Unit 8: Grey Matter Flashcards
What are the three types of neurons?
Relay, Motor, Sensory
What is the role of the motor neuron?
Carry impulses from the CNS to the effector muscles/glands. Cell body, short dendrites, long axon. Cell body + dendrites in CNS and axon outside CNS.
What is the role of the sensory neuron?
Receptors to the brain and spinal cord. Cell body, medium dendrons, medium axon. Cell body (middle of the neurone) and dendrites outside CNS, axon inside CNS
What is the role of the relay neuron?
To connect the motor and sensory neurons. Cell body, short dendrons, short axon. Cell body etc. inside CNS.
What is the Schwann cell?
Cells that form the myelin sheath around the nerve cells/neurons in the peripheral system (nerves running to and from the CNS to all parts of the body).
What in the central nervous system made up of?
Brain and spinal cord
What would a transverse section of the myelin sheath look like?
1) Nucleus of the Schwann cell
2) Fold of Schwann cell around fibre
3) Nerve fibre
4) Lipoprotein membrane forming around the myelin sheath
What is MS (multiple sclerosis)?
Multiple sclerosis (MS) is a condition which can affect the brain and/or spinal cord. It involves the breakdown of the myelin sheaths within the central nervous system. Such de-myelinated nerve fibres are no longer able to transmit nerve impulses effectively.
What are the main symptoms of MS (multiple sclerosis)?
- fatigue
- difficulty walking
- vision problems, such as blurred vision
- problems controlling the bladder
- numbness or tingling in different parts of the body
- muscle stiffness and spasms
- problems with balance and coordination
- problems with thinking, learning and planning
Explain why it is important that neurones have insulating myelin sheaths.
Insulates the neurone, allows for rapid electrical impulses
What type of compound is myelin?
Lipid/fatty insulating sheath
Active transport is needed in the conduction of nerve
impulses. What is active transport? How is it different
from other forms of transport across cells?
Against a concentration gradient, uses ATP. Diffusion and osmosis are passive and down a concentration gradient.
Name one human reflex arc.
Blinking, sneezing
How is the neurone cell membrane polarised at rest?
Resting-state (not being stimulated), the outside membrane is positively charged compared to the inside. This is due to more positive ions outside the cell than inside. So the membrane is polarised - there is a difference in charge. The voltage across the membrane when it is at rest is called the resting potential- about -70mV.
What is the voltage in the membrane at resting potential?
70 mV
How is the resting potential created and maintained?
By sodium-potassium pumps and potassium ion channels in a neurone’s membrane
What are sodium-potassium pumps?
These pumps use active transport to move three sodium ions (Na+) out of the neurone for every two potassium ions (K+) moved in. ATP is needed to do this.
What is the potassium channel?
These channels allow facilitated diffusion of potassium ions (K+) out of the neurone, down their concentration gradient
What occurs due to the sodium ions being pumped out of the neurone by the sodium-potassium pumps?
The membrane isn’t permeable to sodium ions, so they can’t diffuse back in. This creates a sodium ion electrochemical gradient (a concentration gradient of ions) because there are more positive sodium ions outside the cell than inside.
How do the potassium ions move in the neuron?
Sodium-potassium pumps move potassium ions into the neurone, but the membrane is permeable to potassium ions so they diffuse back out through potassium ion channels.
What does the movement of potassium and sodium ions create in the neurone?
Makes the outside of the cell positively charged compared to the inside.
What is the stimulus and how does this affect the changes in an action potential?
excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative.
What is depolarisation?
if the potential difference reaches the threshold (around -55 mV) more sodium ion channels open. More sodium ions diffuse into the neurone
What is repolarisation?
at a potential difference of around +30 mV the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This starts to get the membrane back to its resting potential.
What is hyperpolarisation?
potassium ion channels are slow to close so there is a slight ‘overshoot’ where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential (- 70 mV)
What is resting potential?
The ion channel is reset. The sodium-potassium pump returns the membrane to its resting potential and maintains it until the membrane’s excited by another stimulus.
What is the refractory period?
