Ch9: Sensory Concepts

Question 1

Difference between signals and cues

Answer 1

Signals: specifically evolved acts/behaviours or structures that influence the behaviour of a receiver
- they MUST come from a BIOTIC origin

Cues: have incidental impacts on the behaviour of a receiver
- NOT evolved under selection for this intended outcome
- Can come from and a biotic or biotic source

Question 2

Describe chemoreceptors and the 2 different kinds of interactions with them:

Answer 2

A chemical binds to a receptor (must be complimentary)

1) Direct: interaction causes channel to open and allow ions/chemical to pass through

2) Indirect: this binding triggers a signal protein to carry this inside the cell to another protein channel, causing it to open.

Question 3

Describe temperature receptors

Answer 3

They respond to changes in temperature, in which channels open in close in response

Question 4

Describe Motion sensitive receptors

Answer 4

sensors that respond to movement, vibration, stretching/tension and opens/shuts according to this

Question 5

Describe Photoreceptors

Answer 5

respond to specific wavelengths of light, and hence photons hit the receptor. The receptor absorbs the energy from this photon and temporarily changes it conformation to allow ions to pass through the channel

Question 6

What are photoreceptors made up of? What does their activation cause?

Answer 6

A protein bound to a chromophore;

When they’re activated, they trigger a signalling cascade that alters gene expression and morphology (grows plant towards sunlight)

Pr = inactive (ruh-roh)(absorbs red light)

Pfr = active (fo sho) (absorbs far-red light)

Question 7

What do Pr and Pfr reach? What do they effect?

Answer 7

They reach a dynamic equilibrium during the day

they adjust their growth based on ratios of Pr and Pfr

Question 8

What does the biological clock allow for? What is it based on?

Answer 8

Enables plants to recognise seasons and photoperiods (lengths of days)

Depends on ratio of Pr : Pfr
- During NIGHT: begin with Pr
- During the day they convert to Pfr

Question 9

What does the activation of Pfr allow for? Why do Pfr levels fall at night?

Answer 9

Cytoplasmic molecules activate and translocate to the nucleus to regulate gene expression and growth

Pfr levels fall at night;
- because of enzymes destroying Pfr
- because of slow reversion (in dark) of Pfr -> Pr

Question 10

Define Gravitropism

Answer 10

Plant growth in response to gravity

Question 11

What is the difference between positive and negative gravitropism?

Answer 11

Positive: growth in direction of gravity (down - roots)

Negative: growth in opposite direction of gravity (up - shoots)

Question 12

How do roots tell the direction of gravity? Describe how growth of cells occurs?

Answer 12

They have root caps which contain STATOCYTES (specialised gravity-sensing cells)
- contain starch-filled organelles (amyloplasts/statolyths)
- The starch-filled organelles fall to the side of the cell, indicating the direction of gravity

When they fall to the bottom the top side of the root’s growth is stimulated (ASYMMETRIC ELONGATION PATTERN):
- as it elongates, the root curves downward
- lower-side growth = suppressed

Question 13

Define thigmotropism

Answer 13

Directional growth of plant in response to touch

Question 14

Difference between positive and negative thigmotropism

Answer 14

Positive: when.a plant touches an object, touching side contracts, and the non-touching side elongates
- differential growth causes tendrils to wind around the object

Negative: plant grows away from object it touches, path of least resistance

Question 15

What is stimulus intensity measured by?

Answer 15

The number of receptors activated and the RATE of action potentials produced by sensory receptors

Question 16

Describe smell chemoreceptors

Answer 16

receptors in nasal cavity epithelial tissue: odorants bind to receptors which sends information to nerves in olfactory bulb + to brain for processing

Question 17

How does the body discriminant between odorant molecules? Define glomeruli

Answer 17

Due to complexity, odorants have several ways (conformations) that can bond differently to different receptors

Glomeruli: unique combinations of nerve activation may trigger a CLUSTER (glomeruli) in the olfactory bulb

Question 18

Define pheromone

Answer 18

chemical signals used within a species that attracts mates, warning signals, mark food trails or territory

Detected differs based on species: generally through olfactory system

Question 19

What does the suprachiasmatic nucleus (SCN)

Answer 19

sits in the hypothalamus and receives signals from the retinohypothalamic nerve tract to release chemicals to trigger physiological processes (ie~ sleep, digesting, thermoregulation)

Question 20

Define the somatosensory system? What are the 3 levels?

Answer 20

botht eh central and peripheral nervous system
- receptor, circuit, perception levels

Question 21

Define the 1st level of somatosensory system

Answer 21

1) Receptor Level: sensory receptor is excited by a stimulus
- the receptor converts this into an electrical signal = generating a GRADED POTENTIAL
- When this reaches a threshold a NERVE IMPULSE is generated

Question 22

Define the 2nd level of somatosensory system, where do these signals go?

Answer 22

2) Circuit level: this nerve impulse reaches the CNS (central nervous system) through ascending pathways

The majority of sensory impulses reach the primary somatosensory area of the cerebral cortex + some proprioceptive impulses are processes in the CEREBELLUM (Unconsciously)

Question 23

Define the 3rd level of somatosensory system

Answer 23

3) Perception: sensory information = interpreted by the CNS: only impulses processed in the cerebral cortex are consciously perceived