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A Level Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What does Homeostasis mean?

A

The regulation of the internal environment of an organism

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2
Q

What is meant by the term internal environment?

A

The composition of blood and bodily fluids

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3
Q

What are the factors that are controlled by homeostatic mechanisms in mammals?

A
  1. Body temperature
  2. Body water content
  3. Blood pH
  4. Blood glucose concentration
  5. Metabolic waste products such as urea
  6. The respiratory gases oxygen and carbon dioxide
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4
Q

What is the role of a homeostatic systems?

What components should it have in order to fulfil this role?

A
  • They must be able to detect changes and bring about an appropriate response
  • Receptors - To detect the internal and external stimuli
  • Central control and coordinating mechanisms
  • Effectors - To bring about the response
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5
Q

What is negative feedback?

What happens to a particular factor as a result of negative feedback?

A

A process in which a change in some parameter brings about processes which move its level back towards the normal
It does’t stay constant, but rather fluctuates between closely controlled values.

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6
Q

What coordinates the Homeostatic mechanisms?

A
  1. The Nervous system: electrical impulses along with nerve cells
  2. The Endocrine system and hormones that travel in the blood for long distance cell signalling
  3. it may also be a combination of both
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7
Q

What coordinates the following factors?

  1. Adjusting heat loss by changing skin blood flow
  2. Blood glucose concentration
  3. Body water content
A
  1. Nerve impulses
  2. Hormones
  3. ADH which is secreted by the pituitary gland
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8
Q

What happens to excess amino acids in the body?
What is formed in this process?
What can one of these products do?

A

They undergo a process of deamination in the liver.
A Keto acid and ammonia.
The Keto acid can be used as a source of energy or converted to various other compounds including glycogen or fat.

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9
Q

What is the role of the urea cycle?
What is the high level reaction of the urea cycle?
What happens to the final products?

A

Ammonia is highly toxic to cells and in mammals, is immediately converted into urea, through a cycle of reactions in the liver.

Ammonia + carbon dioxide -> urea + water

Urea is carried in the blood stream from the liver and is filtered out of the blood in the kidneys and lost in urine.

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10
Q

What are the main layers of the kidney?

What are the main blood vessels in for the kidney?

A

A tough capsule on the outside, the cortex, a medulla and then the pelvis.
The renal artery supplies the kidney with blood while the renal vein returns blood back to the circulatory system

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11
Q

What is the ureter?

What is the urethra?

A

The ureter conveys urine, formed in the kidney, from the kidney to the bladder.
a tube that carries urine from the bladder to the outside

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12
Q

What is the functional unit of the kidney?

Describe its structure and prevalence

A

The Nephron - It is a microscopic tubule with associated blood vessels
Each kidney has thousands of nephrons

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13
Q

What are the 3 features of tissue fluid that influence cell activities?
How can their deviations affect the organism?

A
  1. Temperature -
    low temperatures slow down metabolic reactions
    high temperatures denature proteins
  2. Water potential -
    low water potentials - loss of water may cause metabolic reactions to slow or stop
    high water potentials may cause bursting
  3. Concentration of glucose -
    low glucose deprives the cell of energy
    high glucose affects water potential, which affects metabolism
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14
Q

How is heat in mammals produced and distributed?

A
  1. Heat is generated during respiration
  2. Much of the heat is produced by liver cells
  3. the blood absorbs this heats a spreads it throughout the body.
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15
Q

What regulates the temperature of the body and how does it recognize the deviations?

A
  1. The hypothalamus has thermoreceptor cells that continually monitor the core temperature of the blood flowing through it.
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16
Q

Describe the thermoregulation of the body by the hypothalamus in the heat.

A

Stimuli:

  1. Central thermoreceptors in the hypothalamus and spinal cord detect an increase in blood temperature
  2. Thermoreceptors in the skin, detect an increase in temperature of the surroundings.

Effectors:

  1. Vasodilation - arterioles in the sin dilate
  2. Sweat glands secrete sweat.
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17
Q

Describe the thermoregulation of the body by the hypothalamus in the cold.

A

Stimuli:

  1. Central thermoreceptors in the hypothalamus and spinal cord detect a decrease in blood temperature.
  2. Thermorecptors in the skin detect the decrease in temperature of surroundings.

