Homeostasis 2

Question 1

How is carbohydrate transported through the human bloodstream?

Answer 1

In the form of glucose solution in the blood plasma

Question 2

What is glucose converted into?

Answer 2

• Glycogen (a polysaccharide made of many glucose molecules linked together that acts as a glucose store in liver and muscles cells) , a large insoluble molecules made up of many glucose units linked together by 1-4 glycosidic bonds with 1-6 branching points
• Glycogen is a short term energy store that is found in liver and muscle cells and is easily converted to glucose

Question 3

What is dangerous about blood glucose concentration dropping?

Answer 3

• Cells may not have enough glucose of respiration and may be unable to carry out their normal activities
• This is especially important for cells that can respire only glucose, such as brain cells

Question 4

What is dangerous about blood glucose concentration rising?

Answer 4

-Disrupts normal behaviour of cells

Question 5

By what is the homeostatic control of blood glucose carried out by? What are they?

Answer 5

• Two hormones secreted by endocrine tissue in the pancreas
• This tissue consists of groups of cells know as the islets of Langerhans (a groups of cell in the pancreas which secrete insulin and glucagon) which are scattered through the pancreas
• The islets contain alpha and beta cells

Question 6

What do alpha cells secrete?

Answer 6

• Glucagon, a small peptide hormone secreted by the alpha cells in the islets of Langerhans in the pancreas that brings about an increase in the blood glucose level
• A cell in the islets of Langerhans in the pancreas that senses when blood glucose levels are low and secretes glucagon in response

Question 7

What do beta cells secrete?

Answer 7

• Insulin, a small entire hormone secreted by beta cells in the islets of Langerhans in the pancreas that reduces blood glucose levels
• A cells in the islets of Langerhans in the pancreas that senses when blood glucose levels are high and secretes insulin in response

Question 8

What do the alpha and beta cells act as?

Answer 8

• The receptors and the central control for this homeostatic mechanism
• The hormones glucagon and insulin coordinate the actions of the effectors

Question 9

What happens after you eat a meal of high carbohydrate?

Answer 9

1. Glucose from the digested food is absorbed from the small intestine and pass into the blood
2. As this blood flows through the pancreas the alpha and beta cells detect the increase in glucose concentration
3. The alpha cells respond by stopping the secretion of glucagon
4. The beta cells respond by secreting insulin into the blood plasma
5. The insulin is carried to all parts of the body, in the blood

Question 10

Describe insulin

Answer 10

• A signalling molecule
• As a protein it cannot pass through the cell membranes to stimulate the mechanisms within the cell directly
• Instead insulin binds to a receptor in the cell surface membrane and affects the cell indirectly through the mediation of intracellular messengers

Question 11

Describe the control mechanisms for concentration of glucose in the blood for low blood glucose concentration

Answer 11

1. Receptors: Alpha and beta cells in the the islets detect fall in blood glucose
2. Effectors: liver cells respond to more glucagon by breaking down glycogen into glucose
3. Liver, muscle and fat cells respond to less insulin and so reduced uptake of glucose

Question 12

Describe the control mechanisms for concentration of glucose in the blood for high blood glucose concentration

Answer 12

1. Receptors: alpha and beta cells in the islets of Langerhans detect rise in blood glucose
2. Effector: liver cells respond to less glucagon, no glycogen breakdown
3. Liver, muscle and fat cells respond to more insulin - increased uptake and use of glucose

Question 13

Where are insulin receptors?

Answer 13

Liver, muscle cells and adipose (fat storage) tissue

Question 14

What does insulin do?

Answer 14

• Stimulates cells with these receptors to increase the rate at which they absorb glucose from the blood, convert it into glycogen and use it in respiration
• This results in a decrease in the concentration of glucose in the blood

Question 15

How can glucose enter cells?

Answer 15

1. Through transporter proteins known as GLUT and there are several different types of GLUT proteins
2. Muscle cells have the type GLUT4
3. Normally GLUT proteins are kept in the cytoplasm in the same way as the aqauporins in collecting duct cells
4. When insulin molecules bind to receptors on muscle cells, the vesicles with GLUT4 proteins are moved to the CSM and fuse with it
5. GLUT4 proteins facilitate the movement of glucose into the cells
   - Brain cells have GLUT1 proteins and liver cells have GLUT2 proteins, whcihbare always in the CSM and their distribution is not altered by insulin

Question 16

What does insulin also stimulate?

