5.6Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
The Brain, Behaviour & Disease — IAL Edexcel Linear Revision Notes & Topical Questions
10 min read 12 parts Lesson 7 of 36 1 quiz
Curriculum Equation Key معادلة التنفس الخلوي الهوائي الموزونة - Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP) | جلوكوز + أكسجين ← ثاني أكسيد كربون + ماء + طاقة
Location & Specifications: الميتوكوندريا (Mitochondria) والسيتوسول.
Lesson summary
5.6 The Brain, Behaviour and Disease — IAL EDEXCEL LINEAR notes: Describe brain regions and investigation techniques, visual development, habituation, brain diseases and drugs, and the gene technology used to make medicines.Cerebrum — about 80% of brain mass, with two hemispheres…
- Hypothalamus
- Pituitary gland
- Cerebellum
- Medulla oblongata
- Linking structure to function
- Why indirect methods
Section 1 of 12Brain regions and their functions
Brain regions and their functions
Cerebrum
- Cerebrum about 80% of brain mass, with two hemispheres joined by the corpus callosum, and the right hemisphere controls the left side of the body.
- It controls conscious activitiesvision, hearing, speech, thinking and memory.
- The cerebral cortex (grey matter) is the folded outer layer of neurone cell bodies, and the folds increase surface area and the number of connections.
- White matter beneath it is made of myelinated axons.
- The frontal lobe handles reasoning, personality and voluntary movement (motor cortex), the parietal lobe handles touch and spatial awareness, the occipital lobe handles vision and the temporal lobe handles hearing, memory and speech.
Hypothalamus
- Hypothalamus it monitors blood flowing through the brain and releases hormones or stimulates the pituitary gland.
- It regulates body temperature, osmoregulation (ADH release), digestive activity and appetite,
- and endocrine functions such as growth, puberty, sleep and mood.
Pituitary gland
- Pituitary gland it lies below the hypothalamus,
- and the anterior pituitary makes hormones while the posterior pituitary stores and releases hypothalamic hormones such as ADH and oxytocin.
Cerebellum
- Cerebellum it coordinates movement and balance using the eyes, semicircular canals and muscles.
Medulla oblongata
- Medulla oblongata it controls unconscious functions through the cardiac and respiratory centres, keeping life going even if other regions are damaged.
Section 2 of 12Techniques to investigate the brain
| Technique | How it works | Strengths and limits |
|---|---|---|
| CT scan | X-rays from all angles give cross-sections; dense tissue absorbs more and appears lighter | Shows structure and bleeding after a stroke; uses higher radiation, so not for pregnant women or children |
| MRI | Magnetic field and radio waves | Higher-resolution images of soft tissue and tumours; no X-rays but costly, and unsuitable for patients with pacemakers or insulin pumps |
| fMRI | Measures the ratio of oxygenated to deoxygenated haemoglobin | Shows active regions in real time while the patient performs tasks |
| PET scan | Radioactive tracer, such as labelled glucose, collects in active areas | Shows activity and metabolism, for example reduced activity in Alzheimer's |
Techniques to investigate the brain
Linking structure to function
- CT and MRI show only structure, so function is inferred by linking damage to symptoms.
Why indirect methods
- Why indirect methods the brain is complex, delicate and protected by the skull, and regions work together.
Section 3 of 12Visual development and nature versus nurture
1Visual cortex development
- Visual cortex development axons from both eyes compete in ocular dominance columns, active synapses are strengthened and inactive ones are lost.
2Critical period
- Critical period early visual input is needed for normal development.
- Hubel and Wiesel sutured one eyelid of newborn kittens, and cortical neurones then responded almost only to the open eye.
- Deprivation in adult animals had no such effect, and children with untreated cataracts may never see normally with that eye.
3Visual pathway
- Visual pathway retina → optic nerve → optic chiasma → thalamus → visual cortex in the occipital lobe.
- (partial crossing)
4Nature versus nurture
- Nature versus nurture both genes and experience shape the brain.
- Evidence includes abilities present at birth, animal deprivation experiments, twin and adoption studies and cross-cultural studies.
