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Biology A-level > Nervous and hormonal control (part 2) > Flashcards

Nervous and hormonal control (part 2) Flashcards

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1
Q

What is a stimulus?

A

Any change in the internal or external environment

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2
Q

What do receptors do?

A

Receptors detect stimuli – they can be cells or proteins on cell surface membranes

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3
Q

What do effectors do?

A

They bring about a response to a stimulus to produce an effect
Eg muscles cells

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4
Q

How do receptors communicate with effectors?

A

Via the nervous or hormonal system

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5
Q

How does the eye respond to dim light?

A
  • Light receptors in the eyes detect a lack of light
  • The CNS processes information
  • The radial muscles in the iris are stimulated by the motor neurones
  • The radial muscles contract to dilate the pupils
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6
Q

How does the eye respond to bright light?

A
  • Light receptors in the eyes detect bright light
  • The CNS processes the information
  • The circular muscles in the iris are stimulated by the motor neurones
  • The circular muscles contract to constrict the pupils
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7
Q

What is the hormonal system comprised of?

A

Glands and hormones

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8
Q

What is a gland?

A

A group of cells that are specialised to secrete a useful substance such as a hormone
Eg the pancreas secretes insulin

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9
Q

What is a hormone?

A

A ‘chemical messenger’ – many are proteins or peptides but some are steroids

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10
Q

When are hormones secreted?

A

When a gland is stimulated

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11
Q

How can glands be stimulated x2

A
  • By a change in concentration of a substance eg another hormone
  • Electrical impulses
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12
Q

Describe how hormones trigger a response in target cells (use blood glucose):

A
  • Receptors on pancreas cells detect low blood glucose concentration
  • The pancreas releases the hormone glucagon into the blood
  • Target cells in the liver detect glucagon and convert glycogen into glucose
  • Glucose is released into the blood so glucose concentration increase
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13
Q

Differences between nervous and hormonal system x4:

A
  • Nervous uses electrical impulses, hormonal uses chemicals
  • Nervous has a faster response, hormonal has a slower response
  • Nervous has a localised response, hormonal has a widespread response
  • Nervous has a short-lived response, hormonal has a long-lived response
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14
Q

Nervous system: What are photoreceptors?

A

Light receptors in the eye

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15
Q

What part of the eye controls the amount of light entering?

A

The muscles of the iris

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16
Q

What part of the eye contains photoreceptors?

A

The retina

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17
Q

Which part of the retina has an abundance of photoreceptors?

A

The fovea

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18
Q

Name the two types of photoreceptors:

A

Rods and cones

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19
Q

Where are rods found + what do they do?

A

Mainly found in the peripheral parts of the retina

They deliver information in black and white

20
Q

Where are cones found + what do they do?

A

In the fovea

They deliver information in colour

21
Q

What are the three types of cone?

A

Red-sensitive, blue-sensitive, green-sensitive

22
Q

What happens to rod cells when stimulated by light?

A

They become hyperpolarised

23
Q

What is the light-sensitive pigment found in rod cells called and what is it made of?

A

Rhodopsin is made of retinal and opsin

24
Q

What happens to rod cells in the dark?

A
  • Sodium ions diffuse into the rod cells, depolarising the cell
  • Neurotransmitters are released across the synapse to the bipolar neurone
  • Inhibitory response occurs so the bipolar neurone does not depolarise, and no action potential is fired
25
Q

What happens to rod cells in the light?

A
  • Rhodopsin absorbs light and breaks down into retinal and opsin
  • Opsin activated a cascade of reactions that result in the closing of cation channels
  • Sodium cannot diffuse into the rod cells, so the cell membrane becomes hyperpolarised
  • No release of neurotransmitters so there is no inhibition of the bipolar neurone, so it depolarises, delivering an action potential to the brain via the optic nerve
26
Q

What is a tropism?

A

A plants growth response to an external directional stimulus

27
Q

What is a positive/negative tropism?

A 
Positive = grow towards the stimulus 
Negative = grow away from the stimulus
28
Q

Relationship between roots/shoots and light:

A

Shoots are positively phototropic

Roots are negatively phototropic

29
Q

Relationship between roots/shoots and gravity:

A

Shoots are negatively geotropic

Roots are positively geotropic

30
Q

How are plant responses brought about?

A

They respond using growth factors that either speed up or slow down plant growth

31
Q

Where are growth factors produced?

A

In growing regions of the plant eg shoot tips and move to where needed

32
Q

How do auxins stimulate growth in shoots?

A

By cell elongation – cells walls become lose and stretchy so get longer

33
Q

What do high concentrations of auxins do to roots?

A

Inhibit growth

34
Q

Name 4 other growth factors:

A

Gibberellins – stimulate flowering
Cytokinin – stimulate cell division
Ethene – stimulates fruit ripening
ABA – stimulates leaf fall

35
Q

What is IAA?

A

An important auxin produced in the tips of shoots in flowering plants

36
Q

How does IAA control cell elongation and growth?

A

When IAA enters the nucleus of a cell it can regulate the transcription of genes involved in elongation and growth

37
Q

How is IAA transported over short distances?

A

Active transport and diffusion

38
Q

How is IAA transported over short distances?

A

Active transport and diffusion

39
Q

How is IAA transported over longer distances?

A

Phloem

40
Q

How do plants detect light?

A

Using photoreceptors called phytochromes

41
Q

Where are phytochromes found?

A

Leaves, seeds, roots, and stems

42
Q

What two states do phytochromes exist in?

A

Pr and Pfr

43
Q

What light + wavelength does Pr absorb?

A

Pr absorbs red light at a wavelength of 660nm

44
Q

What light and wavelength does Pfr absorb?

A

Far-red light at a wavelength of 730nm

45
Q

What is Pr converted to in red light?

A

Converted quickly into Pfr

46
Q

What is Pfr converted to in far-red light?

A

Converted quickly into Pr

47
Q

What happens to Pfr in darkness?

A

Slowly converted into Pr

Biology A-level (8 decks)

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