3.6.1 Stimuli lead to response Flashcards
What is a stimulus?
- A detectable change in the external or internal environment of an organism
- that produces a response in an organism
What is a receptor?
Cells/organs that detect stimuli
How does moving away from harm aid in a species survival
- greater chance of surviving to reproduce and pass on advantageous alleles to next generation
What is an effector?
Cells, tissues, organs, organ systems that carry out a response to a stimulus (e.g. gland secreting hormone, muscle contracting)
How do receptors and effectors in plants and animals communicate?
- Plants: via hormones
- Animals: via hormones, nervous system
Sequence of events leading from a stimulus to a response
- stimulus
- receptor
- co-ordinator
- effector
- response
Describe kinesis
- not directional
- Random movement
- Of a mobile organism (whole organism moves)
- (no positive or negative response)
Describe taxis (pl. Taxes)
- directional response to a directional stimulus
- of a mobile organism
Describe tropism
- a directional response
- growth response of part of a plant to a directional stimulus
What is the kinesis response in favourable vs unfavourable conditions?
- favourable: slow movement, lots of turns
- unfavourable: fast movement, less turns
Describe tropism control by IAA (indoleacetic acid) in shoot tip
- shoot tip cells produce IAA
- which is transported by diffusion down all sides of a shoot
- IAA moves away from light to shaded side
- IAA causes cells to elongate more
- so shaded side grows faster so shoot bends towards light
How is IAA different in roots compared to shoots?
- greater IAA concentration decreases root cell elongation
Compare shape, pigment, number, distribution, visual acuity, sensitivity to light intensity, number of different types, colour detection and connection to bipolar cell of rod and cone cells.
- ROD: Rod shaped, rhodopsin pigment, more than cones, periphery of retina with none at fovea, poor visual acuity, low light intensity needed (higher visual sensitivity), 1 type, black and white, several rod cells to 1 bipolar cell
- CONE: cone shaped, iodopsin pigment, less than rods, at fovea, good visual acuity, high light intensity needed (lower visual sensitivity), 3 type, colour images, 1 cone cell to 1 bipolar cell
Describe what happens when pressure is applied to the Pacinian Corpuscle
- when the corpuscle is deformed by mechanical pressure, the membrane is deformed
- the stretch mediated sodium ion channels in the membrane are deformed and open.
- Sodium ions enter by diffusion
- Depolarising the neurone
- and creating a generator potential
- (action potential only of generator potential exceeds threashold)
- greater the pressure, more stretch mediated sodium ion channels deform and open, more sodium ions diffuse in, more depolarisation
How is heart rate increased?
- rate of respiration increases in muscle cells
- carbon dioxide concentration increases so pH decreases
- chemoreceptors in carotid artery/aorta detect decrease in pH in blood plasma
- send (more) impulses to Medulla oblongata’s cardioacceleratory centre
- which sends more impulses to SAN via sympathetic nervous system
- so MORE impulses to AVN
How is heart rate decreased?
- baroreceptors (pressure receptors) in carotid artery/aorta detect increase in blood pressure
- send impulses to Medulla oblongatas cardioinhibitory centre
- sends impulses to SAN via parasympathetic nervous system
- which decreases number of impulses from SAN
- so less impulses to AVN
The heart muscle is myogenic. What does this mean?
- it contracts on its own accord
- but the rate of contraction is controlled by a wave of electrical activity
What is the sinoatrial node (SAN) known as?
Pacemaker
Control of heart
- SAN releases an impulse across the atria, causing it to contract
- AVN releases another impulse when the first reaches it.
- A non-conductive layer between atria and ventricles prevents the impulse travelling down into the ventricles
- instead, the bundle of His conducts the impulse down the septum and into the Purkyne fibres
- so apex then walls of ventricles contract. Short delay before this happens, while AVN transmits a second impulse
- this allows enough time for atria to pump all blood into ventricles. Cells repolarise, cardiac muscle relaxes
Why are reflexes important? **
- fast - prevents serious damage to body
- involuntary - doesn’t require conscious part of brain so it can be involved in other tasks
- innate
- reducing / avoiding damage to tissues
- escape preditors
- role in homeostasis
- posture
