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AQA A Level Biology > Section 6 - Unit 16: Homeostasis > Flashcards

Section 6 - Unit 16: Homeostasis Flashcards

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1
Q

Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct (5 marks)

A
  • Epithelial cell of tubule cells carry out active transport
  • Transport chloride / sodium ions out (of filtrate)
  • Against concentration gradient
  • Into surrounding tissue / tissue fluid
  • Creates / maintains water potential gradient for water reabsorption
  • Countercurrent multiplier
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2
Q

Explain how ADH is involved in the control of the volume of urine produced (4 marks)

A
  • If water potential of blood falls, detected by receptors in hypothalamus
  • Leads to ADH released from pituitary gland
  • ADH makes cells of collecting duct / distal convoluted tubule permeable to water
  • Water leaves filtrate by osmosis
  • Smaller volume of urine produced
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3
Q

What is meant by homeostasis (1 mark)

A
  • Maintaining a constant internal environment
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4
Q

Giving one example, explain why homeostasis is important in mammals (2 marks)

A
  • Water potential / blood glucose
  • Effect of osmotic / blood glucose imbalance on cells
    OR
  • Temperature / pH; - Optimum for enzyme activity
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5
Q

Give two ways in which people with type 1 diabetes control their blood glucose concentration (2 marks)

A
  • Treat with insulin injection

- Control diet / sugar intake

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6
Q

Give the location of osmoreceptors in the body of a mammal (1 mark)

A

Hypothalamus

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7
Q

Explain why when a person is dehydrated, the cell volume of an osmoreceptor decreases (2 marks)

A
  • Water potential of blood will decrease

- Water moves from osmoreceptor into blood by osmosis

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8
Q

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys (4 marks)

A
  • Permeability of membrane to water is increased
  • More water absorbed from distal tubule / collecting duct
  • Smaller volume of urine
  • Urine becomes more concentrated
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9
Q

Apart from age and gender, give two factors that could affect the concentration of creatinine in the blood (1 mark)

A
  • Muscle mass
  • Ethnicity
  • Exercise
  • Kidney disease
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10
Q

Explain how animals prevent their blood glucose concentration falling when they have not eaten for 48 hours (3 marks)

A
  • Glucagon released
  • Formation of glucose in liver cells
  • From non-carbohydrates / amino acids / fatty acids
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11
Q

If rats are given very high concentrations of sucrose solution to drink, the refractory period makes it impossible for information about the differences in concentration to reach the brain. Explain why (2 marks)

A
  • Refractory period limits number of impulses per second

- When maximum frequency reached, no further increase in information / all concentrations of sucrose seem the same

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12
Q

In humans, when the stomach starts to become full of food, receptors in the wall of the
stomach are stimulated. This leads to negative feedback on the desire to eat. Suggest why
this negative feedback is important (3 marks)

A
  • Negative feedback stops desire to eat
  • Limiting the amount of food eaten
  • Reducing risk of obesity
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13
Q

Suggest why people with type 1 diabetes are described as being insulin-dependent (1 mark)

A

Treatment requires person receiving insulin in some way

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14
Q

Some people with type 2 diabetes have cells which do not respond to insulin. Explain how this leads to a reduced ability to regulate blood glucose concentration (3 marks)

A
  • Abnormal receptors on cell membrane
  • So less glucose can enter cells
  • So less glucose converted to glycogen
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15
Q

Describe how urea is removed from the blood (2 marks)

A
  • Hydrostatic pressure
  • Causes ultrafiltration at Bowman’s capsule
  • Through basement membrane
  • Enabled by small size urea molecule
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16
Q

Explain how urea is concentrated in the filtrate (3 marks)

A
  • Reabsorption of water
  • At the PCT
  • At the DCT
  • Active transport of ions / glucose creates gradient (in context)
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17
Q

Describe how ultrafiltration produces glomerular filtrate (5 marks)

A
  • Hydrostatic pressure
  • Small molecules
  • Pass through basement membrane
  • Protein too large to go through
  • Presence of pores in capillaries
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18
Q

Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (4 marks)

