5.1.1 Communication and Homeostasis Flashcards
why do animals need to respond to their external environment
- animals increase their chances of survival by responding to changes in their external environment
- e.g. avoiding harmful environments such as places that are too hot or cold
why do animals need to respond to their internal environment
- respond to changes in their internal environment to make sure that the conditions are always optimal for their metabolism
what is metabolism
all the chemical reactions that go on inside an organism
do plants also respond to their environment
- yes, respond to changes in their environment
- in order to increase their chances of survival
what is a stimulus
any change in the internal or external environment
what do receptors do
detect stimuli
what does it mean that receptors are specific
- they only detect one particular stimulus
- e.g. light or pressure
- there are many different types of receptors, and they each detect a different type of stimulus
what type of things are receptors
- some are cells: e.g. photoreceptors are receptor cells that connect to the nervous system
- some are proteins on cell surface membranes: e.g. glucose membranes found in the cell membranes of some pancreatic cells
what are effectors
cells that bring about a response to a stimulus, to produce an effect
what are examples of effectors
muscle cells
cells found in glands, e.g. the pancreas
what needs to happen for a response to occur
receptors need to communicate with effectors, and these effectors may need to communicate with other cells
why do receptors and effectors need to communicate
to make sure that the activities of different organs are coordinated, to keep organismsworking effectively
how do receptors and effectors communicate
via cell signalling
how does cell signalling occur between distant and adjacent cells
- distant: hormonal system
- nearby: nervous system
- both examples of communication system
how does cell signaling occur is the nervous system
- the cells communicate by secreting chemicals called neurotransmitters
- these send signals to adjacent cells
- such as other nerve cells or muscle cells
how does cell signalling occur in the hormonal system
- cells release chemicals called hormones
- which travel in the blood
- and act as signals to distant cells
what do cell-surface receptors allow
allow cells to recognise the chemicals involved in cell signalling
what does homeostasis involve
- involves control systems that keep your internal environment roughly constant, within certain limits
- as changes in your external environment can affect your internal environment (e.g. the blood and tissue fluid that surround your cells)
why is maintaining your internal environment constant important
vital for cells to function normally and stop them becoming damaged
- especially your core body temperature
why is is especially important to maintain the right core body temperature
- temperature affects enzyme activity
- and enzymes control the rate of metabolic reactions
what happens if your body temperature is too high
- if too HIGH, e.g. 40°C, enzymes become denatured
- as the enzymes molecules vibrate too much
- this breaks the hydrogen bonds that hold them in their 3D shape
- can change the shape of their active site, so no longer works as a catalyst
- so the metabolic reactions are less efficient
what happens if your body temperature is too low
- enzyme activity is reduced
- slowing the rate of metabolic reactions
what is the optimum body temperature
- about 37°C
- where the highest rate of enzyme activity takes place
why is it also important to maintain the correct concentration of glucose in your blood
so that there’s always enough available for respiration
what do homeostatic systems involve
- receptors
- a communication system
- effectors
how are the different components of a homeostatic system linked
- receptors detect when a level is too low or high
- the information is communicated via the nervous or hormonal system
- this reaches the effectors, which respond to counteract the change
- bringing levels back to normal
what is the negative feedback mechanism
the mechanism that stores the level to normal
what does negative feedback do
- keeps things around a normal level (e.g. temperature around 0.5 above or below 37°C)
what are the restrictions of negative feedback
- only works within certain limits
- of the change is too high
- then effectors may not be able to counteract it
- e.g. a huge drop in temperature caused by prolonged exposure to cold weather may be too large to counteract
explain how negative feedback would work with body temperature
1) body detects temperature too high (via receptors)
2) effectors respond to decrease the temperature to optimum
3) the body detects the temperature is too cold (via receptors)
4) the effectors respond to increase the temperature
5) internal environment stays around normal level, of 37°C optimum
what does positive feedback mechanisms do
amplify a change from the normal level
- useful for rapidly activating something
how does positive feedback mechanisms work
- effectors respond to further increase the level away from the normal level
why is positive feedback not involved in homeostasis
it doesn’t keep your internal environment constant
