Response to Stimuli Flashcards
How do organisms increase their chance of survival?
By responding to changes in their environment
What is a tropism?
- Plant growth in response to directional stimulus
- can be towards (+) or negative (-)
What are the tropisms of the plant shoot?
- Positive phototropism
- Negative geotropism
What are the tropisms for a plant root?
- Negative phototropism
- Positive geotropism
- Positive hydrotropism
What are the advantages of the plant root tropisms?
leaves in most favourable position to capture light
What are the advantages of the plant root tropisms?
- increase probability of roots growing in soil
- increase H2O and nutrient absorption
What are plant growth factors?
- Regulate growth in response to directional stimuli
- Stages: mitosis and cell elongation
What does IAA stand for and what is it?
Indoleacetic Acid
An auxin which can cause cell elongation
How does IAA move thru the plant?
By diffusion
For phototropism in shoot tip, where does IAA accumulate?
The shaded side
How does IAA cause cell elongation?
- attaches to receptors on cell membrane
- causes release of H+ ions
- pH decreases
- hydrogen bonds in cellulose microfibrils disrupted
True or false: in roots, IAA increases cell elongation
False: in roots IAA inhibits growth
For geotropism in roots, where does IAA accumulate and why?
On the lower region to inhibit cell elongation, so top side can grow faster
Name 2 reasons why it is important for organisms to respond to stimuli?
- increase chance of survival
2. increase reproductive success (increase chance of beneficial alleles passes on)
What is taxis?
directional response
What is positive and negative taxis?
\+ = towards stimulus - = away from stimulus
What are the actual names of the taxis for: water, light and chemical?
hydrotaxis, phototaxis and chemotaxis
What is kinesis?
non-directional response
How can you tell if the organism doesn’t favour the environmental conditions?
more rapidly the organism moves and with fewer turns
Receptors respond to only…
1 type of stimulus`
How is an action potential formed?
The generator potential exceeds the threshold
Receptors are transducers. What does that mean?
change one form of energy into an electrochemical impulse
The greater the stimulus….
the greater the frequency of action potentials, and increase time that they go on for
Describe briefly how the Pacinian Corpuscle works
- lamellae deforms
- stretch mediated Na+ ion channels open
- Na+ opens diffuse thru
- depolarises the membrane causing a generator potential
Which eye receptor can sense colour and has high visual acuity?
Cone cell
where are rod and cone cells located in the retina?
Cone: fovea
Rod: periphery
Which eye receptor is stimulated in low light and which is stimulated in high light intensity?
Low: rod
high: cone
What is the name of the pigment that rod cells have?
Rhodopsin
What is the name of the pigment which cone cells have?
Iodopsin
Why do cone cells have high visual acuity?
each cell has own bipolar neuron and so separate signals sent to the brain so can distinguish which was stimulated
How can cone cells produce colour images?
- 3 types responding to different wavelengths
- different type of iodopsin which breaks down in presence of specific wavelength
Why are cone cells stimulated at high light intensities?
- own separate bipolar neuron so multiple cells can’t be combined to exceed threshold
- iodopsin need more energy to break down
Why do rod cells have low visual acuity?
- Many rod cells attached to a single bipolar neuron
- single impulse to brain so can’t distinguish
How can rod cells respond to low light intensity?
- many rod cells connected to 1 bipolar neuron = increase chance of threshold exceeded
- rhodopsin doesn’t need lots of energy to break down
Define sensory neuron
carry nerve impulses from receptor towards CNS
Define motor neuron
Carry nerve impulses away from CNS to effectors
Define CNS
Made up of brain and spinal cord
Define the peripheral nervous system
made up of pairs of nerves that originate from either brain or spinal cord
Define the voluntary nervous system
What is the difference between the voluntary nervous system and the autonomic nervous system?
voluntary: conscious control
autonomic: not voluntary
Name 3 reasons why the reflex arc is important
- very rapid
- reduce/avoid damage/injury
- helps to maintain balance/posture
What is the autonomic nervous system?
Controls involuntary activities of internal muscles/glands (sympathetic and parasympathetic)
What does antagonistic mean?
Sympathetic and Parasympathetic nervous systems oppose one another
What is the parasympathetic nervous system?
Stimulates effectors = speeds up activity (in response to stressful stimuli)
What is the parasympathetic nervous system?
Inhibits effectors = slows down activity (in response to stimuli)
The importance of the parasympathetic nervous system (2)
- helps conserve energy
2. Replenishes body’s reserves
What is the role of the Sinoatrial node?
Generates + sends out electrical waves across wall of atrium = atrium contracts
What is the role of the atrioventricular septum?
Non-conductive tissue that prevents electrical wave crossing to ventricles
What is the role of the atrioventricular node and why is there a short delay in sending an impulse?
- detects impulses from atria
- allow atria to finish contracting
Why is the electrical impulse sent from the apex up the ventricle walls?
Prevents blood pooling in the apex
The medulla oblongata has 2 centres:
- Acceleratory
- Inhibitory
How does the medulla oblongata increase heart rate?
Impulse sent to SAN via sympathetic system
How does the medulla oblongata decrease heart rate?
Impulse sent to SAN via parasympathetic system
What are chemoreceptors and where are they located?
- detect changes in the pH (due to CO2 conc.)
- located in the carotid arteries
Where are pressure receptors located?
in the carotid arteries and aorta
Pressure increases: ___________ system
Pressure decreases: ___________ system
increase: parasympathetic
decrease: sympathetic