Unit 8 - Stimuli + Receptors Flashcards
What is a stimuli?
A detectable change to an organisms environment.
Definition of tropism?
A tropism is a directional growth response of a plant to a stimulus.
These can be positive (towards stimulus) or negative (away from stimulus).
What phototropism and gravitropism do shoot show?
Positive phototropism
Negative gravitropism
What phototropism and gravitropism do roots show?
Negative phototropism
Positive gravitropism
How do plants respond to a stimulus?
In flowering plants, specific growth factors move from growing regions (shoot tip and root tip) to other tissues where they regulate growth. IAA is a growth factor.
The effect of IAA in roots and shoots?
Shoots-stimulates cell elongation
Roots-inhibits cell elongation
Explain positive phototropism in shoots?
-Cells in the tip of the shoot produce IAA
-IAA diffuses to the shaded side of the shoot increasing its concentration
-IAA stimulates cell elongation on shaded side
-Cells elongate more on the shaded side than the light side, bending the shoot towards the light.
Explain gravitropism in roots?
-Cells in the tip of the root produce IAA
-IAA diffuses to the lower side of the root due to gravity
-IAA inhibits cell elongation
-Cells elongate less in the lower side than the upper side
Exam Q: Explain how a shoot grows upwards when placed on its side (negative gravitropism)?
Cells in the tip of the shoot produce IAA
IAA diffuses to the lower side of the shoot due to gravity
IAA stimulates cell elongation on the lower side
Cells elongate more on the lower side and less on the upper side bending and growing the shoot upwards
Definition of taxis?
A taxis is directional movement to a stimulus
2 types of taxis?
1) Positive taxis = movement towards stimuli
2) Negative taxis = movement away from stimuli
Definition of kinesis?
Kinesis is non-directional movement to a stimulus.
It involves increasing/decreasing random movements
Definition of reflexes?
Reflexes are rapid, involuntary responses to a stimulus. They do not need to be learned.
Explain why organisms have reflexes?
-They protect against damage to body tissues
-Can help escape from predators
Part of a reflex arc?
Stimulus - Receptor - Sensory neurone - Intermediate neurone - Motor neurone - Effector
What is the role of a receptor?
It detects stimuli. Each type of receptor detects one specific stimuli.
Structure of a pavilion corpuscle?
Explain how pressure causes an electrical impulse in the sensory neurone of a Pacinian corpuscle?
1) The lamellae deform
2) Stretch mediated sodium ion channels in the neurone membrane open
3) Sodium ions diffuse into the neurone - depolarising it
4) This produces a generator potential, which, if reached threshold, causes an action potential (nerve impulse)
5) The greater the pressure, the more Na+ channels open and the greater the generator potential.
What is light detected using and how do they work?
Light is detected using 2 types of photoreceptors in the retina of the eye - rods and cones
They contain light sensitive pigments which breakdown when light hits them forming a generator potential.
Where are rods found?
Rods are found in the periphery of the retina
Where are cones found?
Cones are found in the fovea
Why do we get a blind spot?
It is when there are no rods or cones.
Why do rods only see black + white?
They contain a pigment called rhodopsin which cannot distinguish between different wavelengths of light.
How do cones allow us to see in colour?
They contain a pigment called iodopsin. 3 different types of cone cells (with different iodopsin), each identifies a different wavelength of light. Blue, green + red cones.
Why do rods have a higher sensitivity to light? (Sensitive at low light intensities)
Multiple rod cells connect to a single neurone (retinal convergence)
Generator potentials combine (spatial summation) to reach threshold in the neurone.
Why do cones have a lower sensitivity to light? (Only sensitive to high light intensities)
One cone cell connects to a single neurone
A high light intensity is required for the generator potential to reach threshold in the neurone.
Why do rods have a low visual acuity (lack of detail)?
Several rods connect to a single neurone (retinal convergence)
One set of nerve impulses sent to the brain from multiple rods.
Why do come shave a high visual acuity? (More detail)
Each cone connects to a single neurone
Separate set of nerve impulses sent to the brain from each cone cell.
Structure of the heart?
Why is the heart myogenic?
It will contract in the absence of nervous input from the brain.
Describe how a heartbeat is initiated and coordinated?
1) The sinoatrial node initiates the heartbeat by generating electrical impulses
2) These electrical impulses are sent across the atria causing the atria to contract
3) A layer of non-conducting tissue prevents the impulses spreading to the ventricles so the ventricles don’t contract
4) the atrioventricular node delayed the impulses to give time for blood to leave the atria and fill the ventricles before the ventricles contract
5) The impulses then travel down the bundle of His and up the Purkinje fibres
6) The ventricles contract from the base up.
Which part of the nervous system is involved with the control of heart rate?
Sympathetic + parasympathetic
How do the sympathetic and parasympathetic nervous systems differ?
Sympathetic = stimulate effectors, speeds up heart rate
Parasympathetic = inhibits effectors, slows down heart rate
How does changes in CO2 levels of the blood affect the pH of the blood?
CO2 forms a weak acid in solution and lowers blood pH. The more CO2 present the lower the blood pH.
During exercise why does your heart rate increase,
During exercise, muscles aerobically repairs more to produce more ATP for muscle contraction. This produces more CO2.
The increase in CO2, lowers the blood pH.
This is detected by chemoreceptors in the carotid artery and the aorta
The chemoreceptors send more nerve impulses to the medulla in the brain
The medulla sends more nerve impulses to the sympathetic nerve and less nerve impulses down the parasympathetic nerve to the sino atrial node.
The sino atrial node produces more frequent nerve impulses resulting in an increased heart rate.
After exercise, the heart continues to beat quickly. How does it eventually slow down to normal heart rate?
Chemoreceptors detect a decrease in blood CO2, so an increase in blood pH
Less nerve impulses sent to the medulla
More nerve impulses sent down the parasympathetic nerve and less nerve impulses are sent down the sympathetic nerve to the sinoatrial node
Less frequent electrical impulses from the sinoatrial node
What are barorecpetors and where are they find?
They are pressure receptors and are found within the walls of the carotid artery and aorta
What happens when blood pressure is above normal?
Goal is to lower heart rate:
Pressure receptors detect a rise in blood pressure
Less nerve impulses are sent from the pressure receptors to the medulla
More nerve impulses down the parasympathetic nerve and less nerve impulses down the sympathetic nerve to the the sinoatrial node
Less frequent electrical impulses from the sinoatrial node, which decrease heart rate.
What happens when blood pressure is below normal?
Goal is to increase heart rate:
More nerve impulses are sent from the pressure receptors to the medulla
The medulla sends more nerve impulses down the sympathetic never and less nerve impulses down the parasympathetic nerve to the sinoatrial node
The sinoatrial node produces more frequent nerve impulses, which increases heart rate.
