Commnication and Homeostasis Flashcards
What is cell signalling
this is the way that cells communicate with each other
what are the set of conditions that all living things need to maintain
- a suitable temperature
- a suitable pH
- an aqeous environment that keeps the substrates and products in solution
- freedom from toxins and excess inhibitors
What happens when cell conditions are not maintained
- the cells become inactive and die, in multicellular organisms cells are specialised and rely upon each other therefore they must be able to communicate in order to coordinate their activities without this they may die
what threat can the external environment cause
- if the external environment changes it may put pressure on the organism, for example cooler environment will cause greater heat loss
- if the organism wants to survive then it has to monitor the changing environment and change its behaviour and physiology to reduce stress
- environmental is a stimulus and the way which the organism changes its behaviour or physiology is a response
- may adapt slowly as the environment changes throughout the year
How do organism change there internal environment
- range of tissues that are protected by epithelial tissues and organs
- internal cells and tissues are bathed in tissue fluid and this is the environment of the cells
- cells undergo metabolic activities and use up their unwanted substrates and create new products these move into and out of the tissue fluid therefore the cells create their own environment
- for example a waste product is co2 this goes into the tissue fluid and alters the ph of the cells which can stop enzymes from functioning, this change in environment is a stimulus and causes a response
How does the body maintain its internal environment
- composition of tissue fluid is maintained by the blood - blood is a transport so gets rid of unwanted substances and brings wanted substances to the cells
- wastes are removed by excretion
- concentrations are monitored closely to make sure that they do not excrete to much useful substances and too little waste
What does a good communication system have
- covers the whole body
- enables cells to communicate with each other
- enable specific communication
- enable rapid communication
- enables both short term and long term responses
Why is a multicellular organism more effective than a single celled organism
Because cells are differentiated
- cells perform specific jobs and work together in tissues
- cells monitor blood can remove waste substances
What are the two major systems of communication
Neuronal system
Hormonal system
Describe the neuronal system
- interconnected network of neurones that signal to each other across synapse junctions
- very quick and get rapid responses to stimuli that may be quickly changing
Describe the hormonal system
- uses blood to transport signals
- cells in endocrine organ release signal directly into the blood this is then transported throughout the whole body but is recognised by specific target cells
- long term responses
What are the aspects maintained by homeostasis
- body temperature
- blood glucose concentration
- blood salt concentration
- water potential of the blood
- blood pressure
- carbon dioxide concentration
describe the standard response pathway
stimulus - receptor - communication pathway - effector - response
what is needed for the response pathway to work
- sensory receptors
- communication system
- effector
describe sensory receptors
- for example temperature receptors
- receptors may be on the surface of the skin, monitor changes in the external environment
- other monitor internal conditions in the body
- when it detects a change it will be stimulate to send a message to an effector
describe an effector
- cells such as liver or muscle cells
- bring about a response
What is homeostasis
- maintaining a constant internal environment despite changes in external and internal factors
what is negative feedback
the mechanism that reverses change bringing the system back to the optimum
what is positive feedback
the mechanism that increases a change taking the system further away from the optimum
Describe how negative feedback works
- condition changes
- receptors detect
- coordination centre sends an output to the effectors
- effector responds to output
- reverses the initial change in conditions and stimulus is reduced as it returns to its optimum
- receptors detect reduction
- reduce the input to the coordination centre and therefore the output is reduced as the system gets closer to the optimum
what has to happen for negative feedback to work
- a change to the internal environment must be detected
- the change must be signalled to other cells
- must be an effective response that reverses the change in conditions
Describe the negative feedback loop for temperature
Rise in temperature
- thermoregulatory centre in hypothalamus detects change
- nervous and hormonal system carry signals to skin, liver, and muscles
- less heat generated and more heat lost
- temperature falls
decrease in temperature
- thermoregulatory centre in hypothalamus detects change
- nervous and hormonal systems carry signals to skin, liver, and muscles
- more heat generated and less heat lost
is it possible to maintain a constant environment
- slight range in when the optimum internal environment can happen
- when stimulus occurs it may take time to response this can cause a slight overshot
what is positive feedback used for
- to increase the original response
describe how positive feedback works
- optimum condition
- optimum condition changes away
- receptor detects change
- input
- communication system informs effector
- output
- effector reacts to increase change
change away from optimum….
