AQA Biology Essay Practice – Part 2

“The importance of...” questions – let’s keep going!

Author

Jen - Primrose Kitten
November 16, 2025

Welcome to Part 2 of this three-part blog series all about tackling those tricky 25-mark “importance of…” essay questions from the AQA A-level Biology paper. These essays are your chance to show off how well you understand the whole course – so I’ve broken them down into manageable chunks to help you prepare, revise, and feel more confident going into the exam.

If you missed Part 1, go back and check it out – it covers some of the foundational ideas like the importance of carbon dioxide, nitrogen-containing substances, water, hydrogen bonds, and energy transfer. All brilliant topics to help you build strong, well-rounded essays.

This second post picks up with processes and mechanisms that are central to how living organisms function. As before, each section includes:
✅ Key links to the AQA spec
✅ Core content you must include
✅ Ideas that go beyond the spec for those top-band marks

Here’s what’s covered in Blog Post 2:

  1. The importance of movement within organisms

  2. The importance of enzymes to living organisms

  3. The importance of DNA within living organisms

  4. The importance of ions to living organisms

  5. The importance of cycles to living organisms

These topics are great for connecting across different parts of the spec – enzymes link to metabolism and gene expression, ions link to nerves and water potential, and the biological cycles turn up all over the place!

Then, once you’re ready, Blog Post 3 dives into more advanced concepts like shape specificity, membranes, variation and diversity, and homeostasis – perfect for that top-level evaluation and application.

So whether you're working through these step by step, or jumping in where you need the most support, you're doing great. Keep going, take breaks, and remember – your ability to learn is far more important than your ability to memorise.

Let’s get into it!

Table of Contents

🧩 The Perfect Structure: 10 Paragraphs, 5 Topics

How to Build a High-Scoring Biology Essay

Before diving into this set of “importance of…” questions, let’s pause for a quick reminder on structure – because how you organise your answer is just as important as what you write.

This is where the magic formula ✨ comes in. Don’t stress about writing a fancy English-style intro or a poetic conclusion – this isn’t Shakespeare, it’s science. You just need to show what you know and explain why it matters.

👇 Here’s the plan:

➡️ Pick 5 different topics from across the A-level spec that link to the question
➡️ For each topic, write two clear paragraphs:

1️⃣ AO1 Paragraph – What do you know?
Facts, definitions, processes, diagrams if helpful. This is your science knowledge.

2️⃣ AO2 Paragraph – Why is it important?
How does this idea help organisms survive, reproduce, adapt, or function in ecosystems?

This structure gives examiners lots of material to work with. They’ll mark your four best topics – so even if one’s a bit wobbly, you’ve got backup.

✏️ Make a Plan (It’s Worth It!)

Start your essay with a quick 1–2 minute plan. Just jot down:

  • Your 5 chosen topics

  • A few AO1 and AO2 bullet points for each

It keeps your thoughts organised and your writing focused – and examiners love a well-structured answer 🧠🗂️

📺 Need Help Visualising This?

We’ve got you covered over in the Skills Lab!
✅ Watch step-by-step essay planning videos
✅ See full sample essays with examiner-style commentary
✅ Learn exactly what earns those top-level marks

Because sometimes seeing it done is the best way to really get how it works.

The importance of movement within organisms

1. Diffusion

2. Osmosis

  • AO1: Diffusion of water across a selectively permeable membrane.

  • AO2: Regulates cell volume and maintains turgor in plant cells.

3. Active Transport

4. Co-Transport

  • AO1: Sodium-potassium pump creates a gradient used to transport glucose/amino acids.

  • AO2: Key in glucose reabsorption in the kidney and nutrient absorption in the gut.

5. Mass Transport in the Blood

6. Gas Exchange in the Lungs

  • AO1: Oxygen moves into the blood; CO₂ moves out across alveolar membranes.

  • AO2: Supplies O₂ for respiration and removes toxic CO₂.

7. Haemoglobin and Oxygen Transport

8. Tissue Fluid Formation

9. Phloem Translocation

10. Xylem Transport

11. Muscle Contraction

  • AO1: Involves actin-myosin sliding filament mechanism using ATP.

  • AO2: Enables movement of the organism and internal processes (e.g. peristalsis, ventilation).

12. Neurone Transmission

  • AO1: Movement of action potentials via ion movement across membranes.

  • AO2: Enables fast communication and coordinated responses.

13. Synaptic Transmission

14. Ultrafiltration in Kidneys

  • AO1: Movement of small molecules out of the blood into the nephron at the glomerulus.

