Homeostasis And Feedback Mechanisms

Question 1

Why is homeostasis important

Answer 1

Maintain optimal conditions for enzyme action and cell function

Question 2

Examples of homeostasis

Answer 2

Body temp
Metabolic waste
Blood pH
Concentration of glucose in blood
Water potential of blood
Concentration of respiratory gases in blood

Question 3

Two coordiantion systems for homeostasis

Answer 3

Nervous and endocrine system

Question 4

Describe the nervous system

Answer 4

Allows us to make sense of our surroundings and respond to them and coordinate and regulate bodily functions
Nerves coordinate activities of sensory receptors

Question 5

Describe the endocrine system

Answer 5

Hormones transmit information from one part of the organsism to another to bring about change
Alters activity of one or more target organs

Question 6

Describe receptors and hormones

Answer 6

Receptors have to be complementary to hormones for there to be an affect

Question 7

Why do temperatures and pH’s of the body need to be controleld

Answer 7

Enzymes have a specific optimum temperature and pH to catalyse reactions at the maximum rate

Question 8

What type of reactions are prevented or slowed down due to low temperatures

Answer 8

Molecules move slower
Lower frequency of successful collisions between substrate molecules and the active site of enzymes
Less frequent enzyme-substrate complex formation occurs
Substrate and enzyme collide with less energy making it less liekly for bonds to be formed or broken

Question 9

What type of reactions speed up due to high temps

Answer 9

Molecules move more quickly
Higher frequency of successful collisions between substrate molcules and enzymes active sites
More frequent enzyme-substrate complex formation
Substrate and enzyme collide with more energy making it more likely for bonds to be formed or broken

Question 10

What happens to reactions when temperatures increase too much

Answer 10

Bonds holding enzyme molcules break causing tertiary structure of protein to change
Damaging the active site permanently so substrate can’t bind
Denaturation occurs if substrate can no longer bind

Question 11

What happens when pH changes

Answer 11

Hydrogen and ionic bonds holding tertiary structure of the protein together
Below and above optimum pH;s of an enzyme solutions with an excess of H+ and OH- ions can cause these bonds to break
Alters shape of active site so enzyme-substrate complexes form less easily
Enzyme-substrate complexes can no longer form
Complete denaturation of an enzyme has now occurred

Question 12

Why do negative feedback loops occur

Answer 12

To maintain homeosmotic balance

Question 13

What is involved in a negative feedback loop

Answer 13

Receptor to detect stimulus involved
Coordination system to transfer info between different parts of the body
Effector to carry out the response

Question 14

Outcomes of a negative feedback loop

Answer 14

Stimulus continuously monitored
Increase in factor = body decreases factor and vice versa

Question 15

Describe the corrective mechanisms for an increase and decrease in negative feedback loops

Answer 15

1) Factor increases above normal range
2) Receptor detects stimulus change triggering corrective mechanism A
3) factor returns to within normal range

Same with decrease

Question 16

Whats a positive feedback

Answer 16

ORiginal stimulus produces response causing factor to deviate more from noral range

Question 17

Descrube the positive feedback loop in bone repair

Answer 17

Osteoblasts secrete osteocalcin
Osteoclasts secrete acid to lower the pH of acidic conditions causing an inactive form of osteocalcin to change into an active form of osteocalcin
The active osteocalcin binsd to receptors on beta cells in the pancreas to stimulate the release of insulin

Question 18

Define the term homeostasis

Answer 18

Maintaining internal conditions constant

Question 19

How does the endocrine bring about responses in the body

Answer 19

1) Releases hormones from endocrine glands
2) Transports hormones in the blood
3) binds hormones to complementary receptors

Question 20

Why is body temperature regulation important

Answer 20

ENzymes function best at optimum temperatures
So below the optimum there would be less kinetic energy and reactions take place too slowly as molecules move slower resulting in less successful collisions so less enzyme-substrate complexse form
So if above optimum temperatures, enzymes denature due to bonds breaking losing their teriary structure and altering active site

Question 21

How does a negative feedback mechanism work (2 marks)

Answer 21

Receptors detect changes in normal internal conditions
A corrective mechanism acts so the body responds and returns conditions to normal reversing the effects of the change

Question 22

Why is blood glucose regulation important

Answer 22

It’s a respiratory substrate/ energy is released from it during respiration
Can affect water potential of blood

Question 23

What organ detects the rise/ fall in blood glucose concentration

Answer 23

The pancreas

Question 24

what are the three effects of insulin that lead to a fall in blood glucose

Answer 24

1) Increase in uptake of glucose by the cells
2) Glycogenesis
3) Increased respiration at which glucose is used by cells

Question 25

What hormone is released to increase blood glucose concentration

Answer 25

Glucagon is released for glycogenolysis and gluconeogenesis

Question 26

How does ADH increase the net movement of water from the lumen of the collecting duct into the blood

Answer 26

ADH causes aquaporins to be inserted into cell surface membrane Water enters cells through aquaporins by osmosis down the water potential gradient into blood capillary via interstitial fluid A smaller volume of more concentrated urine is produced

Question 27

Why does the conc of glucose decrease despite the blood containing no insulin

Answer 27

1) Glucose used in cell respiration 2) Glucose is converted to glycogen 3) Glucose is excreted

Question 28

WHy does high blood pressure occur when diabetes isnt controlled

Answer 28

1) Blood glucose concentration in blood is high, lowering water potential of blood 2) Water will enter the blood from body tissues by osmosis 3) This measn there will be a greater volume of blood in the circulatory system

Question 29

Describe selective reabrotption 5 marks

Answer 29

1) Takes place in proximal convoluted tubule 2) from the glomerular filtrate 3) Somem molecules are reabsorbed by active transport into the tubule cells 4) Some urea is is reabsorbed by diffusion 5) Glucose/ amino acids/ mineral ions/ water moves into the blood capillaries by osmosis

Question 30

How is the loop of henle and antidiuretic hormone adapted to dessert environments

Answer 30

1) Loop of henle allows more water to leave filtrate in descending loop 2) Longer loop of henle, more Na+ and Cl- to leave filtrate in ascending 3) ADH acts on collecting duct 4) ADH makes cells more permeable 5) More water reabsorbed to blood 6) urine more concentrated

Question 31

Describe how insulin reduces glucose conc in blood

Answer 31

1) Insulin binds to specific receptors 2) This activates carrier proteins causing more channels to form 3) Which increases the permeability of liver cells to glucose 4) insulin activates enzymes involved in glycogenesis (glucose -> glycogen)

Question 32

WHy does blood gucose increase in the presence of glucagon

Answer 32

1) Glucagon binds to complementary receptors on surface of target cells 2) Glucagon activates adenylate cyclase 3) ATP is converted intp cyclic AMP 4) cAMP activates the enzyme protein kinase A and this results in the breakdown of glycogen to glucose

Question 33

How is ultrafiltration affected by high blood pressure

Answer 33

Ultrafiltration takes place at high blood pressure so they will be affected by the drop in blood pressure The rate of ultrafiltration would decrease