what is an example of positive feedback
- during blood clotting after an injury:
- platelets become activated and release a chemical
- this triggers more platelets to be activated, and so on
- the process ends with negative feedback, once the body detects that a blood clot has been formed
how are animals classed, depending on how they control their body temperature
ectotherms and endotherms
what are ectotherms
- CANNOT control their body temperature internally
- control their body temperature by changing their behaviour (e.g. reptiles gaining heat by basking in the sun)
- their internal body temperature depends on the external environment (their surroundings)
- they have a variable metabolic rate, and they generate very little heat themselves
- their activity levels depend on the external environment, and are more active at higher temperatures, and less active at lower temperatures
what are examples of ectotherms
reptiles and fish
what are endotherms
- CONTROL their body temperature internally by homeostasis
- they can also control their body temperature by behaviour (e.g. finding shade)
- their internal temperature is less affected by the external temperature (with certain limits)
- they have a constantly high metabolic rate, and generate a lot of heat from metabolic reactions
- their activity level is largely independent of the external temperature, so can be active at any temperature, within limits
what are examples of endotherms
mammals and birds
how can mammals reduce their body temperature (IF TOO HIGH TO BEGIN WITH)
- sweating
- hairs lie flat
- vasodilation
how does sweating help reduce body temperature
- more sweat is secreted by sweat glands when the body is too hot
- the water in sweat evaporates from the surface of the skin
- this takes heat from the body
- the skin is cooled
how does hair lying flat help reduce body temperature
- mammals have a layer of hair that provides insulation by trapping air ( as air is a poor conductor of heat)
- when it’s hot
- the erector pili muscles relax
- the hair lie flat
- less air is trapped
- so the skin is less insulated
- and heat can be lost more easily
how does vasodilation help to reduce body temperature
- when it’s hot, arterioles near the surface of the skin dilate
- more blood flows through the capillaries in the surface layer of the dermis
- this means more heat is lost from the skin by radiation
- and the temperature is lowered
what are the mechanisms that increase body temperature in mammals (WHEN ITS TOO COLD)
- shivering
- much less sweat
- hairs stand up
- vasoconstriction
- hormones
how does shivering help to increase body temperature
- when its cold, muscles contract in spasms
- this makes the body shiver
- more heat is produced
- from increased respiration
how does producing less sweat help increase body temperature
- less sweat is secreted from sweat glands when its cold
- reduced the amount of heat loss
how does hairs standing up help increase body temperature
- erector pili muscles contract when its cold
- makes the hairs stand up
- this traps more hair
- creating an insulating layer
- preventing heat loss
how does vasoconstriction help increase body temperature
- when its cold, arterioles near the surface of the skin constrict
- less blood flows through the capillaries in the surface layer of the dermis
- reduces heat loss
how do hormones increase body temperature
- the body releases adrenaline and thyroxine
- these increase metabolism
- so more heat is produced
what part of the brain is responsible for maintaining body temperature at a constant level
the hypothalamus
where does the hypothalamus receive information about temperature from
- the hypothalamus receives information about temperature from thermoreceptors (temperature receptors)
what receptors detect internal temperature changes
thermoreceptors in the hypothalamus
- from the temperature of the blood
what receptors detect external temperature changes
thermoreceptors in the skin
- called peripheral temperature receptors
- from the temperature of the skin
how does the hypothalamus work to create a response to temperature chain
1) thermoreceptors send impulses along sensory neurones to the hypothalamus
2) this sends impulses along the motor neurones to effectors (e.g. skeletal muscles, sweat glands and erector pili muscles)
3) the effectors respond to restore the body temperature back to normal
how does the body respond to a rise in body temperature
1) thermoreceptors detect that temperature is too high
2) information travels through the sensory neurones to hypothalamus
3) this sends signals to effectors via motor neurones
4) CHANGES (e.g. vasodilation, sweating, hair lying flat, no shivering, no adrenaline or thyroxine released)
5) means more heat is lost, and less heat is produced by the body
- normal body temperature is restored
how does the body respond to a fall in body temperature
1) thermoreceptors detect that temperature is too low
2) signal travels to hypothalamus via sensory neurones
3) this sends signals to effectors via motor neurones
4) CHANGES occur (e.g. vasoconstriction, much less sweating, hairs standing up right, shivering, adrenaline and thyroxine is released)
5) more heat is produced and conserved by the body
- normal body temperature is restored
