GCSE Biology Paper 1 Revision

Introduction

• Topics: All key content for GCSE Biology Paper 1.
• Includes: Cell structure, cell biology, cell transport, cell division, DNA structure, microscopy, enzymes, photosynthesis, respiration, and disease.

Cell Structure and Cell Biology

Cell Types

• Eukaryotic Cells: True nucleus, DNA in chromosomes (plant and animal cells).
  • Plant Cells:
    • Chloroplast (photosynthesis)
    • Permanent vacuole (cell sap storage)
    • Cell wall (structure & support)
  • Animal Cells:
    • Mitochondria (energy for respiration)
    • Cytoplasm (reaction space)
    • Cell membrane (controls entry/exit)
    • Ribosomes (protein synthesis)
    • Nucleus (contains DNA)
• Prokaryotic Cells: Free DNA in nucleoid, e.g., bacteria.

Specialized Cells

• Animal Cells:
  • Nerve Cells: Insulating sheath, long branches.
  • Muscle Cells: Many mitochondria.
  • Sperm Cells: Acrosome, haploid nucleus, tail, mitochondria.
  • Egg Cells: Mitochondria, nutrients, haploid nucleus.
  • Ciliated Epithelial Cells: Line respiratory system.
  • Red Blood Cells: Hemoglobin, no nucleus, biconcave, thin membrane.
• Plant Cells:
  • Root Hair Cells: Large surface area (water/mineral absorption).
  • Xylem: Lignin, allows water movement.
  • Phloem: Companion cells, transport sugars.

Cell Transportation

Mechanisms

• Diffusion: Passive, high to low concentration (e.g., glucose, gases).
• Osmosis: Passive, net movement of water (dilute to concentrated solution).
• Active Transport: Requires energy, low to high concentration (e.g., ions in root hair cells).

Cell Division

Mitosis

• Produces genetically identical daughter cells.
• Steps: Grow, DNA replicate, chromosomes separate, cell divides.

Meiosis

• Produces genetically different gametes.
• Steps: DNA replicate, two divisions, gametes form.

DNA Structure

• Polymer, double helix, nucleotides (phosphate, nitrogen bases, deoxyribose sugar).
• Base Pairing: A-T, C-G.

Microscopy

• Magnification Calculation: I = A x M; Conversion (mm to µm multiply by 1000).
• Types:
  • Light Microscope (portable, less expensive).
  • Electron Microscope (higher magnification & resolution).

Enzymes

Characteristics

• Biological catalysts, proteins, specific shape (lock and key model), denatured by changes in temp/pH/substrate concentration.

Types

• Amylase: Starch to glucose.
• Protease: Proteins to amino acids.
• Lipase: Lipids to fatty acids and glycerol.

Photosynthesis

• Equation: CO₂ + H₂O → C₆H₁₂O₆ + O₂
• Factors: Light intensity, carbon dioxide concentration, temperature.
• Glucose Use: Stored as starch, used for respiration, or converted into cellulose, lipids, amino acids.

Respiration

Types

• Aerobic: With oxygen (glucose to CO₂ and H₂O).
• Anaerobic: Without oxygen (produces lactic acid in muscles or ethanol and CO₂ in yeast).
• Fermentation: Used in bread/beer production.

Disease

Immune System

• White Blood Cells:
  • Phagocytes: Engulf pathogens.
  • Lymphocytes: Produce specific antibodies and antitoxins.
• Vaccines: Contain dead/weakened form of pathogen to trigger immune response.

Types of Diseases

• Fungal: Athlete's foot, Rose Black Spot.
• Protist: Malaria.
• Viral: TMV, influenza, measles.
• Bacterial: Gonorrhea, salmonella.

Blood and Circulatory System

• Components: Red blood cells, white blood cells, platelets, plasma.
• Double circulatory system: Blood passes through heart twice.
• Blood Vessels:
  • Capillaries: Thin walls.
  • Veins: Valves, low pressure.
  • Arteries: Thick walls, high pressure.

Respiratory System

• Pathway: Trachea → Bronchi → Bronchioles → Alveoli (gas exchange).

Plant Defenses

• Physical: Thorns, waxy cuticles.
• Chemical: Poisons.
• Mechanical: Bark.

Non-Communicable Diseases

• Cancer: Uncontrolled cell growth.
  • Benign vs. malignant tumors.
• Coronary Heart Disease: Cholesterol plaque in arteries, leads to heart attacks. Treatment: diet, exercise, stents.