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A-level Biology > Internal And External Stimuli > Flashcards

Internal And External Stimuli Flashcards

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1
Q

What is a reflex?

A

A response to an environment which is not processed by the brain

They have a short neurological pathway

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2
Q

What is the process of a reflex arc?

A
  1. Stimulus
  2. Receptors (sensory)
  3. Sensory neurone
  4. Relay neurone/intermediate
  5. Motor neurone
  6. Effector cell (muscles)
  7. Response
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3
Q

What is the importance of a reflex action?

A

Help us to protect us from danger
Help us to move quickly
Help us to see

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4
Q

What are the main types of neurone in a reflex arc?

A

Sensory neurone

Relay neurone

Motor neurone

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5
Q

What is the structure of a neurone?

A

Very long

Contain ion channels (voltage gated Na+. K+. Ca2+)

Sodium potassium pumps

Cell body (nucleus many mitochondria and ribosomes )

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6
Q

What are the Schwann cells?

A

They insulated electrical energy

(Can be unmyelinated or myelinated

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7
Q

What are the nodes of ranvier?

A

Gaps on a neurone between a myelinated neurone

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8
Q

What is the purpose of myelination?

A

Increases the speed of transmission as an electrical impulse (wave of depolarisation) will jump from Node to node rather than be transported along the length of the neurone.

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9
Q

What are sensory receptors?

A

Specialised cells that can detect changes in our surroundings

(Most are transducers)

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10
Q

What is a transducer?

A

Convert energy from one form to another.

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11
Q

Give some examples of sensory receptors?

A

Rod and cone cells- photoreceptors

Pacinian corpuscle- detect change in pressure or vibrations

Baroreceptors- detect changes in blood pressure

Chemoreceptors- changes in partial pressure

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12
Q

What is the structure and function of the pacinian corpuscle?

A

Concentric rings of connective tissue

Only respond to changes in pressure, eg adding pressure causes the corpuscle to deform

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13
Q

What are photoreceptors and what are the two types?

A

Transduce light energy into electrical energy which are found in the retina of the eye.

Rod cells
Cone cells

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14
Q

What is the structure and function of the rod cell?

A

Multiple rod cells are connected to one bipolar cells (retinal convergence)

Black and white ( cannot distinguish between different wavelengths of light) due to the retinal convergence

Used in the dark (low light intensities)

Contain the pigment rhodopsin

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15
Q

What does retinal convergence do?

A

Increase the chance that the threshold value of electrical energy is exceeded.

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16
Q

What are the structure of cone cells?

A

3 different types (red green and blue)

One cone cell per bipolar cell

No summation and so will only respond to higher light intensities

Contain the pigment iodopsin

Better visual acuity

17
Q

How is a resting potential generated?

A
  1. Na+/K+ pump pumps 3Na+ out of the cell and 2K+ into the cell over a period of time. This means that there is a slight difference in the positive charge. Inside of cell being less positively charged
  2. At rest the membrane is differentially permeable to K+band Na+ ions. This means more K+ ions can diffuse out of the cell and a lot fewer Na+ ions will diffuse into the cell
  3. As a result the external charge is more positive than internal charge (but still positive) and therefore the membrane is polarised.
18
Q

What is resting potential on average?

A

-70mv

19
Q

How is an action potential generated?

A
  1. Na+ ions can diffuse into the cell down concentration gradient starting a small depolarisation.( generator potential)
  2. If many generator potentials are generated then they may be summed to create a larger overall depolarisation
  3. If the magnitude of the depolarisation passes the threshold of the cell (-40mv) an action potential will be generated.
  4. Positive feedback:
    Na + depolarisation causes causes the voltage gated Na+ channels to open near by causing he cell to depolarise even more. Voltage of the cell becomes depolarised (+40mv) inside of the cell is more positive than outside.
  5. After a delay the Na+ channels close
  6. K+ channels open and K+ ions diffuse outside of the cell, starting repolarisation however voltage overshoots resting potential and becomes hyperpolarised.
20
Q

What is the refractory period?

A

Na+ channels are closed so there is no way to generate another generator potential.
Also Na+ and K+ ions are in the wrong place and so must be rectified by the sodium potassium pump and this takes time.

21
Q

Why is an action potential unidirectional?

A

The concentration of sodium ions is still in refractory period and so cannot have action potentials going backwards

22
Q

What is saltatory conduction?

A

No ion channels are in myelinated Schwann cells and so depolarisation jumps from nose to nose ( passes via elongated local current without depolarising the membrane)

23
Q

How is an action potential transmitted across a synapse?

A
  1. Action potential arrives at the synaptic bulb
  2. Change in membrane potential causes voltage gated Ca2+ channels to open
  3. Ca2+ ions diffuse into the synaptic bulb
  4. Ca2+ cause vesicles to move and fuse with the presynaptic membrane
  5. Neurotransmitters (eg acetylcholine) are exocytosed into the synaptic cleft where they diffuse across and bind on to protein receptor sites of the Na+ channel proteins. This opens them.
  6. Na+ ions diffuse across the post synaptic membrane and into the post synaptic neurone generating an excitatory post synaptic potential (EPSP).
24
Q

What is a stimulus?

A

A detectable change in the internal or external environment of an organism

25
Q

What is a response?

A

A coordinated reaction to a stimulus that usually increases the chance of survival of an organism

26
Q

Define taxes

A

Directional response to a stimulus whether it is favourable or unfavourable

Positive taxes - movement towards a stimulus
Negative taxes - movement away from a stimulus

27
Q

Define kinesis

A

Non directional response

Changes the speed of movement and rate of turning

Eg temperature humidity

28
Q

Give an example of a plant growth hormone? (An auxin)

A

IAA (indoleacetic acid)

Type of auxin

29
Q

Explain how IAA causes a plants shoot to grow?

A
  1. IAA made in the tip of the the shoot cells
  2. Transported down the shoot
  3. Light causes IAA to move to the shaded side of the shoot cells
  4. As IAA stimulates cell growth in shoots the shaded side grows more than the lighter side and so the shoot tip will elongate and bend towards the light
30
Q

Explain how IAA also controls negative phototropism?

A

IAA causes cell elongation in the shoots but and increased concentration in the roots inhibits cell elongation

31
Q

Explain how IAA causes plants roots to grow ( positive gravitropism)

A
  1. Cells in the tip of the roof produce IAA
  2. This is transported up the root
  3. Gravity cause IAA to be transported to the lower sides of the root
  4. As IAA inhibits elongation of toot cells the top side of the roots grow more and faster and bend down in the direction of gravity
32
Q

How does IAA cause cell elongation?

Mechanism of auxin action

A
  1. IAA is produced I. The shoot tips
  2. Light causes the auxin to be transported to the shaded side of the cells
  3. Auxin causes active transport of H+ ions into the cell wall
  4. This decreases the pH of the cell wall meaning the hydrogen bonds between the cellulose layers become disrupted. This is now the optimum pH for expansins to loosen the walls
  5. Walls are less rigid and allows cells to elongate as they take up water

A-level Biology (23 decks)

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