Stimuli and Response Flashcards
Why do plants use growth factors?
To respond to changes in their environment to increase their chance of survival e.g. towards light to increase the rate of photosynthesis
What is a tropism?
The response of a plant to a directional stimulus
How do plants respond to changes in their environment?
Growth factors because they dont have circulatory systems or nervous systems
What do auxins (e.g. IAA) do?
Cause cell elongation in shoots
What do gibberellins do?
Cause flowering and germination
Where are growth factors made?
In root and shoot tips
How do growth factors move short distances?
By active transport and diffusion
How do growth factors move long distances?
In the phloem
How does IAA cause phototropism?
IAA moves to the shaded side of the root or the shoot causing: - Shoots: Cells to elongate and grow towards light - Roots: (IAA inhibits cell growth) roots to grow away from light
How does IAA cause gravitropism?
IAA moves to the underside of the root or the shoot causing: - Shoots: Cells to elongate and grow against gravity - Roots: (IAA inhibits cell growth) roots to grow with gravity
What are taxes and kineses?
Simple responses that keep mobile organisms in favourable environments
What are taxes?
Mobile organisms move towards or away from a directional stimulus
What are kineses?
Mobile organisms change their movement in response to a non-directional stimulus
Which stimulus’s cause a taxes?
- Predators- Water loss- Heat
How do unfavourable conditions cause a kinesis?
- Move more/faster - Turn more- Allows them to move to a new area
How do favourable conditions cause a kinesis?
- Move less/slower- Turn less- Allows them to remain in a favourable area
What is a reflex?
A rapid response to a stimulus without conscious or deliberate control
What is the reflex arc?
- Stimulus - Receptor- Sensory neurone- Relay neurone in CNS- Motor neurone- Effector- Response
What are the advantages of reflexes?
- Help avoid damage- Very fast- Unconscious - Doesn’t need to learnt
What are pacinian corpuscles?
They detect pressure, touch and vibrations in the skin
What happens when pacinian corpuscles are stimulated?
- Pressure causes the lamellae to stretch and deform- Stretch mediated sodium ion channels open- Sodium ions diffuse into the neurone- The more sodium ions, the greater the stimulus - Causes depolarisation of the neurone (generator potential)- If threshold is reached then an action potential is initiated
How is light seen by the human eye?
- Light is focused on the retina by the lens- Light is absorbed by the pigments in photoreceptors - Causes sodium ion channels to open (how many depends on the strength) (generator potential)- If threshold met then action potential generated and transmitted along the bipolar neurone to the optic nerve where it is transmitted to the brain
What are the two photoreceptors in the eye?
Cone and rod cells
Rod cells…
- Detect monochromatic pigments - Are sensitive to low light- Have low visual acuity- Are mostly in peripheral parts of retina- Cannot differentiate the position of light but get an action potential at lower light because many rod cells are joined to one bipolar neurone
