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AQA A Level Biology > B16 Homeostasis > Flashcards

B16 Homeostasis Flashcards

1
Q

What is homeostasis

A

The maintenance of a stable internal environment

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2
Q

Why is homeostasis important

A

For cells to function normally and for optimum enzyme activity for metabolic reactions

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3
Q

What happens when body temperature is too high

A
  • enzymes vibrate too much due to higher kinetic energy
  • this breaks the hydrogen bonds that hold them in their 3D shape
  • shape of the enzymes active site is altered so ES complexes can’t form
  • rate metabolic reactions slow down
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4
Q

What happens if blood pH is too high/ low

A
  • hydrogen bonds holding enzymes in their 3D shape are broken

-shape of enzymes active site is altered

  • enzyme denatures
  • metabolic reactions slow down
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5
Q

What happens if blood glucose conc is too high

A
  • the water potential of blood is greatly reduced to a point where water molecules diffuse out of the cells into the blood via osmosis
  • cells shrivel up and die
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6
Q

How do homeostatic systems work

A

Receptors detect when a level is too high or too low

Info is communicated via the nervous system or hormonal system

Reaches the effectors which counteract the change and restores the level

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7
Q

What is negative feedback

A

Restores systems to their original level by reversing a change in the body

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8
Q

Why is having multiple negative feedback mechanisms useful

A

You can actively increase or decrease a level so it returns to normal

Gives more control

Faster response

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9
Q

What is a positive feedback mechanism

A

Amplifies a detected change

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10
Q

Which organ controls the blood glucose concentration

A

Pancreas

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11
Q

Insulin is secreted from

A

Beta cells in islets of Langerhans

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12
Q

Glucagon is secreted from

A

Alpha cells in islets of Langerhans

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13
Q

Insulin

A

Lowers blood glucose conc

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14
Q

Glucagon

A

Increases blood glucose conc

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15
Q

How does insulin lower blood glucose conc
5 things

A

Binds to specific receptors on liver and muscle cells and increases their permeability of glucose so glucose can more easily diffuse into cells

This causes more carrier proteins to move to the cell membrane

Stimulates glucose -> amino acids/fats/lipids

Increases the rate of respiration

Stimulates glycogenesis

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16
Q

Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose conc

A

Glucose conc in cells creates a glucose conc gradient

Glucose leaves the blood via facilitated diffusion

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17
Q

How does glucagon work

A

Binds to specific receptors on liver cells

Stimulates gluconeogenesis and glycogenolysis by activating enzymes from the second messenger model

Decreases the rate of respiration

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18
Q

Where is adrenaline released from

A

Adrenal glands

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19
Q

How does adrenaline work

A

Stimulates glycogenolysis

Secretion of glucagon

Inhibition of insulin

20
Q

How does the 2nd messenger model work

A

1) 1st messenger binds to receptors on liver cell

2) This activates adenylyl cyclase

3) This stimulates the conversion of ATP -> cAMP

4) cAMP activates protein kinase A which activates a cascade of reactions that break down glycogen to glucose

21
Q

What happens in type 1 diabetes

A

The immune system attacks the Beta cells in the islets of Langerhans so they can’t secrete insulin

22
Q

What is the main issue for people with type 1 diabetes

A

Hyperglycaemia as after eating the blood glucose level rises and stays high

23
Q

How can type 1 diabetes be treated

A

Insulin therapy
Eating regularly
Controlling simple carbohydrates intake

24
Q

What happens in type 2 diabetes

A

When Beta cells don’t produce enough insulin OR when the body’s cells don’t respond properly to insulin

25
Risk factors causing Type 2 Diabetes
Obesity Lack of exercise Age Poor diet
26
Treatments for type 2 Diabetes
Eating a healthy balanced diet Losing weight Regular exercise Eventually insulin injections
27
How you can indicate if someone has diabetes
By using colorimetry to indicate blood glucose conc in someone’s urine
28
Colorimetry basic steps
1) Using quantitative Benedict’s Reagent 2) Use a colorimeter to measure the light absorbance of the solution after the Benedict’s test has been carried out 3) The higher the conc of glucose the more the blue colour will be lost which would decrease the absorbance of the solution 4) Plot a calibration curve showing absorbance against glucose conc
29
What is quantitative Benedict’s Reagent
When heated with glucose, the blue colour will just be lost. No brick red precipitate will be formed
30
How to make serial dilutions
1) line up 5 test tubes 2) add 10cm of initial whatever conc glucose solution to the first test tube 3) add 5cm of distilled water to each of the other 4 test tubes 4) use a pipette to draw out 5cm from first test tube and transfer to the second test tube and mix 5) repeat till 5th test tube Each will be half conc compared to test tube before it
31
Function of the kidneys
Regulating water potential of the blood Excrete waste products e.g. urea
32
Ultrafiltration process
Blood enters from afferent arteriole under high hydrostatic pressure and enters the glomerulus The higher pressure forces small molecules out of the capillary’s via podocytes and through the basement membrane into the Bowman’s capsule Larger molecules such as proteins and blood cells are unable to pass through as they are too large.
33
Differences between afferent and efferent arterioles
Afferent is larger in diameter/ larger lumen as it needs to withstand higher pressures than efferent
34
Selective reabsorption
Useful substances leave the tubules and enter the capillary network around them e.g. Glucose via active transport and facilitated diffusion at pct Water enters the blood via osmosis as WP of blood is lower than in the filtrate. This diffusion occurs at pct loop of henle dct and collecting duct
35
How is the pct’s epithelial cells adapted for selective reabsorption
Microvilli to provide a large surface area Many ribosomes to provide channel proteins for facilitated diffusion of glucose Many mitochondria for production of ATP for active transport of glucose
36
What is urine made up of
Water Dissolved salts Hormones Excess vitamins
37
How is water lost
Sweat Excretion Breathing
38
Osmoregulation definition
The regulation of the water potential of blood through kidneys
39
Loop of Henle
Near the top of ascending limb, Na+ ions are pumped out into the medulla using active transport. The ascending limb is impermeable to water so no water is lost or gained. This creates a low WP in the medulla as there’s a high conc of ions Low WP in medulla means water moves out the descending limb into the medulla via osmosis. Therefore filtrate becomes more concentrated as ions can’t diffuse out of descending limb. Water in medulla is reabsorber into the blood via capillary network. Near the bottom of the ascending limb, Na+ ions diffuse out into medulla which furthers the lowering of the WP in the medulla. Water moves out the DCT via osmosis and is reabsorbed by the blood The lower WP of the medulla means water can move out of the collecting duct via osmosis
40
Where are osmoreceptors found and what do they do
Hypothalamus They monitor the WP of blood
41
What happens when there’s a low WP in the blood
Water moved out of the osmoreceptors via osmosis This causes the cells to decrease in volume This send a signal to other cells in the hypothalamus which sends a signal to the posterior pituitary gland This gland releases ADH
42
How does ADH work
More ADH means DCT and collecting duct becomes more permeable to water so more water is reabsorbed into the blood via osmosis
43
Negative feedback definition
When a change triggers a response which reduces the effect of the change
44
Why is glucose found in the urine of a person with untreated diabetes 3 marks
They have a high blood glucose concentration They have high glucose concentration in filtrate Not all the glucose can be selectively reabsorber into the blood As channel and carrier proteins are working at maximum rate
45
Describe role of glucagon/ insulin
-> activates enzymes
46
Main issue for people with Type 2 Diabetes
Faulty receptors so less responsive to insulin
47
What does a thicker medulla mean
A longer loop of Henle

AQA A Level Biology (8 decks)

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