  • AO2: Initiates urine formation and removal of waste/toxins.

15. Selective Reabsorption

  • AO1: Useful substances (e.g. glucose, water) move back into blood from nephron.

  • AO2: Conserves valuable nutrients and maintains water balance.

16. Transpiration Stream

  • AO1: Water moves from roots to leaves, then evaporates.

  • AO2: Enables mineral transport, cooling, and maintains water potential gradient.

17. Mitosis and Chromosome Movement

18. Cilia and Flagella

  • AO1: Structures that move fluid or cells (e.g. in airways or sperm).

  • AO2: Critical for clearing mucus or enabling reproduction.

Going beyond the spec for those last 2 marks

✨ Including any of these shows awareness of cellular and physiological processes beyond the spec, which examiners reward in top-band essays.

1. Cytoplasmic Streaming in Plant Cells

In some plant cells (e.g. Elodea), cytoplasmic streaming moves organelles around the cell using actin filaments. This improves the distribution of nutrients and molecules, showing how movement within cells enhances efficiency.

2. Movement of Cilia in the Respiratory Tract

Ciliated epithelial cells move mucus up the trachea to remove pathogens and debris. While students learn about gas exchange, the detail of ciliary movement isn’t on the spec and illustrates internal transport.

3. Axonal Transport in Neurones

Motor proteins like kinesin and dynein move vesicles and organelles along microtubules inside axons. This intracellular movement is vital for neurotransmitter release and nerve function.

4. Cytoskeletal Role in Cell Division

Beyond spindle fibres, actin filaments contract during cytokinesis to split the cytoplasm. This intracellular movement is critical for producing viable daughter cells.

5. Peristalsis in the Digestive System

Coordinated muscle contractions move food along the gut. It’s a specific physiological example of internal movement that links to nutrient absorption and energy supply.

The importance of enzymes to living organisms

1. Enzyme Structure and Function

2. Lock-and-Key vs. Induced Fit Model

  • AO1: Models explaining enzyme-substrate specificity.

  • AO2: Illustrates how precise enzyme structure is essential for correct function.

3. Effect of Temperature and pH on Enzymes

4. Digestive Enzymes

5. ATP Synthase

  • AO1: Enzyme that synthesises ATP from ADP and Pi during respiration and photosynthesis.

  • AO2: Provides energy for all cellular activities—critical to life.

6. DNA Polymerase and DNA Helicase

  • AO1: Enzymes involved in DNA replication.

  • AO2: Ensure accurate copying of genetic information for inheritance and cell division.

7. RNA Polymerase

8. Restriction Endonucleases and Ligase

  • AO1: Enzymes used in genetic engineering to cut and join DNA.

  • AO2: Enable biotechnology applications such as producing insulin or GM crops.

9. Enzymes in Photosynthesis

  • AO1: Rubisco catalyses carbon fixation in the Calvin cycle.

  • AO2: Essential for glucose production and the base of food chains.

10. Enzymes in Respiration

  • AO1: Dehydrogenase and decarboxylase enzymes involved in glycolysis and Krebs cycle.

  • AO2: Facilitate ATP production—without which cells cannot function.

11. Intracellular vs. Extracellular Enzymes

  • AO1: Some enzymes work inside cells (e.g. DNA polymerase), others outside (e.g. digestive enzymes).

  • AO2: Enables efficiency in both metabolism and digestion.

12. Inhibition (Competitive and Non-Competitive)

  • AO1: Molecules that reduce enzyme activity by binding to active/allosteric sites.

  • AO2: Regulation of metabolic pathways and target for drugs (e.g. antibiotics).

13. Enzyme-Substrate Complex

  • AO1: Temporary binding of enzyme and substrate at the active site.

  • AO2: Central to enzyme specificity and catalytic activity.

14. Metabolic Pathways

  • AO1: Series of enzyme-controlled reactions (e.g. respiration, photosynthesis).

  • AO2: Each step depends on enzyme function—disruption leads to metabolic failure.

15. Enzymes in the Immune System

  • AO1: Lysozymes break down bacterial cell walls; proteases in phagocytes digest pathogens.

  • AO2: Critical for defence against infection.

16. Enzymes in Protein Synthesis

  • AO1: Peptidyl transferase forms peptide bonds during translation.

  • AO2: Ensures correct assembly of polypeptides for structure and function.

17. Temperature Regulation and Enzyme Activity

  • AO1: Thermoregulation ensures enzymes remain at optimal temperature.

  • AO2: Prevents denaturation and maintains consistent metabolic rate.

