communication and homeostasis

Question 1

all living things need to maintain a certain limited set of conditions inside their cells, these include

Answer 1

-a suitable temperature
-a suitable PH
an aqueous environment that keeps the substrates and products in solution
-freedom from toxins and excess inhibitors

Question 2

describe the changing of external environments

Answer 2

the external environment changes, which may place stress on the living organism
-organisms must change its behaviour or physiology to reduce stress

eg the cooler environment will cause greater heat loss

the environment may change slowly as the seasons change, and these elicit a gradual response eg thick coat thin coat

environment may change quickly eg appearance of a predator

Question 3

describe the changing of internal environments

Answer 3

• in many animals the internal cells and tissues are bathed in tissue fluid, this is the environment of the cells
• as cells undergo their various metabolic activities , they use up substrates and create new products, some of these compounds may be unwanted or even toxic. these substances move out of the cells into the tissue fluid, therefore the activities of the cells alter their own environment
• the build up of waste products in the tissue fluid may also act directly on the cells, which respond by reducing their activities so that less waste is produced . however this response may not be good for the whole organism

Question 4

describe maintaining the internal environment

Answer 4

the composition of the tissue fluid is maintained by the blood. blood flows throughout the body and transports substances to and from the cells. any waste or toxins accumulating int he tissue fluid are likely to enter the blood and be carried away. in order to prevent their accumulation in the blood they must be removed from the body by excretion

it is important that the concentrations of waste products and other substances in the blood are monitored closely. this ensures that the body does not excrete too much of any useful substances but it removes enough of the waste product to maintain good health. it also ensures that the cells in the body are supplied with the substrates they need

Question 5

describe coordinating the activities of different organs

Answer 5

a multi cellular organism is more efficient than a single celled organism,because its cells are differentiated . this means that its cells specialized to perform particular functions . groups of cells specialised to perform a particular function form tissues and organs . the cells that monitor the blood may be in a different part of the body well away from the source of the waste product . they may also be some distance from the tissue or organ specialised to remove the waste from the body.

therefore a good communication system is required to ensure that these different parts of the body work together effectively

Question 6

a good communication system will

Answer 6

-cover the whole body
-enable cells to communicate with each other
-enable specific communication
-enable rapid communication
=enable both short term and long term responses

Question 7

define cell signalling

Answer 7

the way in which cells communicate with each other

Question 8

what are the two major systems of communication that work by cell signalling

Answer 8

hormonal

neuronal

Question 9

describe neuronal systems

Answer 9

an interconnected network of neurones that signal to each other across synapse junctions . the neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly

Question 10

describe hormonal systems

Answer 10

a system that uses the blood to transport its signals. cells in an endocrine organ release the signal directly into the blood. the hormone is transported throughout the body , but is only recognized by specific target cells. the hormonal system enables longer term responses to be coordinated

Question 11

define homeostasis

Answer 11

maintaining a constant internal environment despite changes in external and internal factors

Question 12

what aspects are maintained by homeostasis

Answer 12

• body temperature
• blood glucose concentrations
• blood salt concentrations
• water potential of the blood
• blood pressure
• carbon dioxide concentration

Question 13

what is the mechanism of homeostasis

Answer 13

involves a series of tissues and organs that are coordinated through cell signalling . the standard response pathway is

• stimulus- receptor - communication pathway (cell signalling) - effector - response

Question 14

describe sensory receptors

Answer 14

such as temperature receptors. these receptors may be on the surface of the body, such as temperature receptors in the skin, they monitor changes in the external environment. other receptors are internal to monitor condition’s inside of the body , for example temperature receptors in the brain . when one of these receptors detects a change it will be stimulated to send a message to an effector

Question 15

describe effectors

Answer 15

cells such as liver cells or muscle cells. these cells will bring about a response

Question 16

describe feedback

Answer 16

when the effectors responds to the output from the coordination center, they bring about a response that will change the conditions inside the body. such changes will be detected by the receptors. this will have an effect upon the response pathway. in effect the input will change, this effect is known as feedback

Question 17

define negative feedback

Answer 17

in order to maintain a constant internal environment, any change away from optimum conditions must be reversed. in this way, conditions inside the body will be returned to the optimum

brings condition back towards o[optimum

Question 18

describe the negative feedback reaction

Answer 18

• change from optimum
• receptors detects change
• communication system informs effector
• effector reacts to reverse change
• returned to optimum temperature
• optimum temperature

Question 19

for negative feedback to work, what process must occur

Answer 19

1- a change to the internal environment must be detected
2- the change must be signaled to other cells
3-there must be an effective response that reverses the change in conditions

Question 20

describe maintaining a constant internal environment

Answer 20

a negative feedback system can maintain a reasonably constant set of conditions. however the conditions will never remain perfectly constant . there will be some variation around the optimum condition. when a stimulus occurs it may take time to respond and the response may cause a slight overshoot . however as long as this variation is not great, the conditions will remain acceptable.

when negative feedback is applied to living systems, the conditions inside a living organism will remain within a relatively narrow range. the conditions will remain warm enough to allow enzymes to continue functioning efficiently , but cool enough to avoid damage to the body many other proteins

Question 21

define positive feedback

Answer 21

the mechanism that increases a change , taking the system further away from the optimum

Question 22

describe the positive feedback reaction

Answer 22

• optimum condition
• change away from optimum
• receptors detect change
• communication systems informs effector
• effector reacts to increase change
• further change away from optimum

Question 23

what are endotherms

Answer 23

control their body temperature within very strict limits. they use a variety of mechanisms to control body temperature and are largely independent of external temperatures

Question 24

what are ectotherms

Answer 24

are not able to control their body temperatures as effectively as endotherms , they rely on external sources of heat and their body temperature fluctuates with the external temperatures. however using various behavioral mechanisms , some ectotherms are able to control their body temperature in all but the most extreme environments

Question 25

if ectotherms are not warm enough, they try to absorb more heat from the environment, they may ...

