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AQA A Level Biology > 3.6 Organisms respond to changes in their internal and external environments > Flashcards

3.6 Organisms respond to changes in their internal and external environments Flashcards

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1
Q

What is a stimulus?

A

Detectable change in the internal/external environment of an organism that leads to a response

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2
Q

What is a receptor?

A

Detects stimulus, specific to one type of stimulus

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3
Q

What is a co-ordinator?

A

Formulates a suitable response to a stimulus e.g. nervous system/hormal system

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4
Q

What is an effector?

A

Produces a response to a stimulus e.g. muscles/glands

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5
Q

What are the stages of a response to a change in the environment and why is it beneficial?

A

Stimulus
Receptor
Coordinator
Effector
Response

Organisms increase their chance of survival

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6
Q

What is tropism?

A

The growth response of a plant in response to a directional stimulus

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7
Q

What is positive tropism and negative tropism

A

Positive tropism: Growth towards the stimulus
Negative tropism: Growth away from the stimulus

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8
Q

Describe the responses in plants linking to growth factors

A

Growth factors move from growing regions where they a produced to other tissues, where they regulate growth in response to directional stimuli

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9
Q

What is IAA?

A

Indoleacetic Acid (IAA)

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10
Q

How does IAA result in phototropism in shoots?

A

Cell in the tip of shoot make IAA
Transported down the shoot
IAA conc increases on the shaded side
Promotes cell elongation
Shoot bends towards the light positive phototropism

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11
Q

How does IAA result in gravitropism?

A

Cells in tip of shoot produce IAA
Transported down the shoot
IAA conc increases on lower side of the root
Cell elongation
Root curve downwards towards gravity - positive gravitropism

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12
Q

What does a receptor do?

A

Detects a stimulus and converts stimuli energy into impulse

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13
Q

Describe the mechanism of the Pacinian Corpuscle?

A

Stimulus of Pressure deforms the lamellae and stretch mediated sodium channel
Sodium ion channels open and ions diffuse into sensory neuron
Greater pressure leads to more channels opening and greater ions
Depolarisation leading to generator potential as it reaches threshold triggering an action potential

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14
Q

What does the pacinian corpuscle illustrate?

A

Receptors only respond to a specific stimuli
Stimulation of a receptor leads to generator potential

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15
Q

Give the differences of a cone and rod cells

A

Rod
More at periphery of retina
One type of rod containing pigment
Connected in groups to one bipolar neuron
Sensitive to light
Low visual acuity
Black & White vision

Cones
Concentrated at fovea
3 types of cones containing different optical pigments
One cone joins one nuerone
Less sensitive
High visual acuity
Colour (trichromatic) visinon

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16
Q

Describe and explain the differences in sensitivity to light

A

Rods are more sensitive
One bipolar cell so spatial summation as cells connected in groups likely to meet threshold

Cones are less sensitive
One cone joins to one neurone
No spatial summation

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17
Q

Describe and explain differences in visual acuity

A

Cones give higher visual acuity
One cone to one bipolar nuerone to one sensory neuron
Each stimuli can be distinguished

Rods give lower
Connected in groups to one bipolar cell → spatial summation
Many neurons generate one impulse → can’t distinguish stimuli

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18
Q

Describe and explain difference in sensitivity to colour

A

Cones allow colour vision
Different optical pigments absorb different wavelengths
Stimulation of different combinations give range of colour perception

Rods offer monochromatic vision → one type of cone/pigment

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19
Q

How would you describe the cardiac muscle?

A

Myogenic

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20
Q

What prevents electrical waves from crossing directly to the ventricles?

A

A layer of non-conductive tissue

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21
Q

What is the AVN and its role?

A

Delays impulse allowing atria to fully contract and empty
Passes wave of electrical activity to the buncle of His → apex which cause ventricles to contract from bottom up

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22
Q

What are the names of the receptors involved with the control of the heart rate?

