Topic 6: response to stimuli

Question 1

```

~~~

Define stimulus

Answer 1

A stimulus is a detectable chnage in the environment.

These chnages can be detected by receptors

Organisms increase their chnace of survival by responding tot stimuli via different response mechanisms

Question 2

What is a tropism?

Answer 2

Term given to when plants respond via growth to stimuli

Can be negative or positive- grow towards or away from stimulus

Question 3

What are tropisms controlled by?
Give an example

Answer 3

growth factors

e.g. IAA

Question 4

Outline what IAA is

Answer 4

IAA (indoleacetic acid) is a type of auxin and can control cell elongation in shoots and inhibit growth of cells in the roots. It is made in the tip or the roots and shoots but can diffuse to other cells

Question 5

What is a phototropism?

Answer 5

Light is needed for the LDR in photosynthesis so plants grow towards light
This is a positive phototropism

1. shoot tip cells produced IAA, causing cell elongation
2. The IAA diffuses to other cells
3. if there is unilateral light, the IAA will towards the shaded side of the shoot resulting in higher conc of IAA there
4. cells on shaded side elongate more and hence plants bend towards light

roots do not photosynthesise, they must anchor the pplant deep in the soil

In roots, high IAA conc inhibits cell elongation, so roots elongate more on lighter side away from light

this is negative phototropism

Question 6

outline gravitropism

Answer 6

IAA will diffuse from upper side to lower side of a shoot
if a plant is vertical, this causes the cell to elongate and plant grows upwards

if a plant is on its side, it will cause shoot to bend upwards- negative gravitropism

IAA moves to lower sides of roots so that the upper side elongates and the roots bend down towards gravity and anchors the plant in- positive gravitropism

Question 7

what is a reflex

Answer 7

rapid, automatic response to protect from danger

Question 8

Define Taxes

Answer 8

an organism will move its entire body a favourable stimulus or away from an unfavourable stimulus

positive taxes= towards stimulus

Question 9

Define kinesis

Answer 9

an organism changes the speed of movement and rate it changes direction

Question 10

Define receptor

Answer 10

• detect stimuli

only respond to specific stimuliand this leads to establishment of a generator potential

Question 12

Name 3 types of receptor

Answer 12

-pacinian corpuscle
-rods
-cones

Question 13

draw a pacinian corpuscle

Question 14

How does stretch-mediated sodium channels link to pacinian corpuscle function?

Answer 14

membranes of pacinian corpuscle have stretch-mediated sodium channels

these open and allow sodium ions to enter sensory neurone only when they are stretched and deformed

when pressure is applied it deforms and na+ floods in leading to generator potential

Question 15

Describe rod cells

Answer 15

process images in black and white

detect light of very low intensity- many rod cells connect to one sensory neurone- retinal convergence

brain cannot distinguish between separate sources of light- LOW VISUAL ACUITY

Question 16

Describe cone cells

Answer 16

process images in colour

three types with different pigments, red green and blue

need HIGH light intensity

one cone cell to one biolpolar and one ganglion cell and one sensory neurone

high visual acuity

Question 17

where are most cones located?

Answer 17

fovea

Question 18

what is meant by myogenic?

Answer 18

heart contracts on its own accord but the rate of contraction is controlled by wave of electrical activity

Question 19

Describe how SAN controls Hr

Answer 19

• SAN releases a wave of depolarisation across the atria causing it to contract
• AVN releases another wave of depolarisation when the first reaches it. A non-conductive layer between the atria and the ventricles prevents the wave travelling down the ventricles
• instead the bundle of his conducts the wave down the septum and the purkyne fibres
• therfore there is a short delay between second pump so the atria have time to pump blood into ventricles
• finally the cells repolarise

Question 20

2 parts of autonomic NS

Answer 20

1- sympathetic NS
2- parasympathetic NS

Question 21

more impulese sent by sympathetic NS…

Answer 21

increase hr

Question 22

changes in ph are detected by…

Answer 22

chemoreceptors

Question 23

change in pressure….

Answer 23

baroreceptors

Question 24

when ph decreases..

Answer 24

impulses via sympathtic NS to increase Hr to increase heart rate to remove CO2