3.6 Organisms Respond To Changes In Internal And External Environments

Question 1

What is a stimulus and why is it important to respond to them?

Answer 1

•A detectable change in the environment. These changes can be detected by receptors.
•Increases chance of survival

Question 2

What is kinesis?

Answer 2

•if organism moves to an area with harmful stimuli= increase the rate it changes direction to return to the favourable conditions quickly
•if it is in an area with beneficial stimuli it decreases speed
•non-directional response to unfavourable conditions

Question 3

What is taxis?

Answer 3

A directional response, where they move towards or away from a stimulus

E.g -ve chemotaxis = moving away from beneficial chemical
/ +ve phototaxis = moving towards light

Question 4

Why do organisms respond to temperature and humidity via kinesis?

Answer 4

Less directional stimuli where there is often no clear gradient from one extreme to the other

Question 5

What is the effect of IAA in the shoot tip?

Answer 5

•in unilateral light, IAA will diffuse towards the shaded side
•it causes the cells to elongate more and this will bend the top to the light source
=positive phototropism

Question 6

What is the effect of IAA in the root tip?

Answer 6

•IAA will move to the lower side of the root
•this will inhibit cell elongation so that roots anchor into the soil
= positive gravitropism and negative phototropism

Question 7

What are the events involved in a response?

Answer 7

1.stimulus= change in internal/external environment
2.receptor= detects stimulus and respond by producing action potential in neurones
3.sensory neurone= carries impulses from receptor to CNS
4.coordinator=in CNS where info is interpreted
5.motor neurone= impulse from CNS to effector (gland/muscle)

Question 8

What are the features of the endocrine system?

Answer 8

•widespread action
•hormones transported in blood
•long lasting response
•slow effect

Question 9

What are the features of the nervous system?

Answer 9

•localised in a specific area
•neurotransmitters (chemical coordinator)
•short lived
•rapid effect
•impulses directly to target cells

Question 10

What is a reflex action?

Answer 10

•rapid, involuntary response to a stimulus
•innate (not learned)

Question 11

Why are reflexes important?

Answer 11

•increase survival =escape predators
•role of homeostasis
•leave brain free to carry out complex responses
•protect body from harm
•fast as neurone pathway is short

Question 12

What are the structures of a neurone and their functions?

Answer 12

•cell body
•dentrites: receive info and carry it towards cell body
•axon: transmit impulses away from cell body
•myelin sheath: fatty material which insulates the axon so no loss of impulses or crossing over occurs
•Schwann cells wrap around axon to form myelin sheath, gap between called nodes of ranvier
•axonites

Question 13

How is a resting potential established?

Answer 13

•3Na+ out and 2K+ into the axon by active transport via the Na-K pump
•electrochemical gradient produced = K+ diffuse out and Na+ in by facilitated diffusion
•membrane is more permeable to K+ as more K+ channels so more K+ moves out = -70 mv inside the axon

Question 14

What are the steps involved in an action potential?

Answer 14

Depolarisation:
•neurone stimulated opens voltage gates Na+ channels
•+ve feedback = more channels open
•Na+ flood down conc. gradient into axon = +40 mv in axon

Repolarisation:
•+40 mv reached, Na+ voltage gated channels close
•K+ voltage gated channels open and K+ flood down conc. gradient out of axon so -70 mv in axon

Hyper polarisation:
•too many K+ move out of axon so temporarily more -ve than -70 mv (refractory period where no AP can be stimulated)

Question 15

What is the all-or nothing principle?

Answer 15

•if depolarisation < -55mv= no action potential
•all at -55 mv will trigger a depolarisation of same magnitude to +40 mv max
•bigger stimuli increases the frequency of action potentials

This is important as only large stimuli are responded to for increased survival

Question 16

What is the refractory period and why is it important?

Answer 16

(Action potential cannot be stimulated right away after one already)=time delay between AP
•action potentials are separate form one another (distinct)
•AP will travel in one direction
•limits frequency of AP so prevents over reaction to a stimulus so senses not overwhelmed

Question 17

Why does a myelinated axon conduct impulses faster than non-myelinated axon?

