Chapter 14 - Responses To Stimuli Flashcards
What is involved in the pathway that allows organisms to detect and respond to danger to aid survival
1) stimulus - this is a detectable change in the internal or external environment of an organism
2) receptor- this detects specific types of stimulus
3) coordinator - this coordinates a suitable response to a stimulus
4) effector - this produces a response to a stimulus
5) response- this is the action produced by the effector
Why are responses to stimuli crucial for survival
As it allows organisms to:
- navigate to food resources
- evade predators or harmful conditions
Which both increases the probability of survival and successful reproduction
What is a Taxis (Taxes - plural)
a simple response whose direction is determined by the direction of the stimulus. They guide organisms either towards a beneficial stimulus or away from a harmful one.
(Directional response)
What is a positive and negative taxis
- Positive taxes lead towards a favourable stimulus.
- Negative taxes prompt movement away from unfavourable stimuli.
Positive phototaxis
when an organism moves towards light
Negative phototaxis
when an organism moves away from light
Positive chemotaxis
when an organism moves towards a region where a specific chemical is more concentrated
Examples of taxis
Positive phototaxis
Negative phototaxis
Positive chemotaxis
What is Kinesis/Kineses
When an organism changes the speed of movement and the turning frequency (rate it changes direction) based on the favourability of the environment.
(Non directional)
How is kinesis impacted in different conditions
- Increased turning in unfavourable conditions.
- Accelerated movement in favourable conditions.
What is a tropism
When a part of an organism grows in response to a directional stimulus.
What is phototropism
directional growth of parts of the plant towards or away from light.
What is gravitropism (or geotropism)
directional growth of parts of the plant towards or away from the gravitational pull.
What type of tropism does the shoot demonstrate
positive phototropism and negative gravitropism, to optimise light absorption for photosynthesis.
What type of tropism does the roots demonstrate
negative phototropism and positive gravitropism, to increase the probability that roots will grow into the soil, where they can absorb more water and mineral ions.
Two types of responses organism does in response to the environment
Kinesis
Taxis
Differences between plant and animal hormones
- Plant hormones usually act locally at the site of production, while animal hormones usually act on distant organs.
- Plant hormones are produced in a variety of tissues throughout the plant, while animal hormones are produced in specialised cells within glands.
What is hydrotrophism
directional growth of parts of the plant towards or away from moisture.
Where is IAA synthesised (made)
In the meristems of shoots and roots where the cells are dividing
Role of IAA
- stimulates cell elongation in shoots
- inhibit cell elongation in roots
How does positive phototropism/ negative geotropism occurs in the shoots
1) IAA is produced in cells in the tip of the plant shoot.
2) IAA is transported down the plant shoot.
3) Light stimulates IAA to move from the light side of the shoot to the shaded side.
4) IAA becomes concentrated and stimulates more cell elongation on the shaded side of the shoot.
5) The shoot bends towards the light.
How does negative phototropism and positive gravitropism occur in plant roots
1) IAA is produced in cells in the tip of the plant root.
2) IAA is transported along the plant root.
3) Any light available stimulates IAA to move from the light side of the root to the shaded side.
4) Gravity also pulls IAA from the upper side of the root to the lower side of the root.
5) IAA becomes concentrated and inhibits cell elongation in the lower, shaded side of the root.
6) The root bends away from any available light and downwards towards the pull of gravity.
How does auxin play a role in shoot growth via cell elongation
1) Auxin binds to the cell-surface membrane.
2) Hydrogen ions are actively transported from the cytoplasm into the cell wall.
3) The cell wall becomes more plastic.
4) Cells elongate and the plant grows.
What is the nervous system split into
Peripheral nervous system
Central nervous system
Role of CNS and what it consists of
Consists: brain and spinal cord
Role: Serves as the primary command centre for the body
Role of peripheral nervous system and what it consists of
Consists: all the nerves that connect the CNS to the rest of the body.
Role: facilitates bi-directional communication.
What is the peripheral nervous system made up of
- The sensory nervous system - This consists of sensory neurones that carry nerve impulses from receptors to the CNS.
- The motor nervous system - This consists of motor neurones that carry nerve impulses from the CNS to effectors like muscles and glands.
What two ways does the nervous system operate
- The somatic (voluntary) nervous system - This is controlled consciously, for voluntary muscle movements.
- The autonomic (involuntary) nervous system - This is controlled subconsciously, for involuntary activities such as the heartbeat and digestion.
Importance of automatic nervous system
lets the brain focus on complex tasks without the distraction of managing fundamental physiological activities
Two divisions that make up the autonomic nervous system
- The sympathetic nervous system - This activates the body’s ‘fight or flight’ response, generally increasing activity levels.
- The parasympathetic nervous system - This activates the body’s ‘rest and digest’ response, generally reducing activity levels.
Stages of reflex arc
1) stimulus triggers a reflex
2) receptors detect the stimulus and generate nerve impulses
3) sensory neurone transmits nerve impulse to relay neurone
4) relay neurone transfers nerve impulses to the motor neurone
5) motor neurone transfers impulses to the effectors
6) the effector carries out the response
Advantages of reflex arc
- Involuntary - They allow the brain to concentrate on complex processes.
- Rapid - They ensure a swift response.
- Protective - They safeguard the body from potential injuries.
- Innate - They are intrinsic mechanisms present from birth, eliminating the need for learning.
Stages of the activation of Pacinian corpsule muscle
1) The lamellae deform, pressing on the sensory neurone ending.
2) This stretches the neurone’s membrane, causing it to change shape.
3) This opens stretch-mediated sodium ion (Na+) channels in the membrane, increasing its permeability to Na+.
