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AQA A LEVEL Biology > Section 6 Response to stimuli > Flashcards

Section 6 Response to stimuli Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is stimuli?

A

A change in the internal and external environment

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2
Q

Why do organisms respond to stimuli?

A

For survival (For predator prey response and homeostasis)

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3
Q

How do “simple” respond to stimuli?

A

Taxis and kinesis

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4
Q

What are taxis?

A

A directional response to a certain stimuli

E.G. If and organism moves away from light it is known as a negative photo-taxis.

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5
Q

What is kinesis?

A

A non-directional movement from an unfavourable area to a favourable area.

Organisms move rapidly and randomly in an unfavourable area until they reach a favourable area where they slow down and move less randomly

This therefore means that they spend less time in an unfavourable area and more time in a favourable one.

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6
Q

What is the response to stimuli in plants?

A

Tropism

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7
Q

What is tropism?

A

A directional growth in plants in response to certain stimuli (Similar to the taxis in non-plant organisms)

E.g. a root would want to be far away from light therefore possessing a negative phototropism.

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8
Q

What is a plant growth factor?

A

The plant equivalent to animal hormones

The difference is that it is made within the cells and only affects those surrounding cells.

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9
Q

What is the effect of IAA on plants?

A

Promotes growth in the shoots and inhibits growth within the roots.

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10
Q

How does a positive phototropism occur within the shoot? (PROCESS)

A

The shoot tip produces IAA sending it down either side of the shoot to make it grow forwards (upwards)

If light is present on the one side the IAA redistributes to the opposite side (shaded side)

This causes the opposite side to grow faster

This then makes the shoot bend towards the light.

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11
Q

How does negative geotropism occur in the root? (PROCESS)

A

If gravity water is present on the one side, the IAA redistributes to the same side

This causes the same side to grow slowly, so the opposite side grows faster

So the root bends towards the gravity and water

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12
Q

What is the response to stimuli in animals?

A

Animals use the nervous system and the hormonal system

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13
Q

Job of the nervous system? (PROCESS)

A

STIMULI to the RECEPTOR to SENSORY neurone to the SPINAL CORD to the MOTOR NEURONE to EFFECTOR which causes a RESPONSE (e.g. muscle contraction/hormone response).

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14
Q

What do receptors do? (PLUS PROCESS)

A

They are the main detector of stimuli

They convert the stimuli into an nerve impulse

Each type of stimuli has a specific receptor

Uses stimuli energy to send sodium ions into the start of the sensory neurone.

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15
Q

What does a pacinian corpuscle do and what is its structure? (PLUS PROCESS)

A

Its a touch receptor found within the skin

Responds to the pressure of touch

Structure: Corpuscle wrapped around the start of the sensory neurone

Process: Pressure applied, corpuscle compressed, stretch mediated sodium channels opened, sodium ions move into the start of the sensory neurone.

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16
Q

How does the retina of the eye work? (PROCESS)

A

Detects light so the brain can generate an image

Detected by the retina (located at the back of the eye)

Made of cone and rod cells

Cone cells detect high light intensity only, produces colour image, with high visual acuity

Rod cells can detect low light intensity, producing black and white images, with a low visual acuity

Cone cells located in the centre of the retina (fovea) site of high light intensity

Rod cells located in the periphery of retina

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17
Q

What are the properties of cone cells in retina?

A

Made of Iodopsin pigment which is only broken down at high light intensity

One cone cell connects to the one bipolar neurone which connects to one sensory neurone

But because one cone cell connects to one bipolar neurone which connects to one sensory neurone each stimuli can be distinguished high visual acuity

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18
Q

What are the properties of rod cells in retina?

A

Made of rhodopsin pigment which can be broken down at low light intensity

A few rod cells connect to one bipolar neurone which connects to one sensory neurone

But because a few rod cells connect to one biopolar neurone which connects to one sensory neurone the stimuli will be merged together = low visual acuity

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19
Q

What is the central nervous system (CNS) and what is its function?

A

Made of the brain and spinal cord
Brain= analyses and coordinates response to stimuli
Spinal cord= connects brain to sensory and motor neurone

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20
Q

What is the peripheral nervous system (PNS) and what is its function?

A

Made of the sensory and motor neurone

A neurone transmits a nerve impulse

Sensory neurone takes nerve impulse from receptor to CNS

Motor neurone takes nerve impulse from CNS to effector

Sensory neurone has its cell body in the middle and has a dendron and axon

motor neurone has its cell body at the start and only has a long axon

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21
Q

What are the 2 different types of motor neurone and what are their function?

