Responses and Receptors Flashcards
(16 cards)
What is a stimulus?
A change in an organism’s internal or external environment
Why is it important that organisms can respond to stimuli?
Organisms increase their chance of survival by responding to stimuli.
What is a tropism?
Growth of a plant in response to a directional stimulus. Positive tropism = towards a stimulus, Negative tropism = away from stimulus
Describe how indoleacetic acid (IAA) affects cells in roots and shoots
In shoots, high concentrations of IAA stimulates cell elongation. In roots, high concentrations of IAA inhibits cell elongation.
Explain gravitropism in flowering plants
- Cells in tip of shoot / root produce IAA
- IAA diffuses down shoot / root (evenly initially)
- IAA moves to lower side of shoot / root (so concentration increases)
- In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
- So shoots bend away from gravity whereas roots bend towards gravity
Explain phototropism in flowering plants
- Cells in tip of shoot / root produce IAA
- IAA diffuses down shoot / root (evenly initially)
- IAA moves to shaded side of shoot / root (so concentration increases)
- In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
- So shoots bend towards light
whereas roots bend away from light
Describe the simple responses that can maintain a mobile organism in a
favourable environment
- Taxes (tactic response)
* Directional response
* Movement towards or away from a directional stimulus - Kinesis (kinetic responses)
* Non-directional response
* Speed of movement or rate of direction change
* Changes in response to a non-directional stimulus
* Depending on intensity of stimulus
Why are reflexes important?
They are very fast as there are only 3 neurones and therefore few synapses (synaptic transmission is slow). They are also Autonomic (doesn’t involve conscious regions of brain) so doesn’t have to be learnt. They protect us from harmful stimuli, prevents damage to body.
Describe the basic structure of a Pacinian corpuscle
They have a single sensory neurone surrounded by gel. Between the neurone and the gel is a stretch mediated sodium ion channel. Within the gel are layers called lamellae.
Describe how a generator potential is established in a Pacinian corpuscle
- Mechanical stimulus eg. pressure deforms the lamellae and stretch- mediated sodium ion channels
- So the sodium ion channels in membrane open and sodium ions diffuse into sensory neurone
- This causes depolarisation, leading to a
generator potential. If generator potential reaches threshold, it triggers an action potential
Explain the differences in sensitivity to light for rods & cones in the retina
Rods are more sensitive to light. Several rods are connected to a single neurone. Spatial summation occurs to reach the threshold to generate an action potential.
Cones are less sensitive to light. Each cone is connected to a single neurone and there is therefore no spatial summation.
Explain the difference in visual acuity for rods and cones in the retina
Rods give lower visual acuity. 3 rod cells are connected to a single neurone, so 3 rods send a single set of impulses to the brain, and the brain therefore can not distinguish between separate source of light.
Cones give higher visual acuity. Each cone cell is connected to a single neurone, so each cone sends a separate set of impulses to the brain, and the brain therefore can distinguish between separate sources of light
Explain the differences in sensitivity to colour for rods & cones in the retina
Rods allow monochromatic vision as there is only 1 type of rod. Cones allow colour vision as there are 3 types of cones (red, green and blue sensitive). These different optical pigments absorb different wavelengths of light, and stimulating different combinations of cones gives the range of colour perception
Describe the myogenic stimulation of the heart and transmission of a
subsequent wave of electrical activity
- Sinoatrial node (SAN) acts as pacemaker, it sends regular waves of electrical activity across the atria. This causes the atria to contract simultaneously.
- Non-conducting tissue between the atria and ventricles prevents impulse passing directly to ventricles. This prevents immediate contraction of ventricles
- Waves of electrical activity reach atrioventricular node (AVN) which delays the impulse by 0.1 seconds, allowing atria to fully contract and empty before ventricles contract
- AVN sends wave of electrical activity down the Bundle Of His, conducting the impulse between ventricles to the apex where it branches into Purkyne tissue, causing ventricles to contract simultaneously from the base up
Where are chemoreceptors and pressure receptors located?
Chemoreceptors and pressure receptors are located in the aorta and carotid arteries.
Describe the roles of chemoreceptors, pressure receptors, the autonomic
nervous system and effectors in controlling heart rate
When Baroreceptors detect a fall in blood pressure or chemoreceptors detect a rise in blood CO2 concentration or fall in pH, they send impulses to the cardiac control centre of the medulla, which sends impulses to the SAN along the sympathetic neurones. Therefore there is more frequent impulses sent from the SAN, so cardiac muscle contracts more frequently and heart rate increases.
When Baroreceptors detect a rise in blood pressure or chemoreceptors detect a fall in blood CO2 concentration or rise in pH, they send impulses to the cardiac control centre of the medulla, which sends impulses to the SAN along the parasympathetic neurones. Therefore there is less frequent impulses sent from the SAN, so cardiac muscle contracts less frequently and heart rate decreases.