18. Extremophile Enzymes

Enzymes from organisms in hot springs (Taq polymerase) or cold seas are adapted to unusual conditions. Their stability demonstrates the versatility of enzymes and is harnessed in PCR and biotechnology.

Going beyond the spec for those last 2 marks

✨ Dropping in 1–2 of these “bonus” examples shows examiners wider biological awareness and makes the essay stand out.

1. Enzymes in Fertilisation

Acrosome enzymes in sperm digest zona pellucida around egg cell. This enables sperm penetration and successful fertilisation.

2. Enzyme Regulation via Feedback Inhibition

End products sometimes inhibit enzymes in early steps of metabolic pathways e.g ATP synthesis. Maintains homeostasis and resource efficiency in cells.

3. Enzyme Replacement Therapy in Medicine

Some genetic disorders (e.g. Gaucher’s disease) are treated with enzyme replacement therapy. This highlights enzymes’ essential role in metabolism and how medicine uses them when natural production fails.

4. Enzymes in Food Production

Lactase is added to milk to make it lactose-free, and rennin substitutes are used in cheese-making. These applications show enzymes’ importance not only in physiology but also in global nutrition.

5. Enzymes in Drug Design and Diagnostics

Enzymes are used in biosensors (e.g. glucose oxidase in diabetes monitoring) and targeted by drugs (e.g. ACE inhibitors in blood pressure treatment). This demonstrates enzymes’ medical and technological importance beyond natural processes.

6. Enzymes in Industrial Biotechnology

Enzymes like proteases in washing powders or cellulases in biofuel production are used at industrial scale. This shows how humans exploit enzymes’ specificity and efficiency outside of living organisms.

The importance of DNA within living organisms

1. Structure of DNA

2. Complementary Base Pairing

  • AO1: A-T (2 hydrogen bonds), C-G (3 hydrogen bonds); strands are antiparallel.

  • AO2: Ensures accurate DNA replication and transcription—key to inheritance and protein synthesis.

3. DNA Replication

  • AO1: Semi-conservative; involves DNA helicase and DNA polymerase.

  • AO2: Allows genetic continuity between cell generations and during reproduction.

4. Genes and Genetic Code

  • AO1: Genes are DNA sequences that code for polypeptides; genetic code is universal, degenerate, and non-overlapping.

  • AO2: Directs protein synthesis, underpinning cell function and organism traits.

5. Transcription

6. Translation

  • AO1: mRNA is decoded into a polypeptide at the ribosome, with the help of tRNA and rRNA.

  • AO2: Converts genetic information into functional proteins.

7. Regulation of Gene Expression

  • AO1: Includes transcription factors, epigenetics, and operon systems in prokaryotes.

  • AO2: Allows cells to specialise and respond to environmental changes.

8. Mitosis

  • AO1: Produces genetically identical diploid cells with identical DNA.

  • AO2: Supports growth, repair, and asexual reproduction with genetic consistency.

9. Meiosis

  • AO1: Produces haploid gametes with unique DNA through crossing over and independent assortment.

  • AO2: Increases genetic variation—essential for evolution and reproduction.

10. Mutation

  • AO1: Change in base sequence; may be silent, missense, or nonsense.

  • AO2: Source of genetic diversity; can cause genetic disorders or drive evolution.

11. DNA in Genetic Inheritance

12. DNA and Genetic Disorders

13. Genome Projects and DNA Sequencing

14. Gene Therapy

15. Recombinant DNA Technology

16. DNA in Forensics and Identification

  • AO1: Short Tandem Repeats (STRs) used in DNA profiling.

  • AO2: Helps identify individuals in forensic science, paternity testing, and conservation.

17. DNA in Evolutionary Relationships

18. Epigenetics

19. DNA in Cell Differentiation

  • AO1: All cells contain the same DNA, but gene expression varies.

  • AO2: Allows formation of specialised tissues and organs.

20. Plasmids and Prokaryotic DNA

Going beyond the spec for those last 2 marks

✨ Including even one of these shows examiners scientific curiosity and wider knowledge, which is exactly what they reward at the very top level.

1. Mitochondrial DNA in Ancestry Studies

Mitochondrial DNA (mtDNA) is inherited maternally and used to trace human evolution and migration patterns. This shows how DNA can be applied beyond cell biology to study population history.

2. CRISPR-Cas9 and Gene Editing

CRISPR uses guide RNA to target DNA sequences for editing. This demonstrates how DNA can be precisely manipulated in biotechnology and medicine, emphasising its central role in life and innovation.

