HOMEOSTASIS

Question 1

What is homeostasis?

Answer 1

The maintenance of a relatively constant internal environment for the cells within the body.

Question 2

List some factors controlled by homeostasis.

Answer 2

• Core body temperature
• Metabolic wastes (e.g., CO2 & urea)
• Blood pH
• Blood glucose concentration
• Water potential of the blood
• Concentration of blood respiratory gases (CO2 & O2)

Question 3

What is the immediate internal environment for the cells?

Answer 3

The tissue fluid.

Question 4

What are four features of the tissue fluid that influence cell activities?

Answer 4

• Temperature
• Water potential
• Concentration of glucose
• pH

Question 5

Explain the importance of temperature in tissue fluid.

Answer 5

It affects enzymatic reactions; low temperature slows reactions, while high temperature denatures enzymes.

Question 6

How does water potential affect cells?

Answer 6

Low water potential may cause cells to lose water by osmosis, while high water potential may cause cells to gain water and possibly burst.

Question 7

What is the normal pH range of cytoplasm?

Answer 7

Between 6.5-7.0.

Question 8

What is negative feedback?

Answer 8

A process where a change in a factor brings about processes that counteract the change to return it to normal.

Question 9

What are the components of negative feedback?

Answer 9

• Stimulus
• Receptors
• Control Centre
• Effectors

Question 10

What role do receptors play in homeostasis?

Answer 10

They detect stimuli and send information about changes to the control centre.

Question 11

What is the function of the control centre in homeostasis?

Answer 11

Interprets input from receptors and sends impulses to effectors for corrective actions.

Question 12

What are effectors in the context of homeostatic mechanisms?

Answer 12

Muscles or glands that carry out actions to counteract changes.

Question 13

True or False: Negative feedback maintains factors at a constant level.

Answer 13

False; it allows factors to fluctuate around a set point.

Question 14

What are the two coordination systems in mammals for homeostasis?

Answer 14

• Nervous system
• Endocrine system

Question 15

Define excretion.

Answer 15

The removal of toxic substances or waste products of metabolism from the body.

Question 16

What are the two main excretory products?

Answer 16

• Urea
• CO2

Question 17

What is deamination?

Answer 17

The breakdown of excess amino acids in the liver by removing the amine group to form ammonia.

Question 18

What does the remaining keto acid from deamination do?

Answer 18

It may enter the Krebs cycle or be converted into glucose or glycogen.

Question 19

Why is deamination important?

Answer 19

• The body does not store excess amino acids
• Converts toxic ammonia into less toxic urea

Question 20

What is the main function of the kidneys?

Answer 20

To make urine, which excretes urea, excess salts, and water.

Question 21

What is the nephron?

Answer 21

The functional unit of the kidneys.

Question 22

What are the two stages of urine formation in the kidneys?

Answer 22

• Ultrafiltration
• Selective reabsorption

Question 23

How does ultrafiltration occur?

Answer 23

Blood pressure forces water and small molecules from the blood into the Bowman’s capsule.

Question 24

What prevents large proteins from passing during ultrafiltration?

Answer 24

The basement membrane acts as a sieve/filter.

Question 25

What is the glomerular filtration rate (GFR) in humans?

Answer 25

125 cm³ min⁻¹.

Question 26

What is selective reabsorption?

Answer 26

The process where useful molecules from the nephron fluid are taken back into the blood.

Question 27

List some molecules reabsorbed in the proximal convoluted tubule.

Answer 27

* Glucose * Vitamins * Water * Some inorganic ions (e.g., Na+, Cl-) * Amino acids

Question 28

What adaptations do epithelial cells in the proximal convoluted tubule have for reabsorption?

Answer 28

* Microvilli * Tight junctions * Many mitochondria * Co-transporter proteins

Question 29

What is osmoregulation?

Answer 29

The control of the water potential of blood and tissue fluid.

Question 30

What triggers the release of ADH?

Answer 30

A decrease in the water potential of the blood.

Question 31

How does ADH affect the kidneys?

Answer 31

It increases the permeability of collecting duct cells to water.

Question 32

What happens when ADH levels decrease?

Answer 32

Aquaporins are removed from the collecting duct cell membranes, making them less permeable to water.

Question 33

What is the normal range of blood glucose concentration?

Answer 33

80 mg-120 mg of glucose per 100 cm³ of blood.

Question 34

What hormones regulate blood glucose levels?

Answer 34

* Insulin * Glucagon

Question 35

What cells secrete insulin and glucagon?

Answer 35

Islets of Langerhans in the pancreas.

Question 36

What happens when blood glucose concentration increases above the set point?

Answer 36

β cells secrete more insulin, and α cells stop secreting glucagon.

Question 37

How do GLUT proteins function?

Answer 37

They facilitate the diffusion of glucose into cells.

Question 38

What is the role of glucokinase in glucose metabolism?

