Organisms respond to changes in their internal and external environments Flashcards
What is a stimulus?
A change in the internal or external environment of an organism that leads to a response
What type of cells detect stimuli?
Receptors
What type of cells carry out a response?
Effector
What is taxis?
A simple response whose direction is determined by the direction of the stimulus
What is positive taxis?
When the movement is towards the stimulus
What is negative taxis?
When the movement is away from the stimulus
What is kineses?
A form of response whereby the organism changes the speed at which it moves and the rate at which it changes direction
What is a tropism?
The growth of part of a plant is response to a directional stimulus
Plant shoots grow up towards the light. What type of tropic responses are shown?
Positive phototropism
Negative gravitropism
What is an example of a plant growth factor?
IAA - indoleacetic acid
Explain how IAA causes phototropism in flowering plants
Cells in tip of shoot produce IAA
Transported down shoot and initially spread evenly
Light causes IAA to move from light to shady side
Greater conc. of IAA builds up on shady side –> greater elongation of shoot cells
Shaded elongates more than light, bends towards light
What does IAA do?
Causes elongation of shoot cells and inhibits cell elongation in root cells
Explain how IAA causes gravitropism in flowering plants
IAA in tip of root Initially evenly spread along root Gravity causes IAA to move to lower side IAA inhibits cell elongation in roots Higher conc --> less elongation Relatively more growth on top side, root bends down
What makes up the CNS?
Brain and spinal cord
What makes up the peripheral nervous system?
Pairs of nerves that originate from either brain or spinal chord
How can the motor nervous system be subdivided?
Voluntary nervous system
Autonomic nervous system
Describe the main stages of a spinal reflex arc
Receptor detects stimulus
Generates impulse which is sent along sensory neurones
Goes over to synapse to relay neurone which passes it to the spinal cord and to the motor neurone via a synapse
Impulse reaches effector, which carries out the response
Why are reflex arcs important?
Involuntary - don’t require decision making powers of brain, so brain not overloaded with situations w/ similar responses
Protect body from harm
Fast - neurone pathway is short w/ few synapses and no decision to be made
What are the features of sensory receptors?
Specific to a single type of stimulus
Produces a generator potential by acting as a transducer
What are Pacinian corpuscles?
Sensory receptors
What type of stimulus do Pacinian corpuscles react to?
Responds to mechanical pressure
How does the Pacinian corpuscle function?
Resting - stretch-mediated channels too narrow to allow Na+ ions to pass along, resting potential
Pressure applied –> deforms Pc and its membrane becomes stretched
Stretching widens Na+ channels, and Na+ diffuses into neurone
Influx depolarises membrane, produces generator potential
This in turn creates an action potential
Where are rod and cone cells found?
In the eye
Why are cone cells only able to respond to high light intensity?
Often connected to there own separate bipolar cell, and so stimulation of no. of cone cells can’t be combined to help exceed threshold
What is iodopsin and where is it found?
A pigment found in cone cells
What type of cell allows you to see in colour?
Cone cell
What type of cell allows you to see in black and white?
Rod cells
How are rod cells able to allow us to see in low light intensity?
Number of rod cells connected to a single bipolar cell
Therefore, allows for summation –> greater chance threshold will be reached and generator potential made
Why do rod cells give low visual acuity?
Number of rod cells connected to a single bipolar cell, but only one impulse generated
Why is each cone cell sensitive to a specific range of wavelengths?
3 different types of cone cell, each containing a specific type of iodopsin
What are the two divisions of the autonomic nervous system?
Sympathetic and parasympathetic
What system speeds up the heart rate?
Sympathetic nervous system
What system slows down our heart rate?
Parasympathetic nervous system
Describe the sequence of events that controls basic heart rate
Wave of electrical excitation spreads from SA node across both atria, causing them to contract
Layer of nonconductive tissue prevents it from spreading to ventricles
Wave of excitation enters AV nodes
After a shirt delay, this conveys wave between ventricles along specialised muscle fibres called Purkinje fibres, that collectively make up structure called bundle of His
boH conducts wave through AV septum to base of ventricles
Wave released from Purkinje tissue, causing ventricles to contract quickly at same time
What prevents the electrical excitation from the SAN (sinoatrial node) from spreading to the ventricles?
Non-conductive tissue (atrioventricular septum)
After the wave of electrical excitation has caused the atria to contract where does it go?
To the AVN
What region of the brain controls changes to heart rate?
Medulla oblongata - two centres, one to speed up, one to slow
Describe how exercise affects cardiac output
++ muscular/metabolic activity
++ CO2 produced by respiring tissues
blood pH lowered
chemical receptors in carotid arteries increase frequency of impulses to medulla oblongata
Centre there that speeds heart rate, increases impulses to SAN via sympathetic nervous system
SAN increases heart rate
Increased blood flow removes CO2 faster
Where are chemoreceptors found in the heart?
Wall of the carotid arteries
Where are pressure receptors found?
Within the walls of the carotid arteries and the aorta
How do pressure receptors operate when blood pressure is higher than normal?
More impulses to medulla centre that slows heart rate
Centre sends impulses via parasympathetic to SAN
How do pressure receptors operate when blood pressure is lower than normal?
