Drugs

Excitatory drugs

Nicotine
• Nicotine in tobacco products is a stimulant which mimics acetylcholine (Ach). Thus, it acts on the cholinergic synapses of the body and the brain to cause a calming effect. After Ach is received by the receptors, it is broken down by acetyl cholinesterase but the enzyme cannot break down the nicotine molecules which bind to the same receptors. This excites the postsynaptic neuron and it begins to fire, releasing a molecule called dopamine. Dopamine gives the feeling of pleasure, a molecule of the ‘reward pathway’ of our brains.

Amphetamine
• Stimulates transmission at adrenergic synapses and gives increased energy and alertness. Amphetamine acts by passing directly into the nerve cells which carry dopamine and noradrenalin
• It moves directly into the vesicles of the pre synaptic neuron and causes their release into the synaptic cleft. Normally, these neurotransmitters would be broken down by enzymes in the synapse, but amphetamines interfere with the breakdown.
• Thus in the synapse high concentrations of dopamine cause euphoria, and high concentrations of noradrenalin may be responsible for alertness and high energy effect of amphetamines.

Inhibitory Drugs 

Benzodiazepine
• Reduces anxiety can also be used against epileptic seizures.
• Its effect is to modulate the activity of GABA which is the main inhibitory neurotransmitter. When GABA binds to the postsynaptic membrane, it causes Chloride ions to enter the neuron. 
• This hyperpolarizes the neuron, and resists firing.
• Benzodiazepine increases the binding of GABA to the receptor and causes the post synaptic neuron to become more hyperpolarized.

Alcohol
• Inhibitory neurotransmitters, called GABA, are active throughout the brain. These neurotransmitters act to control neural activity along many brain pathways. When GABA binds to its receptors, the cell is less likely to fire.
• However, in another area of the brain, another neurotransmitter called glutamate acts as the brain’s general-purpose excitatory neurotransmitter.
• When alcohol enters the brain it delivers a double sedative punch. First, it interacts with GABA receptors to make them even inhibitorier.
• Second, it binds to glutamate receptors, preventing the glutamate from exciting the cell. 
• Alcohol particularly affects areas of the brain involved in memory formation, decision-making and impulse control.

Cocaine (Excitatory Drug):

Cocaine is a psycho-active drug along with THC (Tetrahydrocannabinol) they affect a mood of a person as they both concentrate on the reward pathways in the brain. In the reward pathways a pleasuable mood enhancing sensation is produces. The cause to this natural 'high' is the secretion of the neurotransmitter dopamine. Dopamine receptors are found in the post synaptic membrane which when activated depolarizes the post synaptic neurone in regions of the brain associated with a feeling of pleasure. Since dopamine is the neurotransmitter in the ‘reward pathway’, the longer it stays in the synapse the better you feel. 

Cocaine blocks Dopamine transporters by attaching to the presynaptic dopamine pumps, leaving dopamine trapped in the synaptic cleft, thus dopamine binds again and again to receptors which over stimulates the cell. Thus cocaine results in post synaptic excitement of cholinergic synapses which are associated will elevated levels of activity. Cocaine is described as creating a mood of euphoria and cocaine users are often described as fidgety and energetic. This drug can also increase body temperature, blood pressure and heart rate. Users risk heart attacks, respiratory failure, strokes, seizures, abdominal pain and nausea. 

Marijuana or Tetrahydrocannabinol (THC) (Inhibitory Drug):

THC is the main psychoactive chemical in marijuana.
Before marijuana enters the system, inhibitory neurotransmitters are active in the synapse. These neurotransmitters inhibit dopamine from being released. When activated by the body’s own native cannabinoid (called anandamide), cannabinoid receptors turn off the release of inhibitory transmitters. Without inhibition, dopamine can be released. THC, the active chemical in marijuana, mimics anandamide and binds to cannabinoid receptors. Inhibition is turned off and dopamine is allowed to squirt into the synapse.

Anandamide is known to be involved in removing unnecessary short term memories. It is also involved for slowing down movement, making us feel mellow and calm. Unlike THC, anandamide breaks down very quickly in the body. That explains why anandamide doesn’t produce a perpetual natural ‘high’.

Explain how pre-synaptic neurons can affect post-synaptic transmissions of impulses [7]

Firstly a nerve impulse coming into the pre synaptic neuron would cause calcium ions to diffuse through channels in the membrane. The calcium influx then causes vesicles containing neurotransmitters to fuse with the pre synaptic membrane, this process is called exocytosis. The neurotransmitters are then released into the synaptic cleft and diffuse across it to bind with the post synaptic neuron. This is called an excitatory synapse. The binding then cause’s ion channels to open and sodium ions will then diffuse through this channel down the concentration gradient. This then initiates the action potential which begins to move down the post-synaptic neuron because it has been depolarized. 

Opposite from an excitatory synapse is an inhibitory synapse. This is when the release of neurotransmitters into the cleft inhibits an action potential being generated in the post-synaptic neuron. This means that instead of the neurotransmitters triggering the opening of ion channels to let sodium out it will instead allow chlorine ions to enter the neurone or potassium to leave. This will then make the post-synaptic neurone more negative (hyperpolarised) and therefore less likely to initiate an action potential.


