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A-Level AQA Biology > Homeostasis is the maintenance of a stable internal environment > Flashcards

Homeostasis is the maintenance of a stable internal environment Flashcards

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1
Q

What is homeostasis?

A

Internal enviroment is maintained within set limits around an optimum.

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2
Q

What is it important that core temeprature remains stable?

A

Maintain stable rate of enzyme controlled reaction & prevent damage to membranes.

Temperature too low = enzyme & substrate molecules have insufficient kinetic energy.

Temperature is too high = enzymes denature.

maintaining a stable core temperature and stable blood pH in relation to enzyme activity.

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3
Q

Why is it important that blood pH remainds stable?

A

Maintain stable rate of enzyme-controlled reactions (& optimum conditions for other proteins).

Acidic pH = H⁺ ions interact with H-bonds & ionic bonds in tertiatry structure of enzymes → shape of active site changes so no ES complexes form.

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4
Q

Why is it important that blood glucose concentration remains stable?

A
  • Maintain constant blood water potential: prevent osmotic lysis/ crenation of cells
  • Maintains constant concentration of respiratory substrate: organism maintains constant level of activity regardless of enviromental condtions.
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5
Q

Describe negative and positive feedback.

A

Negative feedback: self-regulatory mechanisms return internal enviroment to optimum when there is a flucation.

Positive feedback: a flucation triggers changes that result in an even greater deviation from the normal level

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6
Q

Outline the general stages involves in negative feedback.

A

Receptors detect → coordinatior → corrective mechanism by effector → receptors detect that conditions have returns to normal.

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7
Q

Suggest why separate negative feedback mechanisms control fluctuations in different directions.

A

Provide more control, especially in case of ‘overcorrection’, which would lead to a devation in the opposite direction from the original one.

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8
Q

Suggest why coordinators analyse inputs from several receptors before sending impulse to effectors.

A
  • Receptors may sned conflicting information.

- Optimum response may require multiple types of effector.

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9
Q

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

A

It takes time to:

  • Produce hormone
  • Transport hormone in the blood
  • Cause required change to the target protein.
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10
Q

Name the factors that affect blood glucose concentration.

A
  • Amount of carbohydrate digested from diet.
  • Rate of glycogenolysis.
  • Rate of gluconeogenesis.
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11
Q

Define glycogenesis, glycogenolysis, Gluconeogenesis

A

Glycogenesis: liber converts glucose into the storage polymer glycogen

glycogenolysis: Liver hydrolyses glycogen into glucose which can diffuse into blood.

Gluconeogenesis: Liber converts glycerol & amino acids into glucose.

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12
Q

Outline the role of glucagon when blood glucose concentration decreases.

A
  1. α cells in islets of Langerhans in pancrease detect decrease & secrete glucagon into bloodstream.
  2. Glucagon binds to surface receptors on liver cells & activates enzyme for glycigenolysis & gluconeogenesis.
  3. Glucose diffuses from liver into bloodstream.
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13
Q

Outline the role of adernaline when blood glucose concentration decreases.

A
  1. Adrenal glands produce adrenaline. It binds to surface receptors on liver cells & activates enzyme for glycogenolysis.
  2. Glucose diffuses from liver into bloodstream.
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14
Q

Outline what happens when blood glucose concentration increases.

A
  1. β cells in Islets of Langerhans in pancreas detect increase & secrete insulin into bloodstream.
  2. Insulin binds to surface receptors on target cells to:
    a) increase cellular glucose uptake
    b) activaye enzyme for glycogenesis (liver & muscles)
    c) stimulate adipose tissue to synthesis fat.
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15
Q

Describe how insulin leads to a decrease in blood glucose.

A
  • Increase permeability of cells to glucose.
  • Increase glucose concentration gradient.
  • Triggers inhibition of enzymes for glycogenolysis.
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16
Q

How does insulin increase permeability of cells to glucose

A
  • Increase number of glucose carrier proteins.

- Trigger conformational change which opens glucose carrier proteins.

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17
Q

How does insluin increase the glucose concentration gradient?

A
  • Activate enzymes for glycogenesis in liver & muscles.

