Download Some Tips – Provincial Exam Biology 12

Some Tips –Exam Biology 12
The following are examples of questions that students did generally less well on:
1. Recombinant DNA:
(see p. 487 – 500)
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(a) Define
(b) Give 2 uses
Students confused DNA and recombinant DNA, or protein synthesis and recombinant DNA
Students described cloning in terms of the entire organism, rather than just the genes
themselves (p. 487 – 488)
Students demonstrated a lack of understanding of the uses of rDNA, especially in relation to
gene therapy (p. 497)
The following notes from Raycroft may help:
“…B. Recombinant DNA
- is composed of DNA segments from at least two
different organisms
Applications for:
- Mass production of Hormones and similar
proteins
- e.g., interferon, insulin
- Safer vaccines
- A vaccine is an injection of a pathogen (e.g., virus )
which is either “dead” or weakened. The body
thinking it has been infected, responds by building
immunity to the that pathogen (by recognizing
identifying surface proteins, called antigens, on the
pathogen’s surface). If the real pathogen invades, the
body is ready to take immediate defensive action —
but in either case a real “virus” is used, with such
technology it is possible to build a carrier molecule
which has the same identifying antigens, but none of
the possible threats of a weakened pathogen over
taking an even weaker immune system, or of an
allergic reaction to the “dead” pathogen.
- Novel molecule synthesis, example,
- Ribozymes (RNA enzymes)
- interrupt transcription during protein synthesis,
and therefor may be used to stop viruses (e.g.,
HIV) from replicating
- Abyzymes
- antibodies with catalytic properties
- Transgenic organisms (GMO – genetically modified
organism)
- an organism which has had foreign genes added to
its own genetic makeup
- for:
- protecting and enhancing plants
- bioremediation, e.g., enhancing the ability of an
waste consuming bacteria to consume larger
amounts of toxic material
- producing chemicals, and processing minerals
- in BC copper has been “smelted” by
bacteria
- Human Gene Therapy
- to replace defective genes with healthy genes
- via:
- Ex Vivo therapy - outside the living organism
- cells are removed, altered, and then reintroduced
- In Vivo therapy - within the living organism
- no cells are removed, instead an agent such as
modified virus is used to “install” new material
into the patient…”
Source: http://southhill.vsb.bc.ca/Departments/BEST/Biology12/
2. DNA Structure: (see p. 36 – 37, 461 – 468)
(a) Describe Structure using words, diagrams, etc.
(b) Describe the process of DNA replication
-
-
Students did not refer to the nucleotide as the basic subunit of nucleic acids
Students referred to amino acids as the subunits of DNA
Students did not know the structure or function of nucleotides
Students did not go into enough detail on the structure of DNA beyond the basic ‘ladder’
configuration
Students did not refer to sugar-phosphate backbone or did not clearly explain its formation,
complementary base pairing, H-bonds, phosphodiester bonds, the bases (A,T,G,C), purines
and pyrimidines, double helix, etc.
Students did not adequately explain the breaking of H-bonds by helicase
Students confused replication with translation, transcription, and rDNA
Students interchanged terms such as replication and transcription, replication and translation
You may also use diagrams to support your explanation:
3. Protein Synthesis:
(see p. 468 – 483)
Purpose of:
(a) ribosome moving along RNA
(b) adenine bonding to thymine
(c) an a.a. bonding to a specific tRNA
(d) formation of peptide bonds
(e) roles of DNA, mRNA, tRNa
-
Students did not demonstrate an in-depth knowledge of the process of protein synthesis
Students could not describe the relationship of point (b) above to the process of protein
synthesis
Students could not clearly differentiate between the roles of mRNA and tRNA
Students thought that tRNA binding to a.a. was a function of tRNA; it is not a function but
part of the process involved in one of its functions
You should know the processes of replication, transcription, and translation
Replication
DNA
transcription
DNA
-
translation
RNA
PROTEIN
You should know the terms:
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
Codon
Anticodon
Gene
Helicase
DNA polymerase
RNA polymerase
Ribosome
rRNA
tRNA
initiation
elongation
termination
3’ and 5’ ends
Complementary
Amino acid
4. Enzymes: (see p. 77 – 82)
a. Effect of temperature on enzymes/proteins
b. Effect of pH on enzymes/proteins
c. Effect of enzyme and substrate concentration on product formation
d. The effect of the addition of heavy metals, acid and of boiling on the rate
of enzyme- catalyzed reactions
e. Interpretation of graphs: When given a graph showing enzyme function,
explain why it has the given shape, do not simply describe the shape of the
graph.
