Biology GCSE 🧬

• 🧫 Cell biology & microscopy
• 🌱 Organisation in animals & plants (tissues, organs, systems)
• 🦠 Infection & response (pathogens, immunity, vaccines)
• 💉 Bioenergetics (respiration & photosynthesis)
• 🧬 Inheritance, genetics & evolution
• 🌍 Ecology & biodiversity
• 🧪 Required practicals and scientific method

🧪 Exam Tip: Learn your required practicals inside‑out. Biology papers often ask how you’d carry out, interpret, or improve them.

🧫 All living organisms are made of cells. There are two types: prokaryotic (bacteria) and eukaryotic (plants, animals).

Key Differences Summary:

• Eukaryotes have membrane‑bound organelles and a nucleus.
• Prokaryotes are simpler and smaller with no nucleus.
• Prokaryotes have more diverse metabolic capabilities.
• Eukaryotic DNA is linear; prokaryotic is circular.

Microscopes allow scientists to see structures that are too small to be seen with the naked eye. There are two main types you need to know for GCSE: light microscopes and electron microscopes.

🔎 Types of Microscopes

🧠 Key Terms

• Magnification: How many times larger the image is compared to the real object.
• Resolution: The ability to distinguish two separate points clearly – higher resolution gives a clearer, more detailed image.

📐 Magnification Equation

Magnification = Image size ÷ Real size

• Match your units! (e.g. mm to μm)
• 1 mm = 1,000 μm
• Rearrange as needed:
  • Image size = Real size × Magnification
  • Real size = Image size ÷ Magnification

Example Question:

If the image of a cell is 20 mm and the magnification is ×500, what is the real size?
Real size = 20 mm ÷ 500 = 0.04 mm = 40 μm

🛠️ Required Practical: Using a Microscope

1. Place a specimen on a slide with a drop of water or stain (e.g. iodine).
2. Add a coverslip carefully to avoid bubbles.
3. Clip slide onto stage and use coarse focus to find specimen.
4. Use fine focus to sharpen the image under low power.
5. Switch to higher magnification for more detail.
6. Draw labelled diagram and calculate magnification using scale bar if needed.

📚 Exam Tips

• Always label diagrams: cell membrane, cytoplasm, nucleus, etc.
• Know how to use the magnification triangle: M = I ÷ A
• Remember differences between resolution and magnification!
• Light microscopes are good for real‑time viewing of living cells; electron microscopes show ultrastructure in detail.

💡 Summary: Light microscopes are great for basic cells, while electron microscopes allow us to study viruses and organelles in much greater detail. Master the magnification formula and understand practical setup for microscopy questions.

Cells divide for growth, repair, and reproduction. This involves accurately copying DNA and distributing it into new cells via mitosis or meiosis. These processes occur as part of the cell cycle.

📘 DNA Replication (Before Cell Division)

• Occurs during the interphase of the cell cycle.
• The DNA molecule unzips (hydrogen bonds break).
• Free DNA nucleotides match up with complementary bases on each strand (A‑T, C‑G).
• DNA polymerase helps form new sugar‑phosphate backbones.
• This results in two identical DNA molecules, each with one original and one new strand (called semi‑conservative replication).

🔄 The Cell Cycle

• Interphase: Cell grows, replicates DNA and organelles.
• Mitosis: Nuclear division – chromosomes are evenly divided.
• Cytokinesis: Cell splits into two identical daughter cells.

📊 Mitosis vs Meiosis

🧪 Mitosis Stages (IPMATC)

1. Interphase: DNA replicates, cell prepares to divide
2. Prophase: Chromosomes condense, spindle forms
3. Metaphase: Chromosomes line up at cell equator
4. Anaphase: Chromatids pulled apart to opposite poles
5. Telophase: New nuclear envelopes form
6. Cytokinesis: Cell splits into two identical cells

🎯 Key Exam Tips

• Know the differences between mitosis and meiosis.
• Be able to describe DNA replication and why it’s needed.
• Understand the role of base pairing in accuracy (A‑T, C‑G).
• In meiosis, variation occurs due to crossing over and independent assortment (higher tier).

💡 Summary: DNA replication ensures genetic information is copied before cell division. Mitosis creates identical cells for growth/repair; meiosis creates genetically diverse gametes. Both are part of the wider cell cycle essential for life.

☀️ Photosynthesis is how plants make glucose using sunlight:

carbon dioxide + water → glucose + oxygen
(with light and chlorophyll)

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (chlorophyll, light)

🔄 Glucose is used for respiration, making cellulose, amino acids, or stored as starch.