After an action potential, the neurone cell membrane can’t be excited again straight away. This is because the ion channels are recovering and they can’t be made to open- sodium ion channels are closed during repolarisation and potassium ion channels are closed during hyperpolarisation.
How does action potential move along the neurone?
An action potential occurs, and some of the sodium ions that enter the neurone diffuse sideways. This causes sodium ion channels to open in the next region and sodium ions diffuse into that part. This causes a wave of depolarisation to travel along the neurone. The wave moves away from these parts of the membrane in the refractory period because these parts can’t fire an action potential.
How does the refractory period produce discrete impulses?
During the refractory period, ion channels are recovering and can’t be opened. The refractory period acts as a timed delay between one action potential and the next. This makes sure that action potentials don’t overlap but pass along as discrete (separate) impulses. The refractory period also makes sure action potentials are unidirectional (only travel in one direction)
How does a bigger stimulus cause more frequent impulses?
- Once the threshold is reached, an action potential will always fire with the same charge in voltage, no matter how big the stimulus is.
- If the threshold isn’t reached, an action potential won’t fire.
- A bigger stimulus won’t cause a bigger action potential, but it will cause them to fire more frequently.
How is preventing the movement of sodium ions stop action potential?
- Local anaesthetics are drugs that stop you from feeling pain in a localised area of your body.
- They work by binding to sodium ion channels in the membrane of neurones.
- This stops sodium ions from moving into the neurones, so their membranes will not depolarise.
- This prevents action potentials from being conducted along the neurones and stops information about pain from reaching the brain.
How does action potential go faster in myelinated neurone?
- Some of the neurones are myelinated- they have a myelin sheath
- The myelin sheath is an electrical insulator
- Made up of Schwann cells
- Between the Schwann cells are tiny patches of bare membrane called the Nodes of Ranvier. Sodium ion channels are concentrated at the nodes.
- In a myelinated neurone, depolarisation only happens at the node of Ranvier (where sodium ions can get through the membrane)
- The neurone’s cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse ‘jumps’ from node to node.
- This is called saltatory conduction and is fast.
- In a non-myelinated neurone, the impulse travels as a wave along the whole length of the axon membrane.
- This is a slower than saltatory conduction (still pretty quick)
- The speed at which an impulse moves along a neurone is known as the conduction velocity. A high conduction velocity means that the impulse is travelling quickly.
What are restriction enzymes?
- known as restriction endonucleases
- Found in bacteria and archaea
A plant’s roots grow down into the soil – what type of tropism is this?
Positive geotropism
What is the name of the plant hormone that controls the growth of a plant?
Auxin
Auxin accumulates in the shady side of the plant tip. What does it do the cells on this side?
Elongates them
What is negative phototropism?
Growth away from light
How does auxin promote bending of the plant?
Auxin binds to receptors in target cells, activating transcription factors and causing changes in cell expansion. Auxin also causes acidification of the cell wall, disrupting the bonds of the cellulose, and causing loosening of the cell wall. Moving to the shaded side of the plant causes elongation.
What are the symptoms and pathology of Parkinson’s?
- shakiness/tremors
- stiffness/ not smooth movement
- slower movement/can do them but takes longer
- balance/unstable
- a degenerative disorder of the CNS
- 12,000 sufferers in the UK
- damage to the basal ganglia
- few symptoms until 80% of dopamine-producing cells are gone
- trouble with concentration
- sleep disturbance
- dementia
- memory loss
- dopamine working in the neuron cortex
What are the causes and risk factors of Parkinson’s?
- lack of dopamine levels
- unknown causes
- don’t know what triggers the disease
- might be due to genetic mutation as 15% is the inheritance
Risk factors: - age
- concussions
- male
- smokers
- exposure to pesticides
- exposure to cleaning products
- breathing in heavy metal
Why is it difficult to treat Parkinson’s?
- you can’t stop the disease but we can manage it
- most damage is done by the time of diagnosis
- no cure/ palliative drugs are available
- few symptoms until 80% of dopamine-producing cells are gone
- crossing blood-brain barrier is not easy- dopamine cannot cross the BBB or treatment would be much more straightforward
How does L-dopa work and the benefits and problems?
