Section 6 - Unit 14: Response to Stimuli Flashcards
Explain the importance of reflex actions (3 marks)
- Automatic (adjustments to changes in environment) / involuntary
- Reducing damage to tissues / prevents injury
- Role in homeostasis
- Posture / balance
- Finding food / mate / suitable conditions
- Escape from predators
Explain how the resting potential of -70 mV is maintained in the sensory neurone when no pressure is applied (2 marks)
- Membrane more permeable to potassium ions and less permeable to sodium ions
- Sodium ions actively transported/pumped out and potassium ions in
Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed. Explain how this results in slower responses to stimuli (2 marks)
- Less saltatory conduction / action potential / impulse unable to ‘jump’ from node to node
- More depolarisation over length / area of membranes
Explain the effect of myelination on the rate of nerve impulse conduction (2 marks)
- Myelin insulates / prevents ion movement
- saltation / leaping node to node
Explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon (3 marks)
Non-myelinated:
- Next section of membrane depolarised
Myelinated:
- Depolarisation / ion movement only at nodes
- Impulse jumps from node to node / saltatory conduction;
Describe how a Pacinian corpuscle produces a generator potential when stimulated (3 marks)
- Increased pressure deforms stretch-mediated sodium (ion) channel
- Sodium channels open and sodium ions flow in
- Depolarisation (leading to generator potential)
Give one similarity and one difference between a taxis and a tropism (2 marks)
Similarity:
- Directional response to a stimulus
Difference:
- Taxis whole organism moves whereas tropism is a growth response
Describe how a heartbeat is initiated and coordinated (5 marks)
- SAN sends wave of electrical impulses (across atria) causing atrial contraction
- Non-conducting tissue prevents immediate contraction of ventricles
- AVN delays (impulse) whilst blood leaves atria / ventricles fill
- AVN sends wave of electrical impulses down Bundle of His
- Causing ventricles to contract from base up
Describe how the heart controls and coordinates the regular contraction of the atria and ventricles (5 marks)
- SAN → AVN → bundle of His / Purkyne fibres
- Impulses over atria
- Atria contract
- Non-conducting tissue between atria and ventricles
- Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract
- Ventricles contract from apex upwards
Explain how increased intensity of exercise leads to an increased heart rate (3 marks)
- Oxygen / carbon dioxide detected by chemoreceptors
- Medulla / cardiac centre involved
- More impulses to SAN / along sympathetic nerve
Name the process by which IAA moves from the growing regions of a plant shoot to other tissues (1 mark)
Diffusion
When a wave of electrical activity reaches the AVN, there is a short delay before a new
wave leaves the AVN. Explain the importance of this short delay (2 marks)
- Allow atria to empty / ventricles to fill;
- Before ventricles contract
Explain what causes vision using the fovea to be in colour (1 mark)
Three different types of cone cells which are sensitive
to different wavelengths / different frequencies / different colours
Explain what causes vision using the fovea to have high acuity (1 mark)
Each receptor cell connects to separate neurone
Explain how nervous control in a human can cause increased cardiac output during exercise (4 marks)
- Coordination via medulla (of brain) / cardiac centre;
- Increased impulses along sympathetic nerve
- To S.A. node
- More impulses sent from pacemaker