A

Baroreceptors
Chemoreceptors

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23
Q

Where are Baroreceptors and chemoreceptors located?

A

in aorta and carotid arteries

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24
Q

Describe what happens when low blood pressure occurs

A

Baroreceptors stimulated by LOW BP
More frequent impulses to the medulla
More impulses sent to the SAN along sympathetic neuron
More frequent impulses sent from SAN
Cardiac muscle contracts more frequently so heart rate increases

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25
Q

Describe what happens when there is LOW blood Carbon Dioxide Concentration/High PH

A

More frequent impulses sent to the medulla
More frequent impulses sent to SAN along parasympathetic neurons
Less frequent impulses sent from SAN
Cardiac muscle contracts less frequently so heart rate decreases

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26
Q

Describe how a resting potential is established within an axon

A

Sodium-Potassium ion pump actively transports 3Na+ ions out and 2K+ ions in

Electrochemical gradient created as higher concentration of potassium inside than outside

Membrane more permeable to potassium ions causing sodium ion channels to close

Potassium ion move out via facilitated diffusion

Inside of axon negatively charge relative to outside

Axon is polarised = resting potential

27
Q

State the changes in membrane permeability in the generation of an action potential

A

Stimulus
Depolarisation
Repolarisation
Hyperpolarization
Resting Potential restored

28
Q

Explain the changes in membrane permeability in a neuron in the generation of an action potential

A

Stimulus
- Membrane more permeable to sodium ions as sodium ion channels open
- Sodium diffuse into neurone down electrochemical gradient

-Depolarisation
- P.d. reaches threshold, action potential generated
- Because more voltage-gated sodium ion channels open and sodium diffuse rapidly
Repolarisation
- Sodium ion channels close (membrane less permeable to sodium ions) whilst (voltage-
gated) potassium ion channels open so potassium ions diffuse out of neurone

  • Hyperpolarisation
  • Potassium ion channels slow to close so there’s a slight overshoot – too many potassium

ions diffuse out of neurone
Resting potential restored
- By sodium-potassium pump

29
Q

Why Is the Refractory Period important?

A

Discrete and discontinuous impulses (no overlap)
Unidirectional action potential - cannot be propagated in a region that is refractory
Limits frequency of impulse transmission at a certain intensity

30
Q

Define ‘Refractory Period’

A

The time to restore axon to resting potential

31
Q

What factors affect the speed of conductance?

A

Myelination
Axon Diameter
Temperature

32
Q

How does myelination affect speed of conductance?

A

Depolarisation at nodes by saltatory conduction (jumps from node to node)
Unlike non-myelinated that has to depolarise whole length of axon
Faster

33
Q

How does Axon Diameter affect speed of conductance?

A

Bigger diameter means less resistance of ions

34
Q

How does temperature affect speed of conductance?

A

Increases rate of movement of ions Na+ and K+ as more kinetic energy → active transport

Higher rate of respiration so ATP produced faster and energy released faster —> faster active transport

Proteins could denature at some point

35
Q

Explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon.

A

non-myelinated - next section of membrane depolarised / whole
Membrane = slower

myelinated - depolarisation / ion movement only at nodes;
impulse jumps from node to node /saltatory conduction;

36
Q

Explain transmission across a cholinergic synapse?

A
  1. Action potential arrives causing calcium ion channels to open → calcium ions diffuse into pre-synaptic neurone
  2. Causing vesicles containing acetylcholine to fuse to pre-synaptic membrane → release acetylcholine into synaptic cleft (exocytosis)
  3. Neurotransmitters diffuse across synaptic cleft → bind to specific neurotransmitter receptors found only on post-synaptic membrane
  4. Sodium ion channels open → sodium ions diffuse into post-synaptic knob → depolarisation initiates action potential as threshold is met (excitatory synapse)
  5. Neurotransmitter removed from cleft so response doesn’t keep happening by
    an enzyme called acetylcholinesterase
37
Q

Compare transmission across cholinergic and neuromuscular junctions

A

Cholinergic:
Neuron to neuron

Neuromuscular:
Postsynaptic membrane has more receptors than other synapses
Lots of folds on postsynaptic membrane = clefts to store enzyme to break down neurotransmitter

38
Q

Why do synapses result in unidirectional nerve impulses?

