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Biology - Mrs Dudley > 14.1 - 14.5 Response to stimuli > Flashcards

14.1 - 14.5 Response to stimuli Flashcards

1
Q

Define tropism

A

The growth of part of a plant in response to a directional stimulus
Positive = towards stimulus
Negative = away from stimulus

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2
Q

Define phototropism

A

The growth of a plant in response to light

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3
Q

Define geotropism

A

The growth of a plant in response to gravity

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4
Q

Describe how positive geotropism occurs

A
  • IAA produced in root tip
  • IAA accumulates on lower side of shoot
  • IAA inhibits cell elongation, causing root to bend downwards
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5
Q

What is a plant growth factor?

A
  • Hormones that effect growth
  • Usually made by cells throughout the plant rather than by a particular organ
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6
Q

What is the main plant growth factor?

A

IAA (indoleacetic acid)
This belongs to a group of substances called auxins

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7
Q

Where is IAA produced?

A

By cells in the tip of the shoot or root

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8
Q

Describe how positive phototropism occurs

A
  • IAA is produced in shoot tip
  • IAA accumulates on shaded side
  • IAA causes elongation of shoot cells, bending shoot towards the light
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9
Q

Describe how negative phototropism occurs

A
  • IAA produced in root tip
  • IAA accumulates on shaded side
  • IAA inhibits cell elongation, bending root away from light
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10
Q

Describe how negative geotropism occurs

A
  • IAA produced in shoot tip
  • IAA accumulates on the lower side of the shoot
  • IAA causes cell elongation, causing shoot to bend upwards
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11
Q

How does IAA affect plant cells?

A
  • Increases plasticity of plant cell walls
  • Only affects young plant cells as as cells mature they develop greater rigidity
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12
Q

Define stimulus

A

A change in the internal or external environment

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13
Q

Define taxis (plural is taxes)

A

A directional response to stimulus
* Negative = move away from
* Positive = move towards

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14
Q

Define phototaxis

A

Taxis in response to light

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15
Q

Define chemotaxis

A

Taxis in response to the concentration of a substance

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16
Q

Define kinesis

A

A non-directional movement in response to a stimulus

Organisms tend to move faster and change direction more frequently in less favourable environments

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17
Q

List the five stages of a reflex arc

A
  1. Stimulus - detectable change
  2. Receptor - detects stimulus
  3. Coordinator - formulates response
  4. Effector - Produces response
  5. Response
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18
Q

Describe central nervous system

A

Made up of the brain and spinal cord

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19
Q

Describe the peripheral nervous system

Around the CNS

A

* Sensory neurones - transmit electrical impulses from receptors to the CNS
* Motor neurones - transmit electrical impulses from the CNS to the effectors

20
Q

Describe the divisions of the motor system

Conscious control or not

A
  • Voluntary nervous system - transmits electrical impulses to body muscles under voluntary/conscious control
  • Autonomic nervous system - transmits electrical impulses to glands, smooth and cardiac muscle not under voluntary control
21
Q

Define reflex

A

A rapid, involuntary response to a stimulus
e.g blinking, removing the rapidly hand from a hot object, focusing the eye

22
Q

Define reflex arc

A
  • A pathway along which impulses are transmmitted from a receptor to an effector without involving the conscious regions of the brain
  • Faster than any other type of nervous response
23
Q

List the sequence of neurones an electrical impulse travels along during a reflex

A
  1. Sensory neurone
  2. Intermediate/relay neurone
  3. Motor neurone
24
Q

List the advantages of simple reflexes

A
  • Rapid
  • Protect against damage to body tissues
  • Do not have to be learnt
  • Help escape from predators
  • Enable homeostatic control
25
Q

Define generator potential

A

Depolarisation of the membrane of a receptor cell as a result of a stimulus

26
Q

What is the Pacinian corpuscle?

A
  • A receptor
  • Responds to mechanical pressure
  • Found in the skins lower layers and in joints
27
Q

Describe what happens when pressure is applied to the Pacinian corpuscle

A
  • The Pacinian corpuscle is deformed and the membrane around its neurone becomes stretched
  • This widens stretch-mediated sodium ion channels and sodium ions diffuse into the neurone
  • The stronger the pressure, the more sodium ion channels open
  • The influx of sodium ions changes the potential of the membrane so it becomes depolarised
  • This produces a generator potential which then creates an action potential
  • Action potential passes along the neurone to the central nervous system
28
Q

Define photoreceptors

A

Light receptors in the eye

29
Q

Why is there a blind spot in vision?

