Topic 6 - Organisms respond to changes in their internal and external environment Flashcards
Kinesis
Kinesis is a non-directional response to a stimulus
The rate of movement of an organism is affected by the intensity of the stimulus
Flatworms called planarians possess a network of neurones and simple eye-like structures that have light-sensitive cells
Planarians display kinesis when removed from their usual dark environment
Planarians are found on the underside of stones, hidden from daylight
When a stone is removed or turned over the planarians begin to move in random directions
Once these random movements eventually bring them back into the darkness they stop moving
This type of responsive behaviour helps them to protect themselves from predators
taxes
Taxis is a directional response to a stimulus
The organism moves directly away from or towards the stimulus
A single-celled organism called Euglena which is commonly found in ponds exhibits taxis
It has chloroplasts for photosynthesis and a flagellum to help it swim
The flagellum has a receptor close to its base that is sensitive to light
Euglena swims directly towards the light, this is known as phototaxis
This behaviour is highly valuable as it brings the organism towards the light where it can photosynthesise
maggot experiment
-The animals need to be observed during the experiment to see if turning frequency or movement rate changes in different environments
If movement is directional then the turning frequency would decrease when the organism detects the stimulus
-The results showed that there was always more maggots in the shaded half of the chamber at the end of the experiment
As the maggots were not observed during the experiment it can not be said whether kinesis or taxis has occurred
However, the results do conclude that maggots have the ability to detect bright light and respond by moving until they reach a more favourable environment
define stimulus
detectable change in the internal or external environment of an organism that leads to a response
stimulus –> receptor –> coordinator –> effector –> response
true or false –. if an organism crosses a sharp dividing line between a favourable and an unfavourable environment, its turning rate increases
true
notes from spec
A stimulus is a change in the internal or external environment. A receptor detects a stimulus. A coordinator formulates a suitable response to a stimulus. An effector produces a response.
Receptors are specific to one type of stimulus.
Nerve cells pass electrical impulses along their length. A nerve impulse is specific to a target cell only because it releases a chemical messenger directly onto it, producing a response that is usually rapid, short-lived and localised.
In contrast, mammalian hormones stimulate their target cells via the blood system. They are specific to the tertiary structure of receptors on their target cells and produce responses that are usually slow, long-lasting and widespread.
Plants control their response using hormone-like growth substances.
survival
-organisms increase their chance of survival by responding to changes in their environment
-in flowering plants specific growth factors move from growing regions to other tissues where they regulate growth in response to directional stimuli
-Taxes and kineses as simple responses that can maintain a mobile organism in a favourable environment.
necessary needs of an organism
-an organism needs oxygen to allow for aerobic respiration in order to release energy (ATP) for processes such as protein synthesis
-Needs water = photolysis of water in LDR for ETC
-Needs CO2
-needs nitrate ions to form nitrate molecules in DNA
-require warmth to ensure optimum temperature for enzyme activity
role of spiracles
Oxygen levels decrease when spiracles are closed as its acting as the final electron acceptor during oxidative phosphorylation
CO2 levels increase when spiracles are closed as it is produced in the link reaction as pyruvate is dexcarboxylated form acetate
taxes vs kinesis
Taxes –> directional response to stimulus (positive –> moves towards)
Kinesis –> non-direction response to stimulus (Slower + relies on chance) (negative -> moves away)
e.g algal cells will move towards light so can photosynthesis. This is an example of positive photo taxes
orthokinesis vs kilokinesis
Orthokinesis = change in rate of movement
Klinokinesis = change in the amount of turning
investigating kinesis
-Kinesis is a non-directional response to stimulus. Slower bc it requires on chance. Small, simple, mobile organisms
-using maggots in our experiment is ethical bc they don’t have a complex nervous system
-null hypothesis = there is not statistically significant difference between the number of times the maggot turned left or right
statistical response
The Chi squared value is less than the critical value. This means that there is a greater than 5% probability that the difference in direction of the turn is due to chance. The difference is not significant.
chi-squared
-If your chi-square calculated value is greater than the chi-square critical value, then you reject your null hypothesis. If your chi-square calculated value is less than the chi-square critical value, then you “fail to reject” your null hypothesis.
