Communication + homeostasis

Question 1

Conditions organisms need to maintain

Answer 1

-temperature
-pH
-aqueous environment
-freedom form toxins and excess inhibitors

Question 2

Changing external environments

Answer 2

-places stress on organism
-organism must respond to reduce stress
-environmental change= stimulus
-organisms changes in behaviour= response
eg. arctic fox has thick white coat in winter and thinner brown coat in summer

Question 3

Changing and maintaining internal environments

Answer 3

-metabolic activities in cells produces products that may be toxic
-this moves out of cells and into tissue fluid
-accumulation of excess wase acts as stimulus for waste products to be taken up by blood and excreted
eg. CO2 can reduce pH of tissue fluid, this stimulates greater breathing activity to expel CO2

Question 4

Features of good communication system

Answer 4

-covers whole body, so actions can be coordinated
-enables cell/specific communication, so only target cells will respond to signal
-enables rapid communication, to respond to rapid changes in environment
-enables short and long term responses, so response can be suited to environmental change eg. if environmental change is short or long term

Question 5

2 systems that work by cell signalling

Answer 5

Neuronal system
-neurones communicate via synapses
-enables a rapid response to stimuli
Hormonal system
-cells release hormones that are detected by target cells
-enables longer term response

Question 6

Homeostasis

Answer 6

-maintaining constant internal environment despite changes in internal/ external factors
eg. temp, blood glucose conc, blood salt conc, WP of blood, BP, CO2 conc

Question 7

Response pathway and how it works

Answer 7

Stimulus -> receptor -> communication centre -> effector -> response

-sensory receptors, monitor changes in environment
-Communication systems eg. endocrine/neuronal which transmit messages from receptors to effectors
-Effector cells- bring about response eg. liver/muscle cells

Question 8

Negative feedback

Answer 8

The mechanism that reverse a change, bringing the system back to optimum
-receptors detect stimulus and sends message to coordination centre
-this sends output to effectors which bring about change to reverse original change
-this reduces stimulus causing receptors to reduce input to coordination centre
-this reduces output to effectors, reducing their activity

Question 9

Processes needed for NF to work

Answer 9

-change to internal environment detected
-change signalled to other cells
-effective response that reverses change

Question 10

Positive feedback

Answer 10

Mechanism that increases a change, taking system further from optimum

-receptors detect change and input to coordination centre
-this sends output to effectors which react to increase the change
-this then repeats

eg. -in child birth the cervix stretches causing more oxytocin to be released, this increases contractions, further stretching the cervix
-activity of neurones

Question 11

Endotherm definition

Answer 11

organism that uses heat from metabolic reactions to maintain body temp eg. mammals

Question 12

Ectotherm definition

Answer 12

organism that relies on external sources of heat to maintain body temp eg.snake

Question 13

How ectotherms control temp

Answer 13

Too hot:
-move out of sun
-move underground
-reduce SA exposed to sun
Too cold:
-move to sunny area
-lie on warm surface
-expose large SA to sun

Question 14

Ectotherm examples

Answer 14

Snake- basks in sun to absorb heat directly
Locust- in morning face sideways to sun for large SA, but at midday they face the sun for smaller SA
Lizard- use burrows as cool during day but warm at night
Horned lizard- change shape by contracting/expanding rib cage to increase/decrease SA exposed to sun

Question 15

Ectotherm advantages and disadvantages

Answer 15

+less food used in respirations so can be used for growth
+need to find less food
+survive for long periods without food
-less active during cooler temps
-more at risk from predators
-can’t take advantage of food available when cold

Question 16

Organ responses when hot or cold

Answer 16

Skin- Hot- sweat glands secrete sweat, hairs lie flat to decrease insulation, vasodilation of arterioles and sphincters
-Cold- less sweat secreted, hairs stand erect,
vasoconstriction
Gaseous exchange system- Hot panting increase evap. of
water
-Cold- less panting
Liver- Hot- less respiration so less heat released
Cold- increased respiration
Muscles- Hot- fewer contractions so less heat released
Cold- spontaneous contractions (shivering) release
heat
Blood vessels- Hot- dilation to extremities
Cold- constriction to extremities

Question 17

Endotherm advantages and disadvantages

Answer 17

+maintains constant temp.
+remains active when external temp. low
+inhabit cold regions of the planet
-uses significant amount of energy to maintain temp
-need more food
-less energy used for growth

Question 18

Temp regulation in endotherms

Answer 18

-temp receptors in hypothalamus detect change in blood temp
-sends impulse to reverse the change
-either via neuronal system for rapid response or by hormonal system for a long term response
-uses a negative feedback cycle

Question 19

Peripheral temp receptors

Answer 19

-hypothalamus detects changes by monitoring blood temp
-peripheral receptor in extremities monitor temp
-this info is sent to thermoregulatory centre in hypothalamus which signals to the brain the change in external environment
-the brain can then initiate behavioural mechanisms to maintain body temp.