5.1.1 - Communication, Homeostatis And Energy Flashcards
Receptor def
a cell that detects a stimulus and creates action potentials (nervous impulse)
Effector def
A cell, tissue or organ that brings about a response
Stimulus def
change in an environment that causes a response
Response def
change in behaviour/physiology as a result of a stimulus
Internal environment def
the conditions inside an organism
External environment def
the conditions outside an organism
Cell signalling def
communication between cells to help them work together to co‐ordinate their actions
Hormonal system def
- A system that uses the blood to transport its signals.
- Cells in endocrine organ release the signal(a hormone) directly into the blood.
- Hormone is transported throughout the body, but is only recognised by specific target cells
- Hormonal system enables longer-term responses to be coordinated
Neuronal systems def
- A interconnected network of neurones that signal to each other across synapse junctions
- Neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing very quickly
Why do plants and animals need communication systems?
(1 Mark) Model Answer
Plants and animals need communication systems in order to respond to both internal and external environments and coordinate the activities of organs.
What is the importance of organisms being able to respond to the internal environment?
- Some products of metabolic activities are harmful ‐ their build up could be toxic ‐ they act as a stimulus for their own removal.
- Maintains constant internal conditions (homeostasis)
What is the importance of organisms being able to respond to the external environment?
(2 Marks)
- To be able to adjust internal environment in response to external e.g. temperature
- To adapt to changes in environment e.g. weather or scenery (camouflage)
- find resources e.g. tropisms
Homeostatis def
The maintanance of the internal environment in a constant state within narrow limits despite external changes in environment
Negative feedback def
-A process that brings about a reversal of any change in conditions in order to return to an optimum set point
Positive feedback def
-A process that increases any change detected by the receptors, taking the conditions further from the optimum set point. (Tends to be harmful and does not lead to homeostasis)
Endocrine systems def
Hormones are transported in the blood to specific target cells
Outline a negative feedback loop
- Change away from optimum conditions
- Receptor detects a change
- Communication system informs effector
- Effector reacts to reverse change
- Return to optimum condition
- Optimum conditions reached
Examples of a negative feedback loop maintained by homeostasis
- CO2 concentration - detected by chemoreceptors
- Body Temperature - Thermoregulation - detected by thermorecpetors
- Blood-glucose concentration
- Blood-salt concentration
- Water Potential of the blood - osmoregulation - detected by osmoreceptors
- Blood Pressure - detected by barorecptors
(- Iodine - thyroid)
Outline a positive feedback loop
- Conditions are optimum
- Change away from optimum conditions
- Receptor detects change
- Communication system informs effector which brings about a response
- Effector reacts to increase change from optimum
- So there is a greater change away from optimum conditions
Example of positive feedback
- Outline the mechanism
Dilation of the cervix during end of pregnancy
- As cervix stretches, posterior pituitary gland secretes oxytocin - a hormone
- Oxytocin increases uterine contractions which stretch the cervix more
- This causes the secretion of more oxytocin
- Once cervix is fully dilated, baby can be born
- Birth ends oxytocin production
-Activity of neurones also relies on positive feedback
Explain what homeostasis is and why it is necessary and how it is maintained (5)
- Homeostasis is the maintenance of the internal environment in a constant state/ constant set range despite internal and external changes.
- It is vital to keep conditions such as body temperature, blood glucose conc. and blood pressure within a constant set range
- It is maintained through cell signalling to cause negative feedback.
Compare and contrast hormone systems against neuronal systems
Hormone systems:
- slower response to stimuli
- Hormones carried in blood
- Longer term responses
- Hormones are specific to target cells but can have quite a general effects
Neuronal systems:
- Faster response to stimuli
- Electrical impulses carried by neurones, neurotransmitters carry messages across synapse
- Short term response
- Very specific effect
Simple mechanism of homeostasis
- Stimulus detected
- Receptor detects stimulus - creates action potentials
- Communication pathway activated(cell signalling)
- Effector brings about a response
- Response occurs
Different aspects/systems in homeostatsis
- Body temperature/thermoregulation
- Blood glucose concentration
- Blood salt concentration
- Water potential of the blood
- Blood pressure
- Carbon dioxide concentration
Ectotherm def
An organisms that relies on external sources of heat to maintain body temperature
Endotherm def
An organism that uses heat from metabolic reactions to maintain body temperature
Differences between ectotherms and endotherms
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How are hormonal systems specific to target cells?
Molecule/hormones have a specific shape which is complementary to that of the target cell surface receptor.