- Stimulate fat synthesis in adipose tissue.

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18
Q

Use the secondary messenger model to explain how glucagon and adrenaline work.

A
  1. Hormone-receptor complex forms.
  2. Conformational change to receptor activate G-protein
  3. Activate adenylate cyclase, which converts ATP to cyclic AMP (cAMP).
  4. cAMP activates protein kinase A pathway.
  5. Results in glycogenolysis.
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19
Q

Explain the causes of the Type 1 diabetes and how it can be controlled.

A

Body produce insulin e.g. due to autoimmune response which attacks β cells of islets of Langerhans so they can’t produce any insluin.

Treat by injecting insulin.

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20
Q

Explain the causes of Type 2 diabetes and how it can be controlled.

A

Glycoprotein receptors are damaged or become less responsive to insulin.

Strong postive correlation with poor diet/ obesity.

Treat by controlling diet and exercise regime.

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21
Q

Name some signs and symptoms of diabetes.

A
  • High blood glucose concentration
  • Glucose in urine
  • Polyuria
  • Polyphagia
  • Polydipsia
  • Blurred vision
  • Sudden weightloss
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22
Q

Suggests how a student could produce a desired concentration of glucose solution from a stock solution.

A

Volume of stock solution = required concentration x final volume needed / concentration stock solution.

Volume of distilled water = final volume needed - volume stock solution.

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23
Q

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

A
  1. Benedicts test on solutions known glucose concentration. Use colorimtert to record absorbance.
  2. Plot calibration curve: absorbance (y-axis), glucose concentration (x-axis)
  3. Benedict’s test on unknown sample. use calibration cruve to read glucose concentration at its absorbance value.
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24
Q

Define Osmoregulation

A

Control of blood water potential via homeostatic mechanims.

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25
Q

Describe the gross structure of mammalian kidney.

A

Fibrous capsule: protects kidney

Cortext: outer region consists of Bowman’s capusules, convoluted tubles, blood vessels

Medulla: inner region consits of collecting ducts, loops of Henle, blood vessels

Renal pelvis: cavity collects urine into ureter.

Ureter: tube carriers urine to bladder

Renal artery: supplies kidney with oxygenated blood.

Renal vein: Deoxygenated blood from kidney to heart.

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26
Q

Describe the structure of a nephron.

A

Bowman’s capsule at start nephron: cup-shaped, surronds glomerulus, inner layer podcytes.

Proximal convoluted tubule (PCT): series of loops surrounds by capillaries, walls made of epithelial cells with microvilli.

Loop of henle: hairpin loop extends from cortex into medualla.

Distal convoluted tubule: similar to PCT but fewer capillaries.

Collecting duct: DCT from severa; nephrons empty into collecting duct, which leads into pelvis of kidney.

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27
Q

Describe the blood vessels associated with a nephron.

A

Wide afferent arteriole from renal artery enters renal capsule & forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole.

Efferent arteriole branches to form capillary network that surrounds tubules.

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28
Q

Explain how glomerular filtrate is formed.

A

Ultrafiltration in Bowan’s capusle.

High hydrostatic pressure in glomerulus forces small molecule (urea, water, glucose, mineral ions) out of capillary fenestrations AGAINST osmotic gradient.

Base membrane acts as filter. Blood cells & large molecules e.g. protein remain in capillary.

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29
Q

How are cells of Bowan’s capsule adapted for ultrafiltration?

A
  • Fenestrations between epithealial cells of capillaries.

- Fluid can pass between & under folded membrane podcytes.

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30
Q

States what happens during selective reabsorption and where it occurs.

A

Useful molecules from glomerular filtrate e.g. glucose are reabsorbed into the blood.

Occurs in proxial convoluted tubule.

31
Q

Outline the transport proesses in selective reabsorption.

A 
Glucose from filtrate
co-transport with Na⁺ ↓
           Cells lining proximal convoluted tubule
Active transport ↓
intercellular spaces
Diffusion ↓
bloody capillary lining tubule

Refer to PMT

32
Q

How are cells in the proximal convoluted tubule adapted for selective reabsorption?