A
  • High concentration of glucose in blood
  • High concentration in tubule / in filtrate
  • Reabsorbed by facilitated diffusion
  • Requires proteins
  • These are working at maximum rate
  • Not all glucose is reabsorbed / some is lost in urine
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19
Q

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions (6 marks)

A

General Principle:

  • More water (from filtrate) reabsorbed
  • By osmosis
  • From collecting duct
  • Due to longer loop of Henle

For loop of Henle (2 marks):

  • Sodium / chloride ions absorbed from filtrate in ascending limb
  • Gradient established in medulla

For ADH (2 marks):

  • Acts on collecting duct
  • Makes cells more permeable
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20
Q

Explain why the blood glucose concentration of a diabetic is high after eating (3 marks)

A
  • Lack of insulin
  • Reduced uptake of glucose by cells
  • Reduced conversion of glucose to glycogen
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21
Q

Explain why the urine of a non-diabetic person does not contain glucose (2 marks)

A
  • Glucose leaves blood at kidney
  • Reabsorbed into the blood from the kidney tubule
  • Reabsorbed into the 1st convoluted tubule
22
Q

Suggest how a high blood glucose concentration could cause glucose to be present in the urine of a diabetic person (2 marks)

A
  • Large amount of glucose in filtrate

- Cannot all be reabsorbed / 1st convoluted tube too short to reabsorb all of glucose

23
Q

Explain why if the glomerular filtrate of a diabetic person contains a high concentration of glucose, they produce a larger volume of urine (2 marks)

A
  • Glucose in filtrate lowers water potential

- So less water reabsorbed by osmosis

24
Q

In some forms of kidney disease, proteins from the blood plasma are found in the urine.
Which part of the nephron would have been damaged by the disease to cause proteins
from blood plasma to be present in the urine? (3 marks)

A
  • Glomerulus / Bowman’s capsule
  • Basement membrane
  • Proteins are large molecule and can only pass through if the filter is damaged
25
Q

Describe what is meant by negative feedback (1 mark)

A

Where a change triggers a response which reduces the effect of a change

26
Q

Give two ways in which water is removed from the body (other than via the kidneys) (2 marks)

A
  • Sweating
  • Breathing
  • Defaecating
27
Q

Name the part of the brain which acts as the coordinator in the control of water balance (1 mark)

A

Hypothalamus

28
Q

From which gland is ADH released (1 mark)

A

Pituitary gland

29
Q

How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency (5 marks)

A
  • 37 °C is optimum temp for enzymes
  • Excess heat denatures enzymes / alters tertiary structure
  • Reactions slowed
  • Too little reduces kinetic energy of molecules
  • Fewer collisions / fewer ES complexes formed
30
Q

Explain how the cells of the collecting duct are able to absorb water from the filtrate through the protein channels in their plasma membranes (2 marks)

A
  • More negative / lower WP

- Water enters via osmosis

31
Q

Where does ultrafiltration occur (1 mark)

A

Renal capsule / Bowman’s capsule / Glomerulus

32
Q

Give one component of blood which is usually not present in the filtrate (1 mark)

A

Blood cells / platelets / proteins

33
Q

Reabsorption of glucose takes place in the proximal tubule. Explain how the cells of the proximal tubule are adapted for this function (2 marks)

A
  • Many mitochondria for ATP
  • Many carrier proteins for active transport
  • Microvilli provide large surface area for absorption
34
Q

What is homeostasis (1 mark)

A

Maintaining a constant internal environment

35
Q

Describe the role of the hormone glucagon in the control of blood sugar concentration (4 marks)

A
  • Binds to receptor
  • On muscle / liver cell
  • Activation of enzymes (in liver)
  • Hydrolysis of glycogen
  • Facilitated diffusion of glucose out of cells
  • Increases blood glucose levels
36
Q

Explain the role of the loop of Henle in the absorption of water from the filtrate (6 marks)

