Biology T1- Cell structure

• 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
  • Often 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
  • Some 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 circular chromosome of DNA in cytoplasm
  • Contain plasmids with extra genes
  • Lack membrane-bound organelles
  • Some have flagella for movement
• Sperm cells


  • Highly specialised for carrying male DNA to egg cell
  • Small size
  • Streamlined shape
  • Contain mitochondria for energy
  • Have flagellum for movement
• Egg cells


  • Highly specialised for being fertilised and developing into an embryo
  • Large size
  • Contain nutrients for early development
  • Lack flagellum
• Ciliated epithelial cells


  • Highly specialised for wafting bacteria and particles up to throat or down to stomach
  • Have many cilia on surface to move mucus
• Cilia and microvilli are not the same - cilia can move to waft mucus, microvilli increase surface area for absorption
• Development of microscopy


  1. First light microscopes in 17th century

  2. Electron microscopes developed in 1930s

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


  Calculated by dividing size of image by actual size of specimen
• Electron microscopes


  • 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
  • Maximum magnification of approximately 2,000,000×
• Electron micrograph


  • Ciliated epithelium tissue
• Magnification


  Calculated using the equation: Magnification = Drawing size ÷ Actual size
• Magnification does not have any units and is just written as 'X 10' or 'X 5000'
• Calculating magnification


  1. Magnification = image size ÷ actual size

  2. Actual size = image size ÷ magnification

  3. Image size = actual size × magnification
• Magnification of light microscope = Magnification of eyepiece lens × Magnification of objective lens
• • Look at the units given in the question, measure in millimetres NOT centimetres
  • Learn the equation triangle for magnification and always write it down when doing a calculation
• Optical microscopes


  • Invaluable tool for scientists as they allow for tissues, cells and organelles to be seen and studied
  • Light is directed through a thin layer of biological material and focused through several lenses so that an image is visible through the eyepiece
• Key components of an optical microscope

  • Eyepiece lens
  • Objective lenses
  • Stage
  • Light source
  • Coarse and fine focus
• Other apparatus used


  • Forceps
  • Scissors
  • Scalpel
  • Coverslip
  • Slides
  • Pipette
• 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 there is no cross-contamination of foreign cells
• 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 (using a scalpel or forceps)

  3. Some tissue samples need to be treated with chemicals to kill/make the tissue rigid

  4. Gently place a coverslip on top and press down to remove any air bubbles
• A stain may be required to make the structures visible depending on the type of tissue being examined. Commonly used stains include methylene blue to stain cheek cells and iodine to stain onion cells
• Take care when using sharp objects and wear gloves to prevent the stain from dying your skin
• When using an optical microscope always start with the low power objective lens
• Adding a drop of water to the specimen (beneath the coverslip) can prevent the cells from being damaged by dehydration
• Switch to the lower power objective lens and try using the coarse focus to get a clearer image if the image is unclear or blurry
• Care must be taken to avoid smudging the glass slide or trapping air bubbles under the coverslip
• Graticule


  A calibrated graticule and stage micrometer are used to measure the size of the object when viewed under a microscope
• Biological drawings


  • Should be as large as possible, taking up at least half of the page
  • Not supposed to be artistic, but scientific
• • The size of cells or structures of tissues may appear inconsistent in different specimen slides
  • Cell structures are 3D and the different tissue samples will have been cut at different planes resulting in inconsistencies when viewed on a 2D slide
• • Optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that cannot be seen
  • The treatment of specimens when preparing slides could alter the structure of cells
• Converting units


  • 1 mm = 1000 μm
  • 1 μm = 0.001 mm
  • 1 nm = 0.001 μm
• Converting units for magnification calculations


  Convert both measurements to the same unit before proceeding with the calculation