Module 5.1 Communication and Homeostasis

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The environmental change
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The way an organism changes its behavior or physiology is its response
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Why are many cells and tissues not exposed to external environment?
Because they are protected by epithelial tissues and organs. In many naimals the cells and tissues are bathed in tissue fluid.
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What is the environment of cells?
Tissue fluid
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What do cells produce and use when undergoing metabolic activities?
They use up substrates and create new products.
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Are some of teh new compounds created and used toxic?
Yes they are- these move out of the cell into the tissue fluid- therefore the activities of the cells alter there own environment.
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Why is CO2- a waste product- harmful if it builds up in tissue fluid?
It could alter the pH of tissue fluid and disrupt actions of enzymes and other proteins
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Response to the co2 accumulation?
It stimulates the response of breathing more to expel the co2 from the body
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How are toxins and wastes removed from the internal environment?
They are likely to enter blood and to be carried away- to prevent build up in the blood they are removed by excretion.
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Why are multicellular organisms more efficient
Because cells are differentiated, for example cells that monitor teh bloodmay be in a different part of the body-away from the source. So this needs a good communication system.
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What will a good communication system have?
It would cover the whole body, enable cells to communicate with eachother, enable specific communciation, rapid communication and also allow both long term and short term responses.
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Define Cell signalling
the way in which cells communicate with each other
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What is the neuronal system of communication?
Interconnected network of neurones- signalling to each other across synapse junctions. Neurones can conduct a signal super quick and enable rapid responses to stimuli which may change very quickly.
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What is hormonal system?
Cells in endocrine release the hormone which is the signal directly into the blood. This is transported around the whole body but only recognised by a specific target cells. This allow longer term responses.
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What is homeostasis?
Process of maintaining constant internal conditions and environment despite changes in external and internal factors.
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What aspects are maintained by homeostasis?
Body temperature, blood glucose conc, blood salt conc, water potential of blood, blood pressure, co2 conc.
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What is the standard response pathway?
stimulus -> receptor -> communication pathway (cell signalling)-> effector -> response
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What specialised structures are required for pathways to work?
Sensory Receptors, communication system, effector cells
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What are sensory receptors?
cells/ sensory nerve endings that respond to a stimulus in internal/external environment of an organism and can create action potentials.
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Examples fo sensory receptors?
Temperature receptors on skin- monitoring changes of the external environment. Temperature receptors in the brain- monitoring conditions inside the body.
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Communication system in homeostasis
E.g. neuronal or hormonal system- acts by signalling between cells. Transmits a message from teh receptor cells to the effector cells via coordination centre- usually the brain.
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What is INPUT?
Messages from the receptor to the coordination centre.
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What is OUTPUT?
Messages sent to the effectors from the coordination centre.
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What is an effector?
These are cells such as liver cells or muscle cells. These cells will bring about a response.
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Effectors respond to output from coordination centre- teh response given will change conditions in the body. These changes will detected by a receptors in teh body- effecting the response pathway- in a way input will change.
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Negative feedback?
Mechanism that reverses changes, bringing the conditions back to optimum. This is to maintain a constant internal environment,
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What does negative feedback need in order for it to work?
1) A change to the internal environment must be detected. 2) The change must be signalled to other cells 3) There must be an effective response that reverses the change in conditions.
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Positive Feedback?
Mechanism that increases a change, taking the system further away from the optimum.
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Negatives of positive feedback?
Can destabalise the system and are usually harmful. Are less common.
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Positives of positive feedback
It can be used to stimulate an increase in a change. E.g. end of pregnancy- dilation of cervix- as thsi begins to dilate it causes posterior pituitary gland to secrete oxytocin- which increase uterine contractions and stretch cervix more...
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What happens to cells when temperature increases?
Molecules have more kinetic energy and move quicker, collide more frequently- essential reactions occur faster. Opposite can be said in cooler conditions as chemical reactions slow down.
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What happens to proteins when body temperature increases?
Most proteins carry out metabolic processes e.g. enzymes. Icreases in temperature could mean teh tertiary structure changes- as bonds break. The active site- shape could change and any change could reduce there abiltiy to function normally and
