van Leeuwenhoek's microscope
Antonie van Leeuwenhoek is credited with constructing the first microscope.
- Size: matchbox
- Held close to the eye
- Magnification: 400x
van Leeuwenhoek was the first to describe sperm and (probably) bacteria, which he called "animalcules" ("little animals").
In a sample from cork oak, Hooke sees what he describes looking like cells in a monastery. Although nobody at the time knew what a (biological) cell is, Hooke coined the term "cell".
A modern light microscope
A modern light microscope works essentially the same way as Hooke's microscope, although the design has changed quite a bit.
What characterizes a cell?
All cells have
- a cell membrane,
- cytoplasm (fluid-like intracellular substance), and
- DNA (in one or several chromosomes).
What the cell theory says
- All organisms consist of one or more cells.
- The cell is the fundamental living unit.
- New cells may only arise from other cells.
What do you need to build a cell?
Lipids are a diverse group of fat or fat-like molecules, insoluble in water.
Cell membranes are made of phospholipids.
The nucleic acids are DNA and RNA.
- Alternating sugar (S) and phosphate (P) residues.
- A always base pairs with T (in RNA, T is replaced with U), and vice versa.
- G always base pairs with C