More impulses to medulla centre that increases heart rate
Centre sends impulses via sympathetic to SAN
Cardiac muscle is myogenic. What does this mean?
Heart can contract on its own without needing nerve impulses
What are the two main forms of coordination in animals as a whole?
The nervous system
The hormonal system
What are the key structures of a mammalian motor neurone?
Cell body Dendrons which subdivide into dendrites Axon Schwann cells Myelin sheath nodes of Ranvier
What are the functions of Schwann cells in a neurone?
Surround the axon and protect it
Provide electrical insulation
Carry out phagocytosis
Play a part in nerve regeneration
How is resting potential established?
Na+ ions actively transported out of axon, K+ actively transported in by Na-K pump
More Na out for every K coming in
Therefore, as outward movement of positive charges is greater than inward movement of positive charges, creates electrochemical gradient - inside = negative relative to outside
Na+ naturally diffuse back in whilst K+ naturally diffuse back out (though limited as gates mostly shut)
Describe and explain how an action potential is generated
Resting potential - some K voltage-gated channels open, but Na ones closed
Energy of stimulus causes some Na channels to open - ++ Na+ diffuse in. Positive charge triggers reversal in potential difference across membrane
Positive feedback - as Na+ floods in, causes behind to close and ahead to open
Once an action potential has been established, Na channels close and K channels open
Repolarisation - Electrical gradient once preventing outward movement of K+ reversed - K+ diffuse out
Hyperpolarisation - Temporary overshoot
Repolarisation - K+ close
Na-K pump out Na+ and K+ in until resting potential reestablished
The inside of the axon is polarised. What is the potential difference?
Resting potential
How do the nodes of Ranvier and mylenated sheath speed up nerves impulses?
Saltatory conduction - action potentials essentially jump from node to node
Give 2 factors that affect the speed at which an action potential travels
Myelin sheath
Diameter of axon - greater –> faster (less leakage)
Temperature - Higher –> faster (faster diffusion rate)
Why are nerve impulses described as all or nothing impulses?
The threshold value must be reached for a potential to be triggered
What is the refractory period?
The period after an action potential has been triggered where the inward movement of Na+ is prevented
Why is the refractory period important?
Ensures action potential travels only in one direction
Reduces discrete impulses (separates)
Limits no. of action potentials
What is temporal summation?
A single neurones release neurotransmitters many times over a short period
What is spatial summation?
A no. of different neurones release enough neurotransmitter to exceed the threshold value
Which of the two myofilaments is thinner?
Actin
Which of the two myofilaments is thicker?
Myosin
In which region would you find myosin myofilaments on their own?
H zone
What is a muscle fibre made up of?
Many muscle cells fused end to end
What is a sarcolemma?
A term used to describe the continuous cell membrane that surrounds each muscle fibre
What is the sarcomere?
The distance between two Z lines. (structural unit of a myofibril in striated muscle)
What is the isotropic band?
The light region in which you would find actin myofilaments on their own
What is a myofibril?
A bundle which is composed of a number of the two different myofilaments (actin and myosin)
What is the sarcoplasmic reticulum?
Basically the endoplasmic reticulum of a muscle fibre.
What is the main function of the sarcoplasmic reticulum?
To store calcium ions which are released during contraction
What is the Z line?
The region at the centre f the Isotropic (I) Bands found through skeletal muscle tissue
What is the anisotropic band?
A darker region in which actin and myosin fibres overlap. This band is basically as long as a myosin filament and never changes in length
During contraction, what happens to the length of the A band?
It stays the same
What is the transverse tubule?
A deep invagination of the sarcolemma.
What does the transverse tubule do?
They carry impulses from the postsynaptic membrane down to the sarcoplasmic reticulum
What type of neurotransmitter is involved in a cholinergic synapse?
Acetylcholine
What is acetylcholine broken down into?
Choline and ethanoic acid (acetyl)
Describe how transmission of an action potential across a synapse occurs
AP from end of presynaptic neuron causes Ca2+ channels to open - Ca2+ enters synaptic knob
Influx of Ca2+ causes synaptic vesicles to fuse w/ presyn membrane
They release acetylcholine into cleft
These molecules diffuse across narrow cleft and bind tor receptor sites on Na+ protein channels in the postsyn membrane
Channels open allowing Na+ to rapidly diffuse in
This influx generates new AP in post syn
Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid
These diffuse back across cleft to presyn
Breakdown of acetylcholine also prevents it from cont. making new AP
ATP from mitochondria used to recombine choline and acetyl - stored for future use
Na+ channels close
How are Ca2+ involved in the transmission of an action potential across a synapse?
Ca2+ diffuse into the synaptic knob, and cause synaptic vesicles to fuse with the presynaptic membrane
What causes Ca2+ ions to diffuse into the presynaptic knob?
An AP arriving at the presynaptic neurone causes the Ca ion protein channel to open - Ca2+ enters via facilitated diffusion
How do Ca2+ ions enter the synaptic knob?
Facilitated diffusion
Name the 3 types of muscle fibres
Voluntary/striped/skeletal
Cardiac
Involuntary/smooth/unstriped
Where is smooth muscle fibre found?
