cell structure 1.1

• Five kingdoms of living organisms


  • Animals
  • Plants
  • Fungi
  • Protoctists
  • Prokaryotes
• Eukaryotic organisms


  Animals, plants, fungi and protoctists
• Eukaryotic organisms


  • Multicellular or single-celled
  • Cells contain a nucleus with a distinct membrane
• Prokaryotic organisms


  • Always single-celled
  • Do not contain a nucleus
• Prokaryotic cells are substantially smaller than eukaryotic cells
• Animals


  • Multicellular
  • Cells contain a nucleus with a distinct membrane
  • Cells do not have cellulose cell walls
  • Cells do not contain chloroplasts
  • Feed on organic substances
  • Store carbohydrates as glycogen
  • Have nervous coordination
  • Able to move from place to place
• Plants


  • Multicellular
  • Cells contain a nucleus with a distinct membrane
  • Cells have cell walls made of cellulose
  • Cells contain chloroplasts
  • Feed by photosynthesis
  • Store carbohydrates as starch or sucrose
  • Do not have nervous coordination
• Fungi


  • Usually multicellular, some single-celled
  • Cells contain a nucleus with a distinct membrane
  • Cells have cell walls made of chitin
  • Cells do not contain chloroplasts
  • Feed by secreting extracellular digestive enzymes and absorbing digested molecules
  • Some are parasitic
  • Store carbohydrates as glycogen
  • Do not have nervous coordination
• Protoctists


  • Mainly microscopic and single-celled, some aggregate into larger forms
  • Cells contain a nucleus with a distinct membrane
  • Some have features like animal cells, some like plant cells
  • Some photosynthesise, some feed on organic substances
  • Do not have nervous coordination
• Bacteria


  • Microscopic single-celled organisms
  • Possess a cell wall, cell membrane, cytoplasm and ribosomes
  • Lack a nucleus but contain a circular chromosome of DNA
  • Lack mitochondria, chloroplasts and other membrane-bound organelles
  • Some have flagella to allow movement
• Specialised cells


  Cells that have developed certain characteristics (adaptations) to perform particular functions
• Sperm cells


  • Highly specialised to carry the male DNA to the egg cell
• Egg cells


  • Highly specialised to be fertilised by a sperm and develop into an embryo
• Ciliated epithelial cells


  • Highly specialised to waft bacteria and other particles up to the throat or down to the stomach
• Cilia and microvilli are not the same - cilia can move to waft mucus, microvilli increase surface area for absorption
• Microscopy


  Techniques using microscopes to visualise cells and subcellular structures
• Development of microscopes


  1. Light microscopes developed in 17th century

  2. Electron microscopes developed in 1930s

  3. Electron microscopes have much higher magnification and resolution than light microscopes
• Magnification


  Calculated as the ratio of the size of the image to the actual size of the object
• Electron microscopes


  • Have much higher magnification and resolving power than a light microscope
  • Can be used to study cells in much finer detail, enabling biologists to see and understand many more subcellular structures such as the mitochondria, chloroplasts and ribosomes
  • Have helped biologists develop a better understanding of the structure of the nucleus and cell membrane
  • Have a maximum magnification of approximately 2,000,000×
• Electron micrograph


  • Of ciliated epithelium tissue produced by an electron microscope
• Magnification


  Calculated using the equation: Magnification = Drawing size ÷ Actual size
• Calculating magnification


  1. Magnification = image size ÷ actual size

  2. Actual size = image size ÷ magnification

  3. Image size = actual size × magnification
• Magnification does not have any units and is just written as 'X 10' or 'X 5000'
• Total magnification of a light microscope


  Magnification of eyepiece lens × Magnification of objective lens
• Optical microscopes


  • Allow tissues, cells and organelles to be seen and studied
  • Light is directed through a thin layer of biological material and focused through lenses to produce an image
• Key components of an optical microscope


  • Eyepiece lens
  • Objective lenses
  • Stage
  • Light source
  • Coarse and fine focus
• Preparing a slide using a liquid specimen


  1. Add a few drops of the sample to the slide using a pipette

  2. Cover the liquid/smear with a coverslip and gently press down to remove air bubbles

  3. Wear gloves to ensure no cross-contamination
• Preparing a slide using a solid specimen

  1. Use scissors to cut a small sample of the tissue

  2. Peel away or cut a very thin layer of cells from the tissue sample to be placed on the slide

  3. Some tissue samples need to be treated with chemicals

  4. Gently place a coverslip on top and press down to remove any air bubbles
• Stains


  Used to make structures visible, e.g. methylene blue for cheek cells, iodine for onion cells
• Using an optical microscope


  1. Always start with the low power objective lens

  2. Add a drop of water to prevent dehydration of the specimen
• Unclear or blurry images


  • Switch to lower power objective lens and use coarse focus
  • Check if specimen sample is thin enough for light to pass through
• Measuring cells, cell structures and organelles


  Use a calibrated graticule and stage micrometer
• Biological drawings


  Should be as large as possible and follow scientific rules
• Converting units


  1 mm = 1000 μm, 1 μm = 0.001 mm, 1 nm = 0.001 μm
• Standard form


  Writing very big or very small numbers using powers of 10
• Examples of using standard form in unit conversions

  • Converting 45 cm to mm, 250 μm to mm