Flashcards in Module 6 Deck (67):
What is a stimulus?
A change in the internal or external environment of an organism
Why do organisms need to respond to stimuli?
For survival (predator/prey awareness, homeostasis)
How to simple organisms respond to stimuli?
Taxis and kinesis
What is taxis?
A directional response to a stimuli (towards or away from)
What is kinesis?
A non-directional movement from an unfavourable area to a favourable area. The organism moves rapidly and randomly in unfavourable areas until they reach favourable conditions where they move slowly and turn less
What is a tropism?
A directional growth in plants in response to a stimuli
What tropisms do shoots show?
Positive phototropism and negative geotropism
What tropisms do roots show?
Positive geotropism and negative phototropism
What is the difference between IAA and animal hormones?
IAA is made by cells throughout the plant, and only affects cells locally and affects growth
What are the effects of IAA?
It promotes growth in the shoot and inhibits growth in the root
How does positive phototropism in the shoot take place?
(1.) if light is present on one side, the IAA redistributes to the shaded side of the shoot
(2.) this causes the shaded side to grow faster
(3.) so the shoot bends towards the light
How does negative geotropism in the shoot take place?
(1.) if gravity is present on one side, the IAA redistributes to the same side
(2.) this causes the same side to grow faster
(3.) so the shoot bends away from gravity and towards the light
How does positive geotropism in the root take place?
(1.) if gravity/water is present on one side, the IAA redistributes to the same side
(2.) this causes the same side to grow slowly, so the opposite side grows faster
(3.) so the root bends towards the gravity/ water
5 pieces of evidence supporting tropisms in the shoot
(1.) removing or covering shoot tip prevents tropism [tip causes tropism]
(2.) placing micin (prevents the movement of chemicals) across shoot does NOT affect tropism [tropism not caused by movement of chemicals]
(3.) placing gelatine (prevents movement of electrical signals) across shoot tip does NOT affect tropism [tropism not caused by movement of electrical signals]
(4.) if shoot tip is moved to one side, that side grows faster and the shoot bends the other way [IAA promotes growth in shoot]
(5.) when in light/darkness the overall Levels of IAA remain the same [light does not inhibit or breakdown IAA but rather redistributes it]
Give the basic pathway of an impulse
What is a pacinian corpuscle?
It is a pressure receptor found in skin, fingers and toes and responds to pressure/touch
What is the structure of a pacinian corpuscle?
It is made of several layers of tissue (corpuscle) wrapped around the start of a sensory neurone
What happens in a pacinian corpuscle when pressure is applied?
When pressure is applied, the corpuscle is compressed and stretch-mediated Na+ channels open so Na+ ions move into the start of the sensory neurone
How does the retina of the eye work?
It detects light so the brain can generate an image. The retina is made from cone and rod cells
Where are cone cells located?
In the centre of the retina; the fovea which is the site of high light intensity
Where are rod cells located?
They're located in the periphery of retina
What are cone cells made of?
Iodopsin pigment which is only broken down in high light intensities
How to cone cells only detect high light intensity?
One cone cell connects to one bipolar neurone which connects to one sensory neurone (therefore no summation of light can take place and so only detects high light intensity)
How do cone cells produce images with high visual acuity?
Because one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimulus can be distinguished and so the image have high visual acuity
What are rod cells made out of?
They're made of rhodopsin pigment which can be broken down at low light intensity
How to rod cells detect low light intensity?
A few rod cells connect to one bipolar neurone which connects to one sensory neurone (therefore summation of light can take place so rod cells can detect low light intensity)
Why do rod cells produce images with low visual acuity?
Because a few rod cells connect to one bipolar neurone which connects to one sensory neurone, so the stimuli will be merged together and not distinguished so the image is low quality
What is the CNS?
It is made of the brain and spinal cord
What is the role of the brain in the CNS?
To analyse and coordinate response to stimuli
What is the role of the spinal cord in the CNS?
It connects the brain to sensory and motor neurones
What is the peripheral nervous system (PNS)?
It is made up of the sensory and motor neurone. A neurone transmits a nerve impulse. The sensory neurone takes the impulse from the receptor to the CNS and the motor neurone takes the impulse from the CNS to the effector
What is the structure of a sensory neurone?
The sensory neurone has its cell body in the middle and has a dendron and axon
What is the structure of a motor neurone?
The motor neurone has its cell body at the start and ONLY has a long axon
What are the two different types of motor neurone?
Somatic (voluntary) and Autonomic (involuntary)
What do the somatic neurones supply?
The skeletal muscles and are under conscious control
What do autonomic neurones supply?
Cardiac muscle, smooth muscle and glands and are under subconscious control
How can the autonomic neurones be divided?
Into the sympathetic and parasympathetic
What is an action potential?
A change in membrane potential
What is the resting potential of a neurone?
It is the membrane potential at rest and is around -65mV
What is the resting potential of a neurone caused by?
