic membrane of a cholinergic synapse has less receptors than the post synaptic membrane of a neuromuscular junction.
What are the similarities between cholinergic synapses and the neuromuscular junction?
Neurotransmitters are transported by diffusion.
Both synpases have receptors that cause an influc of sodium ions when neurotransmitter binds.
Both use a sodium/potassium pump to repolarise the axon.
What are the effects of drugs on synapses?
Similar shape to a type of neurotransmitter so can also bind to receptors and trigger sodium ion channels to open, triggering more action potentials to occur.
They may act as blockers, preventing neurotransmitters from binding and fewer sodium ion channels open meaning fewer action potentials are triggered.
Drugs may also inhibit enzymes that break down neurotransmitter meaning more neurotransmitter remains the synaptic cleft that can bind to receptors meaning more action potentials can continue to be triggered.
What does antagonistic mean?
- One muscle contracts whilst the other relaxes.
What cells make up muscles?
- Muscle fibres
What are muscle fibres made up of?
- Myofibrils
What is the cytoplasm of muscle fibres called?
- The sarcoplasm
What is the role of the sarcoplasmic reticulum?
- Contains calcium ions needed for contraction.
What are myofibrils?
- Bundles of thick and thin myofilaments that move past each other to make muscles contract.
What is actin?
- Thin myofilament that appears light
What is myosin?
- Thick myofilament that appears dark
What are sarcomeres?
- Single contractile units
What is the Z-line?
- The ends of the sarcomere.
What is the A-band?
- Length of myosin
What is the I-band?
- Contains actin only
What is the H-zone?
- Contains only myosin
What is the M-line?
- The middle of myosin
What is the interaction between myosin and actin during contraction?
- Myosin and actin slide over each other too make sarcomeres contract.
What happens to the length of sarcomeres, I bands, H zones and A bands during contraction?
- Sarcomeres return to their original length as the muscle relaxes.
- I band gets shorter
- H zone gets shorter
- A band stays the same
What is tropomyosin?
- Substance which blocks the myosin head from binding to the actin-myosin binding site during rest.
How does contraction happen step by step?
1) Action potential reaches the neuromuscular junction.
2) Acetylcholine diffuses over to the post synaptic membrane and binds to receptors.
3) The sarcolemma depolarises causing an influx of sodium ions.
4) There is a wave of depolarisation which spreads along the T-tubules and sarcoplasmic reticulum.
5) The sarcoplasmic reticulum releases calcium ions into the sarcoplasm.
6) Calcium ions bind to troponin, causing it to change shape, pulling tropomyosin out of the acting-myosin binding site.
7) Myosin head is now able to bind to the actin-myosin binding site to form an actinmyosin bridge.
8) Calcium ions activate ATP hydrolase which hydrolysis an ATP that is bound to the myosin head, the energy released causes myosin head to bend.
9) Another ATP attaches to myosin and is hydrolysed, providing energy to break the actinmyosin bridge.
How is ATP generated?
- During aerobic respiration
- During anaerobic respiration
How does phosphocreatine produce ATP?
ADP + PCr -> ATP + Cr
Function of slow muscle fibres…
- Work for long periods of aerobic respiration
- Thin in diameter, red in colour
Function of fast muscle fibres…
- Get tired quickly
- Anaerobic
- Thick in diameter, pale in colour
- Found in arms and legs
What is the definition on homeostasis?
- The maintanance of the internal environment by control systems in response to internal and external stimuli.
What do we control?
- Core body temperature
- Blood pH
- Blood glucose
- Water concentration
What is the purpose of negative feedback?
- Restores systems to their original level
Why is glucose important?
- Needed as a constant supply in order to carry out aerobic respiration.
What are factors that influence the blood glucose concentration?
- Food intake (glucose is absorbed into the blood during digestion)
- Exercise (Demand for glucose increases)
- Metabolic rate (Increases the demand for glucose)
What are the 3 processes that affect the concentration of glucose in the blood.
- Glycogenesis (The conversion of glucose to glycogen done by the role of insulin)
- Glycogenolysis (The conversion of glycogen to glucose done by the role of glucagon)
- Gluconeogenesis (The production of glucose from the hydrolysis of non-carbohydrate sources)
What icells do the pancreas contain to control blood glucose?
- Contains alpha cells which release glucagon when there is too little blood glucose.
- Contains beta cells which release insulin when there is too much blood glucose.
Outline the process when blood glucose levels are too high?
- Beta cells detect the increase and secrete insulin.
- Insluin binds to specific receptors on the cell surface membrane of target cells.
- This triggers glucose channel proteins to change shape and open more which will allow more glucose to enter the cell.
- Can also increase the fusion of channel containing vesicles with the cell surface membrane of the target cell, increasing the number of glucose channel proteins in the membrane so more glucose can enter the cell.
