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Overview of Cell Biology Concepts

Apr 26, 2025

Topic 1: Cell Biology - AQA Biology GCSE

Cell Structure (1.1)

Eukaryotes and Prokaryotes (1.1.1)

  • Eukaryotic Cells (Animal and Plant):
    • Components: Cell membrane, Cytoplasm, Nucleus containing DNA.
  • Prokaryotic Cells (Bacterial):
    • Components: Cell wall, Cell membrane, Cytoplasm, Single circular strand of DNA, Plasmids.
    • Smaller than eukaryotic cells.

Orders of Magnitude

  • Helps understand the size comparison between cells.
  • Example: If an object is 10 times bigger, it's 10^1 times bigger.

Prefixes for Measurement

  • Centi: 0.01
  • Milli: 0.001
  • Micro: 0.000001
  • Nano: 0.000000001

Animals and Plants (1.1.2)

Subcellular Structures

  • Animal and Plant Cells:

    • Nucleus: Contains DNA, enclosed in a nuclear membrane.
    • Cytoplasm: Site of chemical reactions, contains enzymes and organelles.
    • Cell Membrane: Regulates what enters and exits the cell.
    • Mitochondria: Site of aerobic respiration, provides energy.
    • Ribosomes: Protein synthesis, found on rough endoplasmic reticulum.
  • Only in Plant Cells:

    • Chloroplasts: Site of photosynthesis, contains chlorophyll.
    • Permanent Vacuole: Contains cell sap, maintains cell rigidity.
    • Cell Wall: Made from cellulose, provides structural support.

Cell Specialisation (1.1.3)

  • Differentiation: Process by which cells become specialized.
  • Animal Cells Examples:
    • Sperm Cells: Streamlined for swimming, many mitochondria, acrosome contains enzymes.
    • Nerve Cells: Long axon for impulse transmission, dendrites for connections, neurotransmitter production.
    • Muscle Cells: Contract for movement, contain proteins myosin & actin, store glycogen.
  • Plant Cells Examples:
    • Root Hair Cells: Large surface area, absorb water & minerals.
    • Xylem Cells: Transport water & minerals, lignin strengthens cells.
    • Phloem Cells: Transport food, sieve plates allow movement.

Cell Differentiation (1.1.4)

  • Stem cells differentiate by gene activation/inactivation.
  • Animal Cells: Differentiate early, mitosis for replacement.
  • Plant Cells: Retain ability to differentiate and re-differentiate as needed.

Microscopy (1.1.5)

Light Microscopes

  • Used for viewing tissues and cells.
  • Maximum magnification of x2000.
  • Resolving power of 200nm.

Electron Microscopes

  • Two types: Scanning (3D images) and Transmission (2D images).
  • Magnification up to x2,000,000.
  • Higher resolving power than light microscopes.

Culturing Microorganisms (1.1.6 - Biology Only)

  • Methods of Growth:
    • Nutrient broth solution.
    • Agar gel plates.
  • Steps for Preparing Agar Plates:
    • Sterilize Petri dishes and inoculating loops.
    • Seal dishes partially to avoid contamination.
    • Incubate at 25 degrees to prevent harmful bacteria growth.

Cell Division (1.2)

Chromosomes (1.2.1)

  • Chromosomes contain DNA; 23 pairs in each body cell.
  • Gametes have 23 chromosomes in total.

Mitosis and Cell Cycle (1.2.2)

  • Stages:
    • Interphase: Cell growth, DNA replication.
    • Mitosis: Chromosomes align and separate.
    • Cytokinesis: Division of cytoplasm, forming two daughter cells.
  • Essential for growth, repair, asexual reproduction.

Stem Cells (1.2.3)

  • Types:
    • Embryonic: Differentiate into any cell type.
    • Adult: Found in bone marrow, limited differentiation.
    • Plant Meristems: Retain differentiation ability for life.
  • Therapeutic Cloning:
    • Produces cells with patient’s DNA.
    • Potential medical applications.

Transport in Cells (1.3)

Diffusion (1.3.1)

  • Movement from high to low concentration.
  • Influenced by concentration gradient, surface area, temperature.

Osmosis (1.3.2)

  • Movement of water across membranes from high to low water potential.
  • Affects cell turgor in plants, can cause animal cells to burst.

Active Transport (1.3.3)

  • Movement against concentration gradient, requires energy.
  • Important in root hair cells and nutrient absorption in the gut.