4) Na+ diffuses into the neurone, depolarising it and resulting in a generator potential.
5) If this signal reaches the threshold, an action potential is triggered.
Structure of Pacinican corpsule
Lamellae (allow it to detect pressure and vibration)
Sensory neurone axon
Myelin sheath
Sensory neurone ending
Explain the process of how receptors detect a stimulus
1) At rest, the receptor cell-surface membrane has a voltage across it due to differences in ion concentration inside and outside the cell, known as the resting potential.
2) When a stimulus is detected, the cell-surface membrane becomes more permeable, allowing more ions to flow in and out.
3) This alters the membrane’s voltage, creating a generator potential (or receptor potential).
4) A larger stimulus results in a bigger change in voltage, producing a larger generator potential.
5) If the generator potential reaches a threshold level, it triggers an action potential, which is an electrical signal sent along a neurone.
Explain the process of how receptors detect a stimulus
1) At rest, the receptor cell-surface membrane has a voltage across it due to differences in ion concentration inside and outside the cell, known as the resting potential.
2) When a stimulus is detected, the cell-surface membrane becomes more permeable, allowing more ions to flow in and out.
3) This alters the membrane’s voltage, creating what is called the generator potential (or receptor potential).
4) A larger stimulus results in a bigger change in voltage, producing a larger generator potential.
5) If the generator potential reaches a threshold level, it triggers an action potential, which is an electrical signal sent along a neurone.
Explain how photoreceptors convert light into an electrical impulse
1) Light hits photopigments, which are light-sensitive proteins in photoreceptor cells.
2) Light bleaches and causes a chemical change in the photopigments.
3) This increases the permeability of photoreceptor cells to sodium ions.
4) An influx of sodium ions generates a receptor potential.
5) If this reaches threshold, a bipolar sensory neurone carries a signal to the optic nerve and then the brain.
Key features of rods:
- Pigment
- Type of vision
- Location in retina
- Sensitivity to light
- Visual acuity
Pigment: Contain rhodopsin pigment, which makes rods sensitive to dim light
Type of vision: Provide black-and-white vision
Location: Located in the peripheral retina, allowing for peripheral vision in low-light conditions
Sensitivity: very sensitive to light
Visual acuity: low
Explain why do rods have a very low visual acuity but is very sensitive to light
- As several rods connect to one bipolar neurone
- this means that the spatial summation of signals allows the rods to reach threshold , this means they high visual sensitivity , and hence can detect light at low intensities
- however they have a low visual acuity, as signals from multiple rods merge in one bipolar neurone, so two close light points appear as one
Key features of cones :
- Pigment
- Type of vision
- Location in retina
- Sensitivity to light
- Visual acuity
Pigment: Contain iodopsin pigments, which makes cones sensitive to bright light of different wavelengths
Type of vision: 3 different types of cone cell provide colour vision
Location: Densely packed in the fovea, because they require higher light intensities
Sensitivity: low
Visual acuity: high
Explain why cones have a low sensitivity and a high visual acuity
Each cone has its own bipolar neurone, so more light is needed to trigger an impulse, this means that they are less sensitive than rods, so can only detect light at high intensities and that they have a High visual acuity, as one-to-one connections between cone cells and bipolar neurones allow discrimination of fine details
What is visual acuity
sharpness of vision and ability to distinguish fine details.
Where is the SAN (siniatrial node) located
In the right atrium
Where is the AVN located
In the border of the left and right ventricle
Describe the process that controls the cardiac cycle
1) SAN releases a wave of depolarisation across the atria causing it to contract (atrial systole)
2) The AVN releases another wave of depolarisation and a non conductive layer between the atria and ventricles prevents the wave of depolarisation travelling down to the ventricles
3) The bundle of His running through the septum can conduct and pass the wave of depolarisation down the septum
4) the Purkyne fibres branch off the bundle of His, causing the right and left ventricles to contract from the bottom upwards.
What is the advantage of the non conductive tissue
It provides a short delay between the atria contracting and ventricles contracting, allowing enough time for the atria to contract and pump all the blood to the ventricles and fullly empty, causing the ventricles to be provided with enough blood to contract
Effect of high and low blood pressure
- can damage the walls of the arteries - high
- insufficient supply of oxygenated blood to respiring cells and removal of waste - low
Effect on pH during times of high respiratory rate
pH decreases due to production of carbon dioxide or lactic acid
What is the response to an increase in blood pressure
1) The baroreceptors in the wall of the aorta and carotid artery are stretched
2) More electrical impulses are sent to the medulla oblongata and then the impulses are sent via the parasympathetic nervous system to the SAN to decrease frequency of electrical impulses
3) This causes the heart rate to decrease
What is the response to a low blood pressure
1) Baroreceptors in the walls of the aorta and carotid artery are not stretched
2) More electrical impulses are sent to the medulla oblongata and then the impulses are sent via the sympathetic nervous system to the SAN to increase frequency of electrical impulses
3) This causes the heart rate to increase
What is the response to a decrease in pH
1) chemoreceptors are found in the wall of the aorta and carotid artery
2) more electrical impulses are sent to the medulla oblongata and then the impulses are sent via the sympathetic nervous system to the SAN to increase the frequency of electrical impulses
3) This increases heart rate to deliver blood to lungs and rapidly remove carbon dioxide
What is the response to an increase in pH
1) chemoreceptors are found in the wall of the aorta and carotid artery
2) more electrical impulses are sent to the medulla oblongata and then the impulses are sent via the parasympathetic nervous system to the SAN to decrease the frequency of electrical impulses
3) This decreases heart rate
