Organisms respond to changes in their internal and external environments Flashcards
What is a taxes
Movement of a motile organism in response to a stimulus (usually an environmental change)
What is a positive taxis
organism moves towards a stimulus (usually favourable)
What is a negative taxis
organism moves away from a stimulus (usually unfavourable)
What is the purpose of a taxis
Increases chances of the organism’s’ survival in all cases
What is kineses
A form of response in which the motile organism does not move towards/away from a stimulus, but instead shows a random, non-directional response (eg. the organism changes the speed at which it is moving and the rate at which it changes direction in response to a stimulus)
What is a tropism
The growth of plants in response to a directional stimulus
e.g. The plant grows towards (positive response) or away (negative response) from a stimulus
What is the kinesis for water
hydrotropism (positive in roots)
What is the kinesis for gravity
gravitropism (positive in roots, negative in shoots)
What is the kinesis for light
phototropism (positive in shoots, negative in roots)
What is a reflex arc
a completely involuntary and instantaneous movement in response to a stimuli
Describe the structure of a myelinated motor neurone
- dentrites/dendrones
- cell body
- nucleus
- axon
- myelinated sheath
- schwann cells
- nodes of ranvier
- axon terminals
Definition of the nervous system
a system that uses nerves to pass electrical impulses to communicate
Definition of the hormonal system
a system that produces chemicals that are transported in the blood to their target cells (via receptors) to communicate
Differences between the nervous and hormonal systems
NERVOUS SYSTEM
- short-lived
- transmission by neurones
- very rapid acting
- usually temporary and reversible
- muscles
HORMONAL SYSTEM
- long lasting
- transmission by blood stream
- relatively slow
- may be permanent and irreversible
- glands
How does phototropism work in plants
SHOOTS
IAA moves to the shaded side of stem, causes elongation of cells here, so the plant will bend towards the unidirectional light
this is positive phototropism
ROOTS
IAA moves to the shaded side of the stem, but inhibits the elongation of cells, so the roots bend away from the unidirectional light
this is negative phototropism
How does gravitropism work in plants
IAA moves to the underside of shoots and roots and either inhibits or stimulates growth, causing the plant to bend against/with gravity
In shoots, there is negative gravitropism and in roots there is positive gravitropism
What is the nervous system made up of
receptors
sensory neurones
CNS and relay/intermediate neurone
motor neurone
effectors
What is smooth muscle
muscle that contracts without conscious control, found within walls of internal organs
What is cardiac muscle
muscle that contracts without conscious control but only found in the heart
What is skeletal muscle
muscle that we use to move limbs and ourselves
What are antagonistic pairs of muscles
Muscles that move a bone together, where one contracts (agonist) and the other relaxes (antagonist).
Examples are our triceps and biceps
What are the features of a neurone
Cell body
Nucleus
Schwann cells
dendrones/dendrites
axon
nodes of ranvier
axon terminals
axoplasm
What is an action potential
A nerve impulse is an action potential that moves along a neurone in one direction
What ensures that the action potential only travels in one direction along a neurone
The section behind the action potential is repolarising
The refractory period is where a neurone cannot be stimulated anymore and has to wait to be stimulated again
the voltage gated Na+ channels are closed and will not open. In addition, the voltage gated K+ channels are open.
Describe what happens during an action potential
A stimulus arrives and disturbs the resting membrane potential (of -70mV), causing voltage-gated Na+ channels to open.
Na+ rushes into the axoplasm by diffusion, down its concentration/electrochemical gradient, causing the membrane to depolarise (the inside now becomes more positively charged than the outside).
When the membrane potential reaches +40mV the voltage-gated Na+ channels close and the voltage-gated K+ channels open.
K+ rushes out of the axon into the surrounding tissue fluid by diffusion, causing the membrane to repolarise (becoming more negatively charged on the inside again compared to the outside).
The membrane potential overshoots the resting membrane potential to lower than -70mV (e.g. -80mV) -> hyperpolarises
At this point, the voltage-gated K+ channels close.
The Na+/K+ pump then restores the membrane back to the normal resting membrane potential of -70mV.
