3.6.1.2- Stimuli detection & response

Question 1

Tropism=

Answer 1

GROWTH of part of plant in response to a DIRECTIONAL stimulus

Question 2

What are tropisms controlled by?

Answer 2

specific growth factors (e.g. Indoleacetic acid (IAA))

Question 3

Effect of IAA in roots vs shoots

Answer 3

• In roots IAA INHIBITS cell
  elongation
• In shoots IAA PROMOTES cell
  elongation

Question 4

Phototropism in Shoots vs Roots

Answer 4

• Shoots POSITIVELY phototropic

- Roots NEGATIVELY phototropic

Question 5

Phototropism in shoots- process

Answer 5

1) shoot tip cell produce IAA,
2) If exposed to uneven light source, IAA transported to SHADED side of shoot
3) Higher conc of IAA promotes cells in shaded part to ELONGATE
4) Cell elongation causes shoot to bend towards the light

Question 6

Gravitropism in shoots-

( - Gravitropism) process (3)

Answer 6

1) IAA will diffuse from upper> lower side of shoot
2) If plant vertical, plant cells elongate & plant grows UP
3) If plant on its side, shoot will BEND upwards

Question 7

Gravitropism in roots (+ gravitropism)

Answer 7

1) IAA transported to UNDERSIDE
2) Higher conc of IAA in underside INHIBITS cell elongation on underside; so upper side elongates
3) Root bends towards gravity

Question 8

Taxes= (2)

Answer 8

1) Organism moves towards favourable stimuli (+ taxes)/ away from unfavourable stimuli (-taxes)
2) Directional response

Question 9

Kinesis=(2)

Answer 9

1) Organism changes SPEED of movement/ rate of direction change
2) Non-directional response

Question 10

Reflex arc=(3)

Answer 10

Sensory
Relay
motor

Question 11

Importance of reflex arc (3)

Answer 11

• rapid (short pathway)
• autonomic (doesn’t involve brain)
• protect from harmful stimuli

Question 12

important features of receptors=(2)

Answer 12

1) Only respond to SPECIFIC stimuli

2) Stimulation leads to establishment of a GP, which can cause a response

Question 13

3 receptors need to know=

Answer 13

1) Pacinian Corpuscle
2) Rods
3) Cones

Question 14

Structure of Pacinian corpuscle (2)

Answer 14

1) sensory neurone wrapped in layers of connective tissue

2) plasma membrane of Sn has stretch-mediated sodium channels

Question 15

Stages in generating GP- in Pacinian Corpuscle (5)

Answer 15

1) Mechanical stimulus applied,
2) This stretches & deforms stretch-mediated Na+ channels in sensory neurone membrane
2) Na+ channels now open & Na+ diffuse in to SN
4) Causes D leading to establishment of a GP
5) If GP reaches TV, triggers AP

Question 16

Rod vs cone- visual acuity

Answer 16

R= LOW visual acuity (Brain CANNOT distinguish between separate sources of light due to RC &SS)
C= HIGH visual acuity (one 1 synapses with 1 bipolar cell, brain CAN distinguish where light was detected)

Question 17

Rod vs cone= image colour

Answer 17

R= Processes images B+W images
C= Processes images in colour

Question 18

Rod vs cone- sensitivity to light

Answer 18

R= MORE sensitive as SEVERAL synapse to one bipolar cell (SS)
C= LESS sensitive as EACH synapse with one bipolar cell (TS)

Question 19

Distribution or Rods & cones in retina

Answer 19

R= most evenly distributed & absent in FOVEA
C= most in FOVEA

Question 20

Rod vs Cone- sensitivity to colour

Answer 20

R= monochromatic vision; 1 type of pigment
C=
- trichromatic each with different optical pigments that absorb different wavelengths
- Stimulation of different combos gives a range of colour perception