-null hypothesis = no significant difference
-alternate hypothesis = there will be a significant difference
-chi squared measures the significance of deviations from expected results. Association between 2 co-variables -> categorical data
types of tropism
-Phototropism –> the growth of plants in response to light
-Geotropism –> the growth of plants in response to gravity
-Chemotropism –> the growth of plants in response to chemicals
-Hydrotropism –> the growth of plants in response to water
plant growth
-IAA is produced in the meristem tissue found in the tips of roots and shoots
-it travels down the coleptile to the “zone of elongation” where it either stimulates or inhibits cell elongation
-IAA is considered a growth factor as opposed to a hormone as it can stimulate or inhibit growth whilst hormones only have one target organ and always result in the same response
tropism
Tropism –> growth of a plant root or shoot in response to a directional stimulus –> allows plant the reach the most favourable conditions e.g roots display negative phototropism and positive geotropism
compare taxes and tropism
-both are a non-directional response to stimulus
-in taxes there is movement of the whole organism whilst in tropism just part of the organism moves
phototropism in flowering plants
-cells in the tip of the shoot produce IAA, which is then transported down the shoot
-the IAA is initially transported evenly throughout all regions as it begins to move down the shoot
-light causes the movement of the IAA from the light side to the shaded side of the root
-a greater concentration of IAA builds up on the shaded side of the root than the light side
-IAA causes elongation so shaded side elongates father than light side causing shoot tip to bend towards the light
gravitropism in flowering plants
-cells in the tip of the root produce IAA, which is then transported along the root
-IAA is intially transported to all sides of the root
-gravity influences movement from upper to lower side
-as IAA inhibits elongation of the root cells
-relative greater elongation on cells of upper side compared to lower side causes root to bend downwards
when describing graphs split into into sections and describe everything despite smaller lines (be descriptive)
can you conclude the woodlice shown turn alteration behaviour when distance between forced and second turn was 10cm
-no
-equal numbers
-random chance
x2 investigations
-due to time not distance
-keep distance the same
-increase time between forced and 2nd turn
using the data in the figure above to explain how behaviour of woodlice results in them moving rapidly out of faviourable conditions
-short distances = more alteration
-prevents going in circles
name the type of behavioural response shown in the investigation
-kinesis
-random non-directional movement
-number of turns depends on strength of stimulus
suggest and explain one advantage of this behaviour
-stays in favourable condition
-remains on host
push vs pull stimulus
push = drives pest away from crop plant
pull = attracts pest
taxes movement
towards the stimulus
describe how the maize plants could be selected at random
-make grid/measure plot of maize plants
-use random number generators to make co-ordinates
why was there bare ground between maize and grass species
-avoid contamination between maize and grass
-reduce movement of pests
explain what the results from group A suggest about the factors controlling the behaviour of winged termites
-gravity (geotaxis) -> 60 degree angle
-eyes covered so cannot see light stimulus
-antannea (B) are involved
increased movement =
increased chance of moving away from unfavourable conditions
explain the growth using knowledge of IAA
-IAA produced at tip
-diffuses to shoot
-more elongation of cells on one side than the other
what conclusions can you make of IAA from the figure
-IAA moves to shaded side
-IAA is produced in the dark
taxis =
increase dispersion
no stats test =
dont know significance
why did the student keep the lid on
to reduce/prevent evaporation
could affect IAA concentration
high IAA
stimulates cell elongation
colorimeter = measure
colour / light etc
phototropism in shoot
-stimulate cell elongation
-IAA formed on darker side of the stem as it doesn’t receive light
-IAA diffuses down shoot tip which stimulates cell elongation towards unilateral light
phototropism in roots
-inhibits cell elongation
-increased conc of IAA on bottom sside of root (darkened)
-diffuses up the root reducing cell elongation
-due to gravity the root grows downwards into the soil to avoid light
IAA = move away from light
replace amount with
volume
nervous system
The nervous system is a complex network of cells, tissues, and organs that is responsible for controlling and coordinating the functions of the body. It collects and processes sensory information from the environment and internal organs, and then sends signals to the muscles and glands to produce a response.