A

There are no photoreceptor cells here as this is the point where the optical nerve connects to the eye

30
Q

Must also:

A
  • Label pacinian corpuscle
  • Label receptors in the retina diagram
31
Q

Describe the number and distribution of rods and cone cells

A

Rods:
* Greater number
* More at the periphery of the retina
* Absent at the fovea

Cones:
* Fewer
* Fewer at the periphery of the retina
* Concentrated at the fovea

32
Q

Describe the visual acuity of rods and cones

A

Rods:
* Low
* 3 rod cells connected to a single bipolar neurone
* Only one impulse sent to the brain so cannot distinguish between separate sources of light

Cones:
* High
* Each cone cell is connected to a single neurone and sends seperate impulses tp the brain
* Separate impulses sent to the brain so separate sources of light can be distinguished

33
Q

Describe the sensitivity to light of rods and cones

A

Rods:
* Sensitive to low light intensities
* Rhodopsin breaks down in dim light
* As mutliple rods are connected to the same neurone, the threshold value is more likely to be exceeded, creating a generator potential

Cones:
* Not sensitive to low light intensities
* Iodopsin breaks down in bright light only

34
Q

Describe the sensitivity to different wave lengths of rods and cones

A

Rods:
* One type of rod containing one pigment
* Can’t distinguish between wave lengths

Cones:
* Three different types of cone cells that respond to different wavelengths i.e red sensitive, green senitive and blue sensitive

35
Q

Name the different visual pigments found in rods and cones

A
  • Rods = Rhodopsin
  • Cones = Iodopsin
36
Q

Define myogenic

A

Contraction is initiated from within the muscle itself, rather than by nervous impulses from outside e.g cardiac muscle

37
Q

What is the pacemaker?

A
  • Sinoatrial node
  • Within the wall of the right atrium
38
Q

Describe the control of heart rate

A
  1. A wave of electrical activity spreads out from the SAN over the atria causing them to contract. A layer of non-conducting tissue prevents the wave of electrical activity from being passed directly to the ventricles.
  2. The electrical activity reaches the AVN where there is a short delay to make sure the atria have emptied before the ventricles contract
  3. AVN sends the wave of electrical activity between the ventricles along the Purkyne tissue that makes up the bundle of His
  4. Bundle of His conducts the wave through the septum to the base of the ventricles where the bundle branches into smaller fibres of Purkyne tissue
  5. Purkyne tissue carries the electrical activity into the muscular walls of the ventricles, causing them to contract from the base up
39
Q

Define autonomic nervous system

A

Self-governing nervous system which controls involuntary activities of internal muscles and glands

Split into:
1. Sympathetic nervous system
2. Parasympathetic nervous system

40
Q

What is the difference between the sympathetic and the parasympathetic nervous sympathetic?

A
  • Sympathetic - Stimulates effectors and so speeds up any activity
  • Parasympathetic - Inhibits effectors and so slows down any activity

These sysems are antagonistic

41
Q

Define chemoreceptors

A
  • Stimulated by changes in pH of the blood due to changes in CO2 conc
  • Found in the walls of the carotid arteries and the aorta
42
Q

Define pressure receptors

A
  • Stimulated by high and low blood pressure
  • Found in the walls of the carotid arteries and the aorta
43
Q

Describe how the rate of resting heart rate is controlled

A
  • Region of the brain called the medulla oblongata
  • A centre that increases the heart rate is linked to the sinatrial node by the sympathetic nervous system
  • A centre that decreases heart rate is linked to the sinoatrial node by the parasympathetic nervous system
44
Q

Describe the effect of exercise on cardiac output

A
  • Increased metabolic activity
  • More CO2 produced by tissues from increased respiration
  • Blood pH is lowered
  • Chemical receptors in the carotid arteries increase frequency of impulses to the medulla oblongata
  • Centre in the medulla oblongata that speeds heart rate, increases frequency of impusles to SA node via sympathetic nervous system
  • SA node increases heart rate
  • Increased blood flow removes CO2 faster so CO2 conc returns to normal
45
Q

Describe the effect of high blood pressure on cardiac output

A
  • Pressure receptors in the walls of the carotid arteries and aorta detect high blood pressure
  • Pressure receptors transmit more nervous impulses to the medulla oblongata
  • Centre that decreases heart rate sends impulses to the SA node via the parasympathetic nervous system
  • Decreases rate of heart beats

Biology - Mrs Dudley (12 decks)

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