In the internal organs
Which protein(s) make up the thick filaments of myofibrils?
Myosin
Which protein(s) make up the thin filaments of myofibrils?
Actin, tropomyosin and troponin
What are the two different types of fibres skeletal muscle contains?
Fast twitch and slow twitch
Which type of fibre contains large numbers of phosphocreatine in its cytoplasm?
Fast twitch
Which type of fibre contains a high concentration of myoglobin?
Slow twitch
Why do slow twitch fibres have large numbers of myoglobin?
Myoglobin stores O2 - can be used for aerobic respiration
Which type of fibre produces powerful and quick contractions?
Fast twitch fibres
How does having a large store of phosphocreatine in the cytoplasm make the fast twitch muscle fibre more effective?
Phosphocreatine stores inorganic phosphate - provides a quick source of ATP which is a quick source of energy
What kind of respiration occurs in slow twitch fibres?
Aerobic
How are slow twitch fibres adapted for aerobic respiration?
Large store of myoglobin (stores oxygen)
Rich supply of blood vessels to deliver oxygen and glucose
Lots of mitochondria to produce ATP
How are fast twitch fibres adapted for their role?
Thicker and more numerous myosin filaments
High conc. of glycogen
High conc. of enzymes involved in anaerobic respiration which rapidly provides ATP
Store of phosphocreatine (can rapidly generate ATP from ADP in anaerobic conditions)
How does a neuromuscular junction differ from a cholinergic synapse?
Neuromuscuar only excitatory, cholinergic can be excitatory or inhibitory
Neuro only links neurones to muscles, chol links neurones to neurones, or neurones to other effector organs
Neuro only motor neurones involved, chol can have motor, sensory or relay neurones involved
Neuro = final step of neural pathway, chol can produce a new action potential
Neuro - acetylcholine binds to receptors on membrane of muscle fibre, chol - acetylcholine binds to receptors on membrane of post-synaptic neurone
What are the similarities of a neuromuscular junction and a synapse?
Have neurotransmitter that are transported by diffusion
Have receptors that on binding w/ the neurotransmitter, cause an influx of sodium ions
Use a Na-K pump to depolarise the axon
Use enzymes to breakdown the neurotransmitter
Muscles can only pull. True or false?
True
What is homeostasis?
The maintenance of an internal environment within restricted limits in organisms.
What is the importance of maintaining a stable temperature?
Reactions take place at a suitable rate
Prevent damage to enzymes
What is the importance of maintaining a stable pH?
Reactions take place at a suitable rate
Prevent damage to enzymes
What is the optimum point, with regards to homeostasis?
The point at which the system best operates
What is positive feedback?
When a deviation from the optimum causes changes which result in even greater deviation from the norm.
What is negative feedback?
When the change produced by the control system leads to a change in the stimulus. This is detected by the receptor and leads to the system being turned off
What are the two main differences between the endocrine gland and exocrine gland?
Endo is ductless, exo has a duct
Endo produce hormones which are released directly into the blood, exo produce hormones AND enzymes which are released indirectly into the blood
The exocrine gland releases hormones directly into the blood. True or false?
False
What is the role of the pancreas in blood glucose regulation?
Produces digestive enzymes and hormones (Insulin and glucagon)
What are the two main types of cells found in the islets of Langerhans?
alpha and beta
What do beta cells secrete?
Insulin
What do alpha cells secrete?
Glucagon
How does insulin lower blood glucose levels?
Stimulates uptake of glucose, increases glycogenesis (glucose –> glycogen)
What is glycogenesis?
Conversion of glucose to glycogen
What is glycogenolysis?
The conversion of glycogen to glucose
What is gluconeogenesis?
Conversion of amino acids and glycerol to glucose
How does glucagon increase blood glucose levels?
Activate enzymes which catalyse glycogenolysis
Stimulates gluconeogenesis
Inhibits glycolysis, glucose uptake into cells, fat storage and protein production
Describe the second messenger model with regards to blood glucose regulation
Adrenaline binds to a receptor w/in the CSM of a liver cell –> causes to change shape on inside –> activates adenyl cyclase (enzyme)
AC converts ATP to cyclic AMP (cAMP)
Acting as 2nd messenger, binds to, changes shape of and therefore activates kinase
Kinase catalyses the conversion of glycogen to glucose
Which reaction does kinase catalyse?
The conversion of glycogen to glucose (glycogenolysis)
In the 2nd messenger model relating to blood glucose regulation, adrenaline binds to what?
A transmembrane protein receptor within the CSM of a liver cell
In the 2nd messenger model relating to blood glucose regulation, which hormone binds to the transmembrane protein receptor?
Adrenaline
In the 2nd messenger model relating to blood glucose regulation, what does the activation of adenyl cyclase cause it to do?
Convert ATP to cyclic AMP (cAMP)
In the 2nd messenger model relating to blood glucose regulation, the binding of adrenaline to a liver cell receptor cause what?
The receptor to change shape inside and activate adenyl cylase
In the 2nd messenger model relating to blood glucose regulation, what activates kinase?
The binding of cAMP to kinase, causing it to change shape