explain the importance of reflex actions
-automatic and unconscious response that prevents tissue harm
-involuntary role in homesostasis (maintaing regulation of internal conditions)
describe the sequence of events which allows information to pass from one neurone to next neuron across cholinergic synapse
-an electrical impulse causes calcium ions to enter the axon
-vesicles move to fuse with the pre-synaptic membrane
-acetylcholine is released an diffuses across the synaptic cleft
-it binds with receptors on the post-synaptic membrane
-sodium ions enter the neuron resulting in the depolarisiation of post-synaptic membrane
-if above the threshold a nerve impulse is produced
give 2 differences between a cholingeric synapse and a neuromuscular junction
1) no summation in neuromuscular junction
2) neuron to neuron in choli but neuron to muscle in junction
dendrites
Dendrites – dendrites are thin extensions of the cell body that carry impulses received from neighbouring neurones to the cell body.
cell body
Cell body – the cell body contains the nucleus, mitochondria, and many ribosomes.
axon
Axon – the axon is a long cytoplasmic extension that carries impulses away from the cell body. It is covered in Schwann cells, that surround and support the neurones.
nodes of ranvier
Nodes of Ranvier – these are gaps in the myelin sheath. They occur between adjacent Schwann cells.
resting potential
Neurones are excitable cells, meaning that they can change their resting potential.
The resting potential is the difference in charge across the neuronal membrane when the neurone is at rest. When neurones are at rest, the outside of the cell is more negative than the inside of the cell – this is caused by differences in ion concentrations and maintained by proteins called ion channels
mainting resting potential
The membrane contains many sodium-potassium pumps. Sodium-potassium pumps use active transport to pump three sodium ions (Naᐩ) out of the neurone, and two potassium ions (Kᐩ) in. The membrane is not permeable to sodium ions, so they cannot diffuse back in, creating a sodium ion electrochemical gradien
Potassium ion channels make the membrane permeable to potassium ions. The channels allow Kᐩ ions to diffuse back out of the neurone, so they move from an area of high concentration (the cytoplasm) to an area of low concentration (extracellular space), increasing the positive charge outside.
Anion concentrations are higher inside the neurone. Anions are large molecules with a negative charge, therefore increasing the electrochemical gradient of the membrane.
changes in membrane permeability
-Changes in membrane permeability lead to depolarisation and the generation of an action potential. The all-or-nothing principle
stimulus to response
Stimulus –> sensory neuron –> intermediate (relay neuron) –> CNS –> intermediate (relay neuron) –> motor neuron –> effector –> response
nervous system
Nervous system is divided into CNS (brain and spinal cord) –> co-ordinate nervous responses and the PNS (all nerves that co-ordinate impulses going towards or away from the CNS)
sensory and motor pathways
-The sensory pathways collects impulses from receptors detecting changes that occur in or around the body
-The motor pathways then coordinate the response to those changes —> somatic nervous system coordinates voluntary responses and the autonomic nervous system coordinates involuntary responses
-sympathetic = fight or flight
-parasympathetic = rest and digest
sympathetic nervous system
-The sympathetic nervous system prepares the body for any possible type of emergency. When the fight or flight response takes over, the SNS is activated. During the activation when the body is under stress, the heart rate and breathing increases in response to a release of adrenaline, as well as changes to the organ’s function. Pre- and post-ganglionic nerves send information between the central nervous system (CNS) and the sympathetic nervous system (SNS).
somatic vs autonomic
The overall function of the somatic nervous system is to:
Relay information from the sensory receptors to the brain
Provide a muscle response through the motor pathways
The autonomic nervous system is in control of automatic involuntary functions, playing an important role in homeostasis. It works to make sure the functions run without an issue and takes control during emergencies. Reflexes such as sneezing and coughing are also carried out by the ANS
simple reflex pathways
-rapid, autonomic and involuntary
-this is important bc it protects against damage to body tissue
-simple reflext actions do not have to be learned and so are coordinated in the spinal cord as opposed to the brain
-important in homoeostatic control, etc
steps of nerve impulse
-nerve impulse travels along sensory neuron to spinal cord
-impulse crosses synapse and to relay neuron (intermediate)
-information is passed along motor neuron
-the information from the motor neuron is then detected by the effector to stimulate a reponse
structure of motor neuron
-wrapped in schwann cells which form a myelin sheath
-myelin is comprised of glycolipids, cholesterol and proteins. It insulates the axon down which electrical impulses are transmitted
-myelin acts an electrical insulator bc It is impermeable to ions like Na+. Action potentials can only occur in the gaps of the myelin.