3. Gene Silencing as Gene Therapy

DNA methylation and histone modification affect gene expression without changing base sequences. This along with siRNAs and microRNAs could be used to treat genetic disorders by silencing mutated genes.

The importance of ions to living organisms

1. Iron (Fe²⁺) in Haemoglobin

  • AO1: Fe²⁺ binds oxygen in haem groups of haemoglobin.

  • AO2: Allows red blood cells to transport oxygen to tissues for aerobic respiration.

2. Hydrogen Ions (H⁺) and pH

  • AO1: H⁺ concentration determines pH.

  • AO2: pH affects enzyme activity and protein structure; essential for homeostasis.

3. Sodium Ions (Na⁺) in Co-Transport

  • AO1: Sodium ions drive co-transport of glucose/amino acids into epithelial cells.

  • AO2: Enables efficient nutrient absorption in the gut and reabsorption in the kidneys.

4. Potassium Ions (K⁺) and Action Potentials

  • AO1: Involved in repolarisation of neurones during nerve transmission.

  • AO2: Restores membrane potential; essential for nerve and muscle function.

5. Calcium Ions (Ca²⁺) in Muscle Contraction

  • AO1: Ca²⁺ binds to troponin, allowing actin-myosin interaction.

  • AO2: Triggers muscle contraction—important for movement, heartbeat, and peristalsis.

6. Calcium Ions in Synaptic Transmission

  • AO1: Ca²⁺ influx causes vesicles to release neurotransmitters into synaptic cleft.

  • AO2: Enables nerve signal transmission between neurones.

7. Phosphate Ions (PO₄³⁻) in ATP

8. Phosphate Ions in DNA and RNA

  • AO1: Form part of the sugar-phosphate backbone.

  • AO2: Provide structural integrity and stability of genetic material.

9. Magnesium Ions in Chlorophyll

  • AO1: Central Mg²⁺ atom is essential in chlorophyll molecules.

  • AO2: Enables plants to absorb light energy for photosynthesis.

10. Chloride Ions (Cl⁻) in Osmoregulation

  • AO1: Help maintain electrochemical balance in cells and bodily fluids.

  • AO2: Contribute to blood pressure regulation and nerve function.

11. Nitrate Ions (NO₃⁻) in Plants

  • AO1: Absorbed by roots; used to make amino acids, proteins, and DNA.

  • AO2: Essential for plant growth and protein synthesis.

12. Ions in Water Potential

  • AO1: Solutes like Na⁺, K⁺ affect water potential and movement via osmosis.

  • AO2: Crucial for maintaining cell turgor, water uptake, and transport.

13. Ions in Neurone Resting Potential

  • AO1: Na⁺/K⁺ pumps create electrochemical gradients.

  • AO2: Enables neurones to transmit electrical signals.

14. Sodium Ions in Osmoregulation

  • AO1: Influence water reabsorption in kidney nephrons.

  • AO2: Helps regulate blood pressure and hydration.

15. Ions in Electrochemical Gradients

  • AO1: Na⁺ and H⁺ gradients power active transport and ATP synthesis.

  • AO2: Drives co-transport, nutrient uptake, and respiration efficiency.

Going beyond the spec for those last 2 marks

✨ Just one or two of these examples in an essay shows examiners that a student has gone beyond the spec and is thinking like a biologist — exactly what gets rewarded in the higher bands.

1. Calcium Ions in Blood Clotting

Ca²⁺ acts as a cofactor in the clotting cascade. Prevents excessive bleeding and supports wound healing.

2. Ions in Enzyme Activation

Some ions (e.g. Mg²⁺, Ca²⁺) are enzyme cofactors which bind to enzymes and activate them so they are able to work. Enable metabolic reactions by facilitating enzyme function.

3. Bicarbonate Ions (HCO₃⁻) in Carbon Dioxide Transport

Helps maintain blood pH that would be lowered when carbon dioxide enters the blood at respiring tissues by buffering excess H⁺. Maintains enzyme activity and homeostasis.

4. Iron in Medicine (Anaemia and Supplements)

Iron deficiency leads to anaemia, often treated with iron tablets or fortified foods. This highlights the crucial role of iron ions in haemoglobin and human health beyond basic biology.

5. Fluoride Ions in Dental Health

Fluoride strengthens tooth enamel and prevents cavities, which is why it’s often added to drinking water and toothpaste. This shows ions’ role in applied biology and public health.

6. Lithium Ions in Mental Health Treatment

Lithium salts are used to treat bipolar disorder and stabilise mood. This demonstrates the importance of ions in medicine and nervous system regulation.

