Answers for Practice Questions
Biochem
1.
• Channel proteins allow molecules to pass through the membrane freely.
• Carrier proteins allow specific molecules to pass through the membrane freely
(1 mark) or actively (1 mark).
• Cell recognition proteins with attached carbohydrates identify cells to the
immune system.
• Receptor proteins pass chemical signals across the cell membrane.
• Enzymatic proteins allow reactions to occur at the membrane.
2.
• The DNA molecule’s double helix is unwound.
• Hydrogen bonds between nucleotides are broken, separating the strands of the
helix.
• Complementary nucleotides attach to the original nucleotides in each strand.
• New nucleotides are linked together by bonds thus forming new strands
complementary to the original strands.
3.
• Substrates bind to enzymes at the active sites.
• Mercury ions denature the enzymes.
• This results in a change in the shape of the active sites.
• The substrates cannot bind to the active sites.
• The rate of reaction decreases.
Digestion
1.
• The stomach is acidic while the small intestine is basic.
• The stomach contains protein molecules while the small intestine contains
peptides and amino acids.
• The stomach contains fat molecules while the small intestine contains fatty acid
and glycerol molecules.
• The small intestine contains glucose molecules while the stomach does not.
• Any valid enzyme addition (e.g., pepsin is found in the stomach while trypsin is
found in the small intestine).
2.
• Salivary amylase digests starch.
• Pancreatic amylase digests starch. (either one for 1 mark)
AND
• starch to maltose (1 mark)
• maltase digests maltose (1 mark)
• maltose to glucose (1 mark)
Circulation
1.
• has thick walls that resist blood pressure
• has elastic fibres to allow stretching and recoil
• when the arteriole contracts, this increases blood pressure to the remainder of
the body
• endothelium layer provides smooth surface (less friction) for blood movement
• has sphincters which control blood flow to the capillary beds
• has smooth muscles which control blood flow to the capillary beds
Respiration
1.
• Compared to the umbilical vein, blood in the umbilical artery has higher
concentrations of:
– carbon dioxide
– hydrogen ions
– bicarbonate ions
– reduced hemoglobin
– carbaminohemoglobin
– urea.
• Compared to the umbilical artery, blood in the umbilical vein has higher
concentrations of:
– oxyhemoglobin
– glucose
– amino acids
– nucleotides.
2.
• Blood at area X contains high levels of bicarbonate ions (HCO3– )
while blood at area Y contains low levels of HCO3– .
• Blood at area X contains high levels of carbaminohemoglobin
(HbCO2 ) while blood at area Y contains low levels of HbCO2 .
• Blood at area X contains high levels of reduced hemoglobin (HHb+ )
while blood at area Y contains low levels of HHb+ .
• Blood at area X contains high levels of carbon dioxide (CO2 )
while blood at area Y contains low levels of CO2 .
• Blood at area X contains low levels of nutrients while blood at area
Y is rich in nutrients.
• Blood at area Y contains high levels of oxyhemoglobin (HbO2 )
while blood at X contains lower levels of HbO2 .
3.
• increased concentration of carbon dioxide (CO2 )
• increased concentration of bicarbonate ions (HCO3– )
• increased acidity
• decreased concentration of oxygen (O2 )
Nervous
1.
• Calcium ions flow into the synaptic ending, causing the contractile
proteins to contract.
• As they contract, they pull the vesicles to the surface of the presynaptic
membrane.
• They merge with the membrane and release neurotransmitters into
the cleft.
• The neurotransmitters diffuse across the cleft and fit into receptor sites
on the postsynaptic membrane.
• By fitting into receptor sites, an action potential is generated in the
postsynaptic membrane.
• The neurotransmitters are either destroyed by enzymes or reabsorbed.
2.
• Calcium ions are required to cause the contraction of protein
molecules in the synaptic ending.
• Neurotransmitter molecules are not secreted.
• Without neurotransmitters, the sodium gates in the postsynaptic
membrane would not open.
• Depolarization of the postsynaptic membrane would not occur.
• No new nerve impulse would be produced.
3.
• Calcium ions move into the cell.
• They interact with contractile proteins and pull the vesicles to the
surface of the presynaptic membrane.
• The vesicles merge with the presynaptic membrane and release
neurotransmitters into the synaptic cleft.
• The neurotransmitters diffuse across the cleft.
• The neurotransmitters fit into receptor sites, causing the postsynaptic
membrane to depolarize.
Urinary
1.
• Dehydration results in an increased solute concentration in the blood (1 mark)
which is sensed by osmoreceptors in the hypothalamus. (1 mark)
• The osmoreceptors signal the posterior pituitary gland to increase antidiuretic
hormone (ADH) secretion. (1 mark)
• Increased ADH stimulates the kidney to increase the reabsorption of water (1
mark), decreasing the solute concentration in the blood. (1 mark)
• The osmoreceptors stimulate thirst, causing the person to increase water
intake, thereby decreasing solute concentration in the blood. (1 mark)
2.
• Aldosterone stimulates the distal convoluted tubule to reabsorb more
sodium ions from the filtrate. (1 mark)
• Water follows these ions osmotically, raising blood volume. (1 mark)
• Increased volume increases blood pressure (1 mark), which forces more
blood plasma into the tissue fluids (1 mark).
• This increased volume also decreases osmotic pressure (1 mark), causing a
decrease in tissue fluid reabsorption, causing swelling (1 mark).
Reproduction
1.
X:
• Increasing levels of estrogen cause increased secretion of luteinizing
hormone (LH) from the pituitary.
• Increasing levels of estrogen cause decreased secretion of
follicle-stimulating hormone (FSH) from the pituitary.
• Increasing levels of estrogen cause an increase in the thickness of the
endometrium. (1 mark)
AND
Y:
• High levels of progesterone cause a decrease in the secretion of LH from the
pituitary. (1 mark)
• High levels of progesterone from the ovary cause the endometrium to increase
in thickness, become vascularized and to produce mucus. (1 mark)
2.
• In males, follicle-stimulating hormone (FSH) targets the cells of the
seminiferous tubules (1 mark) and causes sperm production (1 mark).
• In females, FSH targets the ovaries (1 mark) and causes follicle
development (1 mark).
• In males, luteinizing hormones (LH) targets the interstitial cells
(1 mark) and causes testosterone production (1 mark).
• In females, LH targets the corpus luteum (1 mark) and causes the
production of progesterone (1 mark).
• In females, the LH “spike” causes the follicle to release the ovum
(ovulation).
3.
• The hypothalamus secretes gonadotropic-releasing hormone (GnRH).
• GnRH stimulates the anterior pituitary to secrete luteinizing hormone (LH).
• LH stimulates the interstitial cells of the testes to produce testosterone.
• As the level of testosterone rises, there is negative feedback exerted on the
hypothalamus.
• As the level of testosterone rises, there is negative feedback exerted on the
anterior pituitary.
• The secretion of LH slows down and testosterone decreases.