Homeostasis (BIOL5)

Question 1

Define homeostasis

Answer 1

Maintenance of constant interval envrionment

Question 2

Homestasis is important because..

Answer 2

Keeping a constant interval envrionment is vital for cells to function normally

Stop them from being damaged

Question 3

Maintenance of temperature/pH level

Answer 3

• Body temp/pH too high enzymes became denatured
• Enzyme H bonds in tertiary structure break, active site changed - no longer works
  
  • metabolic reactions less efficient
• Temp/pH too low - enzyme activity reduced

Question 4

Maintenance of glucose concentration

Answer 4

• Cells need glucose for energy
• Glucose conc affects water potential of blood
  
  • **too high **- water potential reduced, so water molecules diffuse out of cells into blood by osmosis
    
    • cell shrivel and die
  • too low - cells unable to carry out reactions as there isn’t enough glucose for respiration to provide energy

Question 5

Features of negative feedback in homeostasis

Answer 5

• Negative feedback - mechanism that restores normal level
• Receptors detect when level high/low - info communicated via neurones/hormonal system to effectors
  
  • ​respond to counteract change - bring level to normal!
• Only works within certain limits
  
  • ​if change too big, effectors may not be able to counteract

Question 6

Features of multiple negative feedback

Answer 6

• Gives more control over changes in internal environment
  
  • can actively inc/dec level so returns to normal
• If only one negative feedback, only be able to actively change level in one direction
  
  • slower response and less control

Question 7

Features of postive feedback

Answer 7

• Amplifies change
• Effectors respond to further inc level away fr normal
• Used to rapidly activate something
• Can happen when homeostatic system d/s e.g. too cold for too long
  
  • NOT involved in homeostasis, as it doesn’t keep internal envrionment constant!

Question 8

Control of body temp in ectothermic reptiles

Answer 8

• Can’t control internally
  
  • do this by changing behaviour e.g. bask in sun
• Internal temp depends on ext temp
• Activity level depends on ext temp - more active at h temp, less as low temp
• Variable metabolic rate and generate v. little heat themselves

Question 9

Control of body temp in endothermic mammals

Answer 9

• Control body temp internally by homeostasis
• Int temp less affected by ext temp
• Activity level independent on ext temp
  
  • active at any temp (within limits!)
• Have constant h metaboli rate, generate a lot of heat from metabolic reactions

Question 10

Mechanisms of mammals to change body temp:

Heat loss

Answer 10

• Sweating:
  
  • sweat excreted from sweat glands when too hot
  • evaporates fr surface of skin, take heat fr body
• Hair lies flat:
  
  • when hot, erector pili muscles relax - hairs lie flat
    
    • less air trapped - skin less insulated
      
      • heat easily lost!
• Vasodilation:
  
  • hot - arterioles near skin surface dilate
    
    • more blood flows through capillaries in dermis surface layers
    • more heat lost from skin by radiation, temp lowers!

Question 11

Mechanisms of mammals to change body temp:

Heat production

Answer 11

• Shivering:
  
  • when cold, muscles contract in spasms
  • makes body shiver, more heat made from inc respiration
• Hormones:
  
  • body releases adrenaline/thyroxine
  • inc. metabolism - more heat made

Question 12

Mechanisms of mammals to change body temp:

Heat conservation

Answer 12

• Less sweat:
  
  • less sweat secreted fr sweat glands, reducing amount of heat loss
• Hairs stand up:
  
  • erector pili muscles contract when cold
  • make hairs stand up, trap air to prevent heat loss
• Vasoconstriction:
  
  • arterioles near surface of skin constrict, less blood flows through capillaries in surface of dermis
  • reduces heat loss

Question 13

Role of hypothalamus and ANS in maintaining body temperature

Answer 13

• Hypothalamus receives info of ext/int temp fr thermoreceptors:
  
  • int temp - info fr thermoreceptors in hypothalamus that detect blood temp
  • ext temp - info fr thermoreceptors in skin detect skin temp
• Thermoreceptors send impulses along sensory neurones to hypothalamus, sends impulses along motor neurones to effectors
  
  • effectors respond to restore body temp to normal