homeostasis questions 1

Question 1

Scientists investigated the control of blood glucose concentration in mice. They kept a group of normal mice without food for 48 hours. After 48 hours, the blood glucose concentrations of the mice were the same as at the start of the experiment.
(a) Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours.

Answer 1

1) release of glucagon
2) leads to formation of glucose in liver cells
3) From non-carbohydrates / amino acids / fatty acids. (gluconeogensis)

Question 2

(b)
Use information from the graph to suggest how blood glucose concentration is controlled in the mutant mice, compared with the normal mice.

Answer 2

1.Mutant mice (mRNA suggests) make a lot of (the) enzyme;
2. Mutant mice use kidney / intestine (cells) to make glucose;
3. Normal mice do this much less / normal mice use liver cells.

Question 3

The scientists performed statistical tests on the data shown in the graph, to see whether the differences in the amount of mRNA in cells from normal and mutant mice were significant. Both the probability values they obtained were p<0.01.
Explain what this means about the differences in the amounts of mRNA produced.

Answer 3

1 - Differences significant
2 - Probability of difference being due to chance less than 0.01 / 1% / 1 in 100 / probability of difference not being due to chance more than 0.99 / 99% / 99 in 100.

Question 4

Synapses are unidirectional. Explain how acetylcholine contributes to a synapse being unidirectional.

Answer 4

1 - acetylcholine released from presynaptic side
2- Receptors in postsynaptic (side) / binds on postsynaptic (side)

Question 5

Diabetic people who do not control their blood glucose concentration may become unconscious and go into a coma. A doctor may inject a diabetic person who is in a coma with glucagon. Explain how the glucagon would affect the person’s blood glucose concentration.

Answer 5

Glycogen to glucose / glycogenolysis by activating enzymes;
Gluconeogenesis

Question 6

The control of water balance in the body involves negative feedback. (i) Describe what is meant by negative feedback.

Answer 6

where a change triggers a response which reduces the effect of a change.

Question 7

Water is removed from the body via the kidneys. Give two other ways in which
water is removed from the body

Answer 7

• sweating
• breathing

Question 8

Name the part of the brain which acts as the coordinator in the control of water balance.

Answer 8

hypothalamus

Question 9

From which gland is ADH released?

Answer 9

pituitary

Question 10

Use the information given to explain how ADH increases the movement of water from the lumen of the collecting duct into the blood.

Answer 10

1- ADH causes vesicles containing aquaporins / aquaporins to be inserted into membrane / collecting duct wall / plasma;
where a change triggers a response which reduces the effect of a change;
2- water enters cell through aquaporins;
3- by osmosis / diffusion / down a water potential gradient;
4 - (from cell) to capillary;
5- via interstitial fluid

Question 11

The gene for the ADH receptor proteins is found on the X chromosome. One allele of this gene causes a non-functioning receptor protein to be made. This allele is recessive and is one cause of the condition called diabetes insipidus.
(i) What would be the most obvious symptom of diabetes insipidus?

Answer 11

excessive urination / drinking / diluted urine / thirst

Question 12

Suggest why diabetes insipidus is more common in males.

Answer 12

because males only have one X chromosome / do not have Y chromosome;
a single copy of the recessive allele will be expressed

Question 13

A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how.

Answer 13

recessive alleles can be carried by individuals without showing effects / dominant allele always expressed;
organism that are carriers more likely to reproduce / affected organism less likely to reproduce;
therefore recessive alleles are more likely to be passed on / dominant alleles less likely to be passed on

Question 14

The graph shows changes in plasma glucose concentration that occurred in a person who went without food for some time.
Use evidence from the graph to explain the role of negative feedback in the control of plasma glucose concentration.

Answer 14

1. Deviation of a value from norm initiates corrective mechanisms;
2. fluctuations in plasma glucose concentration detected by hypothalmus /islet cells in pancreas;
3. initial decrease, no food given (in plasma glucose) stimulates (increased) secretion of glucagon;
4. increases (in plasma glucose) stimulate (increased) secretion of insulin from β cells as secretors;
5. correct ref. to interconversion of glycogen / glucose / increased /
   decreased uptake of glucose by cells (as appropriate) / correct ref to change in membrane permeability

Question 15

How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency?

Answer 15

1. Body temp. / 37 °C is optimum temp for enzymes;
2. excess heat denatures enzymes / alters tertiary structure / alters shape
   of active site / enzyme so substrate cannot bind / eq;
3. reactions cease / slowed;
4. too little reduces kinetic energy of molecules / moleculesmove more
   slowly;
5. fewer collisions / fewer ES complexes formed

Question 16

Osmoreceptors are specialised cells that respond to changes in the water potential of the blood. Give the location of osmoreceptors in the body of a mammal.

