homeostasis

Question 1

what is homeostasis

Answer 1

internal environment is maintained within set limits around an optimum

Question 2

why is it important that core temperature remains stable

Answer 2

maintain stable rate of enzyme-controlled reactions and prevent damage to membranes

temperature too low = enzyme and substrate molecules have insufficient kinetic energy

too high = enzymes denature

Question 3

why is it important that blood pH remains stable

Answer 3

maintain stable rate of enzyme-controlled reactions

acidic pH - H+ ions interact with H-bonds and ionic bonds in tertiary structure of enzymes

Question 4

why is it important that blood glucose concentration remains stable

Answer 4

maintain constant blood water potential: prevent osmotic lysis / crenation of cells

maintain constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions

Question 5

define positive and negative feedback

Answer 5

positive feedback - a fluctuation triggers changes that result in an even greater deviation from the normal level

negative feedback - self-regulatory mechanisms return internal environment to optimum when there is a fluctuation

Question 6

outline the general stages involved in negative feedback

Answer 6

receptors detect deviation, coordinator, corrective mechanism by effector, receptors detect that conditions have returned to normal

Question 7

suggest why separate negative feedback mechanisms control fluctuations in different directions

Answer 7

provides more control, especially in case of overcorrection, which would lead to a deviation in the opposite direction from the original one

Question 8

suggest why coordinators analyse inputs from several receptors before sending an impulse to signal

Answer 8

receptors may send conflicting information

optimum response may require multiple types of effector

Question 9

why is there a time lag between hormone production and response by an effector

Answer 9

it takes time to:

produce hormone

transport hormone in blood

cause required change to target protein

Question 10

factor that affect blood glucose concentration

Answer 10

amount of carbohydrate digested from diet

rate of glycogenolysis

rate of gluconeogenesis

Question 11

define glycogenesis

define glycogenolysis

define gluconeogenesis

Answer 11

glycogenesis - liver converts glucose into the storage polymer glycogen

glycogenolysis - liver hydrolyses glycogen into glucose which can diffuse into blood

gluconeogenesis - liver converts glycerol and amino acids into glucose

Question 12

explain type 1 diabetes

Answer 12

body cannot produce insulin eg due to autoimmune response that attacked beta cells

treat by injecting insulin

Question 13

explain type 2 diabetes

Answer 13

glycoprotein receptors are damaged or become less responsive to insulin

strong positive correlation with poor diet / obesity

treat by controlling diet and exercise regime

Question 14

outline how colorimetry could be used to identify the glucose concentration in a sample

Answer 14

benedict’s test on solutions of known glucose concentration

use colorimeter to record absorbance

plot calibration curve

y - absorbance
x - glucose concentration

benedict’s test on unknown sample - use calibration curve to read glucose concentration at its absorbance value

Question 15

define osmoregulation

Answer 15

control of blood water potential via homeostatic mechanisms

Question 16

how are cells for bowman’s capsule adapted for ultrafiltration

Answer 16

fenestrations between epithelial cells of capillaries

fluid can pass between and under folded membrane of podocytes

Question 17

state what happens during selective reabsorption

Answer 17

useful molecules from glomerular filtrate eg glucose are reabsorbed into the blood

occurs in proximal convoluted tubule

Question 18

how are cells in the proximal convoluted tubule adapted for selective reabsorption

Answer 18

microvilli - large surface area for co-transporter proteins

many mitochondria - ATP for active transport of glucose into intercellular spaces

folded basal membrane - large surface area

Question 19

explain the role of the collecting duct

Answer 19

reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins

Question 20

why is it important to maintain a sodium gradient

Answer 20

countercurrent principle - filtrate in collecting ducts is always beside an area of interstitial fluid that has a lower water potential

maintains water potential gradient for maximum reabsorption of water

Question 21

what might cause blood water potential to change

Answer 21

level of water intake

level of ion intake in diet

level of ions used in metabolic processes or excreted

sweating

Question 22

explain the role of the hypothalamus in osmoregulation

Answer 22

osmosis of water out of osmoreceptors in hypothalamus causes them to shrink

triggers hypothalamus to produce more antidiuretic hormone

Question 23

explain the role of the posterior pituitary gland in osmoregulation

Answer 23

stores and secretes the ADH produced by the hypothalamus