Scientific Article Potential Questions

How does histamine contribute to inflammation? (3 marks)

• Histamine is secreted by mast cells at the site of cell damage

• It leads to vasodilation, allowing more blood to flow to the affected area.

• It increases capillary permeability, allowing more immune cells to travel to the tissue

Why could heart function decline as a result of immune cell infiltration? (3 marks)

• Immune cells may release cytokines, leading to tissue damage'

• This increases scarring and fibrosis of the cardiac muscle tissue

• The damaged tissue contracts less efficiently, lowering cardiac output

Describe the effects of fibrosis (scarring) on heart muscle tissue (3 marks)

• Fibrosis replaces heart muscle cells with non-contractile scar tissue.

• This reduces the elasticity of the heart muscles and they will contract less efficiently.

• This could eventually lead to reduced stroke volume and high risk of heart failure.

How does chronic inflammation in heart tissue affect heart rhythm? (4 marks)

• Increase in inflammation results in greater accumulation of scar tissue in the heart muscle

• This impairs the conduction of electrical impulses from the SAN to the ventricles.

• The damage to the conduction system can result in arrhythmia or irregular heart beats.

How can antibodies reduce the effect of harmful inflammatory factors? (4 marks)

• Antibodies can directly bind to these inflammatory signaling molecules

• They can secrete perforins to destroy the factor

• This prevents the inflammatory factor from binding to the target cell and initiating an inflammatory response

• Preventing further fibrosis to the heart muscle cells.

How can the blockage of inflammatory molecules by antibodies protect heart tissue? (4 marks)

• Inflammatory molecules contribute to fibrosis/scar tissue accumulation in the heart muscle

• Because they recruit y-chromosome deficient immune cells to the site of damage, leading to infiltration.

• The neutralisation of these molecules by antibodies prevents them from interacting with heart cells & intiating an inflammatory response.

• So less fibrosis occurs and the heart muscle is able to function as normal.

Explain the role of calcium ions in the contraction of skeletal muscles (3 marks)

• Ca2+ ions are released from the sarcoplasmic reticulum and bind to troponin

• Tropomyosin changes shape and moves to expose the myosin binding sites

• Actin head binds to myosin sites to form cross bridges, leading to muscle contraction.

How is ATP involved in sliding filament theory? (3 marks)

• ATP is hydrolysed to provide energy for the power stroke

• It allows the myosin head to detach from actin

• A new atp resets the myosin heads for another cycle

Why does muscle contraction stop in the absence of ATP? (3 marks)

• Myosin heads cannot detach from actin

• Ca2+ ions cannot be actively transported back into the SR

• So the filaments remain in a contractile state, leading to muscle rigidity.

Compare the structural features of fast-twitch and slow-twitch muscle fibres. (4 marks)

• Fast twitch muscle fibres contain less mitochondria because they rely on anaerobic respiration to produce ATP.

• Slow twitch muscle fibres are smaller in diameter as they are needed for endurance rather than quick, powerful movements.

• Slow twitch have more myoglobin because they need to store more o2 to produce ATP by aerobic respiration.

• Fast twitch muscle fibres have lower capillary density as they require less oxygenated blood for aerobic respiration.

Explain how fast-twitch and slow-twitch fibres are adapted for different types of physical activity (3 marks)

• Slow-twitch fibres contract slowly and are fatigue-resistant, making them ideal for endurance activities like long-distance running.

• Fast-twitch fibres contract rapidly and generate greater force, but fatigue quickly — suitable for short bursts of activity like sprinting.

• Their metabolic and structural adaptations match their function.

What is meant by the heart being myogenic? (3 marks)

• Myogenic means that the heart muscle generates its own electrical impulses without nervous input.

• The sinoatrial node (SAN) initiates depolarisation, setting the pace of the heartbeat.

• This allows the heart to beat rhythmically and continuously on its own.

Describe how the myogenic nature of cardiac muscle coordinates the heartbeat. (4 marks)

• The SAN initiates a wave of depolarisation that causes the atria to contract and push blood into the ventricles.

