Cell Biology pt1



Organisms can be Prokaryotic or Eukaryotic:
Eukaryotic - are complex and include all plant and animal cells. Eukaryotes are made up of eukaryotic cells
Prokaryotic  - smaller and simpler. Prokaryotes are a prokaryotic cell.
An animal includes:

  • A nucleus - contains the genetic material
  • Cytoplasm - most of the chemical reactions happen here
  • Cell membrane - holds the cell together
  • Mitochondria - most of the reactions for aerobic respiration
  • Ribosomes - where proteins are made in the cell

A plant cell includes:

  • A nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Cell wall - supports and strengthens the cell
  • Pernament vacuole - contains cell sap
  • Chloroplasts - where photosynthesis occurs. They contain a green substance called chlorophyll.

Bacteria cells are much smaller:

Bacteria are prokaryotes. They contain:

  • Cytoplasm
  • Cell membrane÷
  • Cell wall
  • Plasmids - one or more rings of DNA
  • A single circular strand of DNA

They don't have chloroplasts and mitochondria


Microscopes let us see things that we can't see with the naked eye.

Light microscopes use lights and lenses to form an image of a specimen and magnify it.
Electron microscopes use electrons instead of light to form an image. They have a much higher magnification They also have a higher resolution. Electron microscopes let us see much smaller things in more detail such as the internal structure of chloroplasts.

A formula to work out magnification is:

magnification = image size ÷ real size

Required practical

Prepare the slide

  • Add a drop of water to the middle of a clean slide
  • Cut up the onion and separate it out into layers - use tweezers to peel off some epidermal tissue from the bottom of one of the layers
  • Using the tweezers place the epidermal tissue into the water on the slide
  • Add a drop of iodine solution. This stains the tissue. Stains are used to highlight objects in a cell by adding colour to them
  • Place a cover slip on top. To do this stand the coverslip upright on the slide next to the water droplet. Then carefully tilt and lower it so it covers the specimen. Try not to get any air bubbles under there - it'll obstruct your view of the specimen.

Use a light microscope

  • Clip the slide you've prepared onto the stage
  • Select the lowest-powered objective lens.
  • Use the coarse adjustment knob to move the stage up to just below the objective lens.
  • Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
  • Adjust the focus with the fine adjustment knob until you get a clear image of what's on the slide.
  • If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.

Draw your observations with a pencil

  • Draw what you see under the microscope using a pencil with a sharp point
  • Make sure your drawing take up at least half of the space available and that it is drawn with clear, unbroken lines
  • Your drawing…