Response to stimuli Flashcards
What is a stimulus?
A change in an organism’s internal or external environment
Why is it important that organisms can respond to stimuli?
Organisms increase their chance of survival by responding to stimuli
What is a tropism?
Growth of a plant in response to a directional stimulus
Positive tropism = towards a stimulus; negative tropism = away from stimulus
Summarise the role of growth factors in flowering plants
Specific growth factors such as IAA move from the shoot or root to other tissues where they regulate growth in response to a directional stimulus
Describe how indoleacetic acid (IAA) affects cells in roots and shoots
In shoots, high concentrations of IAA stimulates cell elongation
In roots, high concentrations of IAA inhibits cell elongation
Explain gravitropism in flowering plants
1.Cells in tip of shoot / root produce IAA
2. IAA diffuses down shoot / root
3. IAA moves to lower side of shoot / root
4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
5. So shoots bend away from gravity whereas roots bend towards gravity
Explain phototropism in flowering plants
1.Cells in tip of shoot / root produce IAA
- IAA diffuses down shoot / root
- IAA moves to shaded side of shoot / root (so conc. ↑)
- In shoots this stimulates cell elongation whereas in
roots this inhibits cell elongation - So shoots bend towards light
whereas roots bend away from light
Describe taxes
Movement towards or away from a directional stimulus
describe kinesis
Non-directional response
Speed of movement or rate of direction change
changes in response to a non-directional stimulus
Depending on intensity of stimulus
Describe how the effect of an environmental variable on the movement of an animal (eg. woodlice) can be investigated using a choice chamber
Set up choice chamber (different compartments) to create different environmental conditions
○ Eg. humidity → add a drying agent to one side and damp filter paper to other
○ Eg. light → shine a light but cover one half with black card
- Control other environmental conditions
○ Eg. if investigating humidity control light intensity with a dim even light above - Use a teaspoon to place a set number of animals eg. 12 woodlice on centre of mesh platform and cover with lid
- After a set amount of time eg. 10 minutes record the number of animals in each section
- Repeat after gently moving woodlice back to centre
The woodlice were left for 15 minutes before their movement was recorded when investigating the effect of humidity. Explain why. (2)
Time to establish humidity / for substance to absorb water / water from paper to evaporate
Woodlice no longer affected by handling
So that behaviour is typical of that humidity
Explain why a mesh platform is used when investigating the effect of humidity. (1)
To keep woodlice a safe distance from drying agent
Describe how a generator potential is established in a Pacinian corpuscle
1.Mechanical stimulus eg. pressure deforms lamellae and stretch- mediated sodium ion (Na+) channels
- So Na+ channels in membrane open and Na+ diffuse into sensory neurone
- This causes depolarisation, leading to a generator potential
○ If generator potential reaches threshold it triggers an action potential
Explain the differences in sensitivity to light for rods & cones in the retina
Rods are more sensitive to light
● Several rods connected to a single neurone
- Spatial summation to reach threshold
Cones are less sensitive to light
● Each cone connected to a single neurone
- No spatial summation
Explain the differences in visual acuity for rods & cones in the retina
Rods give lower visual acuity
● Several rods connected to a single neurone
● So several rods send a single set of impulses
to brain (so can’t distinguish between separate sources of light)
Cones give higher visual acuity
● Each cone connected to a single neurone
● Cones send separate impulses to brain
(so can distinguish between 2 separate sources of light)
Explain the differences in sensitivity to colour for rods & cones in the retina
Rods allow monochromatic vision
● 1 type of rod / 1 pigment
Cones allow colour vision
● 3 types of cones - red-, green- and blue-sensitive
● With different optical pigments → absorb different wavelengths
Cardiac muscle is myogenic. What does this mean?
It can contract and relax without receiving electrical impulses from nerves
Describe the myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity
- Sinoatrial node (SAN) acts as pacemaker → releases regular waves of electrical activity across atria, causing atria to contract simultaneously
2.Non-conducting tissue between atria prevents impulse passing directly to ventricles
- Waves of electrical activity reach atrioventricular node (AVN) which delays impulse ○ Allowing atria to fully contract and empty before ventricles contract
- AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue
Where are chemoreceptors and pressure receptors located?
Chemoreceptors and pressure receptors are located in the aorta and carotid arteries
Describe the roles of chemoreceptors, pressure receptors, the autonomic
nervous system and effectors in controlling heart rate
- Baroreceptors detect [fall / rise] in blood pressure and / or chemoreceptors detect blood [rise / fall] in blood CO2 conc. or [fall / rise] in blood pH
- Send impulses to medulla / cardiac control centre
- Which send more frequent impulses to SAN along [sympathetic / parasympathetic] neurones
- So [more / less] frequent impulses sent from SAN and to / from AVN
- So cardiac muscle contracts [more / less] frequently
- So heart rate [increases / decreases]