Answer 16

1. The activation of enzyme glucokinase, which phosphorylates glucose
2. This traps glucose inside cells, because phosphorylated glucose cannot pass thorough the transporters in the CSM
3. Insulin also stimulates the activation of two other enzymes, phosphofuctokinsase and glycogen synthase, which together add glucose molecules to glycogen
4. This increases the size of the glycogen granules inside the cells

Question 17

Summarise how insulin increases the permeability of muscle cells to glucose by stimulating the movement of vesicles with GLUT4 to the CSM

Answer 17

1. Insulin binds to a receptor in the cell surface membrane
2. The receptor signals to the cell and makes vesicles carrying glucose transporter proteins merge with the cell surface membrane
3. Glucose can now diffuse into the cell down its concentration gradient

Question 18

Describe the binding of glucagon to a receptor

Answer 18

1. Glucagon binds to a membrane receptor in CSM of liver cells
2. Activation of G protein and then enzyme
3. Active enzyme produces cyclic AMP (a second messenger) from ATP
4. Cyclic AMP activates protein kinase to activate an enzyme cascade
   - Kinase enzymes activate enzymes by adding phosphate groups to them in phosphorylation and this enzyme cascade amplifies the original signal from glucagon
5. Enzyme cascade leads to activation of many molecules of glycogen phosphorylase that break down glycogen to glucose

Question 19

What does glucagon stimulate?

Answer 19

The activation of glycogen phosphorylase enzymes in liver cells through the action of cyclic AMP

Question 20

How does glycogen phosphorylase act?

Answer 20

1. It is at the end of the enzyme cascade: when activated it catalyses the breakdown of glycogen to glucose
2. Does this by removing glucose units from the numerous ‘ends’ of glycogen
3. This increases the concentration of glucose inside the cell sot hat it diffuses out through GLUT2 transporter proteins into the blood

Question 21

What is glucose made from? What is this process?

Answer 21

1. Amino acids and lipids
2. Gluconeogenesis (formation of glucose in the liver from the non carbohydrate sources such s amino acids, pyruvate, lactate and glycerol)

Question 22

What happens in a decrease in blood glucose concentration?

Answer 22

1. A decrease in blood glucose concentration is detected by alpha and beta cells
   - The alpha cells respond by secreting glucagon
   - The beta cells respond by stopping the secretion of glucose
2. The decrease in the concentration of insulin in the blood reduces the rates of uptake and use of glucose by liver and muscle cells
3. Uptake still continues but at a lower rate
4. Glucagon binds to different receptor molecules in the cell surface membrane of liver cells

Question 23

What happens as a result of glucagon excretion?

Answer 23

1. The liver realises extra glucose to increase the concentration in the blood
2. Muscle cells do not have receptors for glucagon and so do not respond to it

Question 24

What sort of system is glucagon and insulin?

Answer 24

Negative feedback system

Question 25

Why does blood glucose concentration never remain constant?

Answer 25

1. Inevitable time delay between. change in the blood glucose concentration and the onset of actions to correct it
2. Adrenaline increases concentration of blood glucose by binding to different receptors on the surface of liver cells that a activate the same enzyme cascade and ;had to the breakdown of glycogen by glycogen phosphorylase
3. Adrenaline also Stimulation the breakdown of glycogen stores in muscles during exercise
4. The glucose produced remains in the muscle cells where it is needed for respiration

Question 26

What is insulation dependent diabetes?

Answer 26

• Type 1
• Pancreas unable to secrete sufficient insulin
• Due to deficiency in gene that codes for production of insulin or an attack on beta cells by person’s won immune system
• Usually begins in early life

Question 27

What is non-insulin-dependnent diabetes?

Answer 27

• Type 2
• Pancreas does secrete insulin but the liver and muscles cells do not respond properly to it
• Often begins relatively late in life and associated with diet and obesity

Question 28

What are the symptoms of diabetes?

Answer 28

1. After a carbohydrate meal, glucose absorbed into the blood and concentration increases and stays high

Question 29

What are the symptoms of diabetes?