Answer 38

Phosphorylates glucose, trapping it inside the cell.

Question 39

What happens when insulin molecules bind to receptors on muscle cells?

Answer 39

Vesicles with GLUT4 proteins are moved to the cell surface membrane and fuse with it.

Question 40

What is the role of GLUT4 proteins?

Answer 40

Allow movement of glucose into the cell.

Question 41

What are the effects of insulin on muscle and liver cells?

Answer 41

Increase uptake of glucose from blood and convert it into glycogen or respire it.

Question 42

What enzyme does insulin activate that phosphorylates glucose?

Answer 42

Glucokinase.

Question 43

What happens to phosphorylated glucose inside the cell?

Answer 43

It is trapped inside the cell as it cannot pass through the GLUT proteins.

Question 44

What are the two enzymes stimulated by insulin that catalyze the conversion of glucose to glycogen?

Answer 44

* Phosphofructokinase * Glycogen synthase

Question 45

What is the process called that converts glucose to glycogen?

Answer 45

Glycogenesis.

Question 46

What happens to blood glucose concentration when insulin is secreted?

Answer 46

It lowers the blood glucose concentration back to the set point.

Question 47

What cells detect a decrease in blood glucose concentration?

Answer 47

β & α cells of the islets of Langerhans in the pancreas.

Question 48

What is the response of β cells when blood glucose concentration decreases?

Answer 48

They stop the secretion of insulin.

Question 49

What hormone do α cells secrete in response to low blood glucose?

Answer 49

Glucagon.

Question 50

True or False: Glucagon receptors are present on muscle cells.

Answer 50

False.

Question 51

What happens when glucagon binds to receptors on liver cells?

Answer 51

It activates a G protein that activates adenylyl cyclase.

Question 52

What does adenylyl cyclase catalyze the conversion of?

Answer 52

ATP to cyclic AMP (cAMP).

Question 53

What is the role of cAMP in the cell?

Answer 53

It acts as a second messenger.

Question 54

What enzyme does active protein kinase A activate?

Answer 54

Phosphorylase kinase.

Question 55

What does glycogen phosphorylase catalyze?

Answer 55

The breakdown of glycogen to glucose (glycogenolysis).

Question 56

What process does glucagon stimulate that involves formation of glucose from non-carbohydrate sources?

Answer 56

Gluconeogenesis.

Question 57

What is the role of negative feedback in blood glucose control?

Answer 57

Glucagon and insulin work together to return blood glucose concentration to normal.

Question 58

What condition leads to glucose presence in urine?

Answer 58

Diabetes.

Question 59

What happens when blood glucose exceeds the renal threshold?

Answer 59

Not all glucose is reabsorbed in the PCT.

Question 60

What do test strips for glucose in urine contain?

Answer 60

* Glucose oxidase * Peroxidase

Question 61

What is produced when glucose is oxidized by glucose oxidase?

Answer 61

Gluconic acid and hydrogen peroxide.

Question 62

What indicates different concentrations of glucose in urine on test strips?

Answer 62

The resulting color on the pad matched against a color chart.

Question 63

What is a limitation of urine test strips for glucose?

Answer 63

They do not indicate the current blood glucose concentration.

Question 64

What device is used to measure current blood glucose concentration?

Answer 64

A biosensor.

Question 65

What does the biosensor use to detect glucose in blood?

Answer 65

Enzymes glucose oxidase immobilized on a recognition layer.

Question 66

What happens to hydrogen peroxide in the biosensor?

Answer 66

It is oxidized at an electrode that detects electron transfers.

Question 67

What regulates stomatal aperture in plants?

Answer 67

The requirements for carbon dioxide uptake for photosynthesis and conserving water.

Question 68

What conditions cause stomata to open?

Answer 68

* High light intensity * Low CO2 concentration

Question 69

What conditions cause stomata to close?

Answer 69

* Darkness * High CO2 concentration * Low humidity * High temperature * Water stress

Question 70

What is the structure of guard cells that allows stomatal movement?

Answer 70

Unevenly thickened cell walls.

Question 71

How do guard cells open stomata?

Answer 71

By becoming turgid due to K+ influx and water entry.

Question 72

What happens to guard cells when stomata close?

Answer 72

They become flaccid as K+ leaves and water exits.

Question 73

What is abscisic acid (ABA) and its role in stomatal closure?

Answer 73

A stress hormone that triggers stomatal closure during water stress.

Question 74

What is the first effect of ABA on guard cells?

Answer 74

Inhibits proton pumps and stops H+ from being pumped out.

Question 75

What does Ca2+ do in guard cells during ABA response?

Answer 75

Acts as a second messenger and stimulates K+ channels to open and close.

Question 76

What is the outcome of ABA action on guard cells?

Answer 76

Loss of ions raises water potential, leading to stomatal closure.