A

The two types are:

Voluntary (SOMATIC)
Involuntary (AUTOMATIC)

Somatic supplies skeletal muscle under conscious control

Autonomic supplies cardiac muscles, smooth muscle, glands meaning they are under SUBCONCIOUS control.

Autonomic can be divided into sympathetic and parasympathetic (Having opposite effects)

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22
Q

What is a nerve impulse?

A

Movement of an action potential along a neurone

Action potential= change in membrane potential

Changes from negative (polarised) to positive (depolarised) back to negative (repolarised/ hyperpolarised)

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23
Q

What is a resting potential?

A

Membrane potential of neurone at rest

Is -65mV

Polarised

Caused by having more postive ions outside neurone compared to inside

Involves Na/K ions to be pumped (3 Na out, 2 K in)

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24
Q

What happens during and action potential? (PROCESS)

A

Stimuli causes Na ions to enter the start of the neurone

Makes membrane potential less negative

If it reaches a threshold (-50mV), Na channels open

Therefore more Na ions diffuse into the the neurone, therefore membrane potential becomes positive (depolarised)

The membrane potential reaches +40mV

Then the Na channels close, the K channels open

Therefore k ions diffuse out, therefore membrane potential becomes negative (repolarised)

Too many K ions move out, so the membrane potential becomes more negative than normal (hyperpolarised)

one action potential= depolarisation, repolarisation and then hyperpolarisation

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25
Q

How does an action potential move across a neurone? (Process)

A

By local currents

If the stimuli energy is large enough and enough Na ions enter the start of the neurone

Na ions that move in during depolarisation of the generator potential diffuse along the neurone causing the next section to reach a threshold and an AP to occur

This process continues across the neurone

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26
Q

How does the size of a stimuli effect the action potential?

A

The size must exceed a certain threshold known as the all or nothing threshold. If the stimuli is below a threshold nothing with activate. If it goes above it will give all.

27
Q

What 3 factors affect the speed of a nerve impulse and how?

A

Temperature higher temp means a higher kinetic energy meaning a faster rate of diffusion (faster nerve impulse)

Axon diameter a wider diameter means the neurone is less leaky making the impulse faster

Myelination Schwann cells wrap around axon preventing an action potential with the ap only occuring within the gaps known as the node or Ranvier with the ap jumping from node to node =saltory conduction resulting in a faster nerve impulse.

28
Q

What is a synapse and what is its function (PROCESS)?

A

It is the connection between 2 different neurones

Sends nerve impulses across the gap (synaptic cleft) using neurotransmitters

Action potential arrives at the presynaptic cleft

Calcium ions are released via the channels which enter the presynaptic neurone

Causes vesicles containing neurotransmitters to move to the presynaptic membrane

Vesicles bind to membrane releasing neurotransmitters into cleft

Neurotransmitter diffuses across cleft

Binds to complementary receptors on postsynaptic membrane

Sodium ion channels open and the sodium ions enter

If the threshold is reached the action potential occurs

29
Q

What are the properties of a synapse?

A

Unidirectionality ap/ nerve impulses travel in one direction from pre to post pre contains the neurotransmitter and post has the receptors

FILTERS OUT LOW LEVEL OF STIMULI low level stimuli do not release enough neurotransmitters therefore not enough sodium ion channels are opened therefore not enough ions enter the postsynaptic neurone for the threshold to be reached and no AP PRODUCED.

SUMMATION low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, can be temporal or spatial

INHIBITORY normal synapses are excitatory prevent action potential from occuring by making postsynaptic neurone hyperpolarised

30
Q

What is a reflex?

A

A rapid involuntary response to a stimuli

Does not use brain

The sensory neurone connects directly to motor neurone

Ensures less damage done

31
Q

How is the body’s heart rate controlled?

A

The heart is myogenic its heart beat is initiated by the SAN

The medulla oblongata in the brain can increase or decrease heart rate

Receives nerve impulse from chemoreceptors in the carteriod arteries and pressure receptors in the carotid arteries and pressure receptors in the carotid arteries and aorta

Sends impulse in sympathetic nerves to SAN to increase HR and sends impulse in parasympathetic nerves to SAN to decrease HR

32
Q

How does exercise affect heart rate?