A
  • Microvilli: Large SA for co-transporter proteins
  • Many mitochondria: ATP for active transport of glucose into intercelluar spaces.
  • Folded basal membrane: Large SA
33
Q

What happens in the loop of Henle

A
  1. Active transport of Na+ & Cl- out of ascending limb
  2. Water potential of inetstitial fluid decreases
  3. Osmosis of water out of descending limb (ascending limb is impermeable to water.)
  4. Water potential of filtrate decreases going down descending limb: lowest inmedullary region, highest at top of ascending limb.
34
Q

Explain the role of the distal convoluted tubule.

A

Reabsorption:

a) of water via osmosis
b) of ions via active transport

permeability of walls is determined by action of hormones.

35
Q

Explain the role of the collecting duct.

A

Reabsorption of water from filtrate into interstital fluid via osmosis through aqauporins.

36
Q

Explain why it is important to maintain an Na+ gradient.

A

Countercurrent multiplier: filtrate in collecting ducts is always beside an area of inetstital fluid that has a lower water potential.

Maintain water potential gradient for maximum reabsorption of water.

37
Q

What might cause blood water potential to change?

A
  • Level of water intake
  • Level of ion intake in diet
  • Level of ions used in metabolic processes or excreted
  • Sweating
38
Q

Explain the role of the hypothalamus in osmoregulation

A
  1. Osmosis of water out of osmoreceptors in hypothalamus cause them to shrink.
  2. This trigger hypothalams to produce more antidiuretic hormone (ADH).
39
Q

Explain the role of the posterior pituitary gland in osmoregulaton.

A

Stores and secretes the ADH produced by the hypothalamus.

40
Q

Explain the role of ADH in osmoregulation.

A
  1. Makes cells lining collecting duct more permeable to water:
    - Binds to receptor → activates phosphorylase → vesicles with aquaporins on membranes fuse with cell-surface membrane
  2. Makes cells lining collecting duct more permeable to urea:
    - Water potential in interstitial fluid decreases.
    - More water reabsorbed = more concentrated urine.
41
Q

Changes to water potential of blood and tissue fluids

A

May cause cells to shirnk and expand as a result of water leaving or entering by osmosis

42
Q

Benefit of organims with the ability to maintain a constanst internal enviroment

A
42
Q

Benefit of organims with the ability to maintain a constanst internal enviroment

A
43
Q

The control of any self-regulating system involves a series of 5 stages that feature:

A

The optimum point - point in which the systems operates best.. this is monitered by:

The receptor - which detects any deviation from the optimum point and informs..

The coordinator - which coordinates info from receptors and sends instructions to an appropriate

Effector - often a msucle or gland, which brings about changes neeed to return to the optimum point. This return to normality creates a ..

Feedback mechanism - by which a receptor responds to a stimulus created by the change to the system brought about by the effector

44
Q

Feedback loop

A

In this case - negative feedback as it returns system off.

45
Q

Ectotherms [outside heat]

A

Gain heat from the enviroment, so their body temp fluctuates with that of the enviroment.

46
Q

How do Ectotherms control their body temperature?

A

By adapting their behaviour to changes in external temperatures

47
Q

Give an example of an ectortherm?

A

Repties such as LIZARDS as they control body temp by:
Exposing themselves to the sun - so maximum SA of their body is exposed

  • Taking shelter - to prevent over-heating (retreat into burrows in order to reduce heat loss)
  • Gaining warms from the ground - by pressing their bodies into it when required temp is
    reached they raise themselves of ground on their legs
48
Q

Endotherms [inside heat]

A

Gain most of their heat from internal metabolic activities.

49
Q

Give an example of an Endotherm animal

A

Polarbears and pengiun who tend to be bigger (small SA to volume ratio) tend to live in cold climates

50
Q

Vasconstriction

A

The diameter of the ateroes near the suface of the skin is made smaller. Reducing the volume of blood reaching the skin through the capillaies. Most of the blood entering the skin passes beneath the insluating layer of fast so loses little heat to enviroment.