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What happens to enzymes and proteins if temperature drops?
If it drops by 10 rate of enzyme controlled reactiosn fall by half.
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What happens to cells if temperature drops?
Many of the reactions that would release heat in the cells would drop and less heat is releases as well as it becoming slower. This allows the body to cool further- this is a positive feedback.
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Whys is the core temp important?
Because all the vital organs are found in the center of the body. Peripheral part of body may be allowed or increase or decrease in temp to an extent without affecting survival of organism.
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What is an ectotherm?
Organism that relies on external sources of heat to maintain body temperature. They aren't able to control their body temperature effectively.
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How do ectotherms control there temperature?
If they are active their muscle contractions will generate some heat from increased respiration. Regulation relies upon behavioral responses that can later the amount of heat exchanged with the environment.
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What do ectotherms do if they are not warm enough?
Move into a sunny, lie on a warm surface, expose a larger area to the sun.
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What do ectotherms do if they are too hot?
They may move out of teh sun, move underground, reduce body surface area exposed to the sun.
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What are the advantages of ectothermy?
They don't use up energy to keep warm.. so less of their food is used in respiration, more nergy and nutrients gained from food can be converted to growth, they need to find less food, they can survive for long periods without food.
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What are the disadvantages of ectothermy?
Less active in cooler temperatures- making them more at risk to preadtors while they are cold and unable to escape.
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What is an endotherm?
An organism that uses heat from metabolic reactions to maintain body temperature. They do not rely on external sources for heat.
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What ways does an endotherm regulate its temperature?
It relies on effectors in skin and muscles. Skin is in contact with external environment- these changes can then alter the amount of heat being lost to the environment.
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What are many chemical recations in the body?
Exergonic- they release energy in the form of heat. Endotherms can increases repsiration in muscles and liver to simply release heat - using some energy intake to keep warm. Also can direct blood towards or away from skin to alter amount of heat lost
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Behavioral adaptations for endotherms when it is too hot?
Hide away from sun, burrow, shade. Orientate body to reduce SA expsoed to sun. Remain inactive, spread limbs for greater heat loss. Wet skin to use evaporation to help cool the body.
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Behavioural adaptations for endotherms when it it is too cold?
Lie in the sun. Orietnate body towards sun to expose more SA. Move about to generate more heat in the muscles.. extreme: roll into a ball shape to reduce SA and heat loss. Remain dry.
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Physiological adaptations- when its too hot for endotherms? SKIN
Skin: sweat glands secrete fluid onto skin surface- this evaporates- using heat from blood as latent heat of vaporization. Hairs and feathers lie flat to reduce insulation. Vasodilation of arterioles and precapillary sphincters direct blood to skin.
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Physiological adaptations- when its too hot for endotherms? Gaseous exchange system
Some animals pant- increases evaporation of water from surface of lung and airways.
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Physiological adaptations- when its too hot for endotherms? Liver
Less respiration takes place- less heat is released
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Physiological adaptations- when its too hot for endotherms? Skeletal muscles
Fewer contractions.
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Physiological adaptations- when its too hot for endotherms? Blood vessels
Dilation to direct blood to extremities so that more heat can be lost
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Physiological adaptations- when its too cold for endotherms? Skin
Less sweat is secreted- less evaporation means less heat is lost, Hairs and feathers stand erect to trap air, vasoconstriction- blood is diverted away from surface of skin and less heat is lost.
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Physiological adaptations- when its too cold for endotherms?Gaseous exchange
Less panting less heat loss.
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Physiological adaptations- when its too cold for endotherms? Liver
Increased respiartion in the liver cells means that more energy is converted to heat
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Physiological adaptations- when its too cold for endotherms? Skeletal muscles
Sponatneous muscle contractions (shivering) release heat.
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Physiological adaptations- when its too cold for endotherms? Blood vessels
Constriction to limit blood flow to extremities so blood is not cooled too much.
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Advantages of endothermy
Maintains constant body temp whatever the temperature externally, remian active even when external temp is low- can take advantage of prey, inhabit colder parts of the planet.
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Disadvantages of endothermy
Use significant part of there energy intake to maintain body temp when cold, need more food, use energy for growth at lower proportion. may overheat in hot weather.
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The way an organism changes its behavior or physiology is its response

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Why are many cells and tissues not exposed to external environment?


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Card 4


What is the environment of cells?


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Card 5


What do cells produce and use when undergoing metabolic activities?


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