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A Level Biology Paper 2 > Section 6: Stimuli and responses > Flashcards

Section 6: Stimuli and responses 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 1 stimulus
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3
Q

What is a co-ordinator?

A
  • Formulates a suitable response to a stimulus
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4
Q

What is an effector?

A
  • Produces response to a stimulus.
  • E.g muscle/gland
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5
Q

What are the steps in a reflex arc?

A
  • Stimulus - receptor - sensory neurone - co-ordinator - CNS/ Relay Neurone - motor neurone - effector - response
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6
Q

What is the importance of a reflex arc?

A
  • Rapid because only 3 neurones and few synapses
  • Autonomic does not involve passage to the brain - does not have to be learnt
  • Protect from harmful stimuli e.g escape from predators/ prevents damage to the body/tissues
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7
Q

What is Taxes?

A
  • Directional response by a simple mobile organism towards a stimulus (positive taxis) or away from a stimulus (negative taxis)
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8
Q

What is Kinesis?

A
  • Non-directional responses by simple mobile organism who change the speed of movement or the rate of direction change in response to a non-directional stimulus
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9
Q

What is tropism and what is positive and negative tropism?

A
  • Tropism - growth of a part of a plant in response to a directional stimulus
  • Positive tropism - growth towards a stimulus
  • Negative tropism - growth away from a stimulus
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10
Q

What are growth factors?

A
  • Move from growing regions e.g shoot tips/ leaves where they are produced to other tissues where they regulate growth in response to directional stimulus e.g auxins
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11
Q

What does IAA do in roots and shoots?

A
  • In roots, IAA inhibits cell elongation
  • In shoots IAA promotes cell elongation
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12
Q

How IAA promotes phototropism in shoots?

A
  • Cells in tip of shoot produce IAA - transported down shoot
  • IAA concentrates on shaded side
  • Promotes cell elongation
  • Shoot bend towards light
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13
Q

How IAA results in gravitropism in roots?

A
  • Cells in tips of shoot produce IAA - transported down shoot
  • IAA concentration increases on the lower side of the root
  • Inhibits cell elongation
  • Root curves downwards towards gravity
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14
Q

How is a generator potential produced?

A
  • Mechanical stimulus e.g pressure deforms lamellae and stretch-mediated sodium ion channel
  • Sodium ion channels open and sodium ions diffuse into the sensory neurone
  • Greater pressure causes more channels to open and more sodium ions to enter
  • Causes depolarisation, leading to a generator potential - if Generator potential reaches threshold it triggers an action potential.
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15
Q

What does the Pacinian Corpuscle illustrate?

A
  • Receptors only respond only to a specific stimulus (pressure)
  • Stimulation of a receptor leads to establishment of a generator potential. When threshold is reached an action potential sent (all or nothing principle)
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16
Q

What are some of the differences between rod and cone cells?

A
  • Rods - more at periphery end . Cones - concentrated at fovea
  • Rods - 1 type of rod containing 1 pigment. Cones - 3 types of cones containing different pigments
  • Rods - connect in groups to 1 bipolar neurone. Cones - 1 cone joins 1 neurone
  • Rods - Very sensitive to light. Cones - less sensitive to light
  • Rods - Low visual acuity. Cones - high visual acuity
  • Rods - Black and white (monochromatic). Cones - Colour (trichromatic)
17
Q

Why are rods more sensitive to light?

A
  • Rods connected in groups to 1 bipolar neurone
  • Spatial summation
  • Stimulation of each individual cell connected in groups means threshold is more likely met
18
Q

Why do cones have a higher visual acuity?

A
  • 1 cone joins to 1 neurone
  • If 2 adjacent cone cells are stimulated, brain receives separate impulses
18
Q

Why do cones have a higher visual acuity?

A
  • 1 cone joins to 1 neurone
  • If 2 adjacent cone cells are stimulated, brain receives separate impulses
19
Q

Why do rods have a lower visual acuity

A
  • Rods connected in groups to 1 bipolar neurone
  • Spatial summation
  • Many neurones only generate 1 impulse/ action potential, regardless of how many neurones stimulated
20
Q

How does cones allow for colour vision?

A
  • 3 types of cones
  • With different optical pigments that absorb different wavelengths
  • Stimulation of different combinations gives a range of colour perception
21
Q

How is the heart stimulated

A
  • SAN sends out regular waves of electrical activity across both atria
    • Causing right/left atria to contract simultaneously. Non-conducting tissue prevents wave crossing directly to ventricles
  • Waves of electrical activity reaches AVN which delays impulse, allowing atria to fully contract and empty
  • AVN passes wave of electrical activity to Bundle of His which conducts waves between ventricles to the apex of the heart where it branches into smaller fibres - Purkyne fibres
22
Q

Where are the baroreceptors and chemoreceptors located

A
  • In the aorta and carotid arteries
23
Q

What are baroreceptors and chemoreceptors stimulated by

A
  • Baroreceptors are stimulated by high/low blood pressure
  • Chemoreceptors are stimulated by blood pH, CO2 conc, O2 conc
24
Q

What happens when there is a low BP

A
  • Baroreceptors detect the low blood pressure
  • More frequent impulses to the medulla
  • More frequent impulses sent to SAN along sympathetic neurone
  • Cardiac muscle contracts more frequently so heart rate increases
25
Q

What happens when there is high blood pressure

A
  • Baroreceptors detect the high blood pressure
  • More frequent impulses to medulla.
  • More frequent impulses sent to SAN along parasympathetic neurone
  • Less frequent impulses sent from SAN. Cardiac muscle contracts less frequently so heart rate decreases
26
Q

What happens when there is a high blood carbon dioxide concentration/ low pH

A
  • Chemoreceptors detect the high carbon dioxide concentration
  • More frequent impulses are sent to SAN along sympathetic neurone
  • More frequent impulses sent to SAN - cardiac muscle contracts more frequently so heart rate increases
27
Q

What happens when there is a low blood carbon dioxide concentration?

A
  • Chemoreceptors detect low blood CO2
  • More frequent impulses sent to medulla
  • More frequent impulses sent to SAN along parasympathetic neurone
  • Less frequent impulses sent from SAN - cardiac muscle contracts less frequently - heart rate decreases.
28
Q

EXAM QUESTION: Increased intensity of exercise leads to an increased heart rate. Explain why (3)

A
  • Oxygen/carbon dioxide detected by chemoreceptors/ pressure detected by baroreceptors
  • Medulla/ cardiac centre involved
  • More impulses to SAN/ along sympathetic nerve

A Level Biology Paper 2 (10 decks)

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