51
Q

Shivering

A

The muscles of the body undergo involuntary rhythmic contractions that produces metabolic heat

52
Q

Raising of hair

A

The hair erector muscle in the skin contract, raising the hairs on the body. This enables a ticker layer of still air, which is a good insulator, to be trapped next to the skin, insulating and conserving heat in mamals with tick fur.

53
Q

Increased metabolic rate

A

In cold conditions more hormones that increase metabolic rate are produced.As a result activity, including respiration, is increased and so more heat is generated

54
Q

Decrease in sweating

A

Sweating is reduced, or ceases altogether, in cold conditions

55
Q

Behaviour mechanims

A

Shelteriing from the wind. basking in the sun and hudding togeter all help animals to maintain their core body temp

56
Q

Losing heat in response to a warm enviroment

A
57
Q

Vasodilation

A

The diameter of the aterioles near the surface of the skin become larger. This allws warm blood to pass close to the skin surface through the capillaries. The heat from this blood is then raidated away from the body

58
Q

Increased sweating

A

To evaporate water from the skin surface requires energy in the form of heat. In relatively hairless mammals, such as humans sweating is a highly effective means of losing heat. I

Fur animals = cooling is achieved by the evaportatin of water from mouth and tounge during panting. The high latent heat of vaporisation makes sweating an efficent way of losing heat

59
Q

Lowering of body hair

A

The hair erector muscles in the skin relax and the elasticity of the skin causes them to flatten agaisnt the body. This reducing the thickness of the insulating layer and allows more heat to be lost to the enviroment when the internal temp is higher than externa temp.

60
Q

Behaviour mechanims

A

Avoiding the heat of the day by sheltering in burrrows and seeking out shade help to prevent the vody temp rising

61
Q

Define negative and positive feedback?

A

Negative feedback: Self-regulatory mechanism that return internal enviroment to optimum when there is a fluction

Postive feedback: a fluctuation trigger changes that result in an even greater devation from the normal level

62
Q

Outline the general stages involved in negative feedback

A
  1. Receptors detect deviation
  2. Effects respond to countereact the change - bringling levels back to normal
  3. Receptors detect that conditions have returned to normal
63
Q

During exercise, the body experiences changes in the blood pH and the core body temp.

Explain why it is necessary for homeostatic mechanims to resist these changes

A
64
Q

Why is multiple negative feedback mechanism neccessary

A

Having more than one mechanism gives more control over changes in your internal enviroment than just having one.

  • This means u can actively increase or decrease a level so it returns to normal
  • If you have one all you can do is turn it on or off. You’d only be able to actively change a level in one direction so it returns to normal
  • Slower response and less control
65
Q

What is postivie feedback useful for?

A

To rapidly activate something e.g blood clot after an injury.

  1. Platelets become activated and release a chemical - this triggers more platelets to be activated.
  2. Platelets very quickly form a bloody clot at the injury site
  3. The process ends with negative feeback, when th ebody detects the bloody clot has been formed.
66
Q

What type of feedback involves hypethermia?

A

Postive feedback:

  1. Hypothermia is low body temp below 35
  2. It happens when heats lost from the body quicker than it can be produced.
  3. The brain fails do function properly and shivering stops - making temp fall even more.
  4. Postive feedback takes body temp further away from normal level, and it continues to decrease unless action is taken

if this doesn’t occur hypertmia leads to death.

67
Q

Why isn’t postive feedback involved in homeostasis?

A

This is because it doesn’t keep your internal enviroment stable.

68
Q

What is the concentration of flucose in the blood?

What is it monitered by?

A

90 mg per 100cm3

It is monitered by cells in the pancreas

69
Q

When does blood glucose levels rise and fall?

A

Rise = after eating food containing food containing carbohydrates

Falls = after exercise as more glucose is used for respirating to release energy

69
Q

When does blood glucose levels rise and fall?

A

Rise = after eating food containing food containing carbohydrates

Falls = after exercise as more glucose is used for respirating to release energy

70
Q

What 2 hromones are used to control blood glucose concentration?

A

Insulin and Glucagon

71
Q

Function of Alpha and Beta cells in the control of bloody glucose concentration

A

Beta cells = Secret insulin into blood

Alpha cells = secrete glucagon into the bloody

A-Level AQA Biology (77 decks)

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