What is a nerve impulse
an action potential that moves/spreads along a neuron in one direction
Can you explain the meaning of the all-or-nothing principle
- A specific level (strength) of stimulus is required to meet the threshold value to trigger an action potential
- If a stimulus is too small that the threshold is not met, an AP will not be generated
- All APs are more or less the same size - a bigger stimulus will not generate a bigger AP
What is the relationship between size of stimulus and action potential
The larger the stimulus, the higher the frequency of Action potentials that pass along the neuron in a given time
What makes it so the action potentials travel faster along a myelinated neurone opposed to an unmyelinated neurone
Saltatory conduction in myelinated neurones is faster - action potentials only occur at the Nodes of Ranvier
Factors affecting the speed of conduction of an action potential in a nerve
- axon diameter
- myelination
- temperature
What does the pacinian corpuscle respond to
pressure
What is the pacinian corpuscle structure
Layers of connective tissue with a viscous gel inbetween layers
the end of a nerve ending
Strech mediated Na+ channels
Describe how a Pacinian Corpuscle produces a generator potential when stimulated (3 marks).
Increased pressure deforms/changes stretch mediated sodium channel.
sodium channels open and sodium ions flow in.
which cause depolarization which leads to generator potential.
What is a generator potential
The initial depolarisation (diffusion of Na+ ions into the axon), which may or may not reach the threshold at the first node of ranvier and therefore may or may not trigger an action potential
What is a synapse
the point/junction where one neurone connects/joins with another neurone or with an effector
Outline the structure of a synapse
Pre synaptic Knob
- synaptic vesicles
- neurotransmitters
- Ca2+ VGC
- Pre synaptic membrane
- synaptic cleft
Post synaptic Knob
- proteins receptors
- post synaptic membrane
What are the two kinds of synapses and give the examples of each
excitatory (releases acetylcholine) and inhibitory (releases GABA)
Synapses are unidirectional. What does this mean
the impulse travels in one direction only
How is temporal summation created at a synapse
A single presynaptic neurone releases neurotransmitter many times over a short period of time due to a high frequency of action potentials travelling along the presynaptic neurone. This results in the release of enough neurotransmitter to reach the threshold and trigger an action potential on the postsynaptic neurone.
How is spatial summation created at a synapse
Multiple presynaptic neurones together release enough neurotransmitter to reach the threshold and trigger an action potential on the postsynaptic neurone (however, on their own they did not release sufficient)
what is the arrangement of cells in the retina
ganglion cells (optic nerve), bipolar cells and the cones/rods
Compare and contrast cone and rod cells
Cone
- responds to high light intensity
- contains pigment called iodopsin
- used to see coloured light
- has good visual acuity
- each cone synapse connects to one bipolar cell
Rod
- responds to low light intensity
- contains pigment called rhodopsin
- used to see black and white
- has low visual acuity
- 3 rod cells have a synapse to one bipolar cell (spatial summation)
Where are cone cells distributed on the retina
concentrated at the fovea
Where are rod cells distributed on the retina
the periphery of the fovea
What is visual acuity
The ability to tell apart two points that are close together.
Why is visual acuity different in cone and rod cells
Cone cells only connect to one other neuron, so each individual stimuli can be distinguished.
Rod cells connect in 3’s to one bipolar cell, and so the different polarisations of light get merged
Heart muscles are myogenic. What does this mean?
The muscles contracts by itself rather than a nerve.
The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricualr node (AVN). Describe how.
5 marks
SAN is myogenic and acts as a pacemaker.
The SAN depolarises and send a wave of electrical excitation over the atria, causing them to contract (atrial systole)
There is a brief delay where the electrcial impulse travels over nonconductive tissues and the AVN, allowing the atria to fully empty and the ventricles to fill up fully.
The electrical wave of excitation travels down the Bundle of His and towards to apex of the heart, where it spreads up the purkyne fibres.
This causes the ventricles to contract (ventricular systole)
After this, the atria and ventricular muscles relax and fill up passively with blood (atrial and ventricular diastole)
What is the voluntary nervous system
the control system associated with the voluntary control of muscles
What is the autonomic nervous system
What are the two sides of the autonomic nervous system and what are they
Parasympathetic division
- these motor neurones have a suppressive effect on effectors -> involved in conserving energy
Sympathetic division
- these motor neurones have a stimulatory effect on effectors
What is the definition of homeostasis?
The maintenance of more or less constant internal environments in organisms
Explain the formation of tissue fluid
- higher osmotic pressure at the arteriole end, lower at the venule
- higher hydrostatic pressure at arteriole end, lower at the venule
- higher water potential at the arteriole end than the venule
- both of these pressures (osmotic and hydrostatic) force fluid from the bloodstream to move to the tissue cells surrounding the blood vessel
- because the blood has a higher X than the surrounding tissue
- RBCs WBCs plasma proteins all remain in the blood
- so as a result, water potential in the blood vessel decreases below the water potential of the surrounding tissue, so fluid enters back in at the venule end down its pressure/water potential gradient
- 10% of tissue fluid does not make it to the blood vessel, and therefore is removed by the lymphatic system as lymph
Where does the exchange of blood and tissue occur?
capillaries
What are the features of capillaries that make them perfect for exchange between blood and tissue
- one cell thick, so short diffusion pathway
- have pores (fenestrae) that allow water to move out more easily
- the small diameter only allows one RBC to fit through at a time, so direct diffusion
What is the importance of homeostasis?
provides organisms with the ability to maintain a constant internal environment to withstand greater changes in the external environment, allowing them to survive a greater range of habitats
What is the importance of homeostasis specifically, think enzymes, water potential and glucose
Enzymes are sensitive to changes in temperature & pH and are essential for all the chemical reactions inside cells (metabolism).