-glycolipids = covalent bond of a monosaccharide to a glycerol molecule and 2 fatty acids
-increases efficiency along nerve cells + preserves strength of electrical message
where do neurons transmit impulses
Neurones transmit electrical impulses, which travel extremely quickly along the neurone cell surface membrane from one end of the neurone to the other
factors which contribute to establishing membrane potential
The active transport of sodium ions and potassium ions
Differential membrane permeability
difference in membrane potential
The cell-surface membrane of neurones has selective protein channels that allow sodium and potassium ions to move across the membrane by facilitated diffusion
The protein channels are less permeable to sodium ions than potassium ions
This means that potassium ions can diffuse back down their concentration gradient, out of the axon, at a faster rate than sodium ions
active transport
Carrier proteins called sodium-potassium pumps are present in the membranes of neurones
These pumps use ATP to actively transport 3 sodium ions out of the axon for every 2 potassium ions that they actively transport in
This means that there is a larger concentration of positive ions outside the axon than there are inside the axon
The movement of ions via the sodium-potassium pumps establishes an electrochemical gradient
discrete
This makes the action potentials discrete events and means the impulse can only travel in one direction. This is essential for the successful and efficient transmission of nerve impulses along neurones
nerve impulses
When receptors (such as chemoreceptors) are stimulated, they are depolarised
If the stimulus is very weak or below a certain threshold, the receptor cells won’t be sufficiently depolarised and the sensory neurone will not be activated to send impulses
If the stimulus is strong enough to increase the receptor potential above the threshold potential then the receptor will stimulate the sensory neurone to send impulses
This is an example of the all-or-nothing principle
An impulse is only transmitted if the initial stimulus is sufficient to increase the membrane potential above a threshold potential
Rather than staying constant, threshold levels in receptors often increase with continued stimulation, so that a greater stimulus is required before impulses are sent along sensory neurones
phospholipid bilayer
the phospholipid bilayer of axon plasma membrane prevents Na+ and K+ ions diffusing across it so channel proteins /ions channels span the membrane
diffuse vs active transport
action potential = diffusion (passive process)
resting potential = active transport
what part of the nervous system controls voluntary responses
somatic nervous system
sensory neuron
Sensory neuron –> cell body is in the middle, long dendron and short axon
intermediate neuron
Intermediate (relay) neuron –> short axon, short dendrite, found in CNS
motor neuron
Motor neuron –> short dendrite and one long axon (no dendron), cell body at the start not middle, nodes of ranvier, schwaan cells
sensory vs motor
-both sensory and motor neurons are connected by a myelin sheath
-sensory neuron transmits impulses to intermediate neuron
-motor neuron transmits impulses to an effecto
dendron vs axon
Dendron = impulse to cell body
Axon = impulse away from cell body away from cell body
dendrite
Dendrite = transmit impulses from one neuron/receptor to another
nodes of ranvier
Node of ranvier = gaps in the mylein sheath/schwaan cells where there is no insulation
summary establishing resting potential
-ions move through voltage gated channels in neurons plasma membrane (affected by changes in electrical charge)
-charge difference maintained by active transport of Na+-K+ pump of inside and outside cell. 3Na+ pumped out of cell and 2K+ pumped in cell
-external = net positive charge and internal = net negative charge called resting membrane potential
-channels are more permeable to K+ ions
-charge across polarised membrane = -70mv
-nerve impulse = stimulus disturbs plasma membrane on dendrite
action potential
Action potential –> change in electrical potential associated with the passage of an impulse
threshold potential
Threshold potential –> the critical level to which the membrane potential must be depolarized in order to initiate an action potential
repolarisation
Repolarization –> change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential
polarization
Polarization –> the establishment of a negative electrical potential between the inside and outside of the plasma membrane
depolarization
Depolarization –> a loss of the difference in charge between the inside and outside of the plasma membrane
hyperpolarization
Hyperpolarization -> a change in a cell membranes potential that makes it more negative
refractory period
Refractory period –> a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation
