Stimuli and Receptors Flashcards
Tropism definition
Directional growth of a plant to a stimulus
What does IAA do in shoots and roots?
Stimulates cell elongation in shoots, inhibits cell elongation in roots
Describe how positive phototropism occurs in shoots
IAA produced in shoot tip diffuses to shaded side of the shoot and stimulates cell elongation. Cells elongate more on shaded side than light side so shoot bends towards light
Describe how positive gravitropism occurs in roots
IAA produced in root tip diffuses to lower side of root and inhibits cell elongation. Cells elongate more on upper side than lower side so root bends downwards in direction of gravity
Taxis definition
Directional movement to a stimulus
Kinesis definition
Non-directional movement to a stimulus
Describe how woodlice stay in favourable humid conditions
Increase their random non-directional movements and move slower so that they stay in favourable conditions
Reflex definition
Rapid, involuntary response to a stimulus
In what 2 ways do reflexes help organisms?
- Protect against damage to body tissues
- Can help organism escape from predators
What is the pathway from a stimulus to a response?
Stimulus –> receptor –> sensory neurone –> intermediate neurone –> motor neurone –> effector –> response
Receptor definition
Detect a specific stimuli and form a generator potential
What do Pacinian corpuscles detect?
Pressure
What 4 things make up the structure of a Pacinian corpuscle?
- Capsule
- Lamellae
- Sensory neurone
- Schwann cell
Explain how pressure causes a nerve impulse in the sensory neurone of a Pacinian corpuscle
- Lamellae deform
- Stretch-mediated Na+ channels in the neurone membrane open
- Na+ diffuse into the neurone via facilitated diffusion and depolarise it
- Produces a generator potential which causes an action potential if the threshold is reached
- The greater the pressure, the more Na+ channels open and the greater the generator potential
What are the 2 photoreceptors called?
Cones and rods
Where are rods and cones found?
Rods: periphery of the retina
Cones: fovea of the retina
Are there any rods or cones in the blind spot?
No
Which pigment do rods contain?
Rhodopsin
Which pigment do cones contain?
Iodopsin
Why do rods only let us see in black and white?
Rhodopsin can’t distinguish between different wavelengths of light
Why do cones let us see in colour?
3 different types of cone cell with different iodopsin, each identifies a different wavelength of light
Why do rods have higher sensitivity?
Show retinal convergence so generator potentials combine (spatial summation) to reach threshold
Why do cones have lower sensitivity?
One cone cell connects to a single neurone so a high light intensity is needed for generator potential to reach threshold
Why do rods have low visual acuity?
Show retinal convergence so one set of nerve impulses is sent to the brain from several rods
Which part of the nervous system is involved with controlling heart rate?
Autonomic nervous system
Describe how heart beat is initiated and coordinated
- Sinoatrial node sends electrical impulses across the atria, causing atria to contract
- Layer of non-conducting tissue prevents impulses from spreading to ventricles
- Atrioventricular node delays impulses to give time for atria to fully empty before ventricles contract
- Impulses travel down bundle of His and up the Purkynje fibres
- Ventricles contract from the base up
Describe how heart rate increases during exercise
- Muscles aerobically respire which produces CO2 and decreases blood pH
- Chemoreceptors in the carotid artery and aorta detect pH change and send more nerve impulses to the medulla
- Medulla sends more impulses down the sympathetic nerve to the sinoatrial node
- Sinoatrial node produces more electrical impulses across the atria, increasing heart rate
How does above normal blood pressure lead to a decrease in heart rate?
- Pressure receptors in carotid artery and aorta detect an increase in blood pressure
- Less nerve impulses sent to the medulla
- More nerve impulses sent down the parasympathetic nerve to sinoatrial node
- Less nerve impulses from sinoatrial node, decreasing heart rate