A

Exercise =muscle contraction which requires respiration

Therefore, waste product CO2 is released into blood

This lower pH of blood (acidic)

This is detected by the chemoreceptors in carotid arteries

Sends impulses to medulla oblongata

Then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase

Benefit increase blood flow to lungs to remove CO2 and take in O2

33
Q

How does low blood pressure affect heart rate?

A

If a person moves from lying/sitting to standing blood pressure falls reducing the blood flow to the brain

This is detected by pressure receptors in the carotid and aorta

Sends impulses to medulla oblongata

The medulla oblongata sends impulses to the SAN via the sympathetic nerves causing the heart rate to increase

34
Q

What are the different types of muscle?

A

Skeletal muscle
Smooth muscle
Cardiac muscle

35
Q

Structure of skeletal muscle?

A

Basic structure sarcomeres
made up of actin and myosin, actin is thin and has tropomysosin wrapped around it, myosin is thick and has heads, when the sarcomere contracts the whole muscle contracts, contracts/shortens by the sliding filament mechanism

Many sarcomeres=myofibril
Many myofibrils= muscle fibre
Many muscle fibres= bundle
Many bundles= whole muscle

36
Q

What are the 4 locations within the sarcomere and what changes occur within each part during contraction?

A

A band= location of myosin (no change in contraction)

I band= location between myosin (shortens in contraction)

H zone= location between actin (shortens in contraction)

Z line= end line of sarcomere (moves closer together in contraction)

37
Q

What occurs in sliding fillament mechanism?

A

The sarcomere shortens

The myosin heads pull on the actin INWARD

The somatic motor neurone connects to the skeletal muscle via a neuromuscular junction

One motor neurone connects to a few muscle fibres motor unit

Releases acetylcholine that binds to complementary receptors on the muscle fibre membrane

Na+ channels open allowing sodium ions in causing depolarisation

Wave of depolarisation which travels through the sarcorplasmic reticulum

Causes release of Calcium ions into the sarcoplasm

This moves the tropmyosin on the actin exposing the binding sites

myosin heads now bind to the actin

A power stroke occurs the myosin pulling the actin inwards

ATP attaches to myosin head so it detaches

ATP breakdown by ATPase to release energy

Causes myosin heads to return to original position

So it therefore reattaches pulling the actin further inward

38
Q

What is the role of calcium ions and ATP in muscle contraction?

A

Ca ions causes the tropomyosin to move exposing the binding sites on the actin

The calcium ions stimulate the enzyme ATPase

ATP causes the myosin heads to detach

The ATP releases energy so myosin head returns to original position

ATP actively transports calcium ions back into the sarcoplasmic reticulum

39
Q

What are the 2 types of muscle fibres and how do they individually work (PROCESS)?

A

Fast twitch muscles

They provide powerful but short lasting contractions
Found in the biceps and sprinters
Adapted for anaerobic respiration
Has thicker myosin for powerful contractions
Contains more enzymes for anaerobic respiration
Contains phosphocreatine Provides phosphate to ADP to reform ATP

Slow twitch muscles

Provide less powerful but long lasting contractions
found in thigh muscles
Adapted for aerobic respiration 
Has a rich blood supply 
Contains many mitochondria 
Contains glycogen 
Contains myoglobin to store oxygen
40
Q

What is the role of the hormonal system within the body?

A

Coordinates the response to certain stimuli

Involves chemical messengers (hormones) to affect or change a cell

41
Q

What is diabetes?

A

A disease where a person loses control of their blood sugar levels

This usually results in having high blood sugar (Hyperglycaemia)

There are 2 types: type 1 and type 2

Type 1 starts at a young age and is due to the person not producing enough insulin hormone

Type 2 occurs at a later age and is due to cells becoming less sensitive to insulin that is produced due to diet high in simple sugars and or obesity.

Symptoms: Tiredness, increased urination and thirst

Diagnosis: high blood glucose levels on random testing & blood glucose levels remain high following a fasting blood glucose test

42
Q

What is homeostasis?

A

Maintenance of the bodies internal environment

The control of the temperature of body along with pH blood glucose levels as well as blood salt and water levels and blood pressure.

43
Q

What is positive and negative feedback in homeostasis?

A

Positive feedback is where the response to the change is to continue the change

Negative feedback is where the response to the change or bring levels back to normal

44
Q

Why do organisms need to maintain constant body temperature?

