homeostasis questions 1 Flashcards
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.
1) release of glucagon
2) leads to formation of glucose in liver cells
3) From non-carbohydrates / amino acids / fatty acids. (gluconeogensis)
(b)
Use information from the graph to suggest how blood glucose concentration is controlled in the mutant mice, compared with the normal mice.
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.
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.
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.
Synapses are unidirectional. Explain how acetylcholine contributes to a synapse being unidirectional.
1 - acetylcholine released from presynaptic side
2- Receptors in postsynaptic (side) / binds on postsynaptic (side)
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.
Glycogen to glucose / glycogenolysis by activating enzymes;
Gluconeogenesis
The control of water balance in the body involves negative feedback. (i) Describe what is meant by negative feedback.
where a change triggers a response which reduces the effect of a change.
Water is removed from the body via the kidneys. Give two other ways in which
water is removed from the body
- sweating
- breathing
Name the part of the brain which acts as the coordinator in the control of water balance.
hypothalamus
From which gland is ADH released?
pituitary
Use the information given to explain how ADH increases the movement of water from the lumen of the collecting duct into the blood.
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
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?
excessive urination / drinking / diluted urine / thirst
Suggest why diabetes insipidus is more common in males.
because males only have one X chromosome / do not have Y chromosome;
a single copy of the recessive allele will be expressed
A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how.
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
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.
- Deviation of a value from norm initiates corrective mechanisms;
- fluctuations in plasma glucose concentration detected by hypothalmus /islet cells in pancreas;
- initial decrease, no food given (in plasma glucose) stimulates (increased) secretion of glucagon;
- increases (in plasma glucose) stimulate (increased) secretion of insulin from β cells as secretors;
- correct ref. to interconversion of glycogen / glucose / increased /
decreased uptake of glucose by cells (as appropriate) / correct ref to change in membrane permeability
How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency?
- Body temp. / 37 °C is optimum temp for enzymes;
- excess heat denatures enzymes / alters tertiary structure / alters shape
of active site / enzyme so substrate cannot bind / eq; - reactions cease / slowed;
- too little reduces kinetic energy of molecules / moleculesmove more
slowly; - fewer collisions / fewer ES complexes formed
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.
hypothalamus
B- When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why.
1- water potential of blood decreases
2 - water moves from osmoreceptor into blood via osmosis
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.
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.
e - give two factors that could affect the concentration of creatinine in
the blood.
muscle / body mass
exercise.
Give two ways in which people with type 1 diabetes control their blood glucose concentration.
- treat with insulin injection
- (Control) diet/control sugar intake
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.
- usually type 2 produce insulin
- Cells / receptors less sensitive / responsive (to insulin)
- (Treated / controlled by) diet / exercise
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.
- Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;
- Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein)
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.
1.negative feedback stops desire
- (This) limits amount eaten / stops eating;
- Prevents / reduces risk of obesity / too much energy intake
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.
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;
People with type 1 diabetes are described as being insulin-dependent. Suggest why they are described as insulin-dependent.
Treatment requires person receiving insulin (in some way)
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.
- fewer abnormal receptors
- (So) fewer (glucose) transport proteins;
- (So) less glucose can enter (cells);
- (So) less glucose converted to glycogen
- (So, without treatment) blood glucose concentration not lowered when high / above normal
During a glucose tolerance test the person remains at rest. Why is it important that the person remains at rest?
- movement uses muscles
- Movement increases (rate of) respiration
- respiration uses glucose
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.
(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;
Adrenaline binds to receptors in the plasma membranes of liver cells. Explain how this causes the blood glucose concentration to increase.
1.Adenylate cyclase activated / cAMP produced / second messenger produced;
2. Activates enzyme(s) (in cell so) glycogenolysis / gluconeogenesis occurs / glycogenesis inhibited
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.
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;
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.
(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
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.
Broken down by enzymes / digested / denatured (by pH) too large to be absorbed;
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.
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
Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.
Lactose has a different shape / structure;
Does not fit / bind to active site of enzyme / sucrase
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.
Hydrostatic pressure / description of pressure / description of how pressure generated
Causes ultrafiltration
Explain how urea is concentrated in the filtrate.
reabsorption of water by osmosis
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions
Describe how ultrafiltration produces glomerular filtrate.
- Blood pressure / hydrostatic pressure;
- Small molecules / named example;
- Pass through basement membrane / basement membrane acts as filter;
- Protein too large to go through / large so stays behind;
- Presence of pores in capillaries / presence of podocytes;
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.
- high concentration of glucose in the blood
- High concentration in tubule / in filtrate;
- Reabsorbed by facilitated diffusion / active transport;
- Requires proteins / carriers;
- These are working at maximum rate / are saturated;
- Not all glucose is reabsorbed / some is lost in urine
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.
- More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
- By osmosis;
- From collecting duct / from end of second convoluted tubule;
- Due to longer loop of Henle;
5.Sodium / chloride ions absorbed from filtrate in ascending limb; - Gradient established in medulla / concentration of ions increases down
medulla
The urine of a non-diabetic person does not contain glucose. Explain why
Leaves the blood at kidney;
Taken back into blood / reabsorbed (from kidney tubule)
A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how.
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;
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.
Enzyme has specific shape to active site / active site has specific tertiary structure;
Only glucose fits / has complementary structure / can form ES complex
If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.
Glucose in filtrate lowers water potential
Lower Ψ gradient / less difference in Ψ filtrate
Less water reabsorbed by osmosis;
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.
- glomerulus /bowmans capsule
- Basement membrane;
- Proteins are large (molecules) / proteins cannot normally pass through
filter / proteins
can only pass through if filter damaged;
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.
metabolic water / from respiration;
allow condensation reactions. Ignore ‘oxidation’.
aerobic / use of oxygen
Many diabetics require regular injections of insulin. Describe how bacteria can be genetically modified to produce human insulin.
- Use m-RNA + reverse transcriptase to produce gene / (c)-DNA; 2. Restriction enzyme to cut open plasmid;
- Add sticky ends (to insulin gene and to plasmid)
OR Allow: - 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
Name two polymers present in mammals and fish that contain nitrogen.
protein
haemoglobin
Describe how urea is removed from the blood.
hydrostatic pressure / description of pressure;
causes ultrafiltration at Bowman’s capsule / glomeruli / renal capsule; through basement membrane;
enabled by small size of urea molecule
Explain how the cells of the collecting duct are able to absorb water from the filtrate through the protein channels in their plasma membranes.
More negative / lower WP (inside tubule cells)
Water enters / moves by diffusion / osmosis
Which hormone causes the decrease in the water content in the distal convoluted tubule?
ADH
Explain the change in the amount of glucose. (from the graph)
Reabsorption / passes back into blood / tissue fluid; By active transport
Explain the shape of the curve for sodium ions in the loop of Henle (from the graph)
(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
Where does ultrafiltration occur?
bowmans capsule
Give one component of the blood which is not normally present in the filtrate.
blood cells
Reabsorption of glucose takes place in the proximal tubule. Explain how the cells of the proximal tubule are adapted for this function.
(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)
