SvS Biology 2001
Maintaining a Balance: End of Module test
Sample Answers
Your task is to reflect on the questions, and the sample answers below, and make comparisons between these and the responses of whoever's end of module test that you have been given to mark. You must make a fair and unbiased judgment of their answers, and allocate marks according to your opinions of their worth. Following on from this, you will be arranged in a small group to discuss the answers given, and justify the way that you allocated the marks. Justifiable modifications may be compromised at this time.
When blood flows through body tissues, its carbon dioxide
concentration, oxygen concentration, urea concentration and glucose
concentration are altered.
(a) O2 is low in the pulmonary artery, and
CO2 is comparatively high. This is because
the body's active tissues have depleted the O2
in the process of respiration, causing CO2
production. When the blood reaches the alveoli in the lungs, the diffusion
gradient causes O2 to be increased, and CO2
levels to decrease. CO2 is expired in the
process of exhalation.
(b) As glucose travels through skeletal muscles, it is actively uptaken from
the blood in order for the muscles to be able to carry out the process of
respiration in the mitochondria. This process releases energy in the form of
ATP, which allows the cells to function. The uptake of glucose by the cell
is assisted by insulin. Blood glucose levels therefore fall as a product.
(c) Urea concentration in the blood will be higher in the hepatic vein than
in the hepatic portal vein. In the hepatic portal vein, high levels of amino
acids can often be found as a product of digestion. When this occurs, the
blood entering the liver undergoes a process known as deamination, which
causes the excess amino acids (the building blocks of proteins) to be broken
down, thus forming urea. So blood leaving the liver via the hepatic vein
becomes higher in urea. This level remains high until blood undergoes the
process of filtration in the kidneys.
(d) (i) CO2 is
carried in blood as carbaminohaemoglobin, where it combines with the
haemoglobin of the erythrocytes (red blood cells), in a small percentage.
The majority of CO2 is actually dissolved
in plasma proteins.
(ii) Mammalians carry out bodily
respiration to maintain a homeostatic balance of CO2
levels in the bloodstream. This process is characterized by:
* Intercostal muscles and diaphragm contract
* Volume of chest cavity increases
* Pressure in chest cavity decreases
* Inhalation results
To complete the removal of CO2 from the
bloodstream, the mammal then exhales, characterized by:
* Intercostal muscles and diaphragm relax
* Volume of chest cavity decreases
* Pressure in chest cavity increases
* air is forced out (exhalation)
When the body undertakes heavy exercise, a greater amount of
CO2 is produced, along with other waste
products of cellular metabolism, such as urea and water through the process
of cellular respiration mainly carried out by mitochondria and partially
within the cytoplasm of cells. The brain is responsible for detecting the
increase in carbon dioxide levels of the blood. This is achieved by the
respiratory centre of the brain which acts by detecting an increase in CO2
levels and by neuronal means triggering the increased rate of bodily
respiration, which allows the CO2 to be
removed and O2 uptaken. As CO2
levels begin to fall, the rate of bodily respiration also falls.
(a) The concentration of urea will
increase when the filtrate becomes urine.
(b) This is primarily because water has been reabsorbed
back into the bloodstream as a product of active and passive mechanisms.
Salts are actively reabsorbed from the filtrate, which leads to the passive
movement of water from the convoluted tubules into the renal veins.
(c) ADH is a hormone which is transmitted chemically
through blood circulation and when it reaches the target tissues of the
collecting ducts, it causes them to dilate thus leading to higher amounts of
water being removed from the filtrate and returned to the bloodstream. The
product of this is that the urine becomes more concentrated. Aldosterone is
the hormone which is responsible for increasing the reabsorption of salts.
Because this impacts upon the amount of water passively reabsorbed by
osmosis, it is responsible for assisting in the control of blood pressure.
(a) Red blood cells (erythrocytes), White
blood cells (leukocytes), and Platelets (thrombocytes)
(b) Red blood cells increase the transportation of gases
such as O2
and CO2
around the body by having a biconcave shape which presents a high surface
area for transportation. The haemoglobin contained within the RBC has a high
affinity for O2
because of its iron content. If water only were to be used, the O2
transportation would be limited to the amount of O2
that could be readily dissolved in water - which is much lower.