• The impulse is delayed at the AVN so the av valves can close & ventricles can fill with blood.

• The impulse spreads to the bundle of His and then the purkyne fibres

• Ventricles contract from the apex upward, pushing the blood into the pulmonary vein & aorta.

Describe how neurotransmitters transmit a signal across a synapse.(3 marks)

• An action potential arrives at the presynaptic knob, causing Ca²⁺ channels to open.

• Calcium ions bind to vesicles, triggering them to release neurotransmitters into the synaptic cleft.

• The neurotransmitters bind to receptors on the postsynaptic membrane, triggering a new impulse.

Describe how a nerve impulse is transmitted along an axon (3 marks)

• A stimulus causes depolarisation as sodium ion channels open and Na⁺ enters the axon.

• The inside becomes more positive, triggering adjacent sodium channels to open — a wave of depolarisation.

• The impulse travels along the axon; repolarisation follows as K⁺ ions exit the cell.

Explain how myelination affects the speed of nerve impulse transmission.

• Myelin sheath insulates the axon, preventing ion movement except at nodes of Ranvier.

• The impulse “jumps” between nodes via saltatory conduction.

• This increases the speed of transmission compared to unmyelinated fibres.

Describe how an action potential leads to muscle contraction in skeletal muscle. (3 marks)

• The action potential travels down the motor neurone and causes release of acetylcholine at the neuromuscular junction.

• This triggers depolarisation of the muscle fibre and release of calcium ions from the sarcoplasmic reticulum.

• Calcium ions bind to troponin, exposing actin binding sites and allowing myosin heads to form cross-bridges and initiate contraction.

Explain the role of regulatory genes on the Y chromosome and why they are conserved across species. (3 marks)

• Regulatory genes control the expression of other genes, often influencing essential cellular processes.

• The Y chromosome retains a small number of highly conserved regulatory genes important for male development and fertility.

• These genes are preserved by natural selection because mutations in them can be harmful or lethal, reducing reproductive success.

Explain why some men lose the Y chromosome in their cells as they age. (3 marks)

• During repeated cell divisions, errors in chromosome replication can occur.

• The Y chromosome is small and gene-poor, so cells that lose it can often still survive and function.

• As men age, these replication errors become more frequent, leading to loss of the Y chromosome in a proportion of their immune cells.

Explain how mutations in DNA can lead to the loss of the Y chromosome in some cells. (3 marks)

• Mutations affecting genes involved in DNA replication or repair can cause errors during cell division.

• If such mutations affect chromosomal segregation or spindle attachment, the Y chromosome may not be properly distributed.

• Cells that lose the Y chromosome but retain essential autosomal genes may survive, especially because the Y carries relatively few critical genes.

Explain how some mutations do not affect the survival of a cell (3 marks)

• Some mutations are silent; they change a DNA base but not the amino acid due to the degenerate nature of the genetic code.

• Other mutations may occur in non-coding regions (e.g. introns or regulatory sequences) and have no effect on protein function.

• If the altered protein still functions sufficiently, the cell can survive and function normally

Explain how genetic variants of the Y chromosome are formed (3 marks)

• Genetic variation arises through insertion, addition, substitution and deletion mutations that change the base sequence of a gene during DNA replication.

• These changes can occur spontaneously or due to environmental factors like radiation.

• During meiosis, the Y chromosome doesn’t undergo recombination over most of its length, these mutations accumulate and are passed down unchanged from father to son.

Why might immune cells tolerate loss of the Y chromosome? (3 marks)

• The Y chromosome does not carry essential genes for immune function.

• Other chromosomes may compensate for lost functions.

• The cells still perform basic immune roles.

How can loss of the Y chromosome in immune cells cause heart damage? (3 marks)

• It leads to abnormal immune cell signaling.

• Promotes chronic inflammation and scarring of heart tissue.

• Reduces the heart’s ability to function properly.

