Cell biology

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

Microscopy

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…