White blood cells provide the
ability for the body to defend against foreign pathogens, by specific and
non specific means. They can produce a phagocytic response or induce
antibody production. Water cannot defend against invading pathogens.
Platelets are responsible for
causing blood clotting by reacting with chemical proteins dissolved in the
blood to produce a network of fibres that will seal off open wounds and
therefore prevent the entry of further pathogens into the internal
environment. Water is unable to seal the leaks which could result from
insect bites, cuts, scrapes and other abrasions or lesions.
(c) Artificial blood would mean that donor antigen types
would not have to be determined in order for a person to receive a
transfusion. The manufactured blood would consequentially be known to be
free from disease causing pathogens that could otherwise be transmitted from
host to host via transfusions.
(a) Neuronal and Endocrinal systems
control the homeostasis of the human body.
(b) Maintenance of blood glucose levels is attributed to
the secretion of insulin by the pancreas of the body, and is therefore
controlled by an endocrinal system. When glucose levels are high in the
bloodstream, insulin is secreted, and this causes the increased permeability
of cells to glucose as well as promotes the conversion of glucose to
glycogen in the liver (where it is temporarily stored) If glucose levels in
the body fall below the threshold, then glucagon is secreted by the
pancreas, which causes glycogen to be released into the bloodstream as
glucose. The result of these two hormones is that the amount of blood
glucose can be regulated in a feedback cycle.
(a) Plants in arid environments need to
conserve water, so CO2
uptake in the nighttime would reduce the amount of water lost through the
stomates than if they were otherwise open during the day.
(b) If plant cells do not maintain a specific level of
water in their cells, they become flaccid. This impacts upon the turgidity
of the plant, and leads to structural problems where the plant cells no
longer exert a force upon each other and it has no system of support.
(a) Increase in temperature may result in
the increased rate of evaporation from the freshwater environment. This
would cause the accumulation of salts in the water that remained, and
present an osmotic problem for the fish which would then have to struggle to
keep its intra and extracellular osmotic balance.
(b) Silt has the capacity to remain suspended in the
water, and as such it can become clogged in the fish's gill filaments. This
would vastly reduce the surface area for diffusion, and consequently its
ability to uptake oxygen from the water.
(c) Sewerage released into the water contains toxins which
would be inadvertently ingested by fish, as well as passively uptaken
through membranes. These toxins would place undue stress on the organism's
liver and kidneys, leading to organ failure and the death of the animal.
(a) Enzymes can be categorised as either
anabolic (synthetic, or "build up" reactions) or catabolic (break
down reactions). They act to speed up the reaction in which they
participate.
(b) Rates of reactions of enzymes are affected by:
surface area of the substrate
temperature
pH of the environment
(c) substrate: glucose being respired by yeast enzymes to
form CO2
and water.
factor investigated:
temperature's effect on the rate of respiration
In this experiment, 5% glucose solution was made and yeast enzymes added to
the solution. The number of bubbles of CO2
produced were recorded every 30 seconds, and then the temperature of the
solution was raised by 10 degrees Celcius until 90 degrees was
reached.
controls used: blue litmus water
to determine that the acidic CO2
was being produced, and not some other gaseous precipitate; a water bath to
ensure the even distribution of temperature, the increase of the temperature
by 10 degree intervals.
results obtained: as temperature
increased, so did the rate of respiration until 70 degrees, at which point
the number of bubbles (indicating the rate of respiration) rapidly
decreased. By 100 degrees, no more CO2
was being produced.
(a) Active transport occurs when energy is
expended in the uptake or removal of a substance from within a cell or
tissue. This occurs whenever a substance must be accumulated or removed
against the concentration gradient that exists within the cell. An example
of this is when aldosterone is secreted in humans, it causes the
reabsorption of salts from the glomerular filtrate against the concentration
gradient.
(b) Testing the hypothesis in this manner is
inappropriate, as it is difficult to determine whether or not the
concentration of potassium ions was a result of the intake or removal of
potassium, or the result of a passive movement of water. The results
indicate that the Chara are osmoregulators. In order to conclusively suggest
that potassium ions were moving across the membrane and not water, the
students could incorporate a measurement of the volume of water (by weight)
inside and outside of the Chara and compare initial weights with final ones.
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S. van Strien