How can Y chromosome loss contribute to disease? (3 marks)

• Affects gene expression in immune cells.

• Can trigger inflammation and organ damage (e.g. in the heart).

• Linked to increased risk of cancer and shorter lifespan.

What does the survival of cells with chromosomal loss suggest about genetic redundancy? (3 marks)

• Some genes have duplicates or backup pathways.

• Cells can adapt to partial genome losses.

• Essential functions are preserved by regulatory systems.

Explain how natural selection leads to the loss or retention of genes in a population (4 marks)

• Genes that code for advantageous traits (ie: camouflage from predators) increase an organism’s likelihood of survival.

• So, they are conserved (selected for) and passed onto offspring, increasing in frequency.

• Genes coding for disadvantageous traits decrease the biological fitness of an organism, so they are selected against and disappear from the pool.

• Neutral genes can be conserved or lost over generations depending on how they affect the biological fitness of an organism according to the changing selection pressures of the habitat.

What triggers apoptosis in cells? (2 marks)

• Dna damage, infection or intracellular signaling.

• The cell is broken into apoptotic bodies for phagocytosis.

Why is apoptosis important in development? (3 marks)

• It removes unneeded cells (e.g. between fingers in embryos).

• It shapes organs and tissues.

• Prevents overgrowth or malformations.

How does apoptosis lead to neurodegeneration? (3 marks)

• Apoptosis is a controlled process that removes damaged or malfunctioning cells.

• In the brain, excessive activation of apoptosis can lead to the loss of large numbers of neurons.

• This cell loss reduces brain function over time, contributing to neurodegenerative diseases such as Alzheimer’s.

Compare the uses of CT and MRI scans in brain imaging (3 marks)

• CT uses X-rays to create cross-sectional images of the brain and is useful for detecting bleeding, tumors, or bone injuries.

• MRI uses strong magnetic fields and radio waves to produce high-resolution images of soft tissues.

• MRI provides more detail for detecting brain abnormalities like tumors.

Explain how functional MRI (fMRI) shows brain activity. (3 marks)

• fMRI detects changes in blood oxygenation linked to neural activity.

• Active brain regions receive more oxygenated blood, which alters the magnetic properties detected by the scanner.

• These changes are converted into coloured maps showing which areas are active during specific tasks.

Describe how a PET scan works and what it can detect in the brain. (3 marks)

• A radioactive tracer (often a glucose analogue) is injected into the bloodstream.

• Active brain cells absorb more of the tracer, which emits positrons detected by the scanner.

• PET scans measure metabolic activity and are used to detect functional abnormalities, such as those seen in Alzheimer’s disease or brain tumours.

Describe the role of transcription factors in regulating gene expression. (3 marks)

• Transcription factors are proteins that bind to specific DNA sequences (promoters or enhancers).

• They either promote or inhibit the binding of RNA polymerase to the gene.

• This regulates the initiation of transcription and controls gene expression.

Explain how DNA methylation can lead to gene silencing (3 marks)

• Methyl groups are added to cytosine bases near promoter regions.

• This changes the structure of chromatin, making it more condensed (heterochromatin).

• RNA polymerase cannot access the gene, so transcription is prevented.

Describe how histone modification can influence gene expression (4 marks)

• Histones can be modified by acetylation or methylation.

• Acetylation reduces the positive charge on histones, loosening their interaction with DNA and increasing gene accessibility for transcription.

• Methylation can either activate or repress gene expression, depending on which amino acids on the histone are methylated and how many methyl groups are added.

Explain how non-coding RNA (ncRNA) can regulate gene expression. (3 marks)

• Some ncRNAs bind to complementary mRNA.

• This can block translation or lead to degradation of the mRNA.

• As a result, the corresponding protein is not produced.

Describe how a DNA microarray is used to compare gene expression in two tissue samples (3 marks)

• mRNA is extracted from both tissues and converted to complementary DNA (cDNA) using reverse transcriptase.

• The cDNA samples are labelled with different fluorescent dyes and applied to a microarray chip.