Answer 17

•myelin sheath is an electrical insulator
•in myelinated, action potential (depolarisation) can only occur at the node
•nerve impulse jumps from node to node
•action potential does not travel along the whole length of the axon
(Saltatory conduction)

Question 18

Give the structure of a synapse and of a neurotransmitter junction

Answer 18

•synaptic cleft
•neurotransmitter (acetylcholine)
•pre and postsynaptic neurone
•neuro receptor: membrane of the post synaptic neurone has chemical gated ion channels

Question 19

What happens at the synapse?

Answer 19

1.Depolarisation of presynaptic membrane leads to opening of Ca2+ channels and Ca2+ diffuses in
2.vesicles with neurotransmitter move towards and fuse with the pre synaptic membrane and is released in the synaptic cleft
3.neurotransmitter diffuses across the synaptic cleft to bind to complementary receptors on the postsynaptic membrane
4.Na+ ion channels on post synaptic membrane open and Na+ diffuses in (above threshold= depolarisation)
5.neurotransmitter is degraded and released from receptor (back to pre synaptic neurone to be recycled), Na+ channels close and the post synaptic= resting potential

Question 20

What is different in a cholinergic synapse?

Answer 20

•neurotransmitter is acetylcholine and will bind to receptors on post synaptic membrane
•it is broken down to acetyl and choline, moving back to pre synaptic knob.
•ATP energy is used to recombine it and it is stored in vesicles
•more acetylcholine can be made by the smooth endoplasmic reticulum

Question 21

Compare cholinergic synapses and neuromuscular junction

Answer 21

NJ CS
•unidirectional as receptors only on post synaptic membrane
•excitatory |•excitatory or
|inhibitory
•motor neurone|•2 neurones
to muscles |
•end point for AP|•new AP
•acetylcholine |•acetylcholine binds to muscle |binds to post
fibres | synaptic
|membrane

Question 22

Why are transmissions involved in synapses unidirectional?

Answer 22

•vesicles only released in the pre synaptic neurone
•receptors only on post synaptic neurone so only bind to one side

Question 23

What is temporal summation?

Answer 23

One presynaptic neurone releases neurotransmitter repeatedly over a short period of time to add up enough Na+ diffusing to exceed threshold

Question 24

What is spatial summation?

Answer 24

Many different pre synaptic neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold

Question 25

What occurs during inhibition by inhibitory synapses?

Answer 25

•Cl- will move into and some K+ move out of the post synaptic neurone •-ve inside and +ve outside = -80 mv (hyperpolarisation so action potential is unlikely and no depolarisation as not enough Na+ move in to reach threshold)

Question 26

How does the diameter of the axon affect speed of conductance?

Answer 26

•wider diameter, faster speed of conductance •larger the diameter, lower the resistance to the flow of ions so faster wave of depolarisation travels along the neurone •there will be less leakage of ions so action potentials travel faster

Question 27

How does temperature affect speed of conductance along the axon?

Answer 27

1.ions diffuse faster as more KE energy 2.enzymes involved in respiration work faster = so more ATP for active transport in the Na/K+ pump

Question 28

How does the pacinnian corpuscle work and where?

Answer 28

1)mechanical stimulation (pressure) deforms stretch mediated Na+ channels on the membrane of the ending of the sensory neurone 2)stretch mediated Na+ channels widen and allow some Na+ to diffuse into the sensory neurone 3)generator potential is produced 4)leads to an action potential in the neurone if threshold is met Located in joints, tendons, skin and ligaments

Question 29

Why is the pacinian corpuscle described as a transducer?

Answer 29

Transfers energy from mechanical to electrochemical energy (stimuli into a generator potential)

Question 30

What are transducers in the eye and e.g?

Answer 30

Convert light energy to electrical energy e.g rod and cone cells

Question 31

What are rod cells and function?

Answer 31

•rhodopsin pigment is broken down by low light levels to generate action potential •sensitive to light as many rod synapses with one bipolar neurone (retinal convergence) so neurotransmitters add together to reach threshold = action potential •low acuity as different stimuli may produce only one action potential

Question 32

What are cone cells and function?

Answer 32

•iodopsin pigment is broken down by high light levels to generate an action potential •3 different types of cells each sensitive to different wavelengths of light •low sensitivity as one cone synapse with bipolar cell so lots of light is needed to release enough neurotransmitter to reach threshold •high acuity as each cone synapses with one bipolar cell so will produce one action potential for each stimulus, sending separate impulses to the brain (can distinguish between separate light sources close together)

Question 33

How are colours seen?

