6: Organisms Response to Changes Flashcards
How do organisms increase their chances of survival?
- living organisms (plants and animals) increase survival chance by responding to changes in their internal/ external environment
How will organisms react in different environments?
- either move away from harmful environments or towards favourable environments
- ensure their conditions are always optimal for metabolism
How do plants respond to changes in the environment?
tropisms and auxins
What is a tropism and auxins?
a plant response to a stimulus coming from a certain direction
- they do this by regulating their growth
- towards stimulus: positive tropism
- away stimulus: negative tropism
Auxins- a group of naturally occurring and artificially synthesised plant hormones. They play an important role in the regulation of plant growth. (e.g. IAA)
What is phototropism?
shoots of plants grow towards the light, as they need sunlight to photosynthesise (response to light)
- shoots show positive phototropism
- roots show negative phototropism
What is gravitropism/ geotropism?
roots of plants grow down to anchor plants in the soil (response to gravitational pull)
- roots show positive geotropism,
- shoots show negative geotropism
What does IAA (indoleacetic acid) do?
controls cell elongation in plants, produced in tips of shoots, transported down the shoot causing cells to elongate and plant growth
What happens to the shoots and roots in phototropism?
SHOOTS- positive phototropism:
- initially, IAA evenly distributes throughout the shoot region
- when light intensity changes, IAA moves to shaded side of the shoot
- greater concentration of IAA builds on shaded side, causing cells on this side to elongate more than those on the light side
- cells elongate faster causing shoot tip to bend towards the light
ROOTS- negative phototropism:
- initially, IAA evenly distributes throughout the shoot region
- when light intensity changes, IAA moves to shaded side of the shoot
- high concentration of IAA inhibits cell elongation on the shaded side of the roots
- cells on shaded side grow slower than the light side, root bends and grows away from the light
What happens to the shoots and roots in gravitropism/geotropism?
SHOOTS- negative geotropism:
- IAA diffuses from upper to lower side of shoot
- cell elongation causes plant to grow upwards
ROOTS- positive geotropism:
- IAA diffuses to lower side of roots
- inhibits cell elongation causing cells to elongate at a slower rate compared to the top causing roots to grow downwards with gravity
How do different factors affect IAA?
- tip is removed- light can’t be detected, no IAA produced, shoot won’t bend in any direction
- tip of shoot covered- light can’t be detected, no IAA produced, no cell elongation, shoot won’t bend in any direction
- agar block- plant shoot grows naturally towards light as agar block permeable to IAA
- agar on half block- IAA only diffuse down one side, only that side elongates.
- impermeable barrier- no IAA diffuse, plant doesn’t grow
- impermeable barrier on part- IAA diffuse onto only one side, that cell elongates despite postition of light
What is nervous communication?
Response to a stimulus (change in environment) coordinated by the nervous system
made of: sensory neurones, CNS, motor neurones, effector
How does simple reflex work and triggered?
to respond to a stimulus, it must be detected first by receptors (cells/ proteins on surface membrane )
- each receptor is specific to 1 type of stimulus
- when a stimulus is detected by receptor cells an electrical impulse is sent along the sensory neurone
- electrical impulse transmitted to central nervous system
- when the electrical impulse reaches the end of the sensory neurone a chemical (neurotransmitter) is released into the **synapse ** (a gap between 2 neurones)
- this passes on information and the new electrical impulse is generated in the relay neurone in the cns
- cns processes the information and sends impulses along the motor neurone to the effector (muscle/ gland)
What is the simple reflex?
rapid involuntary response to a stimulus
- as it doesn’t involve brain, we don’t waste time thinking (fast response)
- simple reflexes produce a protective effect
why do species have simple responses?
- simple mobile organisms
- to keep them in a favourable environment
What are the 2 types of simple responses?
tactic & kinetic
What is a tactic response?
- directional movement in response to a stimulus and involves the organism either moving towards something (positive tatic response) or away from something (negative tactic response)
- eg.phototaxis (light), thermotaxis (temperature) and chemotaxis (chemicals)
What is a kinetic response?
