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A Level Biology > Unit 6 > Flashcards

Unit 6 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Stimulus

A

A change in an organism’s internal or external environment.

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2
Q

Why is it important for organisms to respond to stimuli?

A

Increased chance of survival.

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3
Q

Tropism

A

-Growth of a plant in response to a directional stimulus.
-Positive tropism- towards a stimulus.
-Negative tropism- away from a stimulus.

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4
Q

Role of growth factors in flowering plants

A

-Specific growth factors move from growing regions to tips of roots or shoots.
-They regulate growth in response to directional stimuli.

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5
Q

How indoleacetic acid (IAA) affects cells in roots and shoots?

A

-In shoots, high conc of IAA stimulates cell elongation.
-In roots, high concentrations of IAA inhibit cell elongation.

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6
Q

Gravitropism in flowering plants

A

-Cells in tips of roots produce IAA.
-IAA diffuses down root.
-IAA moves to lower side of root so concentration increases.
-In the roots, IAA inhibits cell elongation.
-Upper cell elongates and roots bend towards gravity.

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7
Q

Phototropism in flowering plants

A

-Cells in tips of shoot produce IAA.
-IAA diffuses down shoot.
-IAA moves to shaded side of shoot so concentration increases.
-In the shoots, IAA stimulates cell elongation.
-Cells grow and bend towards the light.

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8
Q

Taxes

A

-Tactic response.
-Directional response.
-Movement towards or away from a directional stimulus.

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9
Q

Kinesis

A

-Kinetic response.
-Non-directional response.
-Speed of movement or rate of direction change changes in response to a non-directional stimulus.
-Depending on intensity of stimulus.

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10
Q

Basic structure of Pacinian corpuscle

A

-Lamaellae (layers of connective tissue).
-Sensory neurone ending.
-Sensory neurone axon.
-Gel.
-Myelin sheath.
-Stretch mediated sodium ion channel.

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11
Q

How is a generator potential established in a Pacinian corpuscle?

A

-Mechanical stimulus- pressure deforms lamellar and stretch mediated sodium channels open.
-Na+ diffuse into sensory neurone.
-Greater pressure causes more Na+ channels to open and more Na+ to enter.
-This causes depolarisation which leads to a generator potential.
-If generator potential reaches threshold, it triggers an action potential.

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12
Q

What does the Pacinian corpuscle illustrate?

A

-Receptors respond only to specific stimuli.
-Stimulation of a receptor leads to the establishment of a generator potential.
-When threshold is reached, action potential sent (all or nothing principle).

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13
Q

Rods sensitivity to light intensity

A

-Several rods connected to a single neurone.
-Spatial summation to reach threshold (as enough neurotransmitter released) to generate an action potential.

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14
Q

Cones sensitivity to light

A

-Each cone connected to one single neurone.
-No spatial summation.

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15
Q

Rod cells visual acuity

A

-Low visual acuity.
-Several rods connected to a single neurone.
-Several rods send a single set of impulses to brain (can’t distinguish between separate sources of light).

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16
Q

Cone cells visual acuity

A

-High visual acuity.
-Each cone connected to a single neurone.
-Cones send separate impulses to brain (can distinguish between 2 separate sources).

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17
Q

Rod cells sensitivity to colour

A

-1 type of pigment
-Monochromatic vision.

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18
Q

Cone cells sensitivity to colour

A

-3 types of cones- red-, green- and blue-sensitive.
-Different optical pigments- absorb different wavelengths.
-Stimulating different combinations of cones gives range of colour perception.

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19
Q

Cardiac muscle is myogenic?

A

-It can contract and relax without receiving electrical impulses from nerves.

20
Q

Nodes on the heart

A

-Sinoatrial Node (SAN)
-Atrioventricular node (AVN)
-Purkyne tissue
-Bundle of His

21
Q

Myogenic stimulation of the heart

A

-Sinoatrial node (SAN) acts as a pacemaker- releases regular waves of electrical activity across atria.
-Causes atria to contract simultaneously.
-Non-conducting tissue between atria/ ventricles prevents impulse passing directly to ventricles.
-Preventing immediate contraction of ventricles.
-Waves of electrical activity reach atrioventricular node (AVN) which delays impulse.
-Allowing atria to fully contract and empty before ventricles contract.
-AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue.
-Causing ventricles to contract simultaneously from the base up.

22
Q

Where are chemoreceptors and pressure receptors located?

A

In the aorta and carotid arteries

23
Q

Rise in blood pressure, rise in pH

A

-Baroreceptors detect rise in bp and chemoreceptors detect blood fall in blood CO2 conc or rise in blood pH.
-Send impulses to medulla oblonganta/ cardiac control centre.
-Sends more frequent impulses to SAN along parasympathetic neurones.
-So less frequent impulses sent from SAN to AVN.
-Cardiac muscle contracts less frequently.
-Heart rate decreases.

24
Q

Fall in blood pressure, fall in blood pH

A

-Baroreceptors detect fall in bp and chemoreceptors detect blood rise in blood CO2 conc or fall in blood pH.
-Send impulses to medulla oblonganta/ cardiac control centre.
-Sends more frequent impulses to SAN along sympathetic neurones.
-So more frequent impulses sent from SAN to AVN.
-Cardiac muscle contracts more frequently.
-Heart rate increases.

25
Q

Structure of a myelinated motor neurone

A

-Dendrites
-Cell body (soma)
-Axon
-Myelin sheath
-Node of ranvier

26
Q

Resting potential

A

Inside of the axon has a negative charge relative to the outside.

27
Q

How is resting potential established?

A

-Na+/K+ pump actively transports 3Na out of the axon and 2K into the axon.
-Creates an electrochemical gradient.
-Higher K+ conc inside and higher Na+ conc outside.
-Differential membrane permeability.
-More permeable to K+- moved out by FD.
-Less permeable to Na+ (closed channels).

28
Q

Stimulus

A

-Na+ channels open, membrane permeability to Na+ increases.
-Na+ diffuse into the axon down electrochemical gradient (causes depolarisation).

29
Q

Depolarisation

A

-If threshold potential is reached, an action potential is triggered.
-As more voltage-gated Na+ channels open (positive feedback effect).
-More Na+ diffuse in rapidly.

30
Q

Repolarisation

A

-Voltage-gated Na+ channels close.
-Voltage-gated K+ channels open, K+ diffuse out of axon.

31
Q

Hyperpolarisation

A

-K+ channels slow to close so there’s a slight overshoot.
-Too many K+ diffuse out.
-Na+/K+ pump restore resting potential.

32
Q

Action potential graph

A

Draw and label.

33
Q

All-or-nothing principle

A

-For an action potential to be produced, depolarisation must exceed threshold potential.
-Action potentials produced are always same magnitude/size/peak at same potential.
-Bigger stimuli increase frequency of action potentials.

34
Q

Action potential- non-myelinated axon

A

-Action potential passes as a wave of depolarisation.
-Influx of Na+ in one region increases permeability of adjoining region to Na+ by causing voltage-gated Na+ channels to open so adjoining region depolarises.

35
Q

Action potential- myelinated axon

A

-Myelination provides electrical insulation.
-Depolarisation of axon at nodes of Ranvier only.
-Resulting in saltatory conduction (local currents circuits).
-So there is no need for depolarisation along the whole length of axon.

36
Q

Damage to the myelin- slow/ jerky movements

A

-Less saltatory conduction- depolarisation occurs along whole length of axon.
-Nerve impulses take longer to reach neuromuscular junction, delay in muscle contraction.
-Ions may pass to other neurones.
-Causing wrong muscle fibres to contract.

37
Q

Refractory period

A

-Time taken to resture axon to resting potential when no further action potential can be generated.
-As Na+ channels are closed/ inactive/ will not open.

38
Q

Importance of the refractory period

A

-Ensures discrete impulses are produced- AP don’t overlap.
-Limits frequency of impulse transmission at a certain intensity- prevents over reaction to stimulus.
-But only up to a certain intensity.
-Also ensures action potentials travel in one direction- can’t be propagated in a refractory region.
-(In the second half of refractory period, an AP can be produced but requires greater stimulation to reach threshold).

39
Q

Factors that affect speed of conductance

A

-Myelination
-Axon diameter
-Temperature

40
Q

Myelination

A

-Depolarisation at Nodes of Ranvier only- saltatory conduction.
-Impulse doesn’t travel/ depolarise whole length of axon.

41
Q

Axon diameter

A

-Bigger diameter means less resistance to flow of ions in cytoplasm.

42
Q

Temperature

A

-Increases rate of diffusion of Na+ and K+ as more KE.
-But proteins/ enzymes could denature at a certain temp.

43
Q

Cholinergic Synapse

A

-A gap in between two neurones that uses the neurotransmitter acetylcholine (ACh).
-Draw it!!!

44
Q

Describe transmission across a cholinergic synapse

A

-Depolarisation of pre-synaptic membrane causing opening of voltage-gated Ca2+ channel.
-Ca2+ diffuse into pre-synaptic knob.
-Causing vesicles containing ACh to move and fuse with pre-synaptic membrane.
-Releasing ACh into the synaptic cleft by exocytosis.
-ACh diffuses across synaptic cleft to bind to specific receptors on post-synaptic membrane.
-Causing Ligand-gated sodium channels to open.
-Na+ diffuse into post-synaptic knob causing depolarisation.
-If threshold is met, AP is initiated.

45
Q

What happens to acetylcholine after synaptic transmission?

A

-It is hydrolysed by acetylcholinesterase.
-Into acetate and choline.
-Products are reabsorbed by the presynaptic neurone.
-To stop overstimulation- if not removed it would keep binding to receptors causing depolarisation.

46
Q

Unidirectional nerve impulses

A

-Neurotransmitter only made in pre-synaptic neurone.
-Receptors only on post-synaptic membrane.

47
Q

Summation by synapses

A

-Addition of a number of impulses converging on a single post-synaptic neurone.
-Causing rapid buildup of neurotransmitter (NT).
-So threshold more likely to be reached to generate an AP.

A Level Biology (9 decks)

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