Answer 33

•3 different types of cone cells, where each cone has different pigment and absorbs particular wavelengths •overlap in wavelength absorption between the different types of cone cells •different colours due to stimulation of more than one cone

Question 34

Why is the heart described as myogenic?

Answer 34

Heart triggers (Sino atrial node) own beat as it doesn’t require an external signal to beat

Question 35

What does the sympathetic nervous system cause?

Answer 35

Triggers increase in heart rate

Question 36

What does the parasympathetic nervous system cause?

Answer 36

Triggers decrease in heart rate

Question 37

How are CO2 levels in the blood regulated when exercising?

Answer 37

•Chemoreceptors in the aorta and carotid arteries will detect ph of the blood (ph decreases when high CO2) •more electrical impulses sent to medulla oblongata •impulses sent to the sino atrial node and SAN increases its frequency of electrical impulses so increased heart rate

Question 38

How is blood pressure regulated?

Answer 38

If increased blood pressure: •baroreceptors in aorta and carotid arteries will detect high pressure •will send impulses to the heart rate decrease centre in the medulla oblongata •medulla oblongata will send impulses to the SAN via parasympathetic neurones and will cause less electrical impulses so heart rate decreases

Question 39

What causes the fight or flight response?

Answer 39

•stress: adrenal glands release adrenaline and noradrenaline which will send impulses to the SAN via sympathetic nervous system. •this will cause more impulses to be realised by SAN so heart rate increases •more oxygenated blood for muscle contraction

Question 40

What is the structure of myofibrils

Answer 40

•many long thin myofibrils surrounded by sarcoplasm (lots of nuclei/mitochondria and sarcoplasmic reticulum (store Ca2+) •thick filament = myosin protein •thin filament = actin protein •sarcomere (section of myofibrils): *I band= lighter, only thin filaments, with Z line between them *A band=darker, thick and thin filament *H zone= lighter section of A band that only has thick filament *the M line is in the middle of the A band

Question 41

What are slow twitch fibres?

Answer 41

•contracts slower and can respire aerobically for longer periods of time due to rich blood supply and myoglobin oxygen store = endurance e.g calf •anaerobic respiration is delayed so no lactate is formed •contains large store of myoglobin, rich blood supply (lots of capillaries) and lots of mitochondria

Question 42

What are fast twitch fibres?

Answer 42

•contract faster to provide short bursts of powerful contraction= intense exercise e.g sprinting •thicker and more myosin filaments, large store of glycogen, store of phosphocreatine to make ATP from phosphorylation of ADP, high concentration of enzymes for anaerobic respiration

Question 43

What happens to different structures of the myofibril when muscle contracts?

Answer 43

•I band become shorter •H-zone decreases •A-band is constant •Z-lines move closer together so myosin is closer to the Z lines •sarcomere (distance between Z lines) will shorten

Question 44

What is the sliding filament theory?

Answer 44

1.action potential arrives at the end of motor neurone at neuromuscular junction, which releases acetylcholine and action potential is initiated at the sarcolemma 2.this causes sarcoplasmic reticulum to release store of Ca2+ into myofibril 3.Ca2+ enter and cause tropomyosin protein to move and uncover the binding site on the actin 4.whilst ADP is attached to the myosin head it can bind to the actin binding site = cross bridge 5.tension created will cause the actin filament to be pulled and slide along the myosin, releasing ADP+Pi 6.ATP binds to myosin and causes it to detach from the actin 7.enzyme ATPase (activated by Ca2+) will hydrolyse ATP and release energy to return the myosin to its original position

Question 45

Why is ATP important for muscle contraction?

Answer 45

-binding of ATP to myosin head will cause it to detach the actin breaking actinomyosin bridge -bends myosin head for power stroke so actin filament are moved inwards -hydrolysis of ATP provides energy for re-uptake of Ca2+ into sacroplasmic reticulum by active transport

Question 46

What happens when muscle is relaxed?

Answer 46

•Ca2+ is actively transported back into the sarcoplasmic reticulum •tropomyosin will cover the binding site on the actin and myosin heads cannot bind to it

Question 47

What is the role of phosphocreatine in fast twitch muscle fibres?

Answer 47

Provide phosphate to ADP so it can quickly supply ATP

Question 48

Why do neurotransmitters have to be transported back out of synapses?