5Ethics of animal research
- Ethics of animal research animals suffer and cannot consent, so work is justified by the 3Rs and medical benefit, under licensing.
- (replace, reduce, refine)
Section 4 of 12Habituation
Habituation
Habituation learning not to respond to a repeated harmless stimulus, which saves energy.
- It is stimulus-specific, and a changed stimulus produces a response again (dishabituation).
- Examples are not noticing a smell, and wild animals losing fear of humans.
Mechanism at the synapse
- Mechanism at the synapse fewer calcium channels open in the presynaptic knob, so less neurotransmitter is released.
- Fewer receptors are bound, fewer sodium channels open and the threshold is not reached, so the effector does not respond.
1
Place a snail on a clean flat surface at constant humidity and let it emerge.
2
Brush its head gently with a damp cotton bud or grass blade, and it withdraws into the shell.
3
Time how long it takes to re-emerge and extend its eye-stalks fully.
4
Repeat 10–15 times at the same place with the same object.
5
Plot touch number against re-emergence time, which falls as the snail habituates.
- Welfare
- return snails to the place they came from and handle them gently, avoiding heat and dryness.
Section 5 of 12Parkinson's disease
1Cause
- Cause loss of dopamine-producing neurones in the substantia nigra reduces dopamine in the synaptic cleft.
- Fewer sodium channels open, the postsynaptic neurone does not depolarise and fewer action potentials arise.
2Symptoms
- Symptoms tremor, slow movement, stiff muscles, poor balance and changes to speech.
3Treatments
- Treatments dopamine agonists activate dopamine receptors.
- Dopamine precursors such as L-dopa cross the blood–brain barrier and are converted to dopamine, whereas dopamine itself cannot cross.
- MAO-B inhibitors stop dopamine being broken down.
- L-dopa becomes less effective as more neurones die.
4Possible future treatments
- Possible future treatments gene therapy to raise dopamine production or protect cells, deep brain stimulation and stem cells to replace lost dopamine neurones.
Section 6 of 12Depression and MDMA
Depression
- Depression low serotonin has been linked to reduced impulses in mood-controlling areas, and noradrenaline and dopamine are also involved.
- Genetic predisposition and stressful life events increase risk.
Antidepressants
- Antidepressants they raise neurotransmitter levels.
- SSRIs block reuptake of serotonin so it stays in the cleft longer.
- TCAs raise serotonin and noradrenaline.
- MAO inhibitors stop neurotransmitters being broken down.
MDMA (ecstasy)
- MDMA (ecstasy) it blocks the serotonin reuptake transporter and triggers release of more serotonin, causing euphoria and enhanced sensation.
- Risks include overheating, dehydration and depleted serotonin afterwards.
Section 7 of 12Drug development and personalised medicine
1Development stages
- Development stages computer modelling, laboratory tests on tissue, tests on animals, then clinical trials.
- Phase 1 uses a small group of healthy people to test safety and dose.
- Phase 2 uses patients to test effectiveness, often with a placebo.
- Phase 3 compares the drug with an existing treatment in a large double-blind trial.
2Placebo and double blind
- Placebo and double blind a placebo shows whether the drug really works, and a double-blind design stops patient or doctor bias.
3Human Genome Project
- Human Genome Project knowledge of genomes allows personalised drugs matched to a person's genes.
4Ethics
- Ethics drug development raises welfare, safety and ethical issues.
Section 8 of 12Recombinant DNA and GM medicines
- Genetic engineering = transferring a gene for a desired characteristic from one organism to another,
- producing recombinant DNA and a genetically modified organism (GMO).
- The genetic code, transcription and translation are universal, so a gene works in another species.
1
Identify the gene, for example human insulin or pest resistance.
2
Isolate it with a restriction endonuclease, by using reverse transcriptase to make complementary DNA (cDNA) from mRNA, or by building synthetic DNA.
3
Multiply it with PCR.
4
Insert it into a vector cut with the same enzyme, with DNA ligase joining the sugar-phosphate backbones.
5
Transfer the vector into the host cell, which is then transformed.
6
Identify transformed cells with a marker gene such as antibiotic resistance or fluorescence.