A

Neurotransmitter only made in/released from pre-synaptic nuroene
Nueroreceptors only on post-synaptic membrane

39
Q

What is spatial summation?

A

Many presynaptic neurons share the same synaptic cleft
Collectively release sufficient neurotransmitter to reach threshold and trigger action potential

40
Q

What is temporal summation?

A

One presynaptic neurone releases neurotransmitter many times over a short period
Sufficient neurotransmitter to reach threshold to trigger an action potential

41
Q

What do inhibitory synapses do?

A

neurotransmitters that prevent the generation of an action potential in a postsynaptic neurone

42
Q

How do inhibitory synapses cause inhibition?

A

Hyperpolarize the postsynaptic membrane
Inhibits the formation of action potential

  1. opening the gated potassium ion channels in the membrane so that potassium ions are able to diffuse out of the cell body
  2. both excitatory and inhibitory neurons forming synapses:
    a. Sodium ions enter the cell body following stimulation by the excitatory synapse
    b. The stimulation of the inhibitory synapse causes potassium ions to diffuse out of the cell body
    c. This cancels out the effect of the sodium ions entering
    d. The threshold potential is not reached so no action potential is generated
43
Q

Describe the relationship of muscles

A

Antagonistic

44
Q

What is the advantage of the muscle being antagonistic pairs?

A
  • muscles can only contract/pull
  • help maintains posture
45
Q

Describe the structure of a muscle fibres

A

Sacrolemma
Sacroplasm
Myrofibirls
shared nuclei
many endoplasmic reticulum

46
Q

What is Osmoregulation?

A

the control of water and salt levels in the body

47
Q

How does the body respond to a decrease in water potential?

A
  1. Detected by osmoreceptors in hypothalamus
  2. Hypothalamus produces more ADH → posterior pituitary gland secretes more ADH into blood
  3. ADH travels in blood to kidney and attaches to receptors on collecting duct / DTC of kidney
  4. ADH increases permeability of walls of the DTC / collecting duct
  5. (more aquaporins fuse with
    cell membrane) to water → more water absorbed from DCT/collecting duct by osmosis
  6. (Less water lost in urine so) smaller volume of urine, more concentrated
48
Q

How the body responds to an increase in water potential?

A
  1. Detected by osmoreceptors in hypothalamus
  2. Hypothalamus produces less ADH → posterior pituitary gland secretes less ADH into blood
  3. Less ADH travels in blood to kidney and attaches to receptors of collecting duct / DTC of kidney
  4. ADH decreases permeability of cells/walls of the DTC / collecting duct to water and urea to water

→ less water absorbed from/leaves DCT/collecting duct by osmosis
5. (More water lost in urine so) larger volume of urine, less concentrated

49
Q

Describe the stages within the nephron in osmoregulation

A

Formation of glomerular filtrate

reabsorption of glucose and water by the proximal convoluted tubule

maintenance of a gradient of sodium ions in the medulla by the loop of Henle

reabsorption of water by the distal convoluted tubule and collecting duct

50
Q

Describe the formaiton of glomerular filtrare in osomoregulation

A
  • Build-up of hydrostatic pressure
    in glomerulus
  • Water, glucose, mineral ions
    squeezed out of capillary /
    glomerulus into the Bowman’s
    capsule to form
    glomerular filtrate
  • Through pores in capillary
    endothelium, basement
    membrane act as filter
  • Large proteins / blood cells
    aren’t pushed out as too large
51
Q

