Download Biology 12 – Practice Final Exam 5) Describe the changes that occur

Biology 12 – Practice Final Exam
5) Describe the changes that occur in the blood entering the hepatic vein as the body responds to
increased stimulation by the sympathetic nervous system. (3 marks)
The sympathetic nervous system would be triggered by the release of norepinephrine from the
sympathetic neurons of the autonomic nervous system. This would cause the release of adrenaline
from the adrenal medulla therefore there would be a higher [adrenaline] in the blood. Sympathetic
stimulation is involved in the “fight or flight” response therefore the digestive system would be
inhibited. As a result, there would be a lower [amino acid] and [nucleotide] in the blood since
digestion would be reduced and less of these nutrients would have been absorbed. Even though
less glucose would have been absorbed by the small intestine into the blood, since sympathetic
stimulation would cause the liver to convert glycogen to glucose, the [glucose] would be greater
following stimulation. Sympathetic stimulation would also cause an increase in the blood pressure
and blood velocity since the heart has sped up. Since the bronchi have dilated, more O2 would have
been delivered to the organs and the cells would be able to perform more cellular respiration. Since
the hepatic vein is coming from the liver to the posterior vena cava, it would contain a higher
[CO2], [HbCO2], [HHb] and [HCO3-] since it carries deoxygenated blood.
6) Figure 1 below shows a cross-section through the small intestine and Figure 2 an enlarged
longitudinal section through a single villus.
Using these diagrams, outline three ways in which the structure of the small intestine is related to
its function of absorbing food. Provide two additional examples of structures that are modified to
best perform their functions. (7 marks)
The following are the modifications of the small intestine that assist its function of absorbing food.
(1) The villus intestinal wall has many folds to increase the surface area: volume ratio. (2) The
surface of the villus is close to blood vessels so nutrients like glucose, amino acids and nucleotides
can easily diffuse. (3) The surface of the villus is close to the lacteal so lipids can be easily
absorbed. (4) The greater surface area is directly related to a greater rate of diffusion therefore a
more rapid absorption of nutrients occurs. (5) The villus wall consists of only a single layer of
cells therefore the diffusion of nutrients is easier. Although there would be microvilli on the
epithelial cells lining the villus, since these are not visible in the diagrams, they cannot be accepted
as a possible modification.
There are many additional examples of structures that are modified to best perform their functions.
The following is just a few.
The stomach is an excellent organ to show how its structure assists its function. The stomach’s
walls are elastic, which will allow it to expand to help it in its function of storing food. The
stomach’s walls are also muscular, which will allow it to contract to help it in its function of
mechanically digesting food by churning. The mechanical digestion of food will increase the
surface area of the food, therefore allowing chemical digestion to occur faster. The stomach’s
walls also contain gastric glands, which produce gastric juice to allow it to chemically digest
protein. The gastric glands produce: (1) pepsinogen which is an inactive precursor of pepsin that
digests protein into amino acids; (2) hydrochloric acid (HCl) which makes the stomach acidic to
kill bacteria and activate pepsinogen; and (3) mucus which coats the stomach walls to protect the
stomach from the pepsin and HCl.
The alveoli have the following modifications to allow them to best exchange gases during external
respiration in the lungs. (1) There are millions of alveoli, which drastically increases the surface
area found inside the lungs, therefore allowing the diffusion of O2 and CO2 to occur rapidly. (2)
The alveoli are coated in surfactant (a lipoprotein) which reduces their surface tension so that they
do not collapse and stick together. (3) The alveoli are coated in water, which provides a medium
through which the O2 and CO2 diffuse. (4) The alveoli are highly vascularized; therefore the
diffusion of O2 and CO2 occurs at a higher rate since there is an extensive blood supply of
pulmonary capillaries surrounding each alveolus. (5) The alveolar walls are only one cell thick
which allows for easier diffusion of the O2 and CO2. (6) The alveolar walls contain stretch
receptors that will trigger exhalation once the alveoli are adequately expanded.
Other excellent examples of the structure/function relationship would include arteries, veins,
capillaries, the heart, the nephron and layers inside the kidney and sperm.