Answer 16

hypothalamus

Question 17

B- When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why.

Answer 17

1- water potential of blood decreases
2 - water moves from osmoreceptor into blood via osmosis

Question 18

c -
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.

Answer 18

1.cells to water is increased
2. More water absorbed from / leaves distal tubule / collecting duct;
3. Smaller volume of urine;
4. Urine becomes more concentrated.

Question 19

e - give two factors that could affect the concentration of creatinine in
the blood.

Answer 19

muscle / body mass
exercise.

Question 20

Give two ways in which people with type 1 diabetes control their blood glucose concentration.

Answer 20

1. treat with insulin injection
2. (Control) diet/control sugar intake

Question 21

Each year, a few people with type I diabetes are given a pancreas transplant. Pancreas transplants are not used to treat people with type II diabetes.
Give two reasons why pancreas transplants are not used for the treatment of type II diabetes.

Answer 21

1. usually type 2 produce insulin
2. Cells / receptors less sensitive / responsive (to insulin)
3. (Treated / controlled by) diet / exercise

Question 22

When insulin binds to receptors on liver cells, it leads to the formation of glycogen from glucose. This lowers the concentration of glucose in liver cells.
Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration.

Answer 22

1. Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;
2. Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein)

Question 23

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.

Answer 23

1.negative feedback stops desire

2. (This) limits amount eaten / stops eating;
3. Prevents / reduces risk of obesity / too much energy intake

Question 24

Before the glucometer was available, diabetics used test strips to measure the concentration of glucose in their urine as a means of measuring their blood glucose concentration.
Give two reasons why this method of testing urine would not give an accurate measurement of blood glucose concentration.

Answer 24

Only measures glucose concentration above normal / above 170 (mg 100 cm−3) (in blood);

170 (mg 100 cm−3) is an average figure / concentration for loss to urine varies (between people);

Difficult to match colour against chart / colour match is subjective;

Question 25

People with type 1 diabetes are described as being insulin-dependent. Suggest why they are described as insulin-dependent.

Answer 25

Treatment requires person receiving insulin (in some way)

Question 26

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.

Answer 26

1. fewer abnormal receptors
2. (So) fewer (glucose) transport proteins;
3. (So) less glucose can enter (cells);
4. (So) less glucose converted to glycogen
5. (So, without treatment) blood glucose concentration not lowered when high / above normal

Question 27

During a glucose tolerance test the person remains at rest. Why is it important that the person remains at rest?

Answer 27

1. movement uses muscles
2. Movement increases (rate of) respiration
3. respiration uses glucose

Question 28

Give three differences between the method used by the researcher to obtain the results in Figure 2 and the method doctors use to carry out a glucose tolerance test.

Answer 28

(Concentration) measured over 6 hours / 6+ hours / longer v measured at 2 hours;
(After intake) regular monitoring / several measurements v only measured once / at 2 hours only;
No fasting v fasting before test;

Question 29

Adrenaline binds to receptors in the plasma membranes of liver cells. Explain how this causes the blood glucose concentration to increase.

Answer 29

1.Adenylate cyclase activated / cAMP produced / second messenger produced;
2. Activates enzyme(s) (in cell so) glycogenolysis / gluconeogenesis occurs / glycogenesis inhibited

Question 30

A glucose biosensor is an instrument used to measure glucose concentration. It contains an enzyme called glucose oxidase.
(a)
A glucose biosensor detects only glucose. Use your knowledge of the way in which enzymes work to explain why.

Answer 30

Enzyme / active site has a (specific) tertiary structure;
Only glucose has correct shape / is complementary / will bind / fit to active site;
(Forming) enzyme-substrate complex;

Question 31

It is better to use a biosensor than the Benedict’s test to measure the concentration of glucose in a sample of blood. Suggest two reasons why.

Answer 31

(Only detects glucose whereas) Benedict’s detects (all) reducing sugars / named examples;
Provides a reading / is quantitative / Benedict’s only provides a colour / doesn’t measure concentration / is qualitative / semiquantitative

Question 32

Diabetes mellitus is a disease that can lead to an increase in blood glucose concentration. Some diabetics need insulin injections. Insulin is a protein so it cannot be taken orally. Suggest why insulin cannot be taken orally.

Answer 32

Broken down by enzymes / digested / denatured (by pH) too large to be absorbed;

Question 33

A drug company produced a new type of insulin. Scientists from the company carried out a trial in which they gave this new type of insulin to rats. They reported that the results of this trial on rats were positive. A newspaper stated that diabetics would benefit from this new drug. Suggest two reasons why this statement should be viewed with caution.