(Levodopa)
- This is a precursor of dopamine which can cross the BB
- convert into dopamine by dopa decarboxylase
- works by temporarily reducing the motor symptoms
- given intravenously and from the intestinal infusion
- however, only 5-10% of L-dopa administered crosses the BB
- the remainder is metabolised to dopamine elsewhere in the body. This can produce unpleasant side effects like nausea
- effectiveness of L-dopa is reduced as more brain cells die off
- increasing the concentration of dopamine and controlling the symptoms of the disease
- increased levels of dopamine mean that more nerve impulses are transmitted in parts of the brain that control movement, giving suffers better control over their movement and lessening the symptoms of Parkinson’s disease
How does dopamine antagonist work, benefits and problems?
- stimulant
- similar effects to levodopa
- bind to post-synaptic receptors in the brain
- the mimic the effect of dopamine
- generally used just after diagnosis, allowing L-dopa treatment to be delayed
- side effects include drowsiness, hallucinations, insomnia
- less effective at controlling the motor symptoms of Parkinson’s than L-dopa
- more expensive than L-dopa
What are MAOB inhibitors?
- monoamine oxidase B
- works by breaking down dopamine in the brain synapse
- MAOB inhibitors inhibit the action of monoamine oxidase B
- this reduces the destruction of any dopamine that does get made
- stabilises and reduces fluctuations of dopamine levels in the synaptic cleft
How do neurotransmitters transmit nerve impulses between neurones?
Action potential→ opening of calcium channels (voltage-charged ion gates) → influx of calcium→ calcium to move vesicles to the synaptic knob (end of the pre-synapse) → vesicles leave by exocytosis→ neurotransmitters released→ bind to postsynaptic receptors (complementary) → causing sodium ion channels to open→ depolarisation(reaches the threshold) → action potential in the post synapse (only occurs with excitatory neurotransmitters)
What happens to neurotransmissions if it is inhibitory?
With inhibitory neurotransmitters when it is released and binds to the postsynaptic receptors release chlorine ions→ this causes hyperpolarisation→ difficult to trigger an action potential
What does acetylcholine do?
Acetylcholine is a neurotransmitter that when released if not used then acetylcholinesterase catalyses acetylcholine into acetate and choline→ choline is absorbed back into the pre-synapse→ reacts with acetyl coenzyme A to form acetylcholine→ this goes back into vesicles
Acetylcholine is involved in muscle contraction and the control of heart rate
What do the receptors only on the post-synaptic membrane do?
Synapses make sure impulses are unidirectional (only travel in one direction)
How do synapses allow for information to be dispersed or amplified?
- when one neurone connects to many neurones information can be dispersed to different parts of the body (synaptic divergence)
- when many neurones connect to one neurone information can be amplified (made stronger), this is called synaptic convergence.
What is summation at the synapse?
finely tunes the nervous response
- if a stimulus is weak, only a small amount of neurotransmitter will be released from a neurone into the synaptic cleft. This might not be enough to excite the postsynaptic membrane to the threshold level and stimulate an action potential
- summation is where the effect of neurotransmitters released from many neurones (or one neurone that’s stimulated a lot in a short period) is added together.
How do plants respond to stimuli?
- They sense the direction of light and grow towards it to maximise light absorption for photosynthesis
- they can sense gravity, so their roots and shoots grow in the right direction.
- climbing plants have a sense of touch, so they can find things to climb and reach the sunlight
What is tropism?
It is a response of a plant to a directional stimulus (a stimulus coming from a particular direction). Plants respond to directional stimuli by regulating their growth. A positive tropism is a growth towards the stimulus and negative is growth away from the stimulus
What is phototropism?
It is the growth of plants that is the response to light. Shoots are positively phototropic and grow towards light. Roots are negatively phototropic and grow away from the light
What is geotropism?
