B1- Cell biology

AQA GCSE Biology Topic 1: Cell Biology

1.1 Cell Structure

1.1.1 Eukaryotes and Prokaryotes

  • Eukaryotic Cells:

    • Have genetic material (DNA) enclosed in a nucleus.

    • Examples include plant and animal cells.

  • Prokaryotic Cells:

    • Genetic material not enclosed in a nucleus (found in cytoplasm).

    • Bacterial cells, smaller than eukaryotic cells.

  • Genetic Material in Prokaryotic Cells:

    • Consists of a single loop of DNA and may contain small rings of DNA called plasmids.

  • Key Features for Classification:

    • Both eukaryotic and prokaryotic cells share certain features but differ primarily in nucleus presence.

1.1.2 Animal and Plant Cells

  • Functions of Sub-cellular Structures:

    1. Cell Membrane:

      • Controls movement of substances in and out of the cell.

    2. Cytoplasm:

      • Gel-like substance where chemical reactions occur.

    3. Nucleus:

      • Contains genetic material (DNA) and controls cell activities.

    4. Mitochondria:

      • Site of aerobic respiration, releases energy from glucose.

    5. Ribosomes:

      • Site of protein synthesis.

  • Additional Structures in Plant Cells: 6. Cell Wall:

    • Made of cellulose; strengthens cell.

    1. Chloroplasts:

      • Contain chlorophyll; absorb light for photosynthesis.

    2. Permanent Vacuole:

      • Filled with cell sap; helps maintain cell turgidity and support.

1.1.3 Cell Specialisation

  • Cell Specialisation:

    • Cells become modified to perform specific functions.

  • Differentiation:

    • The process by which a cell develops specialized features to perform particular tasks.

1.1.4 Microscopy

  • Light Microscopes:

    • Use light to magnify images; lower magnification.

  • Electron Microscopes:

    • Use electrons, offer higher magnification and resolving power.

1.1.5 Culturing Microorganisms

  • Methods to Culture Bacteria:

    • Use nutrient broth or agar plates.

    • Ensure aseptic conditions to prevent contamination.

1.2 Cell Division

1.2.1 Chromosomes

  • Chromosomes:

    • Tightly coiled strands of DNA; located within the nucleus.

    • Carry genes that code for proteins.

  • Chromosome Arrangement in Humans: 23 pairs (46 total).

1.2.2 Mitosis and the Cell Cycle

  • Importance of Mitosis:

    • Produces two genetically identical cells for growth and repair.

  • Stages of the Cell Cycle:

    1. DNA replication.

    2. Chromosome segregation.

    3. Cytokinesis.

1.2.3 Stem Cells

  • Types of Stem Cells:

    • Embryonic: Can differentiate into any body cell.

    • Adult: Limited to certain types (e.g., blood cells).

1.3 Transport in Cells

1.3.1 Diffusion

  • Diffusion:

    • Movement of particles from high to low concentration.

  • Examples:

    • Oxygen and carbon dioxide in gas exchange.

1.3.2 Osmosis

  • Osmosis:

    • Special case of diffusion involving water through a partially permeable membrane.

1.3.3 Active Transport

  • Definition:

    • Movement of substances against a concentration gradient; requires energy.

  • Examples:

    • Absorption of mineral ions by roots, absorption of sugars in the gut.