- Activates the enzymes involved in the formation of glycogen from glucose. (glycogenesis)
- Blood glucose decreases.
Outline the process when blood glucose levels are too low..
- Alpha cells detect the decrease of glucose levels and secrete glucagon.
- Glucagon will bind to specific receptors on the cell surface membrane of target cells.
- Activates enzymes that convert glycogen to glucose (glycogenolysis)
- Activates enzymes that convert non-carbohydrate sources to glucose (gluconeogenesis)
What is the Second Messanger Model?
- Glucagon/adrenaline binds to receptors on the cell surface membrane of target cells.
- This activates an Adenylate Cyclase enzyme.
- Adenylate Cyclase catalyses the production of cAMP (cyclic Adenosine Monophosphate) from ATP.
- ## cAMP activates protein kinase enzyme which activates a chain of reactions that leads to glycogenolysis.
Why does Type 1 diabetes happen?
- When the pancrease doesn’t produce enough insulin.
What is Type 1 diabetes caused by?
- Caused by an autoimmune disease that destroys beta cells.
What are the symptoms of Type 1 diabetes?
- Thirst is a symptom (cells become too concentrated with glucose)
- Excessive urination (drinking too much water to replace fluids)
- Weight loss as you are hydrolysing lipids more.
What is the type 1 diabetes treatment?
- Consistent injections of insulin.
What is type 2 diabetes?
- When the pancreas doesn’t produce enough insulin or glycoprotein receptors on the cell surface membrane.
- OR, target cells become less responsive to insulin.
What are the risk factors of type 2 diabetes?
- Obesity
- lack of exercise
- too much sugar
How do you treat type 2 diabetes?
- Treatment includes management of diet and exercise.
What is osmoregulation?
- The control of the water potential of the blood.
What are the 3 main steps involved in the osmoregulation?
1) Ultrafiltration (Forming the glomerular filtrate)
2) Selective absorption (reabsorption of useful substances, such as glucose and amino acids, and ions)
3) The reabsorption of water
Outline the process of ultrafiltration..
- Efferent arteriole is smaller in diameter than the afferent arteriole so the hydrostatic pressure in the glomerular capillaries increases.
- Small molecules are forced through a 3-layer filter into the Bowman’s capsule.
- The 3-layer filter consists of the capillary endothelium, basement membranes and podocytes.
- Larger proteins and RBC’s are too large to pass through.
- Glucose, water, urea, amino acids, ions and XS vitamins pass through to form the glomerular filtrate.
Outline the process of selective reabsorption..
- The reabsorption of useful substances, such as glucose, amino acids, and ions.
- This occurs at the proximal convoluted tubules.
- The substances pass back into the blood capillaries wrapped around the proximal convoluted tubules and is reabsorbed the exact same way as in the lining of ileum during co-transport with sodium ions.
- Reabsorption lowers WP of the blood so water moves out of PCT into capillaries by osmosis.
- Epithelium of the PCT has microvilli which provide a large surface area for the reabsorption of material from the glomerular filtrate.
How does osmoregulation happen?
- At the top of the ascending limb, sodium ions are pumped into the medulla by active transport.
- The ascending limb is impermeable to water, so water remains in the tubule.
- The medulla’s WP decreases.
- Water moves out of the descending limb by osmosis.
- Descending limbs isn’t permeable to ions.
- Sodium ions diffuse into the medulla, further lowering the WP of the medulla.
- Now there is a lower WP in the interstitial fluid around the DCT and collecting duct so more water is able to leave the tubule.
- All water that leaves the tubules at this stage is reabsorbed into the capillary network.
How do we control how much water is reabsrobed at the DCT and Collecting Duct?
Water can only leave the DCT and collecting duct through aquaporins embedded in the cell surface membrane of cells lining these tubules
What happens when there is low water potential?
Low water potential is detected by osmoreceptors in the hypothalamus.
Posterior pituitary gland stimulated to release more ADH into blood.
The ADH binds to receptors on the cell surface membrane of cells lining the DCT and collecting duct.
Triggers vesicles containing aquaporins to fuse with the cell surface membrane – more aquaporins incorporated into the cell surface membrane of cells lining the DCT and collecting duct.
DCT and collecting duct more permeable to water, as there are more places for water to leave by osmosis.
More water is reabsorbed into the blood
What happens when a high water concentration is detected?
High water potential detected by osmoreceptors in the hypothalamus.
Posterior pituitary gland releases less ADH into the blood.
Less ADH molecules bind to receptors in the cell surface membrane of cells lining the DCT and collecting duct so less aquaporins incorporated into the cell surface membrane of cells lining these tubules.
DCT and collecting duct less permeable to water, as there are fewer places for water to leave by osmosis.
Less water reabsorbed into the blood by osmosis.