Describe the reabsorption of glucose and water by the proximal convoluted tube

A
  1. Sodium ions actively transported out
    of epithelial cell to capillary
    - Lowers concentration of Na+ in
    epithelial cell
  2. Na+ moves via facilitated diffusion
    from PCT into epithelial cell down
    concentration gradient
    - Co-transporting glucose / amino
    acids / Cl-
    - Increases concentration of
    glucose etc. in epithelial cell
  3. Glucose / amino acids / Cl- move into
    capillary via facilitated diffusion down
    concentration gradient (reabsorbed)
    - Lowers water potential in
    capillary
  4. Water moves via osmosis down water
    potential gradient into capillary
    (reabsorbed)
52
Q

Describe maintaining a gradient of sodium ions in the medulla by the loop of henle

A
  1. Loop of Henle acts as a counter current
    multiplier → maintains water potential
    gradient → water leaves collecting duct
    /DCT by osmosis
  2. Na+ actively transported out of
    ascending limb and ascending limb is
    impermeable to water so water remains
    - Increases conc of Na+ in medulla →
    lowers water potential
  3. Water moves out of descending limbs /
    collecting duct by osmosis into medulla
    - Water reabsorbed by capillaries
  4. Na+ diffuse into descending limb
    - Recycles Na+ in loop of Henle
    - Reduces water potential further
53
Q

What factors influence blood glucose concentration

A
  • eating food containing carbohydrates –> glucose absorbed from intestine to blood
  • exercise –> increase rate of respiration of glucose
54
Q

What factors influence blood glucose concentration

A
  • eating food containing carbohydrates –> glucose absorbed from intestine to blood
  • exercise –> increase rate of respiration of glucose
55
Q

Describe action of insulin

A

Insulin binds to specific receptors on cell surface membranes of liver / muscle cells (target cells)

  • Increases permeability of muscle cell membrane to glucose → by increasing number of
    channel proteins (GLUT4) in cell surface membrane → cells uptake more glucose from
    blood by facilitated diffusion
  • Activation of enzymes in liver / muscle cells that convert glucose to glycogen
    (glycogenesis) → store glycogen in cytoplasm
  • Rate of respiration of glucose also increases
  • DECREASES blood glucose concentration
56
Q

When is insulin used?

A

when blood glucose concentration is too high

secretion by beta cells

57
Q

When is glucagon used?

A

secreted by alpha cells
when blood glucose concentration is too low

58
Q

Describe the action of glucagon

A

Binds to specific receptors on cell surface membranes of liver cells (target cells)

  • Activates enzymes involved in the conversion of glycogen to glucose (glycogenolysis)
  • Activates enzymes involved in the conversion of glycerol / amino acids to glucose
    (gluconeogenesis)
  • Rate of respiration of glucose also decreases
  • INCREASES blood glucose concentration
59
Q

When is adrenaline used?

A

secreted by adrenal glands when blood glucose concentration is low/stressed/exercising

60
Q

Describe the action of adrenaline

A

Binds to specific receptors on cell surface membranes of liver cells (target cells)

  • Activates enzymes involved in the conversion of glycogen to glucose (glycogenolysis)
  • Inhibits glycogenesis
  • Activates secretion of glucagon
  • INCREASES blood glucose concentration (more glucose for respiration)
61
Q

Describe the staged of the secondary messenger model

A
  1. Adrenaline / glucagon bind to specific
    complementary receptors on cell
    membrane
  2. Activate adenylate cyclase
  3. Converts ATP to cyclic AMP
    (secondary messenger)
  4. cAMP activates protein kinase A
    (enzyme)
  5. Protein kinase A activates a cascade to
    break down glycogen to glucose
    (glycogenolysis)
62
Q

What is the cause of type 1 diabetes?

A

Gene mutation → Autoimmune
response on B cells of islets on
Langerhans →Body can’t produce
insulin

63
Q

What is the cause of type 2 diabetes?

A

Poor diet / lack of exercise / obesity→
Glycoprotein / receptor loses responsiveness
to insulin (faulty) → cells less responsive to
insulin / don’t take up enough glucose

AQA A Level Biology (9 decks)

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