It is the growth of a plant that is the response to gravity. Shoots are negatively geotropic and grow upwards. Roots are positively geotropic and grow downwards
How do growth factors impact response?
chemicals that speed up or slow down plant growth. Growth factors are produced in the growing regions of the plant (like shoot tips) and they move to where they’re needed in other parts of the plant. Growth factors called auxins stimulate the growth of shoots by cell elongation (cell walls become loose and stretchy–> so they can get longer). High concentrations of auxins inhibit growth in roots though.
What are some other growth factors other than auxins?
- gibberellins- stimulate flowering and seed germination
- cytokinin- stimulate cell division and cell differentiation
- ethene- stimulate fruit ripening and flowering
- Abscisic acid (ABA)- involved in leaf fall
What is Indoleacetic Acid (IAA) and why is it an important auxin?
important auxin that’s produced in the tips of shoots in flowering plants. When it enters the nucleus of a cell, it’s able to regulate the transcription of genes related to cell elongation and growth. IAA is moved around the plant to control tropism- it moves by diffusion and active transport over short distances, and via the phloem over long distances. This results in different parts of the plants having different amounts of IAA. The uneven distribution of IAA means there’s uneven growth of the plants.
How does IAA create uneven distribution in a plant in phototropism?
- IAA moves to the more shaded parts of the roots and shoots, so there is uneven growth.
Shoot- cells elongate and the shoot bends towards the light
Root- growth is inhibited so the root bends away from the light
How does IAA create uneven distribution in a plant in geotropism?
- IAA moves to the underside of shoots and roots, so there’s uneven growth
Shoots- cells elongate so the shoot grows upwards
Roots- growth is inhibited so the root grows downwards
How do plants detect light using photoreceptors?
- plants detect light using photoreceptors called phytochromes
- found in many parts of the plant including leaves, seeds, roots and stem
- phytochromes control a range of responses (like plants flower in different seasons depending on how much daylight they receive- like some flower in summer in longer days)
- phytochromes are molecules that absorb light. They exist in two states- the Pr state absorbs red light at a wavelength of 660 nm, and the Pfr state absorbs far-red light at a wavelength of 730nm. Phytochromes are converted from one state to another when exposed to light:
- Pr converts to Pfr when exposed to red light (quickly)
- Pfr converts to Pr when exposed to far-red light (quickly)
- Pfr converts to Pr when in darkness (slowly)
Why is more Pr converted to Pfr than Pfr is converted to Pr?
Daylight contains more red light than far-red light. So the amount of Pr and Pfr changes depending on the amount of light (whether it is day, night, summer, winter)
Why is more Pr converted to Pfr than Pfr is converted to Pr?
Daylight contains more red light than far-red light. So the amount of Pr and Pfr changes depending on the amount of light (whether it is day, night, summer, or winter). The differing amounts of Pr and Pfr control the response to light by regulating the transcription of genes involved in these responses.
What is the cerebrum?
- the largest part of the brain
- divides into hemispheres
-outer layer called cerebral cortex- large surface area and is highly folded - involved in thinking, emotions, vision, learning and movement
- different parts involved in different functions like the back is involved in vision and the front is involved in thinking
What is the hypothalamus?
- found beneath the middle part of the brain
- automatically maintains body temperature (thermoregulation)
- produces hormones that control the pituitary gland
What is the medulla oblongata?
- base of the brain, at the top of the spinal cord
- automatically controls breathing and heart rate
What is the cerebellum?
- underneath the cerebrum and it also has a folded cortex
- important for coordinating movement and balance
Why do we use brain scanners?
- investigate the structure and function of the brain, and to diagnose medical conditions, you need to look inside the brain
- this can be done with surgery, but it is risky
- the brain can be visualised without surgery using scanners
- there four different types: fMRI, MRI, CT, PET
How does a CT scan work?
Computer tomography uses lots of X-rays (dense structures in the brain absorb more radiation than less dense structures so show up as a lighter colour on the scan).
- shows major structures of the brain but not the function
- can should disease or damaged brain structures
Medical diagnosis:
- blood has a different density from brain tissue and shows up a light colour
- the extent of bleeding and its location
- work out which blood vessels have been damaged and what brain functions are likely to be affected by the bleeding
How do MRI scans work?