Blood glucose needs to be high enough to supply cells with respiratory substrate. Too much glucose in the the blood lowers its water potential.
Changes in water potential would cause cells to shrink or swell and affect their function. Therefore solute concentrations need to be maintained.
What is negative feedback
when the output from the system counteracts/opposes the input and so turns the system off because the body is brought back to the set point
How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency?
5 marks
- Body temp. / 37 °C is optimum temp for enzymes;
- excess heat denatures enzymes / alters tertiary structure / alters shape of active site / enzyme so substrate cannot bind / eq;
- reactions cease / slowed;
- too little reduces kinetic energy of molecules / molecules move more slowly;
- fewer collisions / fewer ES complexes formed’
What happens during thermoregulation, include both extremes
What is the main store of glucose in animals, and what are the structural relations to its function
- glycogen
- highly coiled, so compacts and a lot can fit into a small space
- highly branched, so more ends/surface area for hydrolysis of the molecule to release glucose more rapidly, and so it is more readily available for respiration
- doesn’t affect water potential within a cell, so won’t force water out of the cell
What does each of the following do to glucose levels in the blood?
- glucagon
- insulin
- adrenaline
- glucagon
increases blood glucose concentrations when they are two low, by causing glycogenolysis in the liver, where glycogen is hydrolysed and stimulating the liver to release glucose into the blood - insulin
decreases blood glucose concentration when they are too high, by causing glycogenesis in the liver, where the liver is stimulated to absorb glucose and condense it into glycogen as a store - adrenaline
increases blood glucose concentrations REGARDLESS of whether they are too high, normal or too low, to make glucose readily available for a predicted increase of respiration rates due to flight or fight activation
Where are glucagon and insulin released and by what
In the endocrine cells called ISLETS OF LANGERHANS, in the pancreas
Glucagon is released by alpha cells
Insulin is released by beta cells
What is an endotherm?
What is an ectotherm?
endotherms are organisms where their body temperature is controlled within themselves (metabolic activities)
ectotherms are organisms where their body temperature is controlled externally, and so they obtain their heat from environmental sources
What are some symptoms of diabetes
- High blood glucose concentration
- Presence of glucose in urine due to high concentration in the blood
- Need to wee excessively (body trying to get rid of excess blood glucose)!
- Weight loss
- Increased thirst and hunger
What causes type I diabetes
- genetic, where no insulin is produced
- beta cells are destroyed
- so NO insulin is produced
- it can also be from an autoimmune response where the immune system has attacked the B cells in the Islets of Langerhans
What causes type II diabetes
- the pancreas still produces insulin but the body becomes ‘resistant’ to/ loses responsiveness to insulin
- Can result from a loss of (fewer) insulin protein receptors on body cells or receptors no longer respond to insulin
- therefore less glucose taken up into cells
What is diabetes?
A metabolic disorder caused by the inability to control blood glucose concentrations by homeostasis either due to the complete lack of the hormone insulin (produced by the beta cells of the pancreas) or a loss of responsiveness to insulin.
Outline the second messenger model
- glucagon/adrenaline binds to their protein receptors on liver/muscle cells
- this changes the tertiary structure, which in turn activates adenylate cyclase
- adenylate cyclase causes ATP to convert into cAMP
- cAMP acts as the 2nd messenger, and activates (switches on) protein kinase
- protein kinase is an enzyme that catalyses the hydrolysis of glycogen into glucose
Describe how the regular contraction of the atria and ventricles is initiated and coordinated by the heart itself. (5)
- the sinoatrial node depolarises which causes a wave of electrical excitation to be sent over the atria , causing them to contract
- the heart is myogenic, meaning it causes itself to contract
- there is a brief delay as the wave of electrical excitation passes over nonconducting tissue, and reaches the atrioventricular node
- this allows the atria to fully empty of blood, and allows the ventricles to fully fill up
- the wave of electrical excitation travels down the septum of the heart towards to apex, and then up the purkyne fibres from the apex up the sides of the ventricles
- this cause the ventricles to contract