Answer 25

- move into a sunny area - lie on a warm surface - expose a larger surface area to the sun

Question 26

if ectotherms are too hot they try to avoid gaining more heat and try to increase heat loss to help environment, they may ...

Answer 26

- move out of the sun - move underground - reduce the body surface exposed to the sun

Question 27

what are the advantages of ectothermy

Answer 27

- 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 - they can survive for long periods without food

Question 28

what are the disadvantages of ectothermy

Answer 28

they are less active in colder temperatures. this means that they are at risk from predators while they are cold and unable to escape and they cannot take advantage of food that is available while they are cold

Question 29

examples of ectotherms and there behavioural adaptations and there benefits

Answer 29

- snake BA- basks in the sun B- absorbs heat directly -lizard BA-use burrows or crevices during the hot parts of the day B-more stable temperature

Question 30

describe the temperature regulation mechanism

Answer 30

temperature regulation relies on effectors in the skin and muscles. the skin is the organ in contact with the external environment. therefore many of the physiological adaptations to control body temperature involves the skin . the change that takes place in the skin alter the amount of heat being lost to the environment may chemical reactions in the body are exergonic - they release energy in the form of heat. endotherms can increase respiration in the muscles and the liver simply to release heat- they are using some of their energy intake to stay warm. they also have other useful physiological mechanisms , such as directing blood towards or away from the skin to alter the amount of heat lost to the environment

Question 31

name the organs and the response if too hot and the response it too cold ( physiological mechanisms for endotherms )

Answer 31

response if too hot skin- sweat glands secrete fluid, when this evaporates it looses heat , hairs lie flat to reduce insulation, vasodilation of arteries so more heat can be lost liver- less respiration take place, so less heat is released skeletal muscles- fewer contractions means less heat is released blood vessels - dilation to direct blood to the extremities so that more heat is lost if too cold skin- less sweat, hairs stand up for insulation , vasoconstraction of arteries so less heat is lost sketetal muscles- spontaneous muscle contractions (shivering ) releases heat liver- increased respiration in the liver cells means more energy from food is being converted to heat gaseous exchange - less panting

Question 32

name the behaviours if an animals is too hot and too cold ( behavioural adaptations by endotherms )

Answer 32

if too hot - hide away from sun in shade or in a burrow - orientate body to reduce surface area exposed to the sun - remain inactive and spread limbs out to enable greater heat loss - wet skin to use evaporation to help cool the body. if too cold - lie in the sun - orientate body towards the sun to increase surface area exposed - move about to generate heat in the muscles or in extreme conditions roll into a ball shape to prevent heat loss - remain dry

Question 33

advantages of endothermy

Answer 33

- maintain a fairly constant body temperature whatever the temperature externally - remain active even when external temperatures are low, which means they can take advantage of prey that may be available or escape from potential predators - inhabit colder parts of the planet

Question 34

disadvantages of endothermy

Answer 34

- use significant part of their energy intake to maintain body temperature in the cold - need more food - use for growth a lower proportion of the energy and nutrients gained from food - may overheat in hot weather

Question 35

describe the control of temperature regulation

Answer 35

the maintenance of a core body temperature is important. if the core temperature changes this alters the temperatures of the blood. temperature receptors in the hypothalamus of the brain detect this change . the hypothalamus then sends out impulses to cause different responses that will reverse the change. some responses need to be quick in order to prevent further changes in body temperature- the neuronal system transmits the output from the hypothalamus in order to make these responses rapid. other responses may need to be longer term, the hormonal system transmits the output to cause these responses

Question 36

if the core temperature is too low, the hypothalamus will bring about ...

Answer 36

- change in the skin to reduce heat loss - release of heat through extra muscular contraction - increased metabolism in order to release more heat from the exergonic reactions

Question 37

define hypothalamus

Answer 37

the part of the brain that coordinates homeostatic responses

Question 38

describe the role of the peripheral temperature receptors

Answer 38

the thermoregulatory center in the hypothalamus monitors blood temperature and detects changes in the core body temperature. however an early warning that the body temperature may change could help the hypothalamus to respond more quickly and reduce variations in the core body temperature . if the extremities start to cool down or warm up this may eventually affect the core body temperature -peripheral temperature receptors in the skin monitor the temperature in the extremities, this information is fed to the thermoregulatory centre in the hypothalamus . if the thermoregulatoty centre signals to the brain that the external environment is very cold or very hot, the brain can initiate behavioural mechanisms for maintaining the body temperature, such as moving to the shade

Question 39

the environmental change is a ....... and the way in which the organism changes its behaviour or physiology is its ........

Answer 39

- stimulus | - response