- non-directional movement in response to stimulus
- woodlice show kinetic response to humidity
- in high humidity, they’ll move slowly and turn less often so they’ll stay where they are
- when air gets drier, woodlice will move faster and will turn more often do they will move into a new area
- this increses their chances of survival with a high humidity as this will reduce water loss and conceal them from predators
What is a receptor?
- can either be cells or proteins on cell surface membrane of cells that detect different stimuli
- CNS detects changes to internal and external environments through receptors
- receptors specific to different specific stimuli
- transducers: change in stimulus detected by sensory neurone, converting change in energy to nervous impulses (generator potential)
What is resting potential?
- if no stimulus, then receptors in nervous system are in their resting state
- membrane of receptors has ion channels and ion pumps, allowing ions to move in and out of the cell
- inside of cell more negative than the outside (as more +ions outside)
- difference in charge means there’s a potential difference across the membrane
What is generator potential?
- if a stimulus is detected, membrane of receptor becomes excited and more permeable
- allows more ions to enter the cell, changing the potential difference across the membrane so generator potential generated
What is an action potential?
- generator potential must reach threshold to be passed onto sensory neurone
- if generator potential big enough, it triggers an action potential (nervous impulse)
- ACTION POTENTIALS ARE THE SAME SIZE SO STRNGTH OF STIMULUS MEASURED BY FREQUENCY
What is the pacinian corpuscle?
mechanoreceptors that detect mechanical stimuli (e.g. pressure and vibration)
- found in skin and soles of feet
- contain end of sensory neurone (sensory nerve ending) wrapped in layers of connective tissue (lamellae)
- plasma membrane of sensory neurone ending has special type of sodium ion (stretch mediated sodium ion channels)
How does the pacinian corpuscle detect changes?
- when stimulus detected, lamellae become deformed and press on sensory nerve ending (no longer in resting potential)
- causes cell membrane of sensory neurone to stretch, deforming ion channels
- causes stretch mediated sodium ion channels to open so sodium ions diffuse in
- influx of sodium ions changes potential difference of membrane and depolarises it, creating generator potential
- if reached threshold level, it’ll trigger an action potential, which is passed onto the central nervous system
What are photoreceptors?
receptors in the eye that detect changes in light
- located on the retina (innermost layer of the eye)
- light enters eye through pupil and focused onto retina
- amount of light entering eye controlled by muscle of iris
- fovea is area of retina contaning lots of photoreceptors
- nerve impulses from photoreceptors cells are carried from retina to brain by the optic nerve (a bundle of neurones
- where optic nerve leaves the eye is the blind spot (as no receptors there)
What are the 2 types of photoreceptors?
- Rods- sensitive to light intensity, lead to images being seen in black and white (monochromatic)
- Cones- respond to different wavelengths of light, allowing us to perceive images in full colour
- both photoreceptors connected to the optic nerve by bipolar neurones
How do we see?
- when light enters the eye, it hits the photoreceptors, the light energy is absorbed and converted into electrical energy (generator potential)
- light bleaches the pigment in these cells (rhodopsin in rods, iodopsin in cones) breaking them down and causing a chemical change,
- altering permeability of cell surface membrane to sodium ions
- threshold level generates action potential
- action potential sent along bipolar neurone, which connects to photoreceptor to the optic nerve, sending impulses to the brain
What do rod cells do?
- don’t distinguish between wavelengths of light, only intensity (monochromatic)
- more numerous than cone cells in retina around peripheral (outside)
- used to detect light at very low light intensities, very sensitive to light intensity
- light detected must exceed threshold to trigger generator and action potential
- as many rod cells connected to single sensory neurone
What is spacial summation in rod cells?
- if generator potential of each rod cell is very low, they all accumulate to create a larger generator potential and reach the threshold
- create an action potential
What is visual acuity?
