homeostasis exam questions Flashcards
Scientists investigated the control of blood glucose concentration in mice. They kept a group of
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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.
___________________________________________________________________ (2)
glucose formed in the liver
from non carbohydrate stores
The scientists then investigated mice with a mutation that prevents their liver cells making
glucose. They kept a group of these mice without food for 48 hours. After 48 hours, the
mean blood glucose concentrations of the mutant mice and the normal mice were the
same.
The scientists investigated how blood glucose concentration is controlled in these mutant
mice. An enzyme required for synthesis of glucose is coded for by a gene called PCK1.
The scientists measured the mean amount of mRNA produced from this gene in cells from
the kidneys and intestines of normal mice and mutant mice. They did this with mice that
had previously been without food for 48 hours.
The scientists’ results are shown in the graph.
(b)
Use information from the graph to suggest how blood glucose concentration is controlled
inthe mutant mice, compared with the normal mice.
-mutant mice make a lot of the enzyme
-use kidney to make glucose
-normal mice use liver cells
The scientists performed statistical tests on the data shown in the graph, to see whetherthe
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. (2)
signfiicant difference
probability of being due to chance is less than 1%
In this investigation, the higher the concentration of sucrose in a rat’s mouth, the higher
thefrequency of nerve impulses from each taste receptor to the brain.
If rats are given very high concentrations of sucrose solution to drink, the refractory period
makes it impossible for information about the differences in concentration to reach the
brain. Explain why. (2)
limits frequency of impulses
when threshold reached, no further increase in information
The release of a substance called dopamine in some areas of the brain increases the desire to
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eat.
Scientists measured increases in the release of dopamine in the brains of rats given different
concentrations of sucrose solution to drink.
Sucrose stimulates taste receptors on the tongue.
The graph shows their results. Each point is the result for one rat.
(a)
The scientists concluded that drinking a sucrose solution had a positive feedback effect on
the rats’ desire to eat.
How do these data support this conclusion?
positive correlation between surcose concentration and dopamine release
–dopamine makes them want to eat more
-positive feedback as eating makes them want to eat even more
In humans, when the stomach starts to become full of food, receptors in the wall of
thestomach are stimulated. This leads to negative feedback on the desire to eat. Suggest
why this negative feedback is important. (3)
-no desire to eat
-eating stops
-reduces risk of obesity
Describe the evidence from the graph that curve A represents the volume of gastric
juice produced by nervous stimulation.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
Complete the table to show the percentage of gastric juice produced by
nervousstimulation at the times shown.
Ti me after meal / ho urs
1
2
Percentage of gastric
juice produced by
nervous stimulation
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(2)
(1)
(Total 5 marks)
Technicians in a hospital laboratory tested urine and blood samples from a girl with
5 diabetes at intervals over a one-year period. Each time the technicians tested her urine, they also
measured her blood glucose concentration. Their results are shown in the graph.
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(i)
The girl who took part in this investigation was being successfully treated with
insulin.The graph shows that on some occasions, the concentration of glucose in her
blood was very high. Suggest why.
_________________________________________________________(2)
just eaten a meal
containing carbohydrates
Use the graph to evaluate the use of the urine test as a measure of blood
glucoseconcentration. (3)
positive correlation
range of values for one urine concentration
colour is subjective
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. (2)
glycogen to glucose
gluconeogenesis
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The control of water balance in the body involves negative feedback.
(i)
(ii)
Describe what is meant by negative feedback. (1)
change triggers response which reduces effect of change
Water is removed from the body via the kidneys. Give two other ways in which water
is removed from the body (2)
breathing
sweating
Use the information given to explain how ADH increases the movement of water
fromthe lumen of the collecting duct into the blood. (3)
ADH causes vesicles containing aquaporins to be inserted into membrane
water enters cell through aquaporins
via osmosis
to capillery
via intestitial fluid
How does maintaining a constant body temperature allow metabolic reactions in cells to
proceed with maximum efficiency? (5)
-body temperature is optimum for enzymes
-too much heat will denature enzymes
-less kinetic energy
-fewer enzyme substrate complexes formed
reaction slowed
Cross-channel swimmers may suffer from muscle fatigue during which the
contractionmechanism is disrupted. One factor thought to contribute to muscle fatigue is a
decrease in the availability of calcium ions within muscle fibres. Explain how a decrease in
the availability of calcium ions could disrupt the contraction mechanism in muscles. (3)
tropomyosin protein not moved from actin binding site
myosin head does not bind to acitn
no cross bridges formed
calcium ions do not activate ATPase
energy not released from ATP.
Furosemide and CVT are drugs used to remove excess fluid from the body. Scientists investigated the effect of these drugs on the volume of urine produced by human volunteers. The scientists used the following method.
* They divided volunteers into three groups, A, B and C at random.
* They gave all the volunteers the same food for 3 days.
* After 3 days, they gave the volunteers in group A a tablet containing furosemide, the volunteers in group B a tablet containing CVT and the volunteers in group C a placebo (a tablet that did not contain either drug).
* They then found the mean volume of urine produced by each group in the 4 hours after taking the tablets.
Some of the results the scientists obtained are shown in Table 1.
A value of ± 2 standard deviations from the mean includes over 95% of the data.
Table 1
Group Mean volume of urine produced in 4 hours / cm3 (± 2 standard deviations)
A
(furosemide) 1980
(± 152)
B
(CVT) 1201
(± 119)
C
(placebo) 312
(± 57)
(a) All the volunteers were given the same food for 3 days.
Suggest and explain one reason why they were given the same food.
would affect water potential
woudl affect volume of urine produced.
