cell biology

• what is a cell

  the smallest unit of life that can live on its own
• what is the difference between eukaryotic and prokaryotic cells?

  (1)eukaryotes are larger than prokaryotes (2) eukaryotes contain membrane-bound organelles whilst prokaryotes don't (3) eukaryotes keep their DNA in the form of chromosomes within a nucleus while prokaryotes have a single circular strand on DNA that floats freely in the cytoplasm.
• for animal, plant and bacterial cells: state whether they're either eukaryotic or prokaryotic

  eukaryotic - animal and plant cells. prokaryotic - bacterial cells
• what is the role of the cell membrane?

  holds the cell together and controls what goes in and out
• what is the cytoplasm, and what's its role?

  the cytoplasm is a gel-like substance where most of the chemical reactions happen. the cytoplasm contains enzymes that control these chemical reactions.
• what is the role of the nucleus?

  contains genetic material that controls the activities of the cell
• what is the role of the mitochondria?

  where most of the reactions for aerobic respiration take place in the form of ATP. (respiration transfers energy the cell needs to work)
• what is the role of the ribosomes?

  where proteins are made (protein synthesis)
• what are the 3 things a plant cell has but an animal cell does NOT?

  rigid cell wall, permanent vacuole, chloroplasts
• what is the role of the (plant) cell wall?

  it is made of cellulose, provides strength and structure to the plant cell. and prevents it from bursting/shrinking when enter enters/leaves the cell via osmosis
• in plants, what is the cell wall made of?

  cellulose
• what is the role of the permanent vacuole?


  contains cell sap - a weak solution of sugar and salts - which helps give the plant cell its shape.
• what is the role of the chloroplasts?


  where photosynthesis occurs(which makes food for the plant.) they contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.
• what is chlorophyll?


  a green pigment, within chloroplasts, that absorbs sunlight for photosynthesis. this is what makes plants green.
• what are plasmids, and what are their role?


  small, circular loops of DNA (that are separate to the main DNA). They contain extra genes which are sometimes useful to the bacteria.
• name the sub cellular structures that are found in bacterial cells


  cytoplasm, cell membrane, cell wall, plasmids, circular strand of DNA that floats freely in the cytoplasm. prokaryotes don't have a nucleus or chloroplasts and mitochondria.
• name 5 sub cellular structures that are found in BOTH animals and plant cells (eukaryotes)


  cell membrane, ribosomes, nucleus, mitochondria and cytoplasm
• what is the definition of magnification?

  how many times larger the image seen through a microscope appears compared to the real object
• what is the role of a microscope?

  to magnify small objects so that they appear larger
• what is the definition of resolution?


  the ability to distinguish between two points or how clear the image is
• how does a light microscope work?


  light (from a mirror/light source) -> passes through the specimen -> objective lens -> the eyepiece lens -> into your eye
• what are the two types of microscopes?

  light microscopes and electron microscopes
• what is the magnifying power of a light microscope?

  x2000
• what is the magnifying power of an electron microscope

  x2000000
• give 5 advantages of light microscopes

  1)cheap 2)easy to use 3)small so easy to transport 4)produces colour images 5)can see living specimens
• what are the main disadvantages of light microscopes

  light microscopes rely on light, whereas electron microscopes rely on electrons (light has a longer wavelength - lower resolution) and light microscopes have a lower maximum magnification so can't see many details within cells
• what are the main advantages of electron microscopes

  electron microscopes have a higher resolution and magnification so can see details within small subcellular structures
• give 5 disadvantages of electron microscopes

  1)expensive 2)difficult to use and require training 3)large so difficult to transport 4)images generated in black and white 5)only view dead specimens
• a microscope slide is a strip of clear glass or plastic onto which the specimen is mounted
• how to prepare a microscope slide

  1)add a drop of water to the middle of a clean slide 2) cut up an onion and separate it into layers. use tweezers to peel off some epidermal tissue from the bottom of a layer 3) using tweezers, place the epidermal tissue into the water on the slide 4) add a drop of iodine solution (stain) to highlight objects in a cell by adding colour to them 5)place a cover slip on top and try not to get any air bubbles
• why don't you want any air bubbles when preparing your microscope slide?

  it will obstruct your view
• How to use a light microscope to look at your slides

  1. Clip the slide you've prepared on the stage

  2. Select the lowest powered objective lens (the one that produces the lowest magnification)

  3. Use the coarse adjustment knob to move the stage up to just below the objective lens

  4. Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

  5. Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide

  6. If you need to see the slide with a greater magnification, swap to a higher powered objective lens and refocus
• Light microscope

  • Uses light and lenses
  • Small in size
  • Produces lower magnification/resolution
  • Cheap
  • Specimens can be dead or alive
  • Easy to use
• Electron microscope

  • Uses electrons
  • Large in size
  • Produces higher magnification/resolution
  • Expensive
  • Specimens have to be dead
  • Difficult to use, requires special training
• rearrange the units of distance below, ordered from smallest to largest

  (smallest)<-- nm , μm , mm , cm , m , km -->(largest)
• units of conversion

  bigger unit -> smaller unit = multiply smaller unit -> bigger unit = divide
• units of conversion 


  km -(x1000)-> m -(x100)-> cm -(x10)-> mm -(x1000)-> μm -(1000x)-> nm
• what is the formula for magnification

  image size divided by actual size

  
• what is the order of magnitude?

  every order of magnitude if 10x greater than the one before 1 order of magnitude = 10x bigger 2 orders of magnitude = 100x bigger
• give 3 reasons why multicellular organisms require a continuous supply of new cells

  1.growth - we need more cells are we grow. 2.development - we need new cell types as we develop new tissues. 3.repair - we need to place the cells we lose each day