LGS A-Level OCR Biology - Unit 5 - Communication and Homeostasis
Communication systems are essential to detect and respond to changes in internal and external environments. They also coordinate the functions of different organs, ensuring the body maintains homeostasis.
The need for communication systems
Respond to changes in the internal and external environment
Coordinate the activities of different organs
Key Terms
The need for communication systems
Respond to changes in the internal and external environment
Coordinate the activities of different organs
How we respond to changes
Hormonal
Neuronal
Cell communication
Process by which a cell detects and responds to signals in its environment. It is the way in which cells interact w/ their environment and other ce...
Properties of a good communication system
Covers entire body
Be v. spp in the communication
Rapid
Enable both long and short-term responses
Methods of cell signalling
Chemical or neuronal
Affecting distant or nearby cells
Types of cell signalling
Autocrine
Gap Junction
Synaptic
Paracrine
Endocrine
Contact - dependent
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| Term | Definition |
|---|---|
The need for communication systems | Respond to changes in the internal and external environment Coordinate the activities of different organs |
How we respond to changes | Hormonal Neuronal |
Cell communication | Process by which a cell detects and responds to signals in its environment. It is the way in which cells interact w/ their environment and other cells around them |
Properties of a good communication system | Covers entire body Be v. spp in the communication Rapid Enable both long and short-term responses |
Methods of cell signalling | Chemical or neuronal Affecting distant or nearby cells |
Types of cell signalling | Autocrine Gap Junction Synaptic Paracrine Endocrine Contact - dependent |
Ending communication | Reuptake by cells Broken down by neurotransmitters Messenger removed from liver e.g. hormone |
Response | A change in behaviour or physiology as a result of a change in the environment |
Stimulus | Any change in the environment that causes a response |
Effector | An organ or cell that acts in response to a stimulus |
Receptors | An organ or cell able to detect and respond to environmental stimuli and transmit an impulse to a sensory nerve |
Homeostasis | The maintenance of a constant or near constant internal environment within a narrow limit even though the environment’s changing |
Homeostatic control and principle | Stimulus Receptor Communication pathway Effector Response |
Negative feedback | Varying physiological value is returned to its mean value by the controlling mechanism |
Positive feedback | Varying physiological value is pushed above its mean value by the controlling mechanism |
Why should body temp be kept constant | To keep enzymes working at their optimum and so that they don’t denature at higher temps |
Why should blood glucose conc. be kept constant | To supply sufficient glucose to tissues for respiration without decreasing the water potential of the blood too much Contributes to oncotic pressure (forming tissue fluid) |
Why should blood salt levels be kept constant | To maintain water potential and blood pressure |
Why should the water potential of blood be kept constant | To maintain blood pressure and to ensure cells are in the correct conditions |
Why should the blood pressure be kept constant | To ensure it is high enough to deliver blood efficiently but without damaging blood vessels |
Why should the carbon dioxide levels be kept constant | CO2 reacts w/ water to form an acid - change in pH can alter protein structure and effect enzymes activity |
Behavioural adaptations of ectotherms when its too hot | Finding shade Reduce contact/decrease SA exposed to the sun Burrow underground |
Behavioural adaptations of ectotherms when its too cold | Basking in the sun Finding a hot surface to lie on Increase SA exposed to sun |
Adaptations of endotherms when its too hot | Sweat Vasodilation Hairs and feathers lie down Panting Decrease respiration rate No shivering |
How does panting cool down endotherms | Lose heat through water vapour |
How does decreased respiration rate cool down endotherm | Respiration is an exothermic reaction |
Vasodilation | Sphincters open Increase in diameter of lumen of arteriole to increase blood flow Heat is lost through radiation |
Vasoconstriction | Sphincters closed Decrease in diameter of lumen of arteriole to decrease blood flow Heat is conserved through radiation |
Thermoregulatory centre | Located in hypothalamus concerned mainly w/ the regulation of heat production, inhibition and conservation to maintain a normal body temp |
Periphery temp receptors | Receptors monitor temp of extremities (early detection for hypothalamus) |
Adaptations of endotherms when its too cold | Vasoconstriction Contraction of erector pilli attached to base hairs Increase respiration Involuntary muscle contraction |
Neuronal signalling | Uses interconnected networks of neurons that signal to each other across synapse junctions Conduct a signal v. quickly and enable rapid response to stimuli that may be changing quickly |
Hormonal signalling | Glands secrete hormones into the bloodstream which bind to receptors on spp cells so the desired response in produced Enables longer term responses |
Endocrine Signalling | Signals are transmitted over longer distances e.g. gland to brain through the blood (insulin) |
Paracrine Signalling | Cytokines diffuse through tissue fluid and act locally on nearby cells No involvement of blood Signal conc. gradient determines how cells act Taken up by cells or degraded by enzymes (short lived) |
Autocrine Signalling | Hormonal/ chemical messenger (autocrine) Binds to autocrine receptors on that same cell, leading to changes to cells Can promote proliferation and therefore cause a tumour |
Contact dependent signalling | Signalling molecule is not secreted but bound to plasma membrane Interacts w/ receptor Particularly important between immune cells (APCs) |
Synaptic Signalling | Electrical signalling | Presynaptic terminal, synaptic terminal, postsynaptic membrane |
Gap Junction Signalling | Communicate directly w/ immediate neighbour through gap junctions Gap junctions connect the cytoplasm via protein channel Allow the passage of ions and small molecules and coordinated contraction of cardiac muscle |
Endotherms | Birds and mammals Control temp within strict limits Variety of mechanisms to control temp Largely independent of external temp |
Ectotherms | Reptiles, fish, amphibians Body temp fluctuate w/ fluctuations in the external temp Relies on behavioural mechanism |
Advantages of endothermy | Largely independent of external temp Activity still possible when external temp is cold Ability to inhabit warmer and colder parts of the world |
Disadvantages of endothermy | Significant part of the energy intake is used in maintaining body temp when cold More food required to be able to respire |
Advantages of ectothermy | Can survive long periods of time w/ out eating | Greater proportion of energy can be used for growth |
Disadvantages of ectothermy | Unable to generate internal heat through respiration Incapable of activity during winter Have to warm up in the day (risk of predators) |