Need to Know:

• Endothermic reaction (takes in energy)
• Occurs in palisade mesophyll cells (most chloroplasts)
• Leaves are adapted with stomata, thin shape, and large surface area

❤️ The heart pumps blood around the body via arteries, veins, and capillaries. Double circulation: heart → lungs → heart → body. Arteries (high pressure), veins (valves), capillaries (exchange).

Need to Know Diagrams:

• Heart structure (label chambers, valves, vessels)
• Artery vs vein vs capillary cross‑sections
• Oxygen dissociation curve (haemoglobin saturation)

Aerobic vs Anaerobic

Exercise & Oxygen Debt

• During exercise: ↑ heart rate, ↑ breathing rate & depth → more O₂ + removal of CO₂.
• Post‑exercise: heavy breathing repays oxygen debt, oxidising lactic acid to CO₂ + H₂O.
• GCSE practical: measure pulse/breathing rate before & after activity.

Homeostasis maintains constant internal conditions. GCSE focuses on nervous and hormonal coordination, glucose, temperature, and (Triple) kidney water balance.

Nervous System & Reflex Arc

1. Stimulus detected by receptor (e.g. heat on skin)
2. Sensory neurone → spinal cord
3. Relay neurone in CNS (synapse neurotransmitters)
4. Motor neurone → effector (muscle/gland)
5. Rapid, automatic response – protective

Endocrine System Overview

Blood‑Glucose Control (Negative Feedback)

• High glucose → pancreas releases insulin → liver & muscle convert glucose → glycogen → level falls
• Low glucose → pancreas releases glucagon → glycogen → glucose → level rises
• Failure of insulin production = Type 1 diabetes; treated with injections.

Thermoregulation (Skin)

• Too hot: vasodilation, sweating, hairs lie flat
• Too cold: vasoconstriction, shivering, hairs erect (insulation)

Triple‑only: Kidney & Water Balance

Nephrons filter blood; selective reabsorption forms urine.

• ADH from pituitary alters permeability of collecting duct.
• Dialysis or transplant for kidney failure.

Exam tip: Practise negative‑feedback flowcharts – GCSE questions love “What happens if…?” scenarios.

🦠 Pathogens (bacteria, viruses, fungi, and protists) cause disease.

🧼 Ways to reduce spread: hygiene, isolation, vaccination.

💉 Vaccines introduce inactive pathogens to stimulate white blood cells to produce antibodies.

🧪 Antibiotics kill bacteria but not viruses. Resistance is a growing issue (e.g. MRSA).

Key Definitions:

• Health: State of physical and mental well‑being
• Pathogen: Disease‑causing organism
• Immunity: Body's ability to resist infection

DNA & Genes

• DNA is a double helix of nucleotides (A‑T, C‑G).
• A gene codes for a protein; alternative forms = alleles.
• Humans: 23 chromosome pairs (22 autosomes + XX/XY).

Punnett Square Example (Dominant Polydactyly)

75 % offspring show polydactyly (dominant).

Genetic Disorders

• Cystic fibrosis – recessive allele, faulty chloride channel.
• Polydactyly – dominant allele, extra digits.

Evolution & Selective Breeding

• Variation arises from mutations + meiosis.
• Natural selection: better‑adapted survive & reproduce.
• Selective breeding: humans pick parents for desired traits → less genetic diversity.
• Genetic engineering: e.g. insulin gene into bacteria plasmid.

Feeding Relationships

• Producer → primary → secondary → tertiary (trophic levels).
• Only ≈10 % energy transfers; rest lost as respiration/heat/faeces.
• GCSE may ask to draw/interpret pyramids of biomass.

Cycles

• Carbon cycle: photosynthesis ↔ respiration, combustion adds CO₂.
• Water cycle: evaporation, condensation, precipitation, transpiration.

Human Impact & Conservation

Flower Structure

• Stamen = anther + filament (makes pollen).
• Carpel = stigma + style + ovary (contains ovules).
• Sepals protect bud; petals attract pollinators.

Pollination vs Fertilisation

Pollination = transfer of pollen to stigma.
Fertilisation = fusion of male gamete with ovule nucleus → zygote → seed.

Seed Dispersal Mechanisms

• Wind (dandelion), animal internal (berries), animal external (burrs), water (coconut).

Asexual Reproduction

• Runners (strawberry), tubers (potato), cuttings.

Students must understand core practicals. These are tested in exams through analysis, planning, and evaluation questions rather than through coursework.

📘 Exam Tip: You will not be asked to recall methods verbatim but should explain why steps are taken, evaluate results, suggest improvements, and apply knowledge to new contexts.