Effectors:
1, Vasoconstriction - Arterioles in the skin contract
2. Shivering - skeletal muscles contract
3. Hair erector muscles contract to raise hairs
4. adrenal gland secretes adrenaline and the thyroid gland secretes thyroxine, which stimulates the liver to release heat.

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18
Q

Describe the behavioural changes caused by the hypothalamus due to changes in temperature.

A

When it’s cold:
1, Curling up
2. Finding a source of warmth
3. putting on warm clothing

When it’s hot:

  1. Spreading out and resting/lying down
  2. Turning on the fan/air conditioner
  3. Taking cold drinks
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19
Q

Describe the relationship between the hypothalamus and the thyroid gland when the temperature changes.

A
  1. Hypthalamus stimulates the anterior pituitary gland to release TSH
  2. TSH stimulates the thyroid gland to release thyroxine
  3. Thyroxine increases metabolism, so heat is produced in the liver
  4. Reverse happens when the temperature starts to become cold.
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20
Q

What is positive feedback?

A

A process in which a change in some parameter brings about processes that move its level even further in the direction of the change

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21
Q

What is excretion?

A

It is the removal of the unwanted products of metabolism.

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22
Q

What are the main two products excreted from the body?
How are they formed?
How are they excreted?

A
  • Carbon dioxide: produced from aerobic respiration and excreted by gas exchange
  • Urea: Produced by the deamination of excess amino acids and released from the body by urine.
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23
Q

What is deamination?

A

the breakdown of excess amino acids in the liver, by the removal of the amine group; ammonia and eventually, urea are formed from the amine group

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24
Q

Describe the deamination reaction.

What are the products formed?

A

Amino acid -> Keto acid + Ammonia

The hydrogen is removed from the amino acid and ammonia is produced using extra hydrogen.

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25
Q

In addition to urea, what are the other nitrogenous excretory products and how are they formed?

A
  1. creatinine; a nitrogenous excretory substance produced from the breakdown of creatine
  2. Uric acid: a nitrogenous excretory product, made by the breakdown of purines
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26
Q

What is a nephron?

A

A Kidney tubule

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27
Q

What is the Bowman’s capsule?

A

It is the cup-shaped part of the nephron that surrounds the Bowman’s capsule and collects filtrate from the blood.

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28
Q

What is the glomerulus?

A

a group of capillaries within the ‘cup’ of a Bowman’s capsule in the cortex of the kidney.

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29
Q

What is the loop of Henle?

A

The part of the nephron between the proximal and the distal convoluted tubule; sometimes the loop of Henle is long and extends into the medulla of the kidney.

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30
Q

What is the collecting duct?

A

It is the last part of the kidney where water can be reabsorbed back before the urine flows into the ureter.

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31
Q

What is the difference between the afferent and the efferent arteriole?

A

Afferent arteriole: Supplies the glomerulus with blood from the renal artery
Efferent arteriole: leads off to form the capillaries running close to the nephron. the blood leads into the renal vein.

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32
Q

What are the 2 processes in the filtration of blood in the kidney?

A
  1. Ultrafiltration: filtration on a molecular scale e.g. the filtration that occurs as blood flows through capillaries, especially those in glomeruli in the kidney.
  2. Selective reabsorption; movement of certain substances from the filtrate back into the blood in the
    kidney nephron.
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33
Q

Describe the endothelium of the Bowman’s capsule.

A
  1. It is the first cell

2. It has gaps in it - there are far more gaps in it than any other membrane.

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34
Q

What is the basement membrane made of?

What is its role?

A

It is made from collagen and glycoproteins it stops the large protein molecules from going through.

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35
Q

What are podocytes?

What is the role of the podocytes?

A

They are one of the cells that make up the lining of the Bowman’s capsule surrounding the glomerular capillaries.
The gaps between the podocytes are quite large and make it easy for blood plasma to get through from the blood into the capsule.

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36
Q

What are the substances that pass through the Bowman’s capsule?

A
  1. Water
  2. amino acids
  3. glucose
  4. urea
  5. uric acid
  6. creatinine
  7. inorganic ions
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37
Q

What is the glomerular filtration rate?

What is the general value in humans?