• Each spot on the chip contains DNA probes for specific genes; the intensity and colour of fluorescence at each spot indicate relative gene expression levels in the two tissues.

Give two advantages of using microarrays in biomedical research and one limitation (3 marks)

• Advantage: Allows simultaneous analysis of thousands of genes in a single experiment.

• Advantage: Helps identify gene expression differences between healthy and diseased cells.

• Limitation: Only detects genes already represented on the array; it cannot discover unknown genes.

Explain what is meant by a gene knock-out (3 marks)

• A gene knock-out involves removing or disrupting a gene so it cannot be transcribed or translated.

• This prevents the production of the protein encoded by that gene.

• Scientists use knock-out models to study the function of specific genes by observing what changes when they are missing.

Describe how gene silencing can prevent a gene from being expressed (3 marks)

• Gene silencing involves blocking the transcription or translation of a gene without changing the DNA sequence.

• This can occur via mechanisms like DNA methylation, histone modification, or non-coding RNA.

• As a result, the protein product of the gene is not produced.

Give one difference and one similarity between gene knock-out and gene silencing (2 marks)

• Difference: Knock-out removes or disrupts the gene itself; silencing prevents its expression without altering the gene sequence.

• Similarity: Both stop the production of the gene’s protein product.

• Both are used to study gene function in experimental systems.

Define CRISPR (2 marks)

• CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a gene-editing tool that uses a guide RNA and the Cas9 enzyme to make precise cuts in DNA.

• It allows scientists to add, remove, or modify specific genes in an organism’s genome.

Define genetic modification and give one example (3 marks)

• Genetic modification involves altering the genetic material of an organism by inserting, deleting, or changing specific genes.

• This is often done using recombinant DNA technology.

• For example, inserting the human insulin gene into bacteria to produce insulin for medical use.

Describe how a gene can be inserted into a bacterial plasmid (3 marks)

• A restriction enzyme cuts the plasmid and the target gene at specific sequences, producing complementary sticky ends.

• The target gene is inserted into the plasmid using DNA ligase.

• The recombinant plasmid is introduced into bacteria via transformation (e.g. heat shock or electroporation)

Explain one advantage and one ethical concern of genetic modification in agriculture (2 marks)

• Advantage: GM crops can be made resistant to pests, increasing yield and reducing the need for pesticides.

• Ethical concern: Some people are concerned about the long-term ecological effects or health impacts of GM foods.

• There are also concerns about the control of food supply by biotech companies.

What causes the symptoms of Parkinson’s disease?

• Parkinson’s disease is caused by the death of dopamine-producing neurons in the substantia nigra of the brain.

• This leads to reduced dopamine levels in motor pathways.

• As a result, muscle control and coordination are affected.

Explain how L-Dopa can be used to treat Parkinson’s disease.

• L-Dopa is a precursor to dopamine that can cross the blood–brain barrier.

• Once inside the brain, it is converted into dopamine.

• This increases dopamine levels, improving motor control and reducing symptoms.

Describe two motor symptoms of Parkinson’s disease and their biological cause.

• Symptoms include muscle rigidity and tremors.

• These result from decreased dopamine levels.

• Dopamine is needed for smooth and coordinated muscle movement.

Describe the biological explanation for depression.

• Depression is linked to low levels of serotonin in the brain.

• This can be due to reduced production, release, or receptor sensitivity.

• Low serotonin affects mood regulation and emotional balance.

How do SSRIs work to treat depression?

• SSRIs block the reuptake of serotonin in the synaptic cleft.

• This increases the concentration of serotonin at synapses.

• Higher serotonin levels improve communication between neurons and help stabilise mood.

Give one reason why not all patients respond to SSRI treatment.

• The cause of depression may involve other neurotransmitters (e.g. dopamine or noradrenaline).

• Some individuals may have receptor-level issues that SSRIs cannot correct.

• Genetic variation can affect drug metabolism or response.

Describe how the medulla oblongata controls heart rate.