This is essential to enable signals to be specific
Why do organisms need to control their body temperatures? (2)
- Temperature will affect rate of metabolic reactions
- Cooler temperatures ‐ reactions would slow down
- Too hot ‐ tertiary structure of enzymes active sites would denature ‐ stop metabolic reactions
Behavioural responses when ectotherms are too cold
- They can move into sunny areas
- They can lie on a warm surface
- They can expose a larger surface area of their body to the sun
Behavioural responses when ectotherms too hot
- Move out of the sun, e.g. into shade
- They can move underground
- Reduce the body surface area exposed to the sun
Advantages of ectotherms
- They rely on external sources of heat to keep warm, so do not use energy
- 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, as they need less energy
- They can therefore survive for longer periods without food
Disadvantages of ectotherms
-They are less active in colder climates
This means they are at a greater risk from predators while they are cold
Behavioural responses when endotherms are too hot
- Hide away from sun in the shade or in a burrow
- Orientate body to reduce surface area exposed to sun
- Remain inactive and spread libs out to enable greater heat loss
- Wet skin to use evaporation to help cool the body. E.g. cats lick themselves and elephants spray water over their bodies
Behavioural responses when endotherms are too cold
- Lie in the sun
- Orientate body towards sun to increases surface area of body exposed
- Remain dry
- Move about to generate heat in the muscles
- Or in extreme conditions, roll into a ball shape to reduce surface area and heat loss
Endotherm organs involved in physiological thermoregulation techniques
- Skin
- Gas exchange system, e.g. lungs
- Liver
- Skeletal muscles
- Blood vessels
Physiological responses of endothermic organs when too hot
Skin:
- Sweat glands secrete fluid(sweat)onto skin surface. As this evaporates it uses heat from the blood as the latent heat of vaporisation
- Hairs and feathers lie flat to reduce insulation and allow greater heat loss
- Vasodilation of arterioles and precapillary sphincters directs blood to the skin surface so more heat can be radiated away from the body
Gas Exchange system:
-Some animals pant, increasing evaporation of water from lung surface and airways
Evaporation uses heat from the blood as the latent heat of vaporisation
Liver:
-Less respiration takes place, so less heat is released
Skeletal muscles:
-Fewer contractions mean that less heat is released
Blood vessels:
-Dilation to direct blood to the extremities so more heat can be lost
Physiological responses of endothermic organs when too cold
Skin:
- Less sweat is secreted, so less evaporation means that less heat is lost
- Hairs and feathers stand erect to trap air, which insulated the body
- Vasoconstriction of arterioles and precapillary sphincters leading to skin surface. Blood is diverted away from surface of skin, so less heat is lost
Gas exchange system/lungs:
-Less panting, so less heat is lost
Liver:
-Increased respiration in liver cells means that more energy from food is converted to heat
Skeletal muscles:
-Spontaneous muscle contractions(shivering) releases heat
Blood vessels:
-Constriction to limit blood flow to the extremities, so that blood is not cooled too much - this can lead to frostbite in extreme conditions(e.g. fingers and toes)
Advantages of endothermy
Endotherms can:
- Maintain a fairly constant body temp whatever the temp externally
- Inhabit colder parts of the planer
- Remain active even when external temperatures are low - this means they can take advantage of prey that may be available or escape potential predators
Disadvantages of endothermy
- Endotherms use a significant part of their energy intake to maintain body temperature in the cold
- Endotherms need more food
- Endotherms use a lower proportion of energy and nutrients gained from food for growth, and more on thermoregulation
- Endotherms can overheat in hot weather
Hypothalamus thermoregulation mechanism
The hypothalamus monitors the blood temperature and if it moves away from the optimum core temperature, it will send signals to bring about the reverse of the changes. This is an example of negative feedback
Peripheral thermoreceptors in the skin sense changes of temperature in the external environment. It too much change is detected this information is sent to the hypothalamus which brings about the relevant responses.
Explain how endotherms control their body temperature when they are too hot. [6]
-Peripheral thermoreceptors in skin stimulated by change in external temp
-Impulses sent to hypothalamus
-Vasodilation of arterioles to increase heat loss by radiation / conduction
decreased metabolic rate / respiration in liver to generate less heat
-Sweating/panting ‐ evaporation to remove heat from skin
-Hair muscles (effectors) cause hairs to lie flat ‐ not insulating air trapped ‐Heat can radiate easier
Explain how endotherms control their body temperature when they are too cold. [6]
-Peripheral thermoreceptors in skin stimulated by change external temp
-Impulses sent to hypothalamus
-Vasoconstriction of arterioles to reduce heat loss by radiation / conduction, as blood vessels are further from skin surface
-Increased metabolic rate/ respiration in liver to generate heat (energy) ;
adrenaline is released
-Rapid contraction/relaxation of sketetal muscles to shiver to generate heat energy
-Hair muscles (effectors) cause hairs to stand up
-This traps a layer of insulating air to prevent heat loss by conduction
What processes must occur for negative feedback to work?
- A change to the internal environment must be detected by receptors
- The change must be signalled to other cells
- There must be an effective response that reverses the change in conditions
Elephants have large, thin ears that they move backwards and forwards when hot.
Explain how this adaptation allows the animal to control its body temperature
(2 Marks)
- large surface area to lose heat
- thin - so blood vessels are closer to the skin surface to lose heat
- movement of the ears inreases air movement over the skin to lose heat
Penguins living in cold climates have ‘shunt’ blood vessels. These shunts link arterioles carrying blood towards their feet with small veins that carry blood away from their feet
- Explain how this adaptation allows the animal to control its body temperature
(1 Mark)
- Blood loses less heat
- As less blood flows to feet
- OR: warm blood diverted from arterioles to veins
Describe how negtaive feedback is used to control blood glucose concentration (5.4 - Endocrine system link)
(6 Marks)
- Beta Cell RECEPTORS detect an increase in blood glucose conentration
- If there is a higher glucose concentration, Beta cells release insulin
- This causes an increased uptake of glucose by liver/effector target cells
- Glucose enters target cells through glucose transport proteins (in cell surface membrane)
- Glucose in converted into glycogen by glycogenesis
- There is an increased use of glucose in respiration (ATP Production)
- If there is a lower concentration of glucose, alpha cells in the pancreas will secrete glucagon
- Glucagon causes increased conversion of glycogne to glucose (glycogenolysis)
- Increased conversion of other compounds to glucose, e.g. amino acids by gluconeogenesis
- glucose leaves cells by facilitated diffusion/through glucose channels
