Responses in plants and Animals / receptors Flashcards
What are plant growth factors and where are they produced?
Chemicals that regulate plant growth respond to directional stimulus.
Produced in plant growing regions (shoot/leaves).
Move to where they are needed in other plants by diffusion via phloem.
What is IAA?
IAA is a specific growth factor found in plants
How does IAA influence cell elongation in plant roots and shoots? (4 marks)
1) IAA binds to protein receptors on cell membranes
2) lowers the pH by releasing hydrogen bonds
3) The lowered pH breaks bonds in the cellulose of the cell wall
4) This causes the cell wall to loosen and be more easily stretched allowing cells to elongate more easily.
Exam qs
Explain how auxins regulate phototropism in plants.
In phototropism, light causes auxins to accumulate on the shaded side of the plant. This promotes cell elongation on that side, causing the plant to bend towards the light source. The increased growth on the darker side results in the plant’s shoot growing towards the light.
Explain why shoots show positive tropism.
IAA diffuses to the shaded part of the shoot.
So there is uneven growth
Cells elongate and bend towards light.
Explain why roots show positive gravitropism.
IAA moves to the underside of the roots
IAA inhibits elongation of root cells
cells on the upper side of the root grow faster so the root tip bends downward
Define taxis and Kinesis. State their advantage.
taxis: organisms move towards/away from a directional stimulus
Kinesis: organisms move towards/away from a non directional stimulus
keeps organisms in a favourable environment
How could a student recognise kinesis in an organisms movement?
1) organism crosses sharp division between favourable environments: turning increases
2)if organism moves considerable distance in an unfavourable environment, sharper turns turning decrease slowly begins to move in long straight lines
Outline what happens in a simple reflex arc
stimulus —receptors-sensory neuron—CNS—-motor neuron —effectors—–response
Exam Question:
Describe the pathway of a reflex action.
The reflex arc involves the following steps:
Stimulus (e.g., heat) detected by receptors (e.g., thermoreceptors in the skin).
Impulse travels along the sensory neuron to the spinal cord.
The impulse is passed to a relay neuron in the spinal cord.
The impulse is transmitted to a motor neuron, which carries it to the effector (e.g., muscle).
The muscle contracts to withdraw the hand from the heat.
Advantages of a simple reflex
Rapid response to dangerous stimuli
Instinctive
What features are common in all sensory receptors
Act as energy transducers which establish a greater generator potential
they respond to specific stimuli
What is the pacinian corpuscle and what do they detect?
Pacinian corpuscle are mechanoreceptors that are found deep in the skin and they detect mechanical stimuli eg pressure and vibrations.
What do pacinian corpuscles contain?
Pacinian corpuscles contain the ending of a sensory neuron, called a sensory nerve ending. which is wrapped in loads of connective tissue called lamellae
How do Pacinian corpuscles detect changes in pressure?
When pressure is applied to the skin, the Pacinian corpuscle is compressed.
This deformation causes the stretch-mediated sodium ion channels to open, leading to the influx of sodium ions.
This depolarizes the nerve ending, generating a receptor potential. If the depolarization is strong enough, an action potential is sent to the brain via the sensory neuron.
