Cell biology

• All cells have a number of features in common with each other
• For a cell to be a cell, it has to have the following components

  • Cellular components & functions
• Eukaryotic cells


  Cells with their genetic material (DNA) enclosed within a nucleus
• Prokaryotic cells


  Cells with their genetic material not enclosed within a nucleus, found as a single loop of DNA within the cytoplasm
• Bacterial cells are a type of prokaryotic cell
• Prokaryotic cells are much smaller in comparison to eukaryotic cells, with many measuring ~ 1 µm in size
• Micrometers (µm)


  Unit used to measure the size of cells, 1 µm = 0.001 mm
• You need to be able to convert between different units of measurement, particularly mm and µm
• Many subcellular structures in eukaryotic cells are the same size as or bigger than prokaryotic cells
• Size of cells


  • Prokaryotic cells: ~1 µm
  • Eukaryotic cells: 10-100 µm
• Standard form


  Used to represent very small (or very big) numbers to avoid confusion
• Eukaryotic cells have subcellular structures, each carrying out a particular function
• Main subcellular structures in animal cells

  • The nucleus
  • Cell membranes
  • Mitochondria
  • Ribosomes
  • Cytoplasm
• Additional subcellular structures in plant cells

  • Cell wall made of cellulose
  • Permanent vacuole filled with cell sap
  • Chloroplasts
• You need to be able to recognise, draw and interpret images of cells
• Specialised cells


  Cells that have a particular structure and composition of subcellular structures to perform specific functions
• Nerve cell (neurone)


  • Elongated structure to coordinate information
  • Cell body with most cellular structures
  • Extensions (dendrites and axons) to communicate with other cells
  • Axon covered in fatty sheath to speed up nerve impulses
• Muscle cell


  • Layers of protein filaments to allow contraction
  • High density of mitochondria for energy
  • Skeletal muscle cells fuse to form multinucleated cells
• Sperm cell


  • Haploid nucleus
  • Acrosome with digestive enzymes
  • Mid-piece packed with mitochondria
  • Tail to propel the cell forward
• Root hair cell


  • Extension to increase surface area for absorption
  • Thin walls for easy water movement
  • Permanent vacuole with concentrated cell sap
  • Mitochondria for active transport of ions
• Xylem vessel


  • Continuous tube for water transport from roots to leaves
• Root hair cell


  • Cell area in contact with soil to maximise absorption of water and minerals
  • Function: absorption of water and mineral ions from soil
• Root hair adaptations


  • Increase surface area so rate of water uptake by osmosis is greater
  • Thinner walls than other plant cells so water can move through easily
  • Permanent vacuole contains cell sap more concentrated than soil water, maintaining water potential gradient
  • Mitochondria for active transport of mineral ions
• Chloroplasts are not found in root hair cells - there's no light for photosynthesis underground
• Xylem vessel


  • Lose top and bottom walls to form continuous tube for water transport from roots to leaves
  • Cells are essentially dead, without organelles or cytoplasm, to allow free passage of water
  • Outer walls thickened with lignin to strengthen and support the plant
• Phloem cells


  • Form tubes similar to xylem vessels, but cells retain some subcellular structures and are living
  • Function: transport of dissolved sugars and amino acids
  • Made of living cells supported by companion cells
  • Cells joined end-to-end with holes in end walls (sieve plates) to allow easy flow of sugars and amino acids
• Cell differentiation


  Process by which a cell changes to become specialised
• Almost all cells in a multicellular organism contain the same genetic information, but only some genes are used to control development
• When a cell differentiates, it develops a structure and composition of subcellular structures which enables it to carry out a certain function
• In animals, most cells differentiate at an early stage of development, and lose ability to differentiate after becoming specialised
• Some animal cells (adult stem cells) retain ability to differentiate throughout life to replace and repair cells
• Many plant cell types retain ability to fully differentiate throughout the life of the plant
• Light microscope


  Uses light and lenses to form a magnified image of a specimen
• Electron microscope


  Uses beams of electrons, rather than light, to visualise specimens, giving much higher resolution and magnification
• Calculating magnification


  1. Magnification = Drawing size ÷ Actual size

  2. Actual size = Image size ÷ Magnification

  3. Image size = Magnification x Actual size
• Magnification does not have units, it is just written as 'X 10' or 'X 5000'
• When converting units, remember that 1mm = 1000μm
• Using a light microscope

  1. Prepare specimen on slide carefully

  2. Start observation with lowest-powered objective lens

  3. Microscope has fixed eyepiece lens and 2-3 objective lenses of different powers
• Biological drawings


  Supposed to be scientific, not artistic
• Blue


  Used to stain cheek cells