Answer 29

1. After a carbohydrate meal, glucose absorbed into the blood and concentration increases and stays high
2. Normally there is no glucose in urine but if the glucose concentration in the blood becomes very high, the kidney cannot reabsorb all the glucose, so that some passes out in the urine
3. Extra water and salts accompany this glucose and the Epson, consequently feels extremely hungry and thirsty

Question 30

Describe the uptake of glucose in a diabetic person

Answer 30

1. Uptake of glucose into cells is slow, even when there is plenty of glucose in the blood
2. Therefore cells lack glucose and metabolise fast and proteins as an alternative energy spruces
3. This can lead to a build up of keto-acids
4. These are produced when the body switches to metabolising fast and they decrease the blood pH
5. The combination of dehydration, salt loss and low blood pH can cause coma in extreme stituations

Question 31

Why between meals the blood glucose contraption of a person with untreated diabetes decrease steeply?

Answer 31

1. There is no glycogen to mobilise, as it was not stored when there was plenty of glucose
2. Coma may result, because of a lack of glucose for respiration

Question 32

How do people manage diabetes?

Answer 32

1. Type 1: receive regular injections of insulin and take blood samples to check that insulin is effective, carefully controlled diet and mini pumps
2. Type 2: rarely need injections, diet and regular and frequent exercise to keep blood glucose within normal limits
   - Diabetics now recieve insulin made by genetically engineered cells

Question 33

Why do people use urine analysis?

Answer 33

1. Easier to collect urine sample than blood sample and can give early indication of health problems
2. Presence of glucose and ketones in urine indicates that a person may have diabetes

Question 34

What happens if the blood glucose concentration above the renal threshold?

Answer 34

• Not all the glucose is reabsorbed from the filtrate in the proximal convoluted tubule of the kidney
• Some present in the urine

Question 35

What happens if presence of protein in urine?

Answer 35

• Problem with kidneys
• As the few proteins they pass through are reabsorbed by endocytosis in the proximal convoluted tubule, broken down and the amino acids absorbed into the blood
• Short term presence in high fever, pregnancy or vigorous exercise
• Large quantity in the long term ,ay be disease affecting the glomeruli or kidney infection
• Protein in the urine also associated with high blood pressure, which is a risk factor in heart diesase

Question 36

What can dipsticks be used for?

Answer 36

Dipsticks, also known as test strips used to test urine for pH, glucose, ketones and proteins

Question 37

What do dipsticks detecting glucose contain?

Answer 37

1. Glucose oxidase (an enzyme that coverts glucose and oxygen to gluconolactone and hydrogen peroxide), peroxidase
2. These two enzymes are immobilised on a small pad at one end of stick
3. Pad immersed inuring and if glucose present, glucose oxidase reaction which glucose is oxidised into gluconolactone
4. Hydrogen peroxide is also produced and peroxidase catalyses the reaction between hydrogen peroxide and colourless chemical in pad to form a brown compound
5. The resulting colour of the pad is matched against a colour chart
6. The chart shows the colours that indicate different concentration fo glucose
7. The more glucose present the darker the colour

Question 38

What is the problem with urine tests?

Answer 38

-Do not indicate the current blood glucose concentration, but rather whether the concentration was higher than the renal threshold in the period of time while urine was collecting the bladder

Question 39

What is a biosensor?

Answer 39

• A device that uses biological material such as na enzyme to measure the concentration of a chemical compound
• Allows people with diabetes to check their blood

Question 40

How does a biosensor work?

Answer 40

1. Pad impregnated with glucose oxidase
2. Small sample of blood placed on pad which is inserted into machine
3. Glucose oxidase catalyses the reaction to produce gluconolactone and at the same time a tiny electric current is detected by an electrode, amplified and read by the meter which produces a reading for blood glucose concentration within seconds
4. The more glucose that is present the greater the current and the greater the reading from the biosensor

Question 41

How do you answer control of blood glucose question?

Answer 41

1. What causes a change in blood sugar?
2. How is blood sugar detected and in which organ?
3. What do alpha and beta cells detect?
4. How do alpha cells respond?
5. How do beta cells respond?
6. How is the change in blood glucose level retuned to normal levels

Question 42

What happen to blood glucose levels after a rich carbohydrate meal?