Answer 33

Study not carried out on humans / only carried out on rats; Long-term / side effects not known;
Scientists have vested interest;
Study should be repeated / further studies / sample size not known

Question 34

Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.

Answer 34

Lactose has a different shape / structure;
Does not fit / bind to active site of enzyme / sucrase

Question 35

In a mammal, urea is removed from the blood by the kidneys and concentrated in the filtrate.
(a) Describe how urea is removed from the blood.

Answer 35

Hydrostatic pressure / description of pressure / description of how pressure generated
Causes ultrafiltration

Question 36

Explain how urea is concentrated in the filtrate.

Answer 36

reabsorption of water by osmosis
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions

Question 37

Describe how ultrafiltration produces glomerular filtrate.

Answer 37

1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;

Question 38

Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin.

Answer 38

1. high concentration of glucose in the blood
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed / some is lost in urine

Question 39

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.

Answer 39

1. More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
   5.Sodium / chloride ions absorbed from filtrate in ascending limb;
5. Gradient established in medulla / concentration of ions increases down
   medulla

Question 40

The urine of a non-diabetic person does not contain glucose. Explain why

Answer 40

Leaves the blood at kidney;
Taken back into blood / reabsorbed (from kidney tubule)

Question 41

A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how.

Answer 41

Large amount / high concentration of glucose in filtrate;
Cannot all be reabsorbed / 1st convoluted tube too short to reabsorb all of glucose / saturation of carriers;

Question 42

A test for glucose in urine uses immobilised enzymes on a plastic test strip. One of these enzymes is glucose oxidase. Explain why the test strip detects glucose and no other substance.

Answer 42

Enzyme has specific shape to active site / active site has specific tertiary structure;
Only glucose fits / has complementary structure / can form ES complex

Question 43

If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.

Answer 43

Glucose in filtrate lowers water potential

Lower Ψ gradient / less difference in Ψ filtrate

Less water reabsorbed by osmosis;

Question 44

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? Explain your answer.

Answer 44

1. glomerulus /bowmans capsule
2. Basement membrane;
3. Proteins are large (molecules) / proteins cannot normally pass through
   filter / proteins
   can only pass through if filter damaged;

Question 45

The kangaroo rat is a small desert mammal. It takes in very little water in its food and it rarely drinks. Its core body temperature is 38 °C.
The kangaroo rat takes in some water by feeding and drinking. Describe another method by which the kangaroo rat could obtain water.

Answer 45

metabolic water / from respiration;
allow condensation reactions. Ignore ‘oxidation’.
aerobic / use of oxygen

Question 46

Many diabetics require regular injections of insulin. Describe how bacteria can be genetically modified to produce human insulin.

Answer 46

1. Use m-RNA + reverse transcriptase to produce gene / (c)-DNA; 2. Restriction enzyme to cut open plasmid;
2. Add sticky ends (to insulin gene and to plasmid)
   OR Allow:
3. Cut out insulin gene / cut open plasmid with restriction enzyme; 2. Use same restriction enzyme on second DNA;
   Use ligase to join 2 DNA molecules; Modified plasmid taken up by bacteria

Question 47

Name two polymers present in mammals and fish that contain nitrogen.

Answer 47

protein
haemoglobin

Question 48

Describe how urea is removed from the blood.

Answer 48

hydrostatic pressure / description of pressure;
causes ultrafiltration at Bowman’s capsule / glomeruli / renal capsule; through basement membrane;
enabled by small size of urea molecule

Question 49

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

Answer 49

More negative / lower WP (inside tubule cells)
Water enters / moves by diffusion / osmosis

Question 50

Which hormone causes the decrease in the water content in the distal convoluted tubule?

Answer 50

ADH

Question 51

Explain the change in the amount of glucose. (from the graph)

Answer 51

Reabsorption / passes back into blood / tissue fluid; By active transport

Question 52

Explain the shape of the curve for sodium ions in the loop of Henle (from the graph)

Answer 52

(sodium) ions pumped out of ascending limb;
Water passes out of descending limb (into high concentration in tissue fluid / interstitial fluid);
Some sodium ions re-enter descending loop (by diffusion);
High concentration at base of loop / some ions diffuse out near base increasing concentration outside loop

Question 53

Where does ultrafiltration occur?

Answer 53

bowmans capsule

Question 54

Give one component of the blood which is not normally present in the filtrate.

Answer 54

blood cells

Question 55

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

Answer 55

(Many) mitochondria provide ATP / energy for active transport;
(Many) carrier proteins for active transport / channel proteins for facilitated diffusion;
Microvilli / brush border provide large surface area (for absorption)