Magnetic resonance imaging using magnetic fields. Cross-section images. Higher quality images than CT scans, better resolution between tissue types and overall better resolution. Clearly see abnormal and normal differences.
Medical diagnosis:
- tumour cells respond differently to a magnetic field than healthy cells, so they show up a lighter colour
- shows the exact size of the tumour and location
- work out brain functions may be affected by the tumour
How do fMRI scans work?
Functional magnetic resonance imaging shows brain activity. More oxygenated blood flows to active areas of the brain. Molecules in oxygenated blood respond differently to a magnetic field than those in deoxygenated blood- the signal returned to the scanner is stronger from the oxygenated blood, which allows more active areas of the brain to be defined.
- gives a detailed, high-resolution picture of the brain and can work out the function of the brain’s structure
- shows activity by being highlighted
Medical diagnosis:
- shows damaged and diseased areas and abnormal activity
- help pinpoint the area that is not working properly
- find the cause of seizures so a patient can receive the most effective treatment for seizures
How do PET scans work?
Positron emission tomography uses radioactive material. It can show how active different areas of the brain are. A radioactive tracer is introduced into the body and absorbed by the tissue. The scanner detects the radioactivity of the tracer- building up a map of radioactivity in the body. Different tracers can be used- e.g. radioactivity-labelled glucose can be used to look at glucose metabolism.
- very detailed and can be used to investigate both the structure and the function of the brain in real-time
Medical diagnosis:
- show if areas in the brain are unusually inactive or active, so they are particularly useful for studying disorders that change the brain’s activity
How is the visual cortex made up of?
- visual cortex is an area of the cerebral cortex at the back of the brain
- the role is to receive and process visual information
- neurones in the visual cortex receive information from either your left or right eye
- neurones are grouped in columns called ocular dominance columns. If they receive information from the right eye they’re called right ocular dominance, the left eye they’re called left ocular dominance columns
- the columns are the same size and they are arranged into alternating patterns
What was Hubel and Wiesel’s study?
- investigate brain development
- the structure of the visual cortex was discovered by them
- used animal models to study electrical activity
- they found that the left ocular dominance columns were stimulated when an animal used its left eye, and the right ocular dominance columns were stimulated when it used its right eye
How did Hubel and Wiesel (1963) investigate visual cortex development by experimenting on very young kittens?
- they stitched shut one eye of each kitten so they could only see out of their other eye
- the kittens were kept like this for several months before their eyes were unstitched.
- They found that the kitten’s eye that had been stitched up was blind
- they also found that the ocular dominance columns for the stitched eye were a lot smaller than normal, and the ocular dominance columns for the open eye were a lot bigger than normal
- the ocular dominance columns for the open eye had expanded to take over other columns that were being stimulated - when this happens, the neurones in the visual cortex are said to have switched dominance
What investigation did Hubel and Wiesel do to adult cats’ brains?
- they stitched shut one eye of each cat, who kept like this for several months
- when their eyes were unstitched, Hubel and Wiesel found that these eyes hadn’t gone blind
- the cats fully recovered their vision and their ocular dominance columns remained the same
They repeated this with young and adult monkeys and saw the same results
How did Hubel and Wiesel’s experiments provide evidence for a critical period in humans?
- a period in early life when a kitten must be exposed to visual stimuli for its visual cortex to develop properly (critical period)
- the human visual cortex is similar to a cat’s visual cortex (the human visual cortex has ocular dominance columns too), so Hubel and Wiesel’s experiment provides evidence for a critical period in humans
How do cataracts provide evidence for visual development in humans?
- cataract makes the lens in the eye go cloudy, causing blurry vision
- if a baby has a cataract, it’s important to remove the cataract within the first few months of the baby’s life- otherwise, their visual system won’t develop properly and their vision will be damaged for life
- if an adult has a cataract then it’s not so serious- when the cataract is removed, normal vision comes back straight away. This is because the visual system is already developed in an adult.
Why is visual information needed for the neurones during the critical period?