give examples of positive feedback
- below a certain core temperature enzymes become less active and exergonic reactions that release heat are slower and release less heat this allows the body to cool further and slows enzyme controlled reactions even more
- end of pregnancy to bring about the dilation of the cervix, as the cervix stretches this causes the pituitary gland to secrete the hormone oxytocin this increases uterine contractions which stretch the cervix even more which causes the secretion of more oxytocin
- activity of neurons
what is ectotherm
an organism that relies on external sources of heat to maintain body temperature
what is endotherm
an organism that uses heat from metabolic reactions to maintain body temperature
What are the advantages of ectothermy
- less of their food is used in respiration
- more of the energy and nutrients gained from food can be converted to growth
- they need to find less food
- they can survive for long periods without food
what are the disadvantages of ectothermy
- they are less active in cooler temperatures, therefore they are at risk from predators while they are cold and unable to escape
- cannot take advatage of food that is available while they are cooled
what happens when body temperature changes
- they have a dramatic effect upon the activity of cell processes
- temperature rises therefore molecules have more kinetic energy this means that they move more quickly and collide more frequently
- chemical reaction happen more quickly
- protein structure is affected, enzymes loose their shape slow their rate of reaction down
describe endotherms
- control body temperature in strict limits
- use a variety of mechanisms to control body temperature
- largely independent of external temperatures
describe ectotherms
- not able to control body temperatures as effectively as endotherms
- rely on external sources of heat ad their body temperatures
- temperature fluctuates with external temperature
- can control their body temperatures in all but most extreme conditions
How do ectotherms control temperatures
if they are not warm enough they try to absorb more heat from the environment
- move into a sunny area
- lie on a warm surface
- expose a larger surface area to the sun
if they are too hot
- move out of the sun
- they move underground
- reduce the body surface exposed to the sun
describe how a snake is behaviorally adapted and how it benefits for controlling temperature
- basks in the sun
- this means that is absorbs heat directly from the sun
describe how a locust is behaviorally adapted and how it benefits for controlling temperature
- in early morning locusts sit side on to the sun and expose a large surface area, climb to the top of a plant at midday, increases both the rate of breathing and the depth of breathing movements when it is hot
- in cool orig they can absorb more heat, midday when the sun is hot they absorb less heat, the soil gets hot and radiates heat, locusts moves away from the soil it gains less heat from the soil
describe how a lizard is behaviorally adapted and how it benefits for controlling temperature
- many lizards use burrows or crevices between rocks, they will hide in a burrow during the hottest art of the day and coolest part of the night
- an underground burrow has more stable temperature than air, hottest part of the day it is cooler and in the night it is warmer than the outside
describe how a horned lizard is behaviorally adapted and how it benefits for controlling temperature
- can change its shape by expanding or contracting its ribcage
- expanding ribcage increases the surface area exposed to the sun so more heat can be absorbed
What are the advantages of endothermy
- can maintain a fairly constant body temperature whatever the temperature externally
- remain active even when external temperatures are low which means they can take advantage of prey that may be available or escape potential predator
- inhabit cooler parts of the plant
what are the disadvantages of endothermy
- use a significant part of their energy intake to maintain body temperature in the cold
- need more food
- use for growth a lower proportion of the energy and nutrients gained from food
- may overheat in hot weather
How do endotherms regulate temperature
- they rely on effectors in the skin and muscles
- skin is in contact with external environments
- many chemical reactions in the body are exergonic this means that release energy in the form of heat
- increase respiration in the muscles and liver simply to release heat
- direct blood towards or away from the skin to alter the amount of heat lost to the environment
describe the response of the skin if its too hot and too cold
Too hot
- sweat glands secrete fluid onto the skin and this evapourates cooling the body
- hairs and feathers lie flat to reduce insulation and allow greater heat loss
- vascodilation of arterioles and precapillary sphincters directs blood to the skin surface so more heat can be radiated away from the body
Too cold
- less sweat secreted, so less evaporation therefore less heat is loss
- hairs and feathers stand erect to trap air which insulates the body
- vasoconstriction of arterioles and precapillary sphincters leading to the skin therefore blood is diverted away from the surface of the skin and less heat is lost
describe the response of the gaseous exchange system if its too hot and too cold
Too hot
- increase evaporation of water from the surface of the lungs and airways, uses heat from the blood as the latent heat of vaporization
Too cold
- less panting so less heat lost
describe the response of the liver if its too hot and too cold
Too hot
- less respiration takes place so less heat is released
Too cold
- increased respiration in the liver cells means that more energy from food is converted to heat
describe the response of the skeletal muscles if its too hot and too cold
Too hot
- fewer contractions mean that less heat is released
Too cold
- spontaneous muscle contractions release heat - shivering
describe the response of the blood vessels if its too hot and too cold
Too hot
- dilation to direct blood to the extremities so that more heat can be lost
Too cold
- constriction to limit blood flow to the extremities, so that blood is not cooled too much - can lead to frostbite in extreme conditions
Behaviour of endotherms if too hot
- hide away from the sun in the shade or in a burrow
- orientate body to reduce surface area exposed to sun
- remain inactive and spread limbs out to enable greater heat loss
- wet skin to use evaporation to help cool the body
Behaviour of endotherms if too cold
- lie in the sun
- remains dry
- orientate body towards sun to increase surface area exposed
- move about to generate heat in the muscles or roll into a ball shape to reduce surface area and heat loss
what is the role of the peripheral temperature receptors
- early warning that temperature may change
- the peripheral temperature receptors in the skin monitor the temperature in the extremities this info is fed to the thermoregulatory centre in the hypothalamus
- if sends signals to the brain that external environment is very cool or hot the brain can initiate behavioral mechanisms for maintaining body temperature
