6.1 Organisms Repsond To Stimuli

Question 1

What is Taxes?

Answer 1

Directional movement
Ie) woodlouse in sunlight

Survival mechanism

Question 2

What is kinesis?

Answer 2

Random movement
Ie) woodlouse in damp conditions
Rate of movement ~p~ stimuli intensity

Question 3

What is tropism?

Answer 3

Directional plant growth
Positive- to stimuli
Negative- against stimuli

Question 4

What is IAA?

Answer 4

Indoloacetic acid
A plant hormone or auxin
Made in shorts and root tips

Question 5

What is the purpose of IAA in phototropism?

Answer 5

1) IAA moves away from light
2) shaded side grows more
3) directs plant towards the light which is advantageous for photosynthetis

Question 6

What are the IAA experiments?

Answer 6

1) Darwin 1880 blocked the root tip
- no growth

2) Boysen Jensen 1913 inserted mica barrier
- shaded barrier- no growth
- sunny barrier- growth

3) Paal 1919 cut tip and set it off centre
- taxes occured. Growth to one side

4) Went 1926 placed gelatin w/ auxin on shoot
- growth still occurred

Question 7

What are the three types of neurones?

Answer 7

Sensory- bn receptor and relay
Relay- bypasses brain but goes to CNS
Motor- connects relay to effector

Question 8

What is a 3 neurone arc?

Answer 8

1) heat is a stimulus
2) detected by thermoreceptor
3) which starts impulse along SENSORY neurone
4) to the RELAY neurone in CNS
5) this passes an impulse to MOTOR neurone
6) to a muscle effector which pulls the hand away

Question 9

What is a receptor?

Answer 9

A bundle of nerve endings which can be stimulated by a change in environment

Mechanoreceptor
Thermoreceptor

Question 10

What is the Pacinian Corpsucle?

Answer 10

Mechanoreceptor
Responds to pressure changes
Deep in skin
Single neurone
Surrounded by connective tissue
Separated by gel

Question 11

What are stretch mediated Na+ channels?

Answer 11

Intrinsic protein in bilayer of P Corpsucle. 
Open when pressure applies
Allows Na+ to flood in
Depolarises neurone
Starts impulse

Question 12

What is the retina?

Answer 12

Photoreceptors in eye made of rods and cones

Light sensitive pigments absorb light.

Question 13

Retina:

What are rods?

Answer 13

Black and white
Respond to low light intensity
Rhodopsin pigment broken down to start impulse
Many-to-one allows small gen potential to build up

Question 14

What is the summation effect?

Answer 14

When in the rods a small potential allows to build up due to rods being many-to-one

Question 15

Retina:

What are cones?

Answer 15

Colour
Respond to different light wavelengths
Idopsin pigment must be broken down to allow impulse to start
High light intensity required to break pigment
One-to-one impulse

Question 16

Retina:

What are Fovea?

Answer 16

Densely packed cones
Sharp vision
Read and drive