2.1.1 cell structure and functions

• what are the different types of microscopes

  • light microscope
  • transmission electron microscope
  • scanning electron microscope
  • laser scanning confocal
• what is resolution

  The ability to distinguish between two points
• what is magnification

  refers to how many times larger the image is compared to the object
• what are the 4 types of sample preparation

  • dry mount 
  • wet mount 
  • squash slide 
  • smear slide
• dry mount

  thin slices with a coverslip on top
• wet mount

  specimens are added to liquid lowered to prevent air bubbles at a 45 degree angle
• squash slide

  wet mounts that are pushed down to ensure a thin layer specimen so light can pass through
• smear slide

  edge of slide is used to smear the sample across the slide creating a thin specimen and placing a cover slip
• how do you calibrate an eyepiece graticle

  • line up stage micrometer and graticule
  • Count how many divisions on the eyepiece graticule fit into the micrometer scale
  • Each division on micrometer is 10 so that can be used to calculate one division on eyepiece graticule
• magnification equation

  Magnification = size of image/size of real object
• positive staining

  Crystal violet and methylene blue are two stains commonly used. They are positively charged and therefore are attracted to and stain negatively charged material
• negative staining

  Nigrosin and congo red are negatively charged and therefore cannot enter the cells as cytosol repels them creating a stained background and unstained cells then stand out
• Gram-positive bacteria


  Gram-positive bacteria appears blue-purple as the stain is retained due to thicker peptidoglycan cell wall absorbing the dye
• gram staining

  • Two different stains are used to identify bacteria Crystal violet and safranin
  • Crystal violet is added
  • Then iodine to fix the stain
  • Alcohol to wash away any unbound stain
• gram-negative bacteria 


  gram-negative bacteria cannot absorb crystal violet as the peptidoglycan cell wall is thinner

  Safranin is used as a counter stain turning the bacteria red
• what are the rules of scientific drawings

  • draw in pencil
  • include title
  • state magnification or scale
  • annotate cell components
  • no sketch lines
  • no colour or shading
• electron microscopes

  • beam of electrons has a very short wavelength and therefore a high resolution
  • Image is created using an electromagnet to focus the beam of electrons
  • must be in a vacuum
  • dead specimens only
  • images are black and white
• transmission electron microscope (TEM)

  • extremely thin specimens are stained and placed in a vacuum
  • an electron gun produces a beam of electrons that passes through the specimen
  • some parts of the specimen absorb the electrons making them appear darker
  • this produces a 2D image and shows detailed images of the internal structure of cells
• scanning electron microscope (SEM)

  • specimen does not need to be thin as electrons do not pass through
  • electrons are beamed onto the surface and electrons are scattered in different ways depending on contours
  • this produces a 3D image
• laser scanning confocal microscope

  • type of fluorescent microscope
  • Image is created using a very high light intensity to illuminate the specimen stained with fluorescent dye
  • Enables scientists to view sections of tiny structure that would be physically challenging to section off e.g embryos creating a 3D image
  • Image is created as microscope scans the specimen point by point using a focused laser beam to create a 2D image or 3D depending on focal points
• nucleus structure 


  the nucleus is a double membrane organelle consisting of a nucleolus inside

  nucleolus is a smaller sphere inside which Is the site of rRNA production and making ribosomes
• nucleus function

  • site of DNA replication
  • contains the genetic code for each cell
  • site of ribosome synthesis (nucleolus)
• flagella 


  whip-like structure functioning for mobility
• cilia

  • hairlike projections out of cell
  • can be mobile or stationary
  • mobile help move substances in sweeping motions
  • sensory cilia are important in sensory organs
• centrioles

  • made of microtubules and pairs form centrosome
  • involved in the production of spindle fibre and organisation of chromosomes in cell division
• cytoskeleton structure

  • network of fibres found within the cytoplasm of all cells
  • consists of microfilaments microtubules and intermediate fibres
• cytokskeleton function

  • provides mechanical strength to cells helping to maintain the shape and stability of a cell
  • Microfilaments are responsible for cell movement
  • Microtubules are responsible for creating a scaffold-like structure and acts as tracks for movement around the cell
  • Intermediate fibres provide mechanical strength
• endoplasmic reticulum (ER) structure

  • Rough and smooth both have folded membranes called cisternae
  • Rough has ribosomes on the cisternae
• endoplasmic reticulum (ER) function

  • RER protein synthesis
  • SER lipids and carbohydrate synthesis
• golgi apparatus and vesicles structure

  • folded membranes making cisternae
  • Secretary vesicles pinch off from cisternae
• golgi apparatus and vesicles function

  • package and modify proteins
  • modification can be through adding carbs to proteins to form glycoproteins
  • Produce secretory enzymes
  • Forms lysosomes
  • Transport, modify and store lipids
  • Molecules are labelled with their destination
  • Finished products are transported to the cell surface in Golgi vesicles where they fuse with the membrane and contents in released
• lysosomes

  bags of digestive enzymes

  Function:

  • hydrolyse phagocytic cells
  • Break down dead cells
  • Exocytosis releases enzymes outside of the cell to destroy material
• mitochondria structure

  • double membrane
  • The inner membrane called the Cristae
  • The fluid centre is called the mitochondrial matrix
  • Loop of mitochondria DNA
• mitochondria function

  • site of aerobic respiration
  • site of ATP production
  • DNA to code for enzymes needed in respiration
• ribosomes

  • small made up of protein and rRNA
  • 80s found in eukaryotic cells
  • 70S smaller found in prokaryotic cells, mitochondria and chloroplasts

  Function - site of protein synthesis
• chloroplasts

  • double membrane
  • Fluid contains enzymes for photosynthesis
  • Found in plants

  Function - site of photosynthesis
• cell wall

  in plants and fungi

  • Plants made of cellulose
  • Fungi made of chitin

  Function - provide structural strength to the cell
• plasma membrane

  found in all cells

  • Phospholipid bilayer with other molecules embedded e.g channel + carrier proteins, glycoproteins, cholesterol

  Function - to control what enters and exits the cell
• production and secretion of proteins

  1. Polypeptide chains are synthesised on the RER

  2. These polypeptide chains move to the cisternae in the RER and are packaged into vesicles to be sent to the Golgi apparatus via the cytoskeleton

  3. In the Golgi apparatus, the proteins are modified and packaged into vesicles

  4. The secretory vesicles carry the protein to the cell surface membrane where it fuses and releases the protein via exocytosis
• prokaryotic cells

  • the cells are much smaller
  • No membrane-bound organelles
  • Therefore no mitochondria, chloroplasts, endoplasmic reticulum or Golgi
  • Smaller ribosomes
  • DNA is not in the nucleus and is not circular
  • The cell wall is made of murein (glycoprotein)