A

The rate at which the filtrate passes from the glomerular capillaries into the Bowman’s capillaries in the Kidneys.
125 cm3min-1

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38
Q

What are the main 2 factors that affect how water moves from the glomerulus into the Bowman’s capsule?
How is it adapted for these 2 factors?

A

Water potential and pressure

The high pressure is built up by the afferent arteriole being wider than the efferent arteriole.

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39
Q

Where do most of the reabsorption take place?

What cells make this up?

A

The Proximal convoluted tubule

Cuboidal epithelial cells

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40
Q

What are the adaptations of the cuboidal epithelial cells?

A
  1. Microvilli
  2. Tight junctions that hold the cells together so that fluid cannot pass between the cells - all the substance absorbed must go through the cells
  3. Many mitochondria provide energy for the sodium-potassium pump in the outer membrane of the cells.
  4. co-transporter proteins in the membrane facing the lumen.
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41
Q

How does the blood coming out of the glomerulus differ from the blood entering the glomerulus?

A
  • it has much less plasma in it than usual

- it has lost much of its water and many of the ions and other small molecules.

42
Q

What are the substances that are reabsorbed by the proximal convoluted tubule?

A
  1. Glucose
  2. Amino acids
  3. Vitamins
  4. Sodium
  5. Chloride ions
43
Q

Describe how water is reabsorbed by the proximal convoluted tubule.

A

It moves down the water potential gradient created by the movement of the solutes from the filtrate.

44
Q

How does the loop of Henle allow for the maximum water to be retained in the body?

A

They create a very high concentration of sodium and chloride ions in the tissue fluid of the medulla.
it allows lots of water to be reabsorbed from the fluid in the collecting duct.

45
Q

how does the descending and ascending limb of the loop of Henle differ in its permeability to water?

A

The descending limb is permeable t water while the ascending limb is not.

46
Q

What happens in the ascending limb of the loop of Henle?

A

The cells that line this loop actively pump out sodium and chlorine into the tissue fluid.
This decreases the water potential in the tissue fluid and increases the water potential in the ascending limb.

47
Q

What happens in the descending loop of the loop of Henle

A

Water from the filtrate moves into the tissue fluid

so that by the time that the filtrate has reached the bottom, the filtrate is more concentrated.

48
Q

What is a counter-current multiplier?

A

an arrangement in which fluid in adjacent tubes flows in opposite directions, allowing relatively large differences in concentration to be built up.

49
Q

Explain how urea enters the collecting tube and how it further allows the loss of water in it.

A

The tissue fluid contains the urea at a high concentration which was lost and this diffuses into the collecting duct.
Water can also further move out of the loop of Henle.

50
Q

What is antidiuretic hormone (ADH) ?

A

a hormone secreted from the pituitary gland that increases water reabsorption in the kidneys and therefore reduces water loss in urine.

51
Q

Describe the regulation of ions in the distal convoluted tubule.

A

Sodium ions are pumped from the fluid in the tubule into the tissue fluid, from where they pass into the blood. Potassium is transported into the tubule.

52
Q

What is osmoregulation?

What main organs carry out this function?

A
  • It is the control of water potential in the body fluids

- it involves the hypothalamus, posterior pituitary gland and kidneys.

53
Q

What detects the decrease in water potential of the blood?

Where is it located?

A

Osmorecpetors: a receptor cell that is sensitive to the water potential of the blood
In the hypothalamus.

54
Q

What is ADH?
What is it made of?
What is its full form?
What is its function?

A
  • Peptide hormone
  • Nice amino acids
  • Antidiuretic hormone
  • It ensures that maximum reabsorption happens by the kidneys
55
Q

What happens when the osmoreceptors detect a decrease in water potential?

A

They send out nerve impulses that terminate at the posterior pituitary gland.
This stimulates the release of ADH

56
Q

What are the target cell for ADH?

How does it do this?

A
  • The cells on the collecting duct

- It makes them more permeable to water than usual.

57
Q

How is the collecting duct wall made permeable to water?

A
  • ADH molecules bind to receptor proteins on the cell surface membrane.
  • Enzymes are activated inside the cells
  • The cells contain ready-made vesicles that have many aquaporins in their membranes.
  • These fuse with the membrane and increase the permeability of it to water.
58
Q

Why is the homeostatic control of the blood glucose concentration important?