A

To provide the optimum conditions for enzymes and enzyme activity

45
Q

What are endotherms and exotherms

A

Endotherms are animals that maintain a strict constant body temperature irrespective of the external environments temperature

Ectotherms animals internal body temperature maintained more generally and varies with changes in external environment temperature.

46
Q

Benefit of being an endotherm?

A

Can maintain activity over a range of settings

47
Q

Benefit of being an ecotherm?

A

Requires less food/ energy

48
Q

How is internal body temperature controlled?

A

Anatomical, behavioural, physiological changes
Ecotherms mainly rely on behavioural changes
Endotherms mainly rely on physiological changes

49
Q

Anatomical adaptations in organisms in warm areas?

A

Small body size means a large surface area to volume ratio

Less fur

Less fat

Large extremities

50
Q

Anatomical adaptations in organisms in cold areas?

A

Large body size meaning a small surface area to volume ratio (Less heat given off)

More fur

More fat

small extremities (less heat loss)

51
Q

Behavioural/physiological changes in ecotherms?

A

Warming up= exposure to sun or pressing on a warm surface, darker skin to absorb more heat, higher amounts of respiration in liver and less breathing

Cooling down= shaded from the sun pressing on a cold surface lighter skin colouration, less respiration in liver and more breathing.

52
Q

Control of body temperature in endotherms?

A

Controlled by hypothalamus in the brain

Recieves nerve impulse from peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus

Peripheral thermoreceptors monitor changes in external environment temperature

Central thermoreceptors monitor changes in core body temperature

53
Q

How an endotherm cools itself down?

A

Increase blood supply to skin surface

Sweating evaporation of water molecules from the skin surface using the heat in the blood

54
Q

What is the structure of the kidneys?

A

Outer region called cortex and middle region called medulla

55
Q

Role of kidneys?

A

Filter blood of urea, salts, excess water

56
Q

Why must urea be removed from the blood?

A

It is a toxic substance and can harm the body

57
Q

Why remove excess salts and water?

A

Maintain correct water potential and pressure in blood.

58
Q

How do kidneys filter the blood?

A

Made up of millions of nephrons

59
Q

Structure of nephron?

A 
1st part bowmans capsules 
2nd part proximal convoluted tubule
3rd part Loop of Henle
4th part of distal convoluted tubule
5th Collecting duct
60
Q

Bowmans capsule

A

Site of nephron

Site of ultrafiltration

Occurs between specialised cappilaries called glomerulus and bowmans capsule

Glomerulus located in the middle of an arteriole

Affirent arteriole before glomerulus into bowmans capsule

small substances filtered glucose, amino acids , salts and urea

Only small substances can pass through the 3 layers

Glucose, and amino acids and some of the salts and water back into the blood (re absorption)

61
Q

Proximal convoluted tube?

A

Second part of the nephron

Site of selective reabsorbtion

All glucose and amino acids and some of the salts and water are send back into the blood

62
Q

Loop of henle?

A

Third part of the nephron

site of further water re absorption

occurs by hairpin counter current multiplier

sodium and chloride ions are actively transported out of the ascending limb of the loop of henle into the surrounding medulla of kidney
this lowers water potential of medulla
so water moves out of the descending limb of loop of henle (and collecting duct) by osmosis into the medulla
this water then moves into the blood
the sodium and chloride ions then diffuse into the descending limb of loop of henle so the above process can be repeated.

63
Q

Distal convoluted tubule ?

A

Fourth part of the nephron
Site of further salt re absorption
Corrects required salt balance between blood and urine

64
Q

Collecting duct? (LONG)

A

final part of nephron
site of further water reabsorption and osmoregulation
end up being left with urine that is sent into the ureter to the bladder

water reabsorption occurs by the hairpin countercurrent multiplier

amount of water being reabsorbed is controlled at this stage, this is known as osmoregulation

osmoregulation is the process by which the hypothalamus controls water potential of the blood (an example of homeostasis)

if water levels become low (dehydration):
osmoreceptors in hypothalamus shrink
this stimulates the release of ADH from the posterior part of the pituitary gland

ADH stimulates the cells lining the collecting duct to increase the number of aqauporins (water channels)
so more water moves from the collecting duct back into blood

so less water is lost in the urine

if water levels become high (overhydration):

less ADH released
l
ess aquaporins in collecting duct

less water moves from collecting duct into blood

more water lost in urine (reduces overhydration)

AQA A LEVEL Biology (8 decks)

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