• Created by: imanilara
  • Created on: 02-06-16 17:47

The need for communication

Changes in the external environment (stimulus)  require a response to the change by the organism. 

Internal environment- cells bathed in tissue fluid- this is their environment. Metablic reactions in the cells release substances that may be toxic, eg CO2 - change ph and stop enzyme activity. 

Build up of toxins - stiumuls- response would be to reduce metabolic activity. 

good communication system:
-cover whole body
-enable cells to communicate w eachother
-specific comm
-rapid comm
-short term/long term responses
Cell signalling: 
-neuronal+hormonal- interconnected network of neurones that conduct signals v quickly - across synapses - hormonal- signal transported in blood recognised by target cells- enables longer term responses 

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Homeostasis+neg feedback

Homeostasis - maintenance of internal environment in a constant state despite external changes, eg 
body temp, blood glucose conc, CO2 conc, blood salt conc, blood pressure 

Negative feedback: process that brings about a reversal of a change in conditions back to the optimum state. Change detected-> signalled to cells->response reverses change. 

stimulus- receptor- cell signalling- effector- response 

Number of structures involved:

-sensory receptors= temp/blood glucose conc receptors - if they detect a change, signal sent
-communications system eg neuronal/hormonal- signalling between cells -used to transmit message from receptor to effector cells
-effector cells- liver/muscle cells- bring about response that reverses the change detected 

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Positive feedback

Receptors detect change, response increases the change away from optimum state - eg when body gets too cold, enzymes become less active, less exogernic reactions, body temp dereases even more. 

Sometimes beneficial- oxytocin- cervix stretches signal sent to pituitary gland which secretes oxytocin- the more it stretches the mroe oxytocin released- the more contractions. 

It will never be constant but it can be around constant- eg body temp warm enugh for enzymes but cool enough not to denature protein structure. 

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Ectotherm- relies on external sources to regulate its body temp. 


  • use less food for respiration
  • can go for long periods of time without food
  • energy obtained from food can be used for growth


  • less active in cooler temps+must warm up before they can be active
  • may be inactive in winter- must have sufficient stores of food to keep alive

They must increase exchange of heat w environment:
-when an ectotherm is cold change its beh or physiology to increase absorption of heat 
-when hot- decrease heat absorption of heat 

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Adaptations of ectotherms

Expose body to sun- enables more heat to be absorbed- snakes 

Orientate body towards the sun- increases sa available for heat exchange- locusts 

Orientate body away from sun- decrease SA available for heat exchange- locusts 

Hide in burrow- decreases exposure to sun- less heat absorption - lizards 

Alter body shape - expose less or more sa to sun- horned lizards 

Increase breathing movements- evaporates more water- locusts 

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Uses internal sources of heat eg energy released from metabolic reactions- to regulate body temp 


  • fairly constant body temp whatever the temp is externally 
  • activity possible when environment temp is cool 
  • ability to inhabit cooler temps in the planet 


  • most of energy intake used to maintain body temp 
  • more food required to release energy needed 
  • less of the energy used from food used for growth 
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Temp regulation in endotherms

Physiological mechs:

Sweat glands in skin- secrete more sweat when hot; evaporates- uses heat from blood to supply latent heat for evaporation - less sweat secreted when cold- less evaporation, less heat loss from blood 

Lungs, mouth, nose: Panting increases evaporation of water from lungs/tongue-using latent heat- less heat, no panting, less evaporation

Hairs on skin: lay flat, little insulation of heat more heat lost by radiation- when cold stand up, trap layer of insulating air-reducing heat loss by radiation 

Arterioles: vasodilation of arterioles allows more blood near capillaries near skin surface-more heat loss by radiation - when cold, vasoconstriction of arterioles- less blood near surface, less lost by radiation 

Liver cells: reduced metabolic rate- less heat generated from exergonic reactions- less heat- more metabolic reactions -more heat from exergonic reactions 

Skeletal muscles- less contractions vs more contractions in shivering - aerobic resp

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Temp regulation in endotherms

Behavioural mechs:

Move into shade/hide in burrow v move into the sun

Orientate body twards the sun v orientate body away from the sun 

Remain inactive and spread out limbs v move about for muscle contractoins and roll into ball when v cold 

Control of temp regulation- negative feedback 

rise in core temp, receptors detect, send signal to hypothalamus - neuronal/hornonal system send signals to effector cells (liver and muscle)- bring about a response which is a reversal of the change eg less heat generated/less heat lost 

fall in core temp- receptors in hypothalamus detect- neuronal and hormonal systems send signals to muscle cells and liver cells- increase met reactions and contractions- body temp increases 

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