- the ability to distinguish between 2 points close together
- rod cells provide low visual acuity, so the brain can’t distinguish between seperate sources of light that’ve been detected
- as only one action potential travelling to the brain due to summation
What do cone cells do?
- packed close together in the fovea , distinguish between wavelengths of light (colours, trichromatic vision), perceive images in full colour depending on proportion
- 3 types, each w/ different optical pigment, each sensitive to dofferemt wavelengths of light (blue,green,red)
- very sensitive to light intensity, only respond at high light intensities (as each cone cell connected to 1 sensory neurone)
- to generate an action pot., generator pot. from each individual cone cell needs to exceed threshold level
- as each cone cell has its own sensory neurone, each trigger has own action potential, 2 impulses and so easily distinguish (though less sensitive to light int., higher visual acuity)
What are the 2 types of nervous system?
- central nervous system (CNS)- made of brain and spinal cord
- peripheral nervous system- made of neurones connecting CNS to body
What is the peripheral nervous system split into?
- somatic- controls conscious activity (e.g. walking/talking)
- autonomic- controls unconscious activity (e.g. breathing/ digestion)
autonmomic split into sympathetic and parasympathetic
- sympathetic- flight or fight response
- parasympathetic- calm body rest and digest
How is our heart rate controlled by our autonomic nervous system?
- cardian muscles are myogenic (contract and relax without signals and nerves)
- patterns of contractions control heartbeat, process starts with sinoatrial node (SAN)
- mass of tissue in wall of right atrium (pacemaker, same as SAN), sets the rhythm of the heartbeat, send out waves of electrical activity to atria wall, causing muscles in atria to contract, forcing blood into the ventricles below
- band of non-conducting collagen tissue prevents wave of electrical energy from being passed directly from atria to the ventricles
- wave of electrical activity transferred to atrioventricular node
- to esure the atria have empties before ventricles contract, there;s a delay before AVN reacts
- AVN responsible for passing waves of electrical activity onto the bundle of His (in septum)
- group of muscle fibres responsible for conducting wave of electric activity between ventricles to heart apex
- splits into fine tissue (purkyne tissue)
- causes wave of electrical activity into muscular ventricle walls
- causes them to contract simultaneously from bottom up, forcing blood out through the pulmonary artery and aorta above
What is the role of the heart and brain in controlling heart rate?
- SAN generates electrical impulses that cause cardiac muscles to contract
- rate of SAN fires unconsciously controlled by brain (medulla oblongata)
- animals need to alter heart rate in response to change in internal stimuli
- detected by pressure receptors and chemical receptors
What receptors are used in maintaining heart rate?
- baroreceptors- detect pressure. found in aorta and carotid arteries (major arteries in the neck). stimulated by high and low blood pressure
- chemoreceptors- detect chemicals. found in aorta, carotid arteris and medulla. monitor O2 levels in the blood (and CO2 and pH, indicate O2 levels)
What occurs in the heart when there’s a change in blood pressure?
- high b.p.- baroreceptors detect change, impulse sent to medulla by parasympathetic neurones, secrete acetylcholine neurotransmitter to bind to SAN, cardiac muscles cause heart rate to slow, reducing b.p.
- low b.p.- baroreceptors detect change, impulse sent to medulla by sympathetic neurones, secrete noradrenaline neurotransmitter to bind to SAN, cardiac muscles cause heart rate to speedm up, increasing b.p.
What occurs in the heart when there’s a change in O2 blood concentration?
CO2/ pH change
- high blood O2- chemoreceptors detect change, impulse sent to medulla by parasympathetic neurones, secrete acetylcholine neurotransmitter to bind to SAN, cardiac muscles cause heart rate to decrease, returning O2, Co2 and pH levels to normal
- low blood O2- chemoreceptors detect change, impulse sent to medulla by sympathetic neurones, secrete noradrenaline neurotransmitter to bind to SAN, cardiac muscles cause heart rate to increase, returning O2, Co2 and pH levels to normal