A

It if gets below 80 mg/100cm3 then there won’t be enough glucose for respiration.
If it gets too high, above 120mg/100 cm3, the metabolism may be affected.

59
Q

What is glucagon?

When is glucagon secreted?

A
  • It is a small peptide hormone that brings about an increase in the blood glucose level.
  • Glucagon is secreted when the concentration is low.
60
Q

What is the mode of action of glucagon?

How does It increase the concentration of glucose?

A
  1. Glucagon binds to the receptor molecule on the surface of the membrane.
  2. G protein is activated
  3. Enzyme activated converts ATP to cyclic AMP (second messenger)
  4. Cyclic AMP binds to Kinase enzymes, which carries out photophosphorylation of enzymes to activate them, initiating a cascade.
  5. Glycogen phosphorylase at the end when activated catalyses the breakdown of glycogen to glucose.
  6. Concentration of glucose increases.
61
Q

What is insulin?

A

It is a small peptide hormone that reduces blood glucose level.

62
Q

How does insulin bring about a response?

Why does it have to do it this way?

A

By acting as a signalling molecule that brings about the response by the use of intercellular messengers.
Because it cannot directly pass through the membrane.

63
Q

How does insulin decrease glucose concentration?

What is the mechanism?

A
  • It increases the rate at which glucose is absorbed
  • Insulin stimulates the GLUT molecules to move to the cell surface membrane and it fuses with it. GLUT facilitates the movement of glucose into the cell.
64
Q

What are the different types of GLUT molecules?

A

GLUT 4: Muscle cells
GLUT 1: Brian cells
GLUT 2: Liver cells

65
Q

How does insulin prevent glucose from passing through the membrane?

A

It stimulates the activation of glucokinase which phosphorylates glucose. Phosphorylated glucose cannot pass through the transporter in the membrane.

66
Q

What are the enzymes that are stimulated by insulin?

A
  1. Phosphofructokinase

2. Glycogen Synthase

67
Q

What are the 2 hormones involved in the homeostatic control of blood glucose concentration?
What are the cells that secrete it?

A

Alpha cells -> Glucose

Beta cells -> Insulin

68
Q

What does adrenaline do in the regulation of blood glucose concentration?

A

It binds to different receptors on the surface of liver cells. This will end up in the break down of glycogen -> glucose.
During exercise, it breaks down glycogen to glucose to provide energy for the muscle cells.

69
Q

What is gluconeogenesis?

A

formation of glucose in the liver from noncarbohydrate sources such as amino acids, pyruvate, lactate and glycerol

70
Q

Where are insulin and glucagon secreted?

A

They are secreted in the endocrine tissue in the pancreas in the cells called the islets of Langerhans

71
Q

Describe the negative feedback of the control of blood glucose conc when it is high

A
  1. Alpha and Beta cells detect the rise in the concentration
  2. Effectors:
    - Liver cells respond to less glucagon
    - Liver muscle and fat cells respond to more insulin - reduced uptake of glucose
72
Q

Describe the negative feedback of the control of blood glucose conc when it is low

A
  1. Alpha and Beta cells detect the fall in the concentration
  2. Effectors:-
    - Liver cells respond more to glycogen by breaking down glucose
    - Liver muscle and fat cells respond to less insulin
73
Q

What are the 2 types of Diabetes Mellitus?

A
  1. Type 1 diabetes: Insulin dependant diabetes

2. Type 2 diabetes: Non-insulin-dependant diabetes

74
Q

Why does Type 1 diabetes occur?

A

The pancreas is incapable of making sufficient insulin

  • Deficiency of the gene that codes for insulin
  • Attack of Beta cells by the immune system
75
Q

What do type 1 diabetes patients have to do?

A

Must take insulin injections frequently

Carefully controlled diet is required.

76
Q

Why does Type 2 diabetes occur?

Why does it occur?

A
  • The liver the and muscle cells do not respond well to insulin
  • Diet and obesity
77
Q

What are the solutions for type 2 diabetes?

A

Diet and exercise to manage blood glucose

New developments allow for a genetically engineered glucose to be given

78
Q

What are the symptoms of diabetes Mellitus?

A
  1. Carb concentration stays high after meals
  2. If the blood glucose conc becomes very high, it may cause glucose in the urine
  3. Constant hunger and thirst because water and salts are lost too
  4. Diabetic coma - dehydration, salt loss and low pH
79
Q

How are Keto acids produced in diabetic patients?

