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Biology > 5: Response to stimuli > Flashcards

5: Response to stimuli Flashcards

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1
Q

Why is it important to be able to respond to stimuli?

A

So that the organism has a greater chance of survival, and therefore have a greater chance of raising offspring and passing their alleles to the next generation

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2
Q

What are stimuli detected by?

A

Receptors such as cells/organs

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3
Q

What do receptors do?

A

Detect the stimuli and transform the energy of the stimulus into some form of energy that is processed by the organism, leading to a response

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4
Q

What is a response carried out by?

A

Effectors such as cells/tissues/organs and systems

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5
Q

Define taxis

A

A simple response whose direction is determined by the direction of the stimulus

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6
Q

Positive taxis

A

Movement is towards the stimulus

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7
Q

Negative taxis

A

Movement is away from the stimulus

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8
Q

What is a kinesis?

A

A form of response in which an organism doesn’t move away from or towards the stimulus.
The more unpleasant the stimulus, the more rapidly the organism moves and changes direction
Results in an increase in random movements
Designed to bring the organism back into favourable conditions

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9
Q

What is a tropism?

A

A growth movement of part of a plant in response to a directional stimulus

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10
Q

What is the simplest type of nervous response to a stimulus?

A

A reflex arc

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11
Q

What are the 2 major divisions that make up the nervous system?

A 
The CNS (Central Nervous System) -> made up of brain and spinal cord
The PNS (Peripheral Nervous System) -> made up of pairs of nerves that originate from either the brain or spinal cord
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12
Q

What is the PNS divided into?

A

Sensory neurones which carry nerve impulses from receptors towards the CNS.
Motor neurones which carry nerve impulses away from the CNS to effectors.

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13
Q

What is the motor nervous system subdivided into?

A

The voluntary nervous system

The autonomic nervous system

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14
Q

What does the voluntary nervous system do?

A

Carries nerve impulses to body muscles and is under voluntary/conscious control

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15
Q

What does the autonomic nervous system do?

A

Carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control.

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16
Q

What is a reflex arc?

A

The pathway of neurones involved in a reflex.

The response is involuntary to a sensory stimulus

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17
Q

Importance of reflex arcs

A

Involuntary- doesn’t require the decision-making powers of the brain
Protects the body from harmful stimuli
Fast- the neurone pathway is short with few synapses (slowest link in a neurone pathway) which is particularly important in withdrawal reflexes.

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18
Q

What does the autonomic nervous system control?

A

The involuntary/subconscious activities of internal muscles and glands

19
Q

The autonomic nervous system consists of…

A

The sympathetic nervous system

The parasympathetic nervous system

20
Q

What does the sympathetic nervous system do?

A

Stimulates effectors + speeds up any activity

Acts like an emergency controller

21
Q

What does the parasympathetic nervous system do?

A

Inhibits effectors + slows down any activity
Controls activities under normal resting conditions
Concerned with replenishing the body’s nerves + conserving energy

22
Q

What is the word meaning the actions of the sympathetic and parasympathetic nervous system oppose one another?

A

Antagonistic

23
Q

Changes to the heart rate are controlled by a region of the brain called the …

A

Medulla oblongata

24
Q

What is the name of the main neurotransmitter of the sympathetic nerves in the cardiovascular system?

A

Noradrenaline

25
Q

Where are chemoreceptors and baroreceptors found in the body?

A

In the walls of the carotid arteries and in the aortic arch

26
Q

What are chemoreceptors sensitive to?

A

Changes in the pH of the blood that result from changes in CO2 concentration

27
Q

In solution, what does CO2 form?

A

Carbonic acid which lowers the pH of the blood

28
Q

Process of controlling an increase in CO2 concentration of the blood

A
  • pH is lowered
  • Chemoreceptors in the walls of the carotid arteries and the aorta detect the decrease in pH + increase the frequency of nerve impulses to the centre in the medulla oblongata that increases heart rate
  • This centre increases the frequency of impulses via the sympathetic nervous system to the SAN which increases the heart rate
  • The increased blood flow as a result leads to more CO2 being removed by the lungs so CO2 level of blood returns to normal
  • pH of blood rises to normal + chemoreceptors in walls of carotid arteries + aorta reduce the frequency of nerve impulses to the medulla oblongata
  • Medulla oblongata reduces the frequency of impulses onto the SAN, decreasing heart rate to normal
29
Q

Role of receptors

A

To detect stimuli

To convert the energy received from stimulus into energy that can be processed by the body

30
Q

What is the role of a Pacinian corpuscle?

A

Responds to changes in mechanical pressure

Produces a generator potential by acting as a transducer -> converting one form of energy into another

31
Q

Describe how a pacinian corpuscle works

A

When pressure is applied, membrane becomes stretched.
This widens the sodium channels in the membrance and sodium ions diffuse into the neurone
This depolarises the membrane and produces a generator potential
This in turn creates an action potential

32
Q

What is a stimulus?

A

A detectable change in the internal/external environment of an organism that produces a response in the organism

33
Q

What is a generator potential?

A

When receptors convert the energy of the stimulus into a nerve impulse

34
Q

Where are light receptors of the eye found?

A

The retina (innermost layer)

35
Q

What are the two types of light receptors?

A

Rod cells

Cone cells

36
Q

How do rod and cone cells act as transducers?

A

By converting light energy into the electrical energy of a nerve impulse

37
Q

Describe and explain the difference in sensitivity and acuity in rods and cones

A

Rods are very sensitive - many rods join to one neurone, so many weak generator thresholds combine to reach threshold
Rods have low acuity - many rods join the same neurone, which means light from two objects cannot be told apart
Cones have low sensitivity - one cone joins one neurone, so it takes more light t reach the threshold
Cones have high acuity - cones are close together and one cone joins one neurone. When light from two points hits two cones, two action potentials go to the brain, so you can distinguish between two points that are close together

38
Q

Where is there the highest concentration of cone cells?

A

the fovea

39
Q

What is the blind spot?

A

The optic nerve carries signals from the retina to the brian, there are no rods or cones in this area, so it’s not sensitive to light

40
Q

Describe how roots and shoots are geotropic and phototropic

A

Shoots are positively phototropic and negatively geotropic

Roots are negatively phototropic and positively geotropic

41
Q

Where are growth factors produced, where do they act and how do they get there?

A

Produced in the growing regions of the plant and they move to where they’re needed in the other parts of the plant. Moves by diffusion and active transport over short distances and by the phloem over long distances

42
Q

How does IAA act in roots and shoots, in response to light?

A

In shoots, IAA promotes growth

In shoots, IAA inhibits growth

43
Q

Explain the role of IAA in the control of phototropism

A

In shoots, IAA redistributed to shaded side
Causes cell elongation
Shoot grows towards light
In roots, high concentrations of IAA inhibits cell elongation
Roots grow away from light

44
Q

Why is phototropism advantageous in roots and shoots?

A

Shoots grow towards the light, in order to maximise leith hitting chlorophyll and increase rate of photosynthesis
Roots grow away from light as most likely to find water deep in soil

Biology (16 decks)

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