A
  • In the ascending limb sodium ions actively removed
  • Ascending limb impermeable to water
  • In descending limb sodium ions diffuse in
  • Descending limb water moves out
  • Low water potential / high concentration of ions in the medulla / tissue fluid
  • The longer the loop / the deeper into medulla, the lower the water potential in medulla / tissue fluid
  • Water leaves collecting duct
  • By osmosis / down water potential gradient
37
Q

Explain the role of ADH in the production of concentrated urine (4 marks)

A
  • When water potential of the blood too low
  • Detected by receptors in the hypothalamus
  • Pituitary releases (more) ADH
  • ADH increases the permeability / recruitment of aquaporins / opens
    channels for water in the DCT / collecting duct
  • More water is reabsorbed / leaves the nephron moves into the blood
  • By osmosis down the water potential gradient
38
Q

Apart from water and glucose, name two substances which will be present in the glomerular filtrate (1 mark)

A
  • Urea
  • Amino acids
  • Fatty acids
  • Glycerol
  • Small proteins
39
Q 
A person with diabetes may have a plasma glucose concentration greater than the
threshold value for glucose reabsorption. Explain what causes this raised plasma
glucose concentration (1 mark)
A
  • Decrease in insulin production

- Receptors not responsive to insulin

40
Q

Explain how the presence of abnormal insulin receptors results in a high blood glucose concentration (2 marks)

A
  • Insulin unable to attach to receptors

- Reduced uptake of glucose into cells / no carrier proteins for glucose transport

41
Q

Explain how the kidneys normally prevent glucose appearing in the urine of a non-diabetic person (3 marks)

A
  • Glucose reabsorbed into blood
  • From proximal tubule
  • By active transport
42
Q

Describe how insulin reduces the concentration of glucose in the blood (3 marks)

A
  • Insulin binds to specific receptors (on membranes)
  • It activates carrier proteins / opens channels
  • Insulin increases the permeability of liver / muscle cells
  • Insulin action results in glucose conversion to glycogen
43
Q

A person hasn’t eaten and so their plasma glucose concentration decreases. It then increases, decreases and keeps fluctuating. Explain the role of negative feedback in the control of plasma glucose concentration (5 marks)

A
  • Deviation of a value from norm initiates corrective mechanisms
  • Fluctuations in plasma glucose concentration detected by hypothalamus / islet cells in pancreas
  • Initial decrease due to no food given stimulates (increased) secretion of glucagon
  • Increase (in plasma glucose) stimulates secretion of insulin from β cells
  • Increased conversion of glucose to glycogen / increased uptake of glucose by cells
44
Q

Define negative feedback (1 mark)

A
  • A change to the normal level initiates a response which reduces the effect
45
Q

Explain how adrenaline causes an increase in blood glucose concentration (4 marks)

A
  • Binds to receptors on liver cell membrane
  • Stimulates enzymes to convert ATP to cAMP
  • Kinase is activated
  • Which then converts glycogen to glucose
46
Q

Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration (2 marks)

A
  • More insulin binds to receptors
  • Stimulating uptake of glucose by channel/transport
    OR
    Activates enzymes which convert glucose to glycogen
47
Q

Explain how inhibiting adenylate cyclase may help lower blood glucose concentration (3 marks)

A
  • Less ATP converted to cAMP
  • So less kinase produced
  • Less glycogenolysis (NOT gluconeogenesis)
48
Q

Describe how ultrafiltration occurs in a glomerulus (3 marks)

A
  • High hydrostatic pressure
  • Two named small substances pass out eg water, glucose, ions, urea
  • Through pores in (capillary) endothelium
  • And through (capillary) basement membrane
49
Q

Describe how glucose and water and reabsorbed by the PCT (2 marks)

A
  • Glucose via facilitated diffusion and active transport

- Water down a water potential gradient

50
Q

Explain why a thicker medulla means a higher concentration of urine (3 marks)

A
  • Thicker medulla means a longer loop (of Henle)
  • So there’s an increase in sodium ion concentration (in medulla)
  • So water potential gradient maintained, so more water (re)absorbed
    OR
    More water is reabsorbed from the loop (of
    Henle) / collecting duct by osmosis

AQA A Level Biology (14 decks)

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