- During the critical period of development, synapses that receive visual stimulation and pass nerve impulses into the visual cortex are retained.
- Synapses that don’t receive any visual stimulation and don’t pass on any nerve impulses to the visual cortex are removed
- this means that if the eyes are not stimulated with visual information during this critical period of development, the visual cortex will not develop properly as many of the synapses will be destroyed
What are the arguments against using animals in medical research?
- animals are different from humans
- experiments can cause pain and distress to animals
- alternatives to using animals in research like a culture of human cells
- animals have the right not to be experimented on
What are the arguments for using animals in medical research?
- animals are similar to humans (led to medical breakthroughs)
- animals experiments are done when it is necessary and scientists follow strict rules
- using animals is currently the only way to study how a drug affects the whole body
- other people think that humans have a greater right to life than animals because we have more complex brains
How do you investigate the role of nature and nurture in brain development?
- Brain development is how the brain grows and how neurones connect
- measures of brain development include the size of the brain, the number of neurones it has and the level of brain function a person has
- your brain develops the way it does because of both your genes (nature) and your environment (nurture)- your brain would develop differently if you had different genes or were brought up in a different environment
- nature-nurture debate
Why is it hard to investigate the effects if nature and nurture?
- genetic and environmental factors interact, so it is difficult to know which one is the main influence
- there are lots of different genes and lots different environmental factors to investigate
- to do an accurate experiment, you will need to cancel out one factor to be able to investigate the other (which is difficult as you need to cut out all environmental influences to investigate the role of a genetics)
How are animal studies used to support nature or nurture in brain development?
- study the effects of different environments on the brain development of animals in the same species. Individuals from the same species will be genetically similar so any difference in brain development will be likely due to nurture
- study the effect of genes- genetically modify/engineer animals of the same gene and place them in similar environments
- for example: mice engineered to lack the Lgl1 gene develop enlarged brain regions and fluid builds up in their brains. This suggests that nature plays a big role in brain development
How are twin studies used to support either nature or nurture in brain development?
- if identical twins are raised separately then they’ll have identical genes but different environments.
- scientists can compare the brain development of separated identical twins- any differences between them are due to nurture not nature, and any similarities are due to nature.
How can cross-cultures show evidence for nature or nurture in brain development?
- children brought up in different cultures have different environmental influences
- study the effects of a different upbringing on brain development by comparing large groups of children who are the same age but from different cultures
- look at differences in characteristics- differences will be due to nurture and similarities will be due to nature
How do new-born studies show evidence for nature or nurture in brain development?
- the brain of a new-born baby hasn’t been affected by the environment
- scientists study the brains of newborn babies to see what function they’re born with and how developed different parts of the brain are- what they’re born with is more likely to be due to nature than nurture.
How do brain damage studies show evidence for nature or nurture in brain development?
- damage to an adult’s brain can lead to the loss of brain function
- if an adult’s brain is damaged, it can’t repair itself so well because it’s already fully developed. But a child’s brain is still developing- so scientists can study the effects of brain damage on their development
- compare the development of a chosen function in children with and without brain damage
- if the characteristics still develop in children with brain damage, then brain development is more likely to be due to nurture than nature for that characteristic.
- if it doesn’t develop in children with brain damage, then brain development is more likely due to nature than nurture for that characteristic.
What is depression?
- there is a link between a low level of serotonin and depression
- serotonin transmits nerve impulses across the synapse in the parts of the brain that control mood
- depression is linked to a low level of serotonin so they’re developed drugs (antidepressants) to increase the level of serotonin in the brain
- some drugs that are used to treat depression (selective serotonin reuptake inhibitors- SSRIs) increase serotonin levels by preventing its reuptake at synapses.
How does MDMA (ecstasy) affect synaptic transmission?
- increase levels of serotonin in the brain
- serotonin is taken back into a presynaptic neurone after triggering an action potential, to be used again
- MDMA increases the level of serotonin by inhibiting the reuptake of serotonin into presynaptic neurones- it binds to and blocks the reuptake proteins on the presynaptic membrane
- also triggers the release of serotonin from presynaptic neurones
- serotonin levels stay high in the synapse and cause depolarisation of the postsynaptic neurones in parts of the brain that control mood
- mood elevation
What is the Human genome project and how is it being used to create new drugs?