Example:
- Why does the rate of reaction increase initially as the amount of substrate
increases?
- Why does the graph ‘level off’ or plateau at a given substrate concentration?
- Why does it fail to increase or decrease as substrate concentration is further
increased?
- Explain the above, referencing your knowledge of enzymes/proteins.
-
students did not use correct terminology such as denature
students confused pH and temperature effects
You should know that
o
the addition of heavy metals, acid or of boiling slow the rate of enzyme-catalyzed reactions
because they can denature the enzyme; less product is formed as a result because fewer
enzyme-substrate complexes can form due to the conformational change in the enzyme (active
site is changed)
5. Graphs: You should be able to plot a graph using provided data.
a. Example question:
An experiment was conducted to measure the effects of the presence of thyroxin and
temperature on oxygen use in human tissue cells. Two tissue samples were prepared as
shown below.
Sample A: 50 grams of muscle tissue was added to a nutrient solution.
Sample B: 50 grams of muscle tissue was added to a thyroxin and nutrient solution.
Oxygen consumption was measured at various temperatures. The results are shown below.
a) Use the grid provided to graph the data in the table above. Label the x-axis as temperature.
(2 marks: 1 mark for correct scale and labels; 1 mark for plotting and lines)
b) Based on your graph of the data for sample B, predict the amount of oxygen consumed
per hour at 20°C. (1 mark)
Amount of oxygen consumed: __________________
c) Explain the difference observed in the results of samples A and B. (1 mark)
________________________________________________________________________
d) Explain the results for sample B at each of the following temperatures.
(3 marks: 1 mark each)
15°C:____________________________________________________________
35°C:____________________________________________________________
55°C:____________________________________________________________
6. Nervous system:
a. Describe the structure and function of a neuron
b. Describe the action potential and how it is generated
c. Describe the transmission of a nerve impulse through a neuron
d. Describe the reflex arc
e. What is the role or action of the effector in the reflex arc?
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students confused action potential with reflex arc
-
students confused neurons and nephrons
students confused the above with the synaptic cleft or the reflex arc
students described vesicles as objects that were released from the presynaptic cell and moved
across the synapse
students confused impulse and stimulus
students referred to the transmission across a synaptic cleft as electrical rather than chemical
students were not clear about the function of the Na/K pump
students confused neurotransmitter with other substances (eg. CO 2)
students did not demonstrate a thorough understanding of the concepts
students were not clear on the role of the cell body in the neuron
students confused depolarization and repolarization
students confused neurons and nerves, effectors and receptors
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You should know the following steps in the transmission of a nerve impulse:
(a) Along a neuron:
o
o
o
o
o
Depolarization of post-synaptic membrane occurs, OR
Neurotransmitter binds to receptors on post-synaptic membrane
Sodium gates open
Sodium ions diffuse into neuron
Depolarization occurs
o
o
o
o
o
o
o
o
o
o
o
Membrane potential (upswing) is + 40mV
Sodium gates close
Potassium gates open
Potassium ions diffuse out of neuron
Repolarization occurs
Membrane potential (downswing) is -65 mV
Sodium- potassium pumps reestablish resting concentrations of sodium and potassium by
pumping them to appropriate locations (interior and exterior of cell)
Transmission occurs as the above is repeated along consecutive portions of the membrane
Transmission occurs in one direction only because of the refractory period
Myelination of fibres results in more rapid transmission
Nodes of ranvier result in salutatory (jumping) conduction as the action potential jumps from
one node to another, and therefore faster conduction
(b) Across a synapse:
o
o
o
o
o
o
o
o
o
Action potential reaches the presynaptic membrane at the end of the axon
Presynaptic membrane becomes permeable to calcium
Calcium ions diffuse into the presynaptic bulb
Calcium ions interact with microfilaments
Microfilaments pull synaptic vesicles toward the inner surface of the presynaptic membrane
Vesicles fuse with presynaptic membrane and release neurotransmitter into the cleft
Neurotransmitter diffuses across the cleft to postsynaptic membrane
Neurotransmitter binds with a receptor on the postsynaptic membrane
Postsynaptic membrane response may be excitatory or inhibitatory
7. Respiratory System:
a. Describe how the upper respiratory tract is specialized to keep the lungs
free of debris
b. Describe the interaction of the lungs, pleural membranes, ribs and
diaphragm during inhalation
-
students did not read the question correctly and described the process and mechanism of
breathing
students used and described cilia and hairs interchangeably
students could not describe the reduction in pressure that occurs in the lungs
students used the term ‘vacuum’ instead of referring to lower pressure
students were unclear on the function of the pleural membranes
students described gas exchange as occurring across the pleural membranes, and not at the
alveoli
students were unclear about the role of the pleural membranes, ribs, and diaphragm in lung
expansion
students confused the muscles involved in inspiration (intercostals and diaphragm)
8. Hormones:
a. Identify a hormone that responds to blood volume, and how that hormone
would respond to a decrease in blood volume and restore normal volume.