7. Calcium Ions in Plant Signalling

In plants, calcium ions act as secondary messengers in response to environmental stimuli like pathogens or drought. This expands the importance of ions from animals to plant physiology.

8. Magnesium Ions in Biotechnology (PCR and Enzymes)

Magnesium ions are essential cofactors for DNA polymerase in PCR. This shows how ions are not only biologically important but also critical in molecular biology techniques.

The importance of cycles to living organisms

1. Carbon Cycle

  • AO1: Movement of carbon between the atmosphere, organisms, and the environment via photosynthesis, respiration, decomposition, and combustion.

  • AO2: Maintains carbon availability for organic molecules like carbohydrates and supports energy transfer in ecosystems.

2. Nitrogen Cycle

3. Water Cycle

  • AO1: Movement of water via evaporation, transpiration, condensation, and precipitation.

  • AO2: Maintains water availability for metabolism, photosynthesis, and transport in organisms.

4. Krebs Cycle (Citric Acid Cycle)

5. Calvin Cycle

6. ATP Cycle

  • AO1: ATP is synthesised from ADP + Pi and hydrolysed to release energy.

  • AO2: Powers biological processes including muscle contraction, active transport, and biosynthesis.

7. Cell Cycle

8. Mitosis

  • AO1: Produces two genetically identical diploid cells.

  • AO2: Supports tissue repair, growth, and asexual reproduction in multicellular organisms.

9. Meiosis

10. Nutrient Cycles in Ecosystems

  • AO1: Movement of elements like nitrogen, phosphorus, and carbon through biotic and abiotic parts of the ecosystem.

  • AO2: Supports sustainable life by replenishing essential nutrients for organisms.

12. Decomposition and Detritus Cycle

  • AO1: Saprobionts break down dead organic matter into inorganic ions.

  • AO2: Recycles nutrients like nitrogen and phosphorus for plant uptake.

13. Oxygen Cycle

  • AO1: Oxygen is produced by photosynthesis and consumed in respiration.

  • AO2: Supports aerobic life and energy production in cells.

14. Phosphorus Cycle

15. Lysogenic and Lytic Cycles (Viral Life Cycles)

  • AO1: Viral DNA integrates into host genome (lysogenic) or immediately replicates and lyses host (lytic).

  • AO2: Explains viral replication and implications for disease spread.

16. Menstrual Cycle

  • AO1: Hormonal regulation of ovulation and uterine lining changes over ~28 days.

  • AO2: Essential for reproduction and preparation of the body for pregnancy.

17. Electron Transport Chain (ETC)

  • AO1: Electrons from NADH and FADH₂ are passed through membrane proteins to drive ATP synthesis.

  • AO2: Produces the majority of ATP in aerobic respiration—essential for life processes.

18. Thermoregulatory Feedback Cycles

  • AO1: Negative feedback loops involving thermoreceptors, hypothalamus, and effectors.

  • AO2: Maintains optimal temperature for enzyme activity and homeostasis.

19. Homeostatic Feedback Cycles

Going beyond the spec for those last 2 marks

✨ Even dropping in one or two of these shows wider scientific awareness and connects biology to earth science and human impact — exactly the sort of thinking examiners reward in the higher bands.

1. The Sulphur Cycle

Sulphur moves between rocks, the atmosphere, and organisms, with bacteria playing key roles in transformations. It’s vital for proteins (cysteine and methionine), showing how additional nutrient cycles support life.

2. The Phosphorus Cycle in Human Health

Beyond the spec, disruption of the phosphorus cycle through fertiliser overuse causes eutrophication. This highlights how human activities impact global nutrient cycles and ecosystem health.

3. The Oxygen Cycle

Oxygen is cycled between photosynthesis and respiration across ecosystems. Including this shows how tightly linked gas cycles are, with oxygen availability underpinning aerobic life.

4. The Water Cycle in Climate Regulation

Students learn water’s role in organisms, but linking it to the hydrological cycle shows its planetary significance. The cycling of water drives climate systems and supports all ecosystems.

5. The Rock (Geological) Carbon Cycle

Long-term storage of carbon in rocks and release through volcanic activity regulates atmospheric CO₂ over millions of years. This adds depth, linking biological processes with Earth’s systems and climate stability.

6. Calcium and Phosphate Cycles in Bones

Bone remodelling involves resorption and deposition of calcium and phosphate. Maintains bone strength and mineral balance in the blood. Helps bones to heal from breaks and fractures