Answer 42

1. Carbohydrate is digested into glucose and absorbed into the blood
2. Blood flows through the pancreas
3. Alpha and beat cells in the islet of Langerhans detect raised glucose levels
4. Alpha cells respond by stopping the secretion of glucagon
5. Beta cells respond by secreting insulin and insulin is carrier to all parts of the body in the blood
6. Insulin has the following effects:
   - An increased absorption of glucose from the blood into the cells
   - An increase in the rate of glucose in respiration
   - An increase in the rate at which glucose is converted into storage polysaccharide glycogen
7. All the above following processes take glucose out of the blood so lowered the blood glucose levels

Question 43

Describe the changes that occur during a marathon to ensure that the blood glucose concentration does not fall to a dangerous level

Answer 43

1. The fall of glucose is detected by alpha and beta cells in the islets of Langerhans
2. Inhibits the production of insulin
3. Stimulates the secretion of glucagon which is realised into the blood
4. Glucagon binds to receptor on the liver cell (heptacyte)
5. Causes glycogenolysis (glycogen converted into glucose)
6. Glucose enters blood stream

Question 44

What is glycogenolysis?

Answer 44

Conversion of stored glycogen into glucose when blood sugar levels fall

Question 45

What is glycogenesis?

Answer 45

The conversion of glucose into glycogen when blood sugar levels rise

Question 46

What is diabetes?

Answer 46

An illness in which the pancreas does not make sufficient insulin, or where the cells do not respond appropriately to insulin

Question 47

How does insulin affect the activity of cells in the liver?

Answer 47

1. Increases permeability of membrane to glucose/increases glucose uptakes
2. Increase respiration of glucose
3. Increase conversion of glucose to glycogen
4. Increase protein/fat synthesis

Question 48

What are the advantages of using GM insulin?

Answer 48

1. Identical to human insulin
2. More rapid respond than non-human insulin
3. Fewer rejection problems
4. No ethical / moral issues
5. Cheaper to produce in large volume
6. Less risk of transmitting disease/infection
7. Good for people who have developed intolerance/allergic reaction to ANIMAL insulin

Question 49

Why is homeostasis important in plants?

Answer 49

• Important for plants to maintains a consent interval environment as it is for animals e.g. mesophyll cells in leaves require constant supply of carbon dioxide if they are to make best use of light energy for photosynthesis
• Stomata control entry of carbon dioxide into leaves
• Guard cells are highly specialised cells that respond to a wide range of of environmental stimuli, consoling the internal atmosphere of the leaf

Question 50

How do stomata act?

Answer 50

1. Stomata show daily rhythms of opening and closing
2. Even when kept in constant light or constant dark these rhythms persist
3. opening during the day maintains the inwards diffusion of carbon dioxide and outwards diffusion of oxygen
4. Also allows the outward diffusion of water vapour in transpiration
5. The closure of stomata at night when photosynthesis cannot occur reduces the rates of transpiration and conserves water

Question 51

What do stomata open in response to?

Answer 51

1. Increasing light intensity
2. Low carbon dioxide concentration in the air spaces within the leaf
   - When stomata are open, leaves gain carbon dioxide for photosynthesis, but tend to lose much water in transpiration

Question 52

What do stomata close in response to?

Answer 52

1. Darkness
2. High carbon dioxide concentrations in the air spaces in the leaf
3. Low humidity
4. High temperature
5. Water stress, when the supply of water from the roots is limited and/or there are high rates of transpiration

Question 53

What is the disadvantage and advantage of closing?

Answer 53

1. Disadvantage of closing is that during daylight, the supply of carbon dioxide decrease so the rate of photosynthesis decreases
2. The advantage is that water is refined inside the leaf which is important in times of water stress

Question 54

Describe guard cells

Answer 54

1. Each stomatal pore is surrounded by two guard cells

2. Guard cells open when they gain water to become turgid and close when they loose water and become flaccid

Question 55

How do guard cells lose and gain water?

