Most cells are too small to see With the naked eye. Scientists became aware of Cells only after microscopes Were invented, in the 1600’s. When the English scientist Robert Hooke used a crude Scope, he saw a bunch of Little boxes he called cells.
In a light microscope, light Passes through one or more Lenses to produce an Enlarged image of something. An electron microscope forms An image of a specimen using A beam of electrons instead Of light.
A year later, the German Physician Theodor Schwann Concluded that all animals Are made up of cells.
Rudolf Virchow stated that All cells come from other cells.
All of these studies combined To form the cell theory, Which has three parts… All living things are composed of one or more cells Cell are the basic units of structure and function All cells come from preexisting cells
All cells have the same Common features… Cell membrane = outer boundary Nucleus = “center” command center Cytoplasm – everything between the cell membrane and nucleus
All cells also have ribosomes Which are where proteins Are made. All of them also have DNA that Provide instructions on how Everything is made and done.
The smallest and simplest cells Are prokaryotes. Prokaryotes are single celled Organisms that lack a nucleus And other internal stuff. Bacteria are prokaryotes.
The DNA of a bacteria is Circular and just floating around In the cytoplasm. All bacteria have a cell wall. Some bacteria are also enclosed In a capsule which allows them To stick to almost anything.
Many bacteria have flagella, Which are long, threadlike Structures that enable them To move around.
The cytoplasm and organelles Of a cell are contained by Its membrane. The membrane is made up of Lipids that stick together. Phospholipids are lipids that are Made up of a phosphate group And 2 fatty acids.
Same in plants, animals and microorganisms Lipid bilayer
electron micrograph of a cell membrane at approx. 240,000x
Plant cells are eukaryotic Cells that have different parts Than animal cells. They have cell walls, Chloroplasts and central Vacuoles.
A cell wall supports and Protects the cell and allows Plant cells to be stacked On top of each other. The cell wall is made up of Proteins and polysaccharides. We (humans) cannot digest Cell walls. (fiber)
The central vacuole is a large Membrane bound space that Stores water and many Substances including ions, Nutrients and wastes. When the vacuole is full, it Presses the cytoplasm against The cell wall, making the cell Very rigid.