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A Level Biology Paper 2 > Topic 6 > Flashcards

Topic 6 Flashcards

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1
Q

What is a stimulus?

A

A detectable change in the environment

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2
Q

How are stimulus detected?

A

Receptor cells

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3
Q

What kind of responses do animals have?

A

Animals have nerves and hormones which allow them to respond quickly to changes in the environment.

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4
Q

What kind of responses do plants have?

A

Plants lack nerves or hormones but sensitive to the environment and correspond by growing in a particular direction

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5
Q

What are tropism?

A

Plant responses via a growth to stimuli

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6
Q

What stimuli the plants respond to?

A

Light
Gravity
Water
Chemicals

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7
Q

What is a positive tropism?

A

Growing towards a stimulus

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8
Q

What is a negative tropism?

A

Growing away from a stimulus

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9
Q

What does phototropic mean?

A

Growing towards or away from light

This is for maximising photosynthesis

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10
Q

What does gravitropic/geotropic mean?

A

Growing towards or away from gravity

This allows shoots to move towards the sun and water in soil to be absorbed by roots

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11
Q

What does chemotropic mean?

A

Growing towards or away from chemicals

For example so that pollen can reach ovaries

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12
Q

What does thigmotropic mean?

A

Growing towards or away from touch

This allows them to grow upwards

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13
Q

What does aerotropic mean?

A

Growing towards or away from air

This allows plants to grow towards water

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14
Q

What are hormones?

A

Chemical messengers that are secreted into the blood to effect organs and tissues

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15
Q

What do plants not have?

A

Blood and so hormones

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16
Q

What do plants have instead of hormones?

A

Chemicals called growth factors such as IAA

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17
Q

Where is IAA produced?

A

In the tip of the roots and shoots

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18
Q

What is IAA an example of?

A

An auxin

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19
Q

What happens when unilateral light shines on the shoot of a plant?

A

This causes IAA, produced in the tip, to move to the shaded side by active transport
Where it diffuses down the shaded side
Causing cell elongation on this side
These cells elongate faster than the other so the plant bends towards the light

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20
Q

How do plant roots grow towards gravity?

A

IAA moves to the lower side of root by active transport due to gravity
IAA inhibits elongation of cells on lower side
Cells elongate more on upper side and root bends downwards

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21
Q

How does a root cell detect the direction of gravity?

A

Amyloplasts (organelles) that are dense due to be packed with starch and so accumulate on the lower side of cells. IAA is actively transported to where the Amylopasts are.

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22
Q

What does removing the tip or using a cover on the tip of a plant shoot show?

A

The photographic response will stop, this shows that the tip of the shoot is responsible for detecting light.

23
Q

What does putting a gelatin block as a barrier between a plant and the cut tip show?

A

When photographic response still occurs as it shows that the stimulus for growth is a chemical, able to travel through the gelatin block.

24
Q

What does the ability to respond to a stimulus due for organisms?

A

Increase the chances of survival

25
Q

What are taxes and kinesis examples of?

A

Innate animal behaviour

26
Q

What is the taxis response?

A

This is where an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus.

This is a response to a directional stimulus.

27
Q

What is a kinesis response?

A

When organisms change the speed of movement and the rate that changes direction due to a nondirectional stimulus.

This is an increase in random movements designed to bring an organism back to favourable conditions.

28
Q

What is the sequence in a reflex arc?

A

Stimulus
Receptor
Sensory neuron
Relay neuron
Motor neuron
Effector
Response

29
Q

What are the parts of the CNS?

A

Brain and spinal cord

30
Q

How many synapses are involved in reflex arcs?

A

2

31
Q

Why do reflex arcs need to be extremely quick and immediate processes?

A

So that no time is wasted processing information in the brain.

32
Q

What are the three things to describe reflex arcs?

A

Invariable: cannot be varied in the light of experience
Involuntary: happens without any conscious thought
Innate: present from birth

33
Q

What are the two things that the nervous system is divided into?

A

The central nervous system and the peripheral nervous system

34
Q

What do sensory neurones do?

A

Carry nerve impulses from receptors towards the CNS

35
Q

What do motor neurons do?

A

Curry nerve impulses from the CNS towards the effectors

36
Q

What is the pacinian corpusle an example of?

A

A receptor

37
Q

What does the Pacinian corpus respond to?

A

Changes in mechanical pressure

They are deformed by pressure

They respond individually

38
Q

What makes the pacinian corpuslespecific?

A

They only respond to changes in mechanical pressure and not any other kind of stimulus, e.g. heat or light

39
Q

How do pacinian corpuscles act as transducers?

A

By converting mechanical energy into electrical energy in the form of a generator potential.

40
Q

Where are Pacinian corpucles found?

A

In the skin

41
Q

What is the structure of pacinian corpuscles?

A

They have layers of connective tissue called lamella
This tissue is wrapped around the nerve ending of a sensory neuron.

42
Q

Describe a neurone at rest?

A

These neurone have no nervous impulse and so are polarised. They are resting potential and are relatively more negative on the inside (-70 MV)

43
Q

Describe a neurone when stimulated.

A

When there is a nervous impulse, your own become depolarised in the form of an action potential and our relatively more positive on the inside (+40 MV)

44
Q

How are action potential triggered by the pacinian corpuscle?

A

The Pacinian corpuscle is stimulated by pressure
The lamellae are deformed and press on the sensory neurone
The neuron membrane stretches deforming stretch mediated sodium iron channels.
The channels widen and sodium ions diffuse in causing deep polarisation and a generator potential.
If this potential reaches the threshold point an action potential triggered.

45
Q

What is the firing threshold?

A

The threshold needed to trigger an action potential.

46
Q

What does pressure need to do to reach the threshold value for the pacinian corpuscle?

A

Be heavy enough

47
Q

Where are photo receptors located in the eye?

A

The retina

48
Q

Where does light into the eye?

A

The cornea

49
Q

What is the role of the fovea ?

A

This is where light is focused by the cornea and lens.

Light intensity is highest here so this is where the most clones are.

50
Q

What is the optic neuron?

A

This is a sensory neurone which passes action potentials to the brain?

51
Q

How do photo receptors act as transducers?

A

They convert light energy into electrical energy in the form of generator potentials, if the threshold value is reached an action potential forms and an impulse sentence to the brain.

52
Q

How do photo receptors work?

A

When light hits a photo receptor a pigment in the photo receptor absorbs the light and breaks it down.

This is called bleaching

The change causes sodium iron channels to open in the membrane and an influx of sodium ions courses a generator potential.

53
Q

What is bleaching in photo receptors?

A

When a pigment in the photo receptor absorbs the light and breaks it down.

54
Q

What happens if a generator potential, as a result of bleaching, reaches the threshold value?

A

An impulse passes to the optic nerve via a bipolar neurone as an action potential

A Level Biology Paper 2 (2 decks)

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