Question 1
• Distinguish between active and passive
movements of materials across plasma
membranes, using named examples. (4)
Passive vs. Active
Passive
Active
General
Examples
Osmosis/ Diffusion/ Facilitated
diffusion
Active transport/ ion
pumps/ exocytosis/
endocytosis
Energy ?
No energy needed
Requires energy/ ATP
Direction of
movement
Down concentration gradient
Against concentration
gradient
Proteins
required
No proteins required for simple
diffusion but proteins required for
facilitated diffusion
Proteins required
Specific
Examples
Oxygen diffusion in alveoli/ other
examples
Sodium- potassium
pump of nerve cells/
other examples
• Explain how an impulse passes along the
membrane of a neuron.(8)
• Resting membrane is polarized;
• During resting potential the interior is –70 mV/negative relative to
outside;
• During Resting Potential there are more sodium ions outside than inside;
• During Resting Potential there are more potassium ions inside than
outside;
• During the start of an action potential disturbance of membrane opens
sodium ion channels;
• During action potential sodium ions rush to inside of cell;
• This movement of sodium ions inside a the cell causes a depolarization;
• After the depolarization sodium ion channels shut;
• After the depolarization potassium ion channels open; and potassium ions
rush out;
• Potassium ions leaving the cell helps to restore polarized state of
membrane;
• To restore resting potential completely after an action potential sodium–
potassium pumps maintain polarity;
• This process is repeated along the length of neuron / sodium ions diffuse
between region with an action potential and the region at resting
potential;
The graph below shows changes in membrane potential
in an axon during the passage of an action potential.
• Explain briefly the principle of negative
feedback in homeostasis.(3)
• A change in environment is sensed / detected;
• A response to bring the system back to normal
state / set point / within limits;
• When the normal state reached, the response is
stopped;
• This stopping prevents over reaction;
• The internal environment fluctuates around norm
/ small fluctuations; 3 max
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• Explain how blood glucose concentration is
controlled in humans. (8)
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pancreatic cells monitor blood glucose;
insulin / glucagon is a hormone;
low glucose level induces production of glucagon;
a-cells of pancreatic islet produce glucagon;
glucagon stimulates the liver to break glycogen into glucose;
glucagon leads to increase in blood glucose;
absorption of glucose from digestive tract causes glucose levels to rise (after
meals);
high level of blood glucose induces production of insulin;
b-cells of pancreatic islet produce insulin;
insulin stimulates uptake of glucose into cells (muscles);
insulin stimulates uptake of glucose into liver / storage of glucose as glycogen in
liver;
insulin leads to decrease in blood glucose;
homeostatic monitoring of blood glucose levels is constantly happening;
skipping meals can cause blood glucose levels to drop;
in diabetes mellitus blood insulin low / target cells insensitive;
blood glucose regulation is an example of negative feedback;
adrenaline leads to increased blood glucose levels;
• Describe the response of the human body to
low external temperatures.
• (Total 4 marks)
• thermoreceptors / sensory input
hypothalamus acts as a thermostat;
• metabolic rate increases;
• shivering / goose bumps / hairs raising / sweat
glands inactive;
• vasoconstriction of skin arterioles;
• blood flow from extremities is reduced / blood
flow to internal organs is increased;
• increased activity;
• heat is transferred in blood; [4]
• Identify two differences between Steroid &
Peptide Hormones (2)
Steroid Hormones Peptide Hormone
1. Enter inside cell and nucleus 1. Bind to a receptor on the
outside of a cell membrane
2. steroid hormones interact
directly with genes
2. protein hormones cause
release of secondary
messenger in cell;
3. steroid hormones control
whether or not particular
enzymes or proteins are
synthesized via DNA
transcription and
translation
3. whereas protein hormones
change the cell’s activity
usually by activating or
inhibiting enzymes;