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AQA Biology GCSE Topic 1: Cell Biology

Cell Structure (1.1)

  • Two main types of cells:
    • Eukaryotes:
    • Found in animals and plants.
    • Structures include:
      • Cell membrane
      • Cytoplasm
      • Nucleus containing DNA
    • Prokaryotes:
    • Found in bacterial cells, usually smaller.
    • Structures include:
      • Cell wall
      • Cell membrane
      • Cytoplasm
      • A single circular strand of DNA and plasmids (small rings of DNA).
  • Organelles: Structures in cells with specific functions.

Orders of Magnitude

  • Use orders of magnitude to compare cell sizes.
    • 10 times bigger: $10^1$ times bigger.
    • 1000 times bigger: $10^3$ times bigger.
    • 10 times smaller: $10^{-1}$ times smaller.
  • Prefixes:
    • Centi: $0.01$
    • Milli: $0.001$
    • Micro: $0.000001$
    • Nano: $0.000000001$

Animals and Plants (1.1.2)

  • Subcellular Structures: Functionality in animal and plant cells.
    • Nucleus:
    • Contains DNA for protein coding.
    • Enclosed in a nuclear membrane.
    • Cytoplasm:
    • Site of chemical reactions.
    • Contains enzymes that act as biological catalysts.
    • Cell Membrane:
    • Regulates entry and exit of substances.
    • Mitochondria:
    • Site for aerobic respiration; produces energy.
    • Ribosomes:
    • Site for protein synthesis, usually on rough endoplasmic reticulum.

Plant Cells Specific Structures:

  • Chloroplasts: Photosynthesis occurs; contains chlorophyll for light absorption.
  • Permanent Vacuole: Contains cell sap; aids cell rigidity.
  • Cell Wall: Composed of cellulose; provides strength.

Bacterial Cells

  • Structure and Function Review:
    • Made of peptidoglycan cell wall.
    • Circular DNA in the cytoplasm.
    • Plasmids present.

Cell Specialisation (1.1.3)

  • Differentiation: Process where cells develop new structures for specialized functions.
    • Stem cells can differentiate throughout life.
    • Most animal cells differentiate only during early development.

Examples of Specialised Cells:

  1. Sperm Cells:
    • Streamlined for swimming; many mitochondria for energy; acrosome for penetrating egg membranes.
  2. Nerve Cells:
    • Long axons for signal transmission; numerous dendrites for connections; mitochondria for synthesizing neurotransmitters.
  3. Muscle Cells:
    • Specialized for contraction; contain proteins myosin and actin; high energy needs met by mitochondria.

Plant Specialised Cells:

  1. Root Hair Cells:
    • Large surface area for absorption of water and nutrients.
  2. Xylem Cells:
    • Hollow tubes formed by dead cells to transport water.
  3. Phloem Cells:
    • Transport photosynthesis products; form sieve plates for transport continuity.

Microscopy (1.1.5)

  • Light Microscope:
    • Uses two lenses; maximum magnification of $x2000$; resolving power typically $200nm$.
  • Electron Microscope:
    • Uses electrons; two types:
    • Scanning Electron Microscope (SEM): 3D images, $x2,000,000$ magnification, $10nm$ resolving power.
    • Transmission Electron Microscope (TEM): 2D images, $0.2nm$ resolving power.
  • Calculations:
    • Magnification formula: eyepiece magnification x objective magnification.
    • Size of object: size of image / magnification.

Culturing Microorganisms (1.1.6)

  • Nutrient media needed for growth.
  • Growing methods:
    1. In nutrient broth solution.
    2. On agar gel plates (colonies formed on the surface).

Steps and Rationale

  • Sterilization is critical to prevent contamination.
  • Incubation at $25^ ext{o}C$ to limit harmful bacteria growth.
  • Zone of Inhibition Measurement: Determines antibiotic effectiveness on bacterial growth.

Cell Division (1.2)

  • Chromosomes: Genetic material in nucleus; 23 pairs (46 total) in body cells; gametes have 23.

Mitosis and the Cell Cycle:

  1. Interphase: Cell grows, organelles increase, DNA replicated.
  2. Mitosis: Chromosomes pulled apart.
  3. Cytokinesis: Division forms two identical daughter cells.

Stem Cells (1.2.3)

  • Types:
    1. Embryonic Stem Cells: Can differentiate into any cell type.
    2. Adult Stem Cells: Limited differentiation capabilities.
    3. Plant Meristems: Continuous differentiation possibilities.

Active Transport (1.3.3)

  • Movement of substances against their concentration gradient; requires energy.
  • Examples:
    • Root hair cells uptake minerals.
    • Glucose and amino acids from gut to blood.