Answer 48

•if not removed it will keep binding to receptors on the postsynaptic membrane so will keep depolarisation continuously

Question 49

What is homeostasis?

Answer 49

Maintaining a constant internal environment when changes in internal and external environments via physiological control systems

Question 50

Which internal conditions need to be maintained and why?

Answer 50

•temp.= optimum for enzyme activity •blood glucose conc.=respiratory substrate and it can effect the water potential of blood •blood pH=optimum for enzyme activity •blood water and ion conc.=effect the water potential of blood

Question 51

What are endotherms and ectotherms?

Answer 51

•endotherms derive most heat from metabolic activities within their bodies •ectotherms derive most heat from their environment

Question 52

What is negative feedback?

Answer 52

Change triggers a response which reduces the effect of a change by stimulating corrective mechanisms

Question 53

What detects changes in temperature?

Answer 53

•thermoreceptors in hypothalamus (blood temp.) or in skin (external temp.) detect changes and send impulses to the heat loss or heat gain centre in the thermoregulatory centre in the hypothalamus

Question 54

what responses bring about a corrective change when organisms is too cold?

Answer 54

•smooth muscle in the arterioles supplying skin capillaries contract which causes vasoconstriction so less heat loss by radiation •sweat glands have less sweat so less heat loss by evaporation •erector pili muscles contract and raise skin hairs to trap insulating layer of still warm air •skeletal muscles rapidly contract and relax to generate heat by friction/metabolic reactions (shivering) •thyroid and adrenal glands secrete adrenaline and thyroxine to increase metabolic rates to generate more heat

Question 55

What is positive feedback?

Answer 55

It causes the corrective mechanisms to remain turned on so the system deviates further from the set norm point e.g when Na+ move into an axon due to stimuli the permeability of neurone to Na+ increases

Question 56

What is the endocrine system?

Answer 56

Hormonal system where glands secrete hormones in blood to bind to receptors on target cells and bring response

Question 57

What is hypoglycaemia?

Answer 57

Very low levels of glucose in the blood (below optimum range)

Question 58

What is hyperglycaemia?

Answer 58

Very high levels of glucose in the blood (above optimum range)

Question 59

What is glycogenesis?

Answer 59

Conversion of glucose into glycogen for storage in the liver or muscle cells

Question 60

What is glycogenolysis?

Answer 60

Glycogen is broken down into glucose in the liver

Question 61

What is gluconeogenesis?

Answer 61

Glycerol and amino acids can be used to form glucose

Question 62

What is the role of the pancreas?

Answer 62

•cells in islets of langerhans will detect changes in blood glucose con. •B cells secrete insulin •alpha cells secrete glucagon

Question 63

What regulation occurs when blood glucose levels increase?

Answer 63

•detected by beta cells in the *islets of langerhans*(pancreas) which will secrete insulin to decrease it back to optimum= 1.insulin attaches to receptors on target cell surfaces (liver or muscle) which changes the tertiary structure of channel protein so more glucose is absorbed by facilitated diffusion (conc. gradient maintained by glycogen forming) 2.more proteins are incorporated into the cell membrane so more glucose is absorbed from blood 3.activating enzymes involved in converting glucose to glycogen (glycogenesis in liver)

Question 64

How can more protein channels be incorporated into the cell membrane by insulin release?

Answer 64

•insulin binds to insulin receptors •this releases intracellular chemicals •which will cause vesicles containing glucose channel proteins to move and fuse with the cell surface membrane •so more glucose diffuses into cell

Question 65

What regulation occurs when blood glucose levels decreases?

Answer 65

detected by alpha cells in the *islets of langerhans* (pancreas) which will secrete glucagon to increase it back to optimum= 1.attaches to receptors on surface membrane of target cells (liver cells or muscle) which activates enzymes involved in glycogen breakdown (glycogenolysis by the 2nd messenger model) 2.activating enzymes involved in the conversion of glycerol and amino acids into glucose

Question 66

What is the second messenger model?

Answer 66

1.glucagon binds to receptors on the liver cells and will activate enzyme adenylate cyclase 2.this enzyme will convert ATP into cAMP (2nd messenger) 3.cAMP activates protein kinase which catalyses hydrolysis of glycogen to glucose

Question 67

What is the role of adrenaline?