• It receives input from baroreceptors and chemoreceptors.

• It sends impulses via the sympathetic or parasympathetic nervous system.

• This alters the frequency of impulses from the SAN.

How do the sympathetic and parasympathetic systems differ in their effects on the heart?

• The sympathetic nervous system increases heart rate and force of contraction.

• It releases noradrenaline onto the SAN.

• The parasympathetic system reduces heart rate by releasing acetylcholine.

What is the role of the sinoatrial node (SAN) in heart control?

• The SAN generates electrical impulses that initiate heartbeats.

• It sets the pace for the heart—known as the pacemaker.

• These impulses spread across the atria, causing them to contract.

Explain the effect of adrenaline on the heart during stress.

• Adrenaline binds to receptors on cardiac muscle.

• This increases the frequency and force of contraction.

• Heart rate and cardiac output increase to supply more oxygen to tissues.

Describe the hormonal changes that occur in response to low blood pressure.

• Adrenal glands release adrenaline and noradrenaline.

• These hormones cause vasoconstriction and increase heart rate.

• This raises blood pressure back to normal.

Describe the process of transcription in protein synthesis.

• RNA polymerase binds to the promoter region of a gene and separates the DNA strands.

• It uses one strand as a template to assemble a complementary strand of pre-mRNA using free RNA nucleotides.

• Transcription continues until a stop signal is reached; the pre-mRNA is then processed (e.g. intron removal) to form mature mRNA.

Explain how the sequence of bases in mRNA determines the structure of a protein.

• The base sequence in mRNA is read in triplets called codons.

• Each codon codes for a specific amino acid.

• The sequence of codons determines the order of amino acids in the polypeptide, which then folds into a specific 3D protein structure

Describe the role of tRNA in the process of translation.

• Each tRNA molecule has an anticodon that is complementary to an mRNA codon.

• It carries a specific amino acid to the ribosome.

• The amino acids are joined by peptide bonds to form a polypeptide chain.

Explain the process of RNA splicing and its role in gene expression.

• Introns (non-coding regions) are removed from pre-mRNA.

• Exons (coding regions) are joined together to form mature mRNA.

• This ensures that only coding information is translated into a protein.

How can alternative splicing lead to different proteins being produced from the same gene?

• Different combinations of exons can be joined during RNA splicing.

• This results in mRNA molecules with different coding sequences.

• Each variant is translated into a different protein, increasing protein diversity from a single gene.

Explain how hormones can affect the function of cells that carry mutations.

• Hormones bind to specific receptors on or in target cells, triggering intracellular signaling pathways.

• In mutated cells, the response to hormones may be altered if the mutation affects hormone receptors or signaling proteins.

• This can lead to abnormal gene expression or uncontrolled growth, such as in hormone-sensitive cancers.

Explain how the loss of the Y chromosome in some cells may contribute to the development of cancer.

• The Y chromosome loss may result in disrupted gene regulation, including genes involved in cell cycle control.

• This can impair immune surveillance, allowing abnormal cells to survive and divide.

• Accumulation of further mutations in such cells may lead to uncontrolled proliferation — a key feature of cancer.

Describe the purpose of phase 1, 2, and 3 clinical trials.

• Phase 1: Tests the drug on a small group of healthy volunteers to assess safety, side effects and dosage.

• Phase 2: Tests the drug on a small group of patients to evaluate effectiveness and side effects.

• Phase 3: Compares the drug to existing treatments in a large group of patients to confirm effectiveness and monitor long-term effects.

Explain why double-blind and placebo-controlled methods are used in clinical trials.

• Double-blind means neither the participants nor researchers know who receives the treatment or placebo, reducing bias.

• A placebo allows comparison with a group not receiving the active drug.

• This ensures that observed effects are due to the drug and not psychological or environmental factors.

Why is randomisation important in clinical trials?

• Randomly assigning participants to treatment or control groups reduces selection bias.

• It ensures that the groups are similar in characteristics like age, sex, or health status.

• This increases the reliability and validity of the results.