Answer 55

-By osmosis
-A decrease in wp is needed before water can enter the cells by osmosis
1. Brought about by transporter proteins in CSM
2. ATP powered proton pumps in membrane actively transport H+ out of guard cells
3. The decrease in H+ conc inside cells causes channel proteins in CSM to open so that K+ move into cell
4. They do this bc removal of H+ have left inside of cell negatively charged and so K+ which is +ve, is drawn down electrical gradient towards negatively charged region
5. And K+ diffuse town a concentration gradient
(this combined gradient is electrochemical gradient)

Question 56

What do the K+ ions do?

Answer 56

1. The extra K+ ions inside guard cells lower the solute portal, and therefore the wp
2. Therefore wp gradient between outside and inside cell so water moves in by osmosis through aquaportins
3. This increases the turgor of the guard cells, and the stoma opens

Question 57

Describe the structure of guard cells

Answer 57

1. Guard cells have unevenly thickened cell walls
2. The walls adjacent to the pore is very thick, whereas the wall furtherest from the pore is thin
3. Bundles of cellulose microfibrils are arranged as hoops around cells so that, as the cell becomes turgid, these hoops ensure that the cell mostly increases in length and not diameter
4. Since the ends of the two guard cells are joined and the thin outer walls bend more readily than the thick inner walls, the guard cells become curved
5. This opens the pore between the two cells

Question 58

Summarise when stomata are closed

Answer 58

1. ATP powered proton pumps in the cell surface membrane actively transport H+ out of the guard cell
2. The low H+ concentration and negative charge inside the cell causes K+ channels to open. K+ diffuses into eh cell down an electrochemical gradient
3. The high contraption of K+ inside the guard cell lowers the water potential
4. Water moves in by osmosis, down a water potential gradient
5. The entry of water increases the volume of the guard cells, so they expand. The thin outer wall expands most, so the cells curve apart

Question 59

When do stomata close?

Answer 59

1. When hydrogen ion pump proteins stop and potassium ions leave the guard cells and enter neighbouring cells
2. Now wp gradient in opposite direction, so water moves out of guard cells by osmosis and they become fallacid and close the stomata

Question 60

What are the effects of closing the stomata?

Answer 60

1. Reduces uptake of carbon dioxide for photosynthesis and reduces the rate of transpiration
2. As transpiration is used for cooling the plant and also maintaining transpiration stream that supplies water and mineral ions to the leaves
3. Therefore stomatal closure only occurs when reducing the loss of water vapour and observing water is the most important factor

Question 61

When is abscisic acid produced?

Answer 61

In conditions of water stress this hormone ABA produced in plants to stimulate stomatal closure

Question 62

Where is ABA found?

Answer 62

• Wide variety of plants, ferns, mosses, flowering plants
• Can be found in every part of plant and synethsied in almost all cells which have chloroplast or amyloplasts (large starch grains but no chlorophyll)

Question 63

What is role of ABA?

Answer 63

1. Called stress hormone as coordinates response to stress
2. If plant subjected to difficult environmental conditions e.g. very high temp or much reduced water supplies, responds by secreting ABA
3. High conc of ABA stimulates the stomata to close, reducing the loos of water vapour from leaf if in drought conc of ABA in leaves increases 40 times normal amount

Question 64

How does ABA act?

Answer 64

• If ABA applied to lead, stomata close within a few mins
  1. Guard cells have ABA receptors on CSM and when ABA binds with these, it inhibits proton pumps to stop H+ being pumped out
  2. ABA also stimulates movement of Ca2+ ions into cytoplasm through the CSM and the tonoplast (membrane around vaculoe)
  3. Calcium acts as second messenger to activate channel proteins to open to allow negatively charged ions to leave the guard cells
  4. This in turn stimulates the opening of channels proteins which allows the movement of K+ ions out of the cells
  5. At same time Ca2+ stimulate the closure of the channel proteins that allows K+ ions to enter
  6. The loss of ions raises the wp of the cells, water masses out y osmosis, the guard cells become flaccid and the stomata close

Question 65

What is abscisic acid (ABA)?

Answer 65

An inhibitory plant growth regulator that cause closure of stomata in dry conditions

Question 66

What is an electrochemical gradient?

Answer 66

A gradient across a cell surface membrane that involves both a difference in concentrations of ions and a potential difference e.g. the entry of sodium ions into neurones