Mark scheme

a)      Pre synaptic neuron can be excitory of inhibitory

b)      Chlorinergenic neurons release acetylcholine

c)       Found in neuromuscular junctions/in autonomic nervous system/most junctions in voluntary nervous system

d)      Adrenic nerons release noradrenaline

e)      Found in sympathetic pathways (in brain)

f)       Both types of neurons can be excitory

g)      Neurotransmitters (NT) bind to receptors on post synaptic membrane

h)      Triggers opening of Na+ gates/channels/Na+ moves across membrane

i)        Causes depolarization

j)        NT’s are degraded/destroyed or recycled e.g. acetyl choline esterase breaks down acetyl choline

k)      Other inhibitory NT’s e.g. GABA (cocaine, alcohol), Dopamine

l)        Inhibitory NT’s less permeable to Na+/cause Cl- ions to diffuse in

m)    Hyper-polarization

n)      By K+ diffusing out 

Explain the process of synaptic transmission [7]

A nerve impulse would first travel to end of pre synaptic neuron, this will then trigger a influx of calcium ions. In the pre synaptic neuron there are swollen membranous areas called terminal buttons and within these there are many vesicles filled with neurotransmitters. The calcium influx then causes synaptic vesicles containing neurotransmitters to fuse with the pre synaptic membrane by exocytosis. The neurotransmitters are then released into the synaptic cleft and diffuse across it to bind with the receptors on the post synaptic neuron. This then causes ion channels to open on neuron and sodium diffuses into postsynaptic neuron. This initiates the action potential to begin moving down the postsynaptic neuron because it’s been depolarized. The neurotransmitter is then degraded and broken into two or more fragments by specific enzymes. They’re then released from the receptor protein. The ion channel closes to sodium ions. The neurotransmitter fragments diffuse back across the synaptic gap to be reassembled into the terminal buttons of the pre synaptic neuron. 


Mark scheme

a)      Pre synaptic neurons pass a stimulus to post-synaptic

b)      Pre synaptic releases NT into cleft

c)       Process involves exocytosis

d)      Exocytosis triggered by Ca2+ into neuron (bulb)

e)      NT binds with receptor on postsynaptic cleft

f)       NT binding causes ion channels to open

g)      Ions diffuse into/out of cell

h)      Depolarization or Hyper-polarization

i)        Outcome depends on type of receptor

j)        E.g. Na+ going into postsynaptic neuron = depolarization

k)      Cl- passing into the post synaptic neuron = hyper polarization

l)        NT destroyed/deactivated by enzymes

Plants are classified together in a kingdom. Other organisms are classified in other kingdoms. Outline the value of classifying organisms [4]

a) Shows how organisms are related

b) Helps cope with the large number of organism

c) Easier to store/find information

d) Easier to find useful organisms (e.g. drugs in animals)

e) Makes it easier to ID organisms

f) Allows predictions to be made about the nature of a organism

g) Traces possible evolutionary links

h) ID homologous structures

Outline the consequences of rising carbon dioxide concentrations in the Earth’s atmosphere [5]

The rising carbon dioxide concentrations in the atmosphere create a blanket over the Earth which keeps the suns wavelengths in the atmosphere; this would then increase global warming as the Earth would continually heat up as it cannot escape due to the build up of gases. With increased heat come many consequences such as the melting of polar ice caps, this will then in turn cause a rise in global sea levels causing flooding in low lying areas. With the heat there can also come natural disasters such as drought which would affect agriculture leading to a decline in food production which has the consequence of decreasing life expectancy. The heat also brings about diseases from mosquitoes, such as malaria and dengue fever, because they thrive in heat. Also warmer temperatures allow pathogens to survive better.

Explain the light-independent reaction of photosynthesis [8]

The energy in the form of ATP and NADPH made in the light dependent reaction is then used in the light independent reaction to fix carbon from carbon dioxide into organic molecules. This reaction is called the Calvin cycle and it takes place in the stroma of the chloroplast and is controlled by enzymes. Firstly a single carbon in carbon dioxide is fixed with RuBP and is catalyzed by the enzyme Rubisco to form 2 molecules of Glycerate-3-phosphate. The Glycerate-3-phosphate is then reduced to triose phosphate by using the energy which comes from the oxidation of NADPH and ATP. Triose phosphate is then used to regenerate Ribulose Bisphosphate. 

The carbon cycle involves both the production and the fixation of carbon dioxide. Draw a labelled diagram to show the processes involved in the carbon cycle [5]

Explain the process of aerobic respiration including oxidative phosphorylation [8]

In aerobic respiration, glucose is split into pyruvate by glycolysis. The pyruvate then enters the mitochondria and reacts with coenzyme A by the process of oxidative decarboxylation to form acetyl CoA, in this process carbon dioxide and NADH is formed. The acetyl group then enters the kreb cycle where FAD+ and NAD+ accept hydrogen to form NADH and FADH2. The energy in these molecules is then used to make many more molecules of ATP. In the inner membrane of the mitochondria there are the proteins. Both NADH and FADH2 donate electrons to the electron transport chain. As electrons move from 1 complex to another they transfer their energy to pump protons across the membrane, this then creates a concentration gradient across the membrane. Oxygen is the final electron acceptor; it will then combine with the protons to form water. 

Describe the process of active transport [4]

Active transport is when a protein moves a certain material across the membrane from a region of lower concentration to a region of higher concentration. This means the substance is absorbed against the concentration gradient and energy is needed for this active transport to work. The energy is usually comes from adenosine triphosphate or ATP, every cell supplies its own ATP by cell respiration. Globular proteins or pump proteins or transporter proteins in membranes carry out the active transport, the membrane must contain a lot of these proteins so that the cell can control the contents of its cytoplasm precisely. An example of active transport is in human nerve cells where potassium ions are pumped in and sodium ions are constantly transported out of the cell by active transport into the external fluid bathing the cell to build up a store of potential energy or an electrical impulse that is used to transmit a nerve impulse.

Draw a diagram of the ultrastructure of an animal cell as seen in a electron micro graph [6]