Answer 67

(Uses 2nd messenger model) 1.adrenaline attached to receptors on the surface of target cells which will activate G protein that converts ATP into cAMP 2.cAMP activates enzyme that hydrolyses glycogen into glucose (Also increases sympathetic nervous system due to fight or flight response)

Question 68

What are type 1 and 2 diabetes?

Answer 68

•type 1:autoimmune disease that’s attacks beta cells so cannot release insulin ( insulin injections) •type 2:target cells lose responsiveness to insulin, caused by obesity/poor diet (regulating carbohydrate intake, exercise)

Question 69

What is the cascade effect?

Answer 69

•rapid increase in blood glucose when glucagon is secreted •>1 cAMP forms from one glucagon •>1 enzyme is activated from the cAMP •each enzyme causes breakdown of >1 glycogen into >1 glucose

Question 70

What happens in ultrafiltration?

Answer 70

•high hydrostatic pressure will force small molecule (glucose/mineral ions) and water out of capillaries= glomerulus filtrate •small substances can move through gaps in capillary endothelium and then through the basement membrane •larger proteins and blood cells are too large to pass the basement membrane •pores present in capillaries/podocytes allows filtration

Question 71

What are adaptations for ultrafiltration?

Answer 71

•gaps in the capillary endothelium •only small molecules can pass through basement membrane •podocytes have foot like projections with lots of gaps for filtration

Question 72

What happens in the proximal convulated tubule (PCT)?

Answer 72

Selective reabsorption= •conc. of Na+ in PCT decreases as they are actively transported to the blood in capillaries •Na+ will this diffuse into PCT from the lumen (glomerulus filtrate) = co-transport with glucose •glucose will then diffuse from PCT into the blood stream = all glucose is *reabsorbed* by active transport

Question 73

What are adaptations for selective reabsorption in the proximal convoluted tubule?

Answer 73

•lots of microvilli to provide large surface area for reabsorption •lots of mitochondria to provide energy for active transport •many carrier proteins for active transport

Question 74

What happens in the loop of Henlé?

Answer 74

1.mitochondria in ascending limb to actively transport Na+ and Cl- out of filtrate to tissue fluid (impermeable to water so water remains inside) 2.accumulation of ions outside in the medulla lowers the water potential 3.in the descending limb water moves out by osmosis and Na+ enter, so water is reabsorbed into the blood 4.at the base of ascending limb, some ions are transported out by diffusion as very dilute outside

Question 75

What happens in the distill convoluted tubule and the collecting duct?

Answer 75

•due to all the ions actively moved out in loop of henle, the filtrate reaching DCT is very dilute •section of the medulla is very concentrated so water diffuses by osmosis

Question 76

What happens when water potential in blood increases? (Osmoregulation)

Answer 76

•osmoreceptors in hypothalamus detect this •pituitary gland releases less ADH •DCT and collecting duct walls become less permeable to water •less water is reabsorbed into the blood and more is lost in urine = large volume of dilute urine

Question 77

What happens when water potential of blood decreases? (Osmoregulation)

Answer 77

osmoreceptors in hypothalamus detect this •pituitary gland releases more ADH •DCT and collecting duct walls become more permeable to water •ADH causes vesicles with aquaporins to move + fuse with cell membrane so more osmosis out •more water is reabsorbed into the blood and less is lost in urine = small volume of concentrated urine

Question 78

How does a lack of insulin affect glucose reabsorption? (Diabetes)

Answer 78

•very high glucose concentration in blood •high concentration of glucose in filtrate •glucose is reabsorbed by facilitated diffusion and active transport which use carrier proteins •too much glucose means that the carrier proteins are all saturated at the proximal convoluted tubule so some glucose won’t be able to be reabsorbed = glucose in urine

Question 79

Why does urine concentration increase when medulla thickness increases?

Answer 79

1.thicker medulla means longer loop of Henle 2.so increases concentration of Na+/Cl- in the medulla 3.so water potential gradient is maintained and more water is reabsorbed by loop/DCT or CD

Question 80

Why do muscles occur in antagonistic pairs?

Answer 80

•muscles can only work in one direction •so need to create opposite forces

Question 81

What is the role of synapses in the nervous system?

Answer 81

•unidirectional flow of impulses •spatial and temporal summation

Question 82

Why do patients with untreated diabetes produce a larger volume of urine?

Answer 82

•higher glucose concentration in the filtrate will lower the water potential •this lowers the water potential gradient •so less water is reabsorbed by osmosis