AQA GCSE Biology - Cell Biology | Whole Topic | Triple Science

Cell Structure

Eukaryotic Cells

  • Types of Eukaryotes: Animals and Plants

  • Components of Animal Cells:

    • Nucleus: The "boss" of the cell, controlling activities and housing DNA for vital protein synthesis.

    • Cytoplasm: The busy workshop where chemical reactions happen.

    • Cell Membrane: The bouncer of the cell, selectively decides who gets in and out.

    • Ribosomes: The builders crafting proteins from amino acids.

    • Mitochondria: Think of these as the power stations, releasing energy through respiration (but they don’t create energy out of thin air!).

Plant Cells Unique Features:

  • Cell Wall: A sturdy fortress made of cellulose, providing strength and support.

  • Sap Vacuole: A sugary storage unit! Think of it as the cell's fuel tank.

  • Chloroplasts: The green energy factories using chlorophyll for photosynthesis magic!

Prokaryotic Cells

  • Characteristics:

    • No nucleus or fancy membrane-bound organelles. It’s like a simple, streamlined machine.

    • Circular DNA: The core instructions for cell activities and protein synthesis.

    • Plasmids: Tiny rings of bonus DNA that can carry extra genes.

    • Components include ribosomes, cell membrane, and cell wall (not made of cellulose but still supportive!).

Relative Sizes of Cells

  • Animal cell: ~10 micrometers (the average size of a sneeze).

  • Plant cell: ~50 micrometers (slightly larger, like a mini jellybean).

  • Prokaryotic cell (bacteria): ~5 micrometres (the tiny rebels of the cell world!).

Cell Differentiation and Specialisation

  • Process:

    • It all begins with the fertilisation of an egg, leading to undifferentiated cells that are on their way to greatness!

  • Specialised Animal Cells:

    • Nerve Cells: The swift messengers with a cell body, dendrites, and axon to send signals on a journey.

    • Sperm Cells: Equipped with a mid-piece (for energy), a tail (for movement), and ready to conquer egg membranes.

    • Muscle Cells: The powerhouses with fibres for contraction and loads of mitochondria to keep the energy flowing.

  • Specialised Plant Cells:

    • Xylem Cells: The dead but mighty cells transporting water, reinforced with lignin.

    • Phloem Cells: The sugar transporters are alive and minimally pulp-filled with pores for efficiency.

    • Root Hair Cells: The absorption champs with extra surface area and lots of mitochondria for energy!

Microscopy

  • Evolution of Microscopes:

    • We've come a long way from simple beginnings to advanced light and electron microscopes.

  • Light Microscopes:

    • Utilize visible light and lenses to magnify specimens, allowing us to see cells and some organelles.

  • Electron Microscopes:

    • Employ beams of electrons for higher resolution imaging, revealing structures at the molecular level.

  • Measurement Units in Microscopy:

    • 1 mm = 1000 µm = 1,000,000 nm (all in metric, all the time!).

  • Magnification Calculation:

    • Magnification = Size of Image / Real Size of Object.

    • Example Calculation:

      • A root hair cell's image is 5 mm (which is 5000 µm) and the real size is 20 µm -> 5000 / 20 = 250x magnification (wow!).

Culturing Microorganisms

  • Bacterial Growth:

    • Binary Fission: The rapid cell replication method allowing bacteria to double every 20 minutes under ideal conditions (like a cell party!).

    • Example:

      • Watch out! 200 bacteria can explode to 409,600 after 4 hours of good times!

  • Growing Uncontaminated Cultures:

    • Follow the golden rules with a sterile petri dish and agar gel while inoculating under controlled conditions—perfect for studying antibiotics and disinfectants.

Mitosis and Cell Cycle

  • Mitosis:

    • Mitosis is the process that divides one cell into two identical cells, each with the same number of chromosomes as the parent.

  • Stages of Mitosis:

    • Prophase: Chromosomes condense, line up, and become visible; nuclear envelope breaks down.

    • Metaphase: Chromosomes align at the cell's equator in preparation for separation.

    • Anaphase: Sister chromatids are pulled apart to opposite ends of the cell.

    • Telophase: Nuclear membranes form around each set of chromosomes; chromosomes de-condense.

Stem Cells:

  • Stem Cells: Undifferentiated cells that can develop into any cell type, crucial for:

    • Development: Supporting growth.

    • Healing: Repairing damaged tissues.

    • Regeneration: Replenishing lost cells.

  • Types of Stem Cells:

    • Embryonic Stem Cells: Pluripotent; can become any type of cell.

    • Adult Stem Cells: Multipotent; limited to a more specific range of cell types.

Diffusion and Active Transport:

  • Diffusion: Movement of particles from high concentration to low concentration, seeking equilibrium.

  • How cells adapt for exchange:

    • Thin membranes: Shorten travel distance for faster movement.

    • Large surface area: Increases exchange capacity.

    • Moist surfaces: Facilitate the diffusion process.

  • Active Transport: Moves molecules against their concentration gradient, requiring energy (ATP). Essential for maintaining ion and nutrient balance within cells.

Osmosis:

  • A special type of diffusion involving the movement of water molecules from lower solute concentration to higher solute concentration. This process is crucial for maintaining cell turgor and homeostasis.