Having more positive ions outside the neurones compared to inside and involves the sodium-potassium ion pump, pumping 3 Na+ ions out and 2 K+ ions in. However the membrane is permeable to potassium ions so they diffuse back out through potassium channels
What happens during an action potential?
(1.) a stimulus causes sodium ion channels to open and so sodium ions diffuse into the start of the neurone
(2.) this makes the membrane less negative
(3.) if a threshold is reached, more sodium ion channels open so membrane potential becomes more depolarised
(4.) around +40mV Na+ channels close and K+ channels open so K+ ions diffuse out and membrane potential is repolarised
(5.) too many K+ ions diffuse out so membrane potential is more negative than original (hyperpolarised)
How are action potentials unidirectional?
Because of the refraction period in which channels are recovering and so an action potential can't be fired so the AP doesn't travel backwards
How does the size of a stimulus affect a nerve impulse?
The size does not affect the size of the AP as APs are "all or nothing".
Larger stimuli increase the frequency of action potentials
What three factors affect the speed of a nerve impulse?
Temperature: higher temperature = more kinetic energy = faster rate of diffusion of ions
Axon diameter: wider diameter = less friction between ions
Myelination: Schwann cells wrap around the axon and insulates it, preventing APs so APs only occur in gaps called Nodes of Ranvier so AP jumps from node to node (saltatory conduction)
What are the roles of calcium ions and ATP in muscle contraction?
(1.) calcium ions cause the tropomyosin to move exposing binding sites on actin
(2.) calcium ions stimulate ATPase
(3.) ATP causes myosin head to detach
(4.) ATP releases energy so myosin head returns to original position
(5.) ATP actively transports calcium ions back into sarcoplasmic reticulum
Give adaptations of Fast twitch muscle fibres
They provide powerful but short lasting contractions
Adapted for anaerobic respiration
Have thicker myosin for powerful contractions
Contains more enzymes for anaerobic respiration
Contains phosphocreatine which provides phosphate to ADP to reform ATP
How do slow twitch muscle fibres work?
They provide less powerful but long lasting contractions
They're adapted for aerobic respiration
They have a rich blood supply
Contain many mitochondria
Contain myoglobin which stores oxygen
What happens when blood glucose Levels are high?
Insulin is released by the beta cells in the iselets of Langerhans
Insulin binds to receptors on liver, muscle and brain cells which causes an increase in glucose channels and carriers
Glucose is taken up by cells and used in respiration. In muscle and liver cells, glucose is also converted into glycogen for storage (glycogenesis)
What happens when glucose Levels are low?
Glucagon is released from the alpha cells
Glucagon binds to liver cells and less glucose is taken up by the cells.
Glycogen is converted into glucose (glycogenolysis) and fats and amino acids are converted in to glucose (gluconeogenesis)
Glucose is released into the blood
What is type 1 diabetes?
The pancreas does not produce insulin as beta cells are damaged by an autoimmune disease
How is type 1 diabetes treated?
What is type 2 diabetes?
The pancreas makes insulin but cells are less sensitive to it. This may be caused by obesity and a diet high in sugar etc.
What are the treatments for type 2 diabetes?
Control diet, exercise, drugs and insulin injections
What is homeostasis?
It is the maintenance of a constant internal environment
What is positive feedback?
The response to the change is to continue the change
Why do organisms need to maintain a constant body temperature?
To maintain the optimum temperature for enzyme activity
What are endotherms?
They are animals that maintain a strict internal body temperature
What are ectotherms?
They are animals whose internal body temperature is more varied with changes in external environmental temperature
What is a benefit of being an endotherm?
They can maintain activity over a range of settings (e.g. Early morning or winter)
What is a benefit of being an ectotherm?
They require less food and energy
What are some anatomical adaptations of organisms which live in warm climates?
They have a small body size and therefore a large surface area: volume ratio so they lose heat
They have less fur
They have less fat
They have large extremities (e.g. Ears/hands/feet) so they lose heat
What are some anatomical adaptations of organisms which live in cold climates?
They have a large body size and therefore a small SA:V ratio so they lose less heat
They have more fur
They have more fat
The have small extremities
How do ectotherms respond to the external environment warming up?
They press on a warm surface, their skin becomes darker so as to absorb heat. There is MORE respiration in the liver and LESS breathing
How do ectotherms respond to the external environment cooling down?
They press on the cold surface, they have lighter skin colouration. There is LESS respiration in the liver and MORE breathing
How is body temperature controlled in endotherms?
By the hypothalamus in the brain
How do endotherms warm themselves up?
They reduce blood flow to the skin surface = vasoconstriction so less heat is lost from the blood by radiation
Hair on skin stands up = hairs trap air particles which forms an insulating layer which reduces heat loss
Shivering = friction of sliding filament mechanism generates heat and respiration produces heat
Increased respiration in liver produces heat