- Human Genome Project (HGP) was a 13-year-long project that identified all of the genes found in human DNA
- information obtained from the HGP is stored in databases
- used to identify genes, and proteins, that are involved in disease
- scientists can create new drugs that target the identified proteins.
- highlighted common genetic variations between people
- it’s known that some of these variations make drugs less effective
- drug companies can use this knowledge to design new drugs that are tailored to people with these variations- personalised medicines
- personalise a patient’s treatment by using their genetic information to predict how well they will respond to different drugs and only prescribe the ones that will be most effective
What are the social, moral and ethical issues of the human genome project?
- increase research costs- only rich people would have access
- some people might be refused an expensive drug because their genetic makeup indicates that it won’t be that effective for them (only drug available)
- information held within a person’s genome could be used by others
- if a drug doesn’t work could cause psychologically damaging
How are microorganisms genetically modified?
- a gene for a protein is isolated using enzymes called restriction enzymes
- the gene is copied using PCR
- copies are inserted into plasmids (small circular molecules of DNA)
- the plasmids are transferred into microorganisms
- the modified microorganisms are grown in large containers so that they divide and produce lots of the useful proteins, from the inserted gene
- the protein can then be purified and used as a drug
How are plants genetically modified?
- the gene for the protein is inserted into a bacterium
- the bacterium infects a plant cell
- the bacterium inserts the gene into the plant cell DNA- the plant cell is now genetically modified
- the plant cell is grown into an adult plant- the whole plant contains a copy of the gene in every cell
- the protein produced from the gene can be purified from the plant tissues, or the protein could be delivered by eating the plant
How are animals genetically modified?
- the gene for the protein is injected into the nucleus of a fertilised animal egg cell
- the egg cell is then implanted into an adult animal- it grows into a whole animal that contains a copy of the gene in every cell
- the protein produced from the gene is normally purified from the milk of the animal
What are the benefits of GMOs (genetically modified organisms)?
- higher crop yield (reduce malnutrition)
- crops are pest resistance
- larger quantities, reduced costs
- treat disorders with human proteins
- vaccines produced in plant tissues don’t need to be refrigerated
- very cheap as using conventional farming methods
What are the risks of genetically modified organisms (GMOs)?
- concerned about the transmission of genetic material and makes them a monoculture (pathogens would kill all the plants)
- don’t know the long-term impacts (consequences)
- some people think it is wrong to genetically modify animals to benefit humans
What is habituation?
- animals increase their chance of survival by responding to stimuli.
- but if the stimuli are unimportant, there is no point in responding
- if an unimportant stimulus is repeated over a period of time, the animal learns to ignore it
- reduced response to an unimportant stimulus after repeated exposure over time is called habituation
- animals don’t waste energy responding to unimportant stimuli. It also means that they can spend more time doing other activities for their survival
- Animals remain alert to important stimuli
How do you investigate habituation?
1) Gently brush something soft, like a blade of grass, across the surface of the snail’s skin
2) using a stopwatch time how long it takes for the snail to fully extend its tentacles again after you touched it
3) repeat this process at regular intervals and record the time it takes for the tentacles to fully extend every time you touch the snail.
If habituation has taken place then the time should be quicker
Why does habituation take place?
Effectors that carry out the response o different stimuli are controlled by nervous stimulation. Habituation to a stimulus means fewer electrical impulses are sent to the effectors:
- repeated exposure to a stimulus decrease the number of calcium ions that enter the presynaptic neurone.
- this decrease in the influx of calcium ions means that fewer neurotransmitters are released from the vesicles into the synaptic cleft, so fewer neurotransmitters can bind to receptors in the postsynaptic membrane
- fewer sodium ion channels on the postsynaptic membrane open- so there is a reduced chance of the threshold for an action potential being reached on the postsynaptic membrane
- fewer signals are sent to the effector to carry out the response
