My topic 2

• magnification


  how much bigger the image is than the specimen.
• magnification calculation

  magnification = size of image/size of real object.
• millimetres to micrometres


  x1000 (1 μm = 0.001 mm)
• micrometres to nanometres


  x1000 (1 nm = 0.000001 mm)
• resolution


  how detailed the image is - how well the microscope distinguishes between two points that are close together.
• types of microscope

  optical (light) microscope or electron microscope.
• optical (light) microscope

  use light to form an image. max resolution = 0.2 μm, so can't view organelles smaller than that e.g. ribosomes, lysosomes, endoplasmic reticulum. max magnification = x1500
• electron microscope


  use electrons to form an image. max resolution = 0.0002 μm (1000x higher than LM). max magnification = x1500000.
• types of electron microscope

  transmission electron microscope (TEM) or scanning electron microscope (SEM).
• transmission electron microscope (TEM)


  use electromagnets to focus a beam of electrons which is transmitted through the specimen. Denser parts of the specimen absorb more electrons, so they look darker. TEMs produce high resolution images - you can see internal structures of organelles e.g. chloroplasts. Can only be used for thin and dead specimens due to use of a vacuum.
• scanning electron microscope (SEM)


  scan a beam of electrons across the specimen which knocks off electrons from the specimen to form an image which shows the surface of the specimen, so image can be 3D. can be used on thicker specimens but have lower resolution than TEMs.
• microscope artefacts


  things that can be seen down the microscope that aren't part of the cell or specimen that you're looking at.
• stages of cell fractionation

  homogenisation (breaking up the cells) - filtration (getting rid of the big bits) - ultracentrifugation (separating the organelles)
• homogenisation


  can be done using vibration or grinding using a blender to break up plasma membrane and release organelles into solution.
• ice cold solution during homogenisation

  to reduce activity of enzymes that break down organelles.
• isotonic solution during homogenisation

  to prevent damage to organelles through osmosis.
• buffer solution during homogenisation


  to maintain the pH.
• filtration

  homogenised cell solution is filtered through a gauze to separate any large cell or tissue debris. organelles are much smaller than any debris so they pass through the gauze.
• ultracentrifugation


  cell fragments poured into a tube and put into centrifuge. tube is spun slowly to separate heavier organelles e.g. nuclei into a pellet of sediment at the bottom. remaining organelles stay in fluid called the supernatant.

  process is repeated at a higher speed to separate next heaviest organelles e.g. mitochondria.

  process continues at higher speed each time.
• Order of organelle separation in ultracentrifugation

  Nuclei, chloroplasts (plant cells only), mitochondria, lysosomes, endoplasmic reticulum, ribosomes. (never, climb, mountains, lying, earth, right)
• Structure - nucleus


  Surrounded by nuclear envelope

  Contains nucleolus and chromatin (genetic material)
• Function - nucleolus

  Ribosomes synthesised
• Function - nuclear envelope


  Separates nucleus

  Allows diffusion

  Has nuclear pores for larger substances
• Function - nucleus


  Control centre of cell

  Stores and transmits genes

  Instructs protein synthesis
• Structure - RER


  Membranes containing cisternae and is attached to nuclear membrane

  Has ribosomes
• Function - RER

  Synthesis and transport of proteins
• Structure - SER


  Membranes of cisternae

  No ribosomes
• Function - SER

  Synthesis and assistance in packaging of lipids and carbohydrates (and steroids)
• Structure - golgi apparatus


  Stack of membrane bound sacs and vesicles. The Golgi consists of a group of stacked, thin, fluid filled membranes near the nucleus
• Function - golgi apparatus

  Modifies, packages and transports proteins (via vesicles), transports lipids
• Structure - mitochondria

  Double membrane

  Inner membrane - cristae

  Inner part is fluid filled matrix
• Function - mitochondria

  Site of ATP production (aerobic respiration)

  Highly abundant in cells requiring a lot of energy e.g. muscle and liver cells
• Structure - chloroplasts

  Double membrane

  Inner membrane continuous with thylakoid stacks (containing chlorophyll)

  Thylakoid stack - granum, surrounded by stroma (matrix)
• Function - chloroplasts


  Site of photosynthesis (chloroplasts, light energy, ATP produced)

  Carbohydrates produced (starch)
• Structure - vacuole

  Fluid filled sac surrounded by tonoplast membrane
• Function - vacuole


  Filled with water and solutes

  Makes plant cells turgid providing structure
• Structure - lysosomes


  Bags with single membrane

  Contain lysozymes for digestion
• Function - lysosomes

  Keeping lysozymes from rest of cell

  Destroys old organelles/foreign bodies
• Structure - vesicles

  Double membrane sac which pinches off RER/golgi and fuses with other membranes
• Function - vesicles


  Transport of substances between organelles & cells