Do Now: Think-Pair-Share What do we have in common with bacteria living in our body ?

Microscope observations of organisms led to the discovery of cells – Robert Hook used the first microscope to discover structures he called ‘cells’ Ten years later, Anton van Leeuwenhoek used a more powerful microscope to observe living organisms in pond water. It took 150 years of improving the microscopes and compiling the observations made by different scientists to come up with

Cell Theory : All living things are made of one or more cells Cells are the basic units of structure and function in living organisms All cells arise from existing cells Contributors to the Cell Theory – Theodor Schwann, Rudolph Virchow, and Matthias Schleiden

Cells vary in size and shape. A cell’s shape reflects the cell’s function.

Cells in Human Body

Cell size is limited by a cell’s surface area-to –volume ratio. Cells with greater surface area – to – volume ratio (smaller cells) can exchange substances more efficiently.

All cells share the following features : Cell membrane Cytoplasm Ribosomes All cells are divided into Prokaryotic cells and Eukaryotic cells.

Prokaryotic cells Very simple in their organization Have cell walls (some have capsule surrounding the cell wall) Small in size 1-15 µm Believed to appear 3.5 billion years ago Do not have nucleus or membrane-bound organelles Examples all bacterial cells Eukaryotic cells Complex organization Can carry out more functions First appeared 1.5 billion years ago Have nucleus Have many different membrane-bound organelles