5.1.1 Communication and Homeostasis

Question 1

the need for communication systems in multicellular organisms

Answer 1

• animals and plants need to respond to changes in their internal & external environment so conditions are optimal for metabolism and to increase survival chances
  eg. temp, blood glucose, light intensity etc.
• coordinate activities of diff organs

Question 2

homeostasis

Answer 2

the maintenance of a constant internal environment despite a changing external environment

Question 3

receptors

Answer 3

• detect a change in condition (stimulus)
• specific so only detect one type of stimulus eg. pressure, temp, glucose conc
• can be outward facing like skin or internal like hypo

Question 4

effectors

Answer 4

muscles/glands that react to a motor stimulus to bring about a change

Question 5

negative feedback

Answer 5

change detected by sensory receptors. effectors work to reverse the change and restore conditions to base level

eg. control of blood glucose levels by insulin and glucagon
eg. control of water content be ADH
eg. temp control

Question 6

positive feedback

Answer 6

change detected by sensory receptors. effectors work to reinforce the change and increase the response

eg. oxytocin produced when baby’s head presses agains cervix stimulates uterus to contract and pushes baby’s head even harder against cervix, releasing more oxytocin
eg. blood clotting cascade

Question 7

endotherms

Answer 7

• rely on metabolic processes to warm up/cool down
• maintain v stable core body temp despite environment
• survive in a wide range of environments
• metabolic rate is x5 higher than ecto. so consume more food to meet needs
• mammals and birds

Question 8

ectotherms

Answer 8

• use surroundings to warm bodies
• core body temp heavily dependant on environment
• many ecto. that live underwater don’t have to thermoregulate due to high heat capacity of water maintaining stable environment (on land air temp varies between seasons & over 24h)
• all invertebrates, fish, amphibians, reptiles

Question 9

endotherms behavioural responses

Answer 9

• hibernation (aestivation avoids heat stress)
• clothes to keep warm
• house insulation
• also same as ecto eg. bask in sun

Question 10

ectotherms behavioural responses

Answer 10

to increase/reduce radiation absorbed from the sun

• bask in sun
• orientate bodies
• press bodies against ground (conduction)
• contract muscles/vibrate wings, increasing cellular metabolism)

Question 11

why is homeostasis important

Answer 11

important because enzyme controlled reactions only occur within narrow pH/temp ranges

Question 12

how do endotherms detect temperature changes?

Answer 12

external -
- peripheral thermoreceptors in skin detect changes in surface temp
internal -
- hypothalamus receptors detect temp of blood deep in body
- hypo. sends impulses to effectors to increase sweating, vasodilation etc.

Question 13

endotherms mechanisms to reduce body temp (physiological)

Answer 13

Vasodilation

• arterioles near skin surface dilate
• arteriovenous shunt vessels constrict, forcing blood into capillaries near skin surface, increasing radiation
• increased sweating
• heat is lost as sweat evaporates from skin surface or water from mouth (panting)
• erector pili muscles on skin surface relax and hair lies flat

Question 14

endotherms mechanisms to increase body temp (physiological)

Answer 14

Vasoconstriction

• arterioles near skin surface contrict
• arteriovenous shunt vessels dilate, so little blood flows into capillaries near skin surface, decreasing radiation
• decreased sweating
• reduced evaporation of water from skin surface
• erector pili muscles on skin surface contract, creating insulating layer
• shivering creates metabolic heat from exothermic reactions