-
students used diagrams of the nephron to help answer the question (good!)
students used abbreviations on the diagram (not good)
students were unclear about the location and function of the distal and proximal convoluted
tubules
students were unclear about the movement of water in response to the hormones
-
You should know the following about hormones and blood volume:
o
o
o
ADH increases the permeability of the collecting duct and distal convoluted tubule to water
Extra fluid is thus absorbed by the peritubular capillaries
This extra fluid increases blood volume
o
o
o
o
ALDOSTERONE causes Na and K ions to be reabsorbed via active transport at the collecting
duct and distal convoluted tubule
The solute concentration of the blood increases due to the increase in ions reabsorbed
Fluid diffuses into the blood due to the increased solute concentration
Blood volume increases
9. Excretory (Urinary) system:
(a) Give the function of the collecting duct
(b) Give the function of the proximal tubule
-
students were generally unclear on the function of the kidneys
students thought that the kidneys filter urine
students thought that the kidneys secrete urine
students had a poor understanding of the functions of the distal and proximal tubules
students did not use appropriate terminology such as ‘selective reabsorption’
-
You should know the following:
o
o
Collecting duct function: to reabsorb water, to carry urine to renal pelvis, to regulate pH, to
regulate blood volume
Proximal tubule function: selective reabsorption of salts, amino acids, and glucose;
reabsorption of water; active transmission of nutrients; movement of filtrate to the loop of
Henle.
10. Biological Molecules:
a. Function of glycogen
b. Function of glucose
-
students confused glycogen and glycerol
students were not clear on the site of glycogen storage in the human body
students were mistaken in stating that glucose regulated blood sugar directly
You should know the following
o
o
o
Glucose acts in cell communication /markers on membranes
Glucose is the building block of starch, cellulose (plant cell wall) and glycogen
Glucose is the source of energy in cellular respiration and the energy released is used to
produce ATP
11. Circulation:
a. Describe the exchange of fluids between the tissues and capillary beds
(see p. 212 – 213)
b. Describe how the sympathetic NS raises blood pressure
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-
students demonstrated a poor understanding of the above
students thought that blood actually left the capillaries instead of just the substances in the
blood
students demonstrated a poor understanding between osmotic and blood pressure
students used inappropriate terminology in describing blood and its contents, such as
‘dissolved gases’ instead of concentrating on CO2 and O2, and ‘new’, ‘old’, ‘fresh’, ‘dirty’,
etc, instead of oxygenated and deoxygenated or arterial and venous blood
students did not adequately explain blood pressure
-
You should know the following
-
o
o
o
o
o
at the arterial end of the capillary bed, blood pressure is higher than the osmotic pressure
water exits the capillary at the arterial end in a filtration process that allows small substances
to exit while retaining large substances (RBC, proteins)
tissue fluid results form this movement of plasma out of the blood, and consists of all plasma
components except proteins
oxygen and nutrients, along with other substances, flow down their concentration gradients
along the length of the capillary (out of blood and into tissues)
waste material (CO2, water) is always more concentrated in tissue fluid than in blood, so it
diffuses into the blood along the length of the capillary (down its concentration gradient)
o
o
o
o
o
o
at the venous end of the capillary bed blood pressure is low and osmotic pressure in high,
resulting in the movement of water into the capillary
not enough water is returned to the blood by osmotic pressure, and the remaining tissue fluid
is carried by the lymphatic vessels and returned to the venous blood at the subclavian veins in
the shoulder region
The sympathetic NS causes the blood vessels to constrict
The medulla oblongata generates sympathetic nerve impulses causing constriction of blood
vessels (vasoconstriction) and increasing cardiac output
Adrenalin increases the heart rate, which results in increased blood flow and pressure
Blood is redirected to the skeletal system from the digestive system
12. General:
a. Review hypertonic and hypotonic
b. Review emulsification, bile, fats, lipids, lipase
c. Review breathing, external and internal respiration, cellular respiration