A

Glucose is not taken up by the cells, so the cells ends up metabolising fats and proteins. This produces Keto acids/ Ketones.

80
Q

What causes a diabetic coma?

A

It happens when he blood glucose becomes very low as glycogen is not there to be metabolised, because it was not synthesised when glucose was available.

81
Q

What does glucose in the urine mean?

A

It suggests diabetes because the blood glucose concentration has exceed the renal threshold, it could not be filtered from the the PCT.

82
Q

What does protein in the urine suggest?

A

It indicates a diseases in the glomeruli or a kidney infection
sometimes, protein is an indicator of high blood pressure which is an indicator of heart disease.

83
Q

What are the 2 enzymes in glucose test strips?

A
  1. Glucose oxidase
  2. Glucose peroxidase

They are immobilised on a test strip

84
Q

What is the role of glucose oxidase on a glucose test strip?

A

it catalyses a reaction in which glucose is oxidised to gluconolacctone. Hydrogen peroxide is also produced.

85
Q

What does glucose peroxidase on a glucose test strip do?

A

Glucose peroxidase catalyses a reaction between hydrogen peroxide and a chemical on the pad that causes a brown ppt to form.
The more glucose there is, the darker the colour on the pad will be.

86
Q

What is the stomata?

A

It is the hole between the two guard cells

87
Q

What are guard cells?

A

They are sausages shaped epidermal cells found with another, in pair bounding a stoma and controlling its opening

88
Q

Why does a plant have to regulate the CO2?

A

because it affects the rate of photosynthesis.

89
Q

Describe the rhythmic opening and closing of the stomata?

A

They open in the day and let carbon dioxide and water out and to let oxygen in.
The closure of the stomata in the night reduces the rate of transpiration in the night.

90
Q

What do the stomata open in response to?

A
  1. Increasing light intensity

2. Low carbon dioxide concentration in the air spaces of the leaf

91
Q

What do the stomata close in response to?

A
  1. Darkness
  2. High carbon dioxide concentration in the air spaces of the leaf
  3. Low humidity
  4. High temperature
  5. Water stress - when transpiration is high or little water is absorbed from the roots.
92
Q

How do guard cells open and close?

A

Guard cells open when they gain water and close when they lose water to become flaccid

93
Q

What is the electrochemical gradient of a stomata?

A

It is a gradient across a cell surface membrane that involves both a difference in concentrations of ions and a potential difference

94
Q

How the electrochemical gradient build up for the closing of the stomata?

A
  1. ATP pumps actively pump out H+ ions out of the guard cells
  2. The decrease in concentration of H+ ions inside the guard cells causes K+ to move into the cell
    - because the H+ made the inside negative and the outside positive - they diffuse down the electrochemical gradient
    - they are also diffusing down their concentration gradients
95
Q

What allows guard cells to open?

A

The build up of solute potential causes water to move in by osmosis through aquaporins. The turbot pressure builds up and the guard cells open.

96
Q

What is the structure and role of cellulose in the guard cell?

A

Cellulose microfibrils are arranged as hoops and thickened in the guard cells
This makes the guard cells to increase in length and not in diameter
Since the guard cells are joint to one end, it causes the it to curve and open the pore.

97
Q

How do guards cells become flaccid?

A
  1. Water leaves
  2. Hydrogen ion pump proteins stop
  3. Potassium stops moving inside
  4. Water potential in the opposite direction
  5. Stomata closes
98
Q

Why do stomata close?

A

When there is a risk of losing lots of water. Otherwise, closure of stomata means reduced CO2 and reduced rate of photosynthesis

99
Q

Where is abscisic acid present?

A

In almost all cells that have chloroplast or amyloplasts

100
Q

What is the role of abscisic acid?

A

it is a stress hormone - coordinates responses to stress

Drought conditions - high ABA causes stomata to close reducing water loss

101
Q

How does ABA work?

A
  1. Binds to ABA receptors
  2. Inhibits protein pumps
  3. Stimulates the movement of calcium ions
    - acts as a secondary messenger that opens the channel proteins which allows K+ to move out
    - stimulates the closing of channel proteins that allow K+ to move in.

A Level Biology (6 decks)

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