Use the following diagram to answer question 7
7) A student set up the experiment illustrated above and kept it at 37°C. After five minutes, the
distilled water in the beaker was tested and found to contain a sugar but no starch.
a) What had occurred inside the tube? (1 mark)
Starch is too large of a molecule to cross the membrane, therefore no starch is found in the
beaker. The amylase had digested the starch into maltose and since maltose is a disaccharide, it
is smaller than starch therefore crossed the membrane by diffusion, from the higher [maltose]
found inside the mixture and entered the lower [maltose] found inside the beaker.
b) What statement can you make about the permeability of the membrane? (1 mark)
The membrane is semi-permeable based on the particle size. Smaller particles like maltose can
cross the membrane, while larger particles like starch cannot cross the membrane.
c) An identical experiment was set up and kept at 5°C. After five minutes, how would the amount
of sugar found in the water differ between the two beakers? Explain your answer. (2 marks)
The amount of maltose in the beaker at 5°C would be much lower than the amount of maltose
in the beaker at 37°C. Since particles move slower at a lower temperature, the rate of diffusion
out of the mixture and into the beaker would be much lower than at the higher temperature. As
the temperature decreases, the amount of kinetic energy possessed by each particle decreases
and as a result, movement slows.
d) Explain what would have taken place if the membrane was only permeable to water. (3 marks)
If the membrane were only permeable to water, the maltose would not have been able to leave
the mixture and enter the beaker to reach a dynamic equilibrium. Since the maltose cannot
cross the membrane to solve its [] gradient problem, water would move by osmosis from the
low [maltose] concentration in the beaker into the high [maltose] found inside the mixture.
Water always moves from low [solute] to high [solute] in an attempt to reach a dynamic
equilibrium. As a result, the water/mixture level would increase inside the tube and the [solute]
inside the mixture would decrease since it is being diluted by the addition of extra water.
Although the water level in the beaker would decrease, since there is no solute inside the
beaker, its [] would not increase as water left it, therefore a dynamic equilibrium could never be
reached and the water/mixture would most likely reach the top of the tube and overflow.
e) Explain how identical results could have been reached in two minutes. (4 marks)
Faster results could have been achieved by the following. (1) An increase in temperature
(higher than 37°C) would increase the kinetic energy possessed by the particles which would
allow the particles to move faster and increase the rate of diffusion. (2) An increase in the
[starch] or (3) an increase in [amylase] in the mixture would increase the number of collisions
between the starch substrate and amylase enzyme, therefore more active sites would be filled
and the hydrolysis reaction of starch ! maltose would be increased. The increase in [maltose]
in the mixture would increase the [] gradient between the mixture and the beaker, therefore
increasing the rate of diffusion.
8) Explain, using specific examples, why the liver is considered to be one of the most important
organs for the proper functioning of all of the body systems. (12 marks)
Digestive system:
• The liver produces bile which emulsifies fat into smaller fat droplets so that the chemical
digestion of fat by lipase occurs more efficiently
• The pancreas releases insulin which converts glucose to glycogen after eating. Once produced,
the glycogen is stored in the liver. When the levels of glucose decrease in the blood, the
pancreas releases glucagon which converts the glycogen into glucose. The glucose is then
released from the liver into the bloodstream.
Circulatory system:
• The liver produces blood proteins like albumin, fibrinogen and prothrombin which help regulate
blood pressure, pH and enable the blood to clot
• The liver detoxifies the blood by removing poisonous substances such as drugs and alchohol
• The liver converts hemoglobin in worn-out red blood cells to bilirubin and biliverdin
Urinary/Excretory system:
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The liver produces bile pigments (bilirubin and biliverdin) which are added to feces
The liver excretes nitrogenous wastes like ammonia (NH3), urea and uric acid
The liver produces urea from the deamination of amino acids
The liver detoxifies the blood, and the poisons leave the body through the excretory system
Respiratory system:
• The liver combines the CO2 produced during cellular respiration with the NH3 produced by
deamination, to form the nitrogenous waste product urea
Nervous system:
• Without the liver maintaining the levels of glucose in the body, the neurons would not have the
ATP required to establish resting potential and recover by using the Na+/K+ pump
Reproductive system:
• Since the venous duct bypasses the fetal liver, the mother’s liver is critical for purifying the
blood of any poisonous substances so that they don’t get passed into the fetal blood by the
placenta and umbilical vein
• Without the liver maintaining the levels of glucose in the body, the many cellular processes
(spermatogenesis, oogenesis, etc.) occurring in the male and female reproductive systems would
not have the ATP required to occur