7
Clone the transformed cells, for bacteria in a fermenter.
1Restriction endonucleases
- Restriction endonucleases each cuts at a specific restriction site leaving single-stranded sticky ends that pair with complementary ends.
- (for example HindIII at AAGCTT)
2GM micro-organisms
- GM micro-organisms bacteria with the insulin gene in plasmids grow in fermenters and make human insulin and clotting factors.
3GM plants
- GM plants a bacterium carrying the gene infects plant cells,
- or a gene gun fires DNA-coated pellets,
- and the cell grows into a plant that makes the protein,
- such as insulin or a cholera vaccine.
4GM animals
- GM animals the gene is injected into a zygote nucleus and the zygote develops in a surrogate,
- so the protein, such as human clotting factors, can be purified from milk.
Section 9 of 12Vectors and gene therapy
Transfer methods
- Transfer methods plasmids, viruses, liposomes, gene guns and microinjection.
- Few transferred genes reach the nucleus of eukaryotic cells, which limits gene therapy.
Gene therapy
Gene therapy inserting non-mutated genes into the cells of people with genetic disorders.
Plasmid vectors
- Plasmid vectors plasmids are cut with a restriction enzyme and joined to the gene by ligase to make a recombinant plasmid.
- Transformation of bacteria uses ice-cold calcium chloride then 40 °C, or electroporation.
- Only a few bacteria are transformed, so marker genes identify them.
Viral vectors
- Viral vectors viruses insert DNA into host cells and carry it to the nucleus, but may trigger an immune response, as when treating cystic fibrosis.
Liposomes
- Liposomes phospholipid vesicles that fuse with cell membranes to carry genes in.
Gene guns
- Gene guns gold or tungsten pellets coated with DNA are fired into cells.
Microinjection
- Microinjection a fine glass pipette injects DNA into animal cells, used for transgenic animals.
Section 10 of 12Microarrays, bioinformatics and GMO issues
Microarrays, bioinformatics and GMO issues
Microarray
- Microarray a grid of gene spots carrying single-stranded DNA probes that identify active genes in thousands of samples at once.
- mRNA from a reference and an unknown sample is converted to cDNA and labelled with different fluorescent tags, green for reference and red for unknown.
- The mixture hybridises with the probes and unbound DNA is washed off.
- Yellow shows equal expression, green more expression in the reference, red more in the unknown, and no fluorescence shows no expression.
- Uses include diagnosing mutations, for example high expression of oestrogen receptor genes in cancer that indicates oestrogen-blocking drugs.
Bioinformatics
Bioinformatics using computers, databases and statistics to collect, store and analyse biological data such as genome sequences.
- It compares gene function and DNA sequences between species, finds drug candidates and simulates their effects.
- It supports personalised treatments, genetic tests and gene therapy design.
Risks and benefits of GMOs
- Risks and benefits of GMOs medical benefits are weighed against concerns about gene changes, animal ethics and GM crops for human consumption.
Section 11 of 12Key terms
| Term | Meaning |
|---|---|
| Cerebellum | The brain region that coordinates movement and balance. |
| Medulla oblongata | The brain region controlling heart rate and breathing. |
| Critical period | A time in early development when stimulation is needed for normal development. |
| Habituation | Reduced response to a repeated harmless stimulus. |
| Recombinant DNA | DNA containing sequences from different organisms. |
| Restriction endonuclease | An enzyme that cuts DNA at a specific base sequence. |
| Vector | A carrier such as a plasmid that transfers a gene into a cell. |
| Microarray | A grid of DNA probes used to identify active genes. |
Section 12 of 12Exam technique
1
Saying CT scans show brain function — CT and MRI show structure, whereas fMRI and PET show activity.
2
Saying dopamine is given directly in Parkinson's disease — it cannot cross the blood–brain barrier, so L-dopa is used.
3
Saying habituation is fatigue — it is reduced neurotransmitter release from fewer calcium channels opening.
4
Saying DNA ligase cuts DNA — restriction endonucleases cut and ligase joins.
Marked practiceQuizzes for this lesson
Last updated:
\n