Topic 1: Cell Biology - AQA Biology GCSE

Cell Structure (1.1)

Eukaryotes and Prokaryotes (1.1.1)

• All living things are made of cells:
  • Eukaryotic cells (animal and plant):
    • Cell membrane
    • Cytoplasm
    • Nucleus containing DNA
  • Prokaryotic cells (bacterial):
    • Cell wall
    • Cell membrane
    • Cytoplasm
    • Single circular strand of DNA and plasmids
• Organelles: Structures in a cell with specific functions.
• Orders of Magnitude: Understanding size comparisons between objects.
  • Prefixes (e.g., centi, milli) indicate multiples of measurement units.

Animals and Plants (1.1.2)

• Subcellular Structures and Functions:
  • Nucleus: Contains DNA, encased in a nuclear membrane.
  • Cytoplasm: Site of chemical reactions, contains enzymes.
  • Cell membrane: Controls cell entry and exit.
  • Mitochondria: Site of aerobic respiration.
  • Ribosomes: Protein synthesis occurs here.
  • Chloroplasts (plant cells): Site of photosynthesis, contains chlorophyll.
  • Permanent vacuole (plant cells): Contains cell sap, improves rigidity.
  • Cell wall (plant and algal cells): Made of cellulose, provides strength.

Cell Specialisation (1.1.3)

• Differentiation: Process where cells gain sub-cellular structures for specific roles.
  • Animal Specialised Cells:
    • Sperm cells: Streamlined, contain mitochondria, have enzymes for fertilization.
    • Nerve cells: Transmit signals, have long axons, dendrites for connections.
    • Muscle cells: Contract for movement, contain proteins and mitochondria.
  • Plant Specialised Cells:
    • Root hair cells: Large surface area for water/mineral uptake.
    • Xylem cells: Transport water and minerals, reinforced with lignin.
    • Phloem cells: Transport products of photosynthesis, have sieve plates.

Cell Differentiation (1.1.4)

• Stem Cells: Differentiate to form specialised cells.
  • Animal cells differentiate early, some can still divide (e.g., red blood cells).
  • Plant cells retain differentiation ability throughout life.

Microscopy (1.1.5)

• Light Microscope: Used to view cells and large structures.
  • Magnification up to x2000, resolving power of 200nm.
• Electron Microscope: View sub-cellular structures in detail.
  • Magnification up to x2,000,000, resolving power 10nm (SEM), 0.2nm (TEM).

Culturing Microorganisms (1.1.6 - Biology Only)

• Growing Microorganisms:
  • Nutrient broth solution and agar gel plates.
  • Sterilisation and proper handling to avoid contamination.
  • Testing antibiotics using inhibition zones.

Cell Division (1.2)

Chromosomes (1.2.1)

• Genetic Information: Found in chromosomes, which contain DNA and genes.
• Human Chromosomes: 23 pairs per cell, 46 chromosomes total.

Mitosis and the Cell Cycle (1.2.2)

• Cell Cycle Stages:
  • Interphase: Growth, protein synthesis, DNA replication.
  • Mitosis: Chromosomes line up and are separated.
  • Cytokinesis: Division into two identical daughter cells.
• Importance: Growth, repair, asexual reproduction.

Stem Cells (1.2.3)

• Types:
  • Embryonic: Differentiates into any cell type.
  • Adult: Found in bone marrow, limited differentiation.
  • Meristems (plants): Differentiates into any plant type.
• Therapeutic Cloning: Produces compatible cells for patients.
• Benefits vs. Problems of Research:
  • Potential medical application vs. ethical issues and technical challenges.

Transport in Cells (1.3)

Diffusion (1.3.1)

• Process: Movement from high to low concentration, passive, no energy.
• Affects rate: Concentration gradient, surface area, temperature.
• Examples: Gas exchange in lungs, urea movement to kidneys.

Osmosis (1.3.2)

• Process: Movement of water across membranes from high to low water potential.
• Effects on Cells:
  • In animals, can cause cells to burst or shrivel.
  • In plants, affects turgor pressure and can lead to plasmolysis.

Active Transport (1.3.3)

• Process: Moves substances against concentration gradient, requires energy.
• Examples: Mineral uptake in roots, nutrient absorption in the gut.