All life is made of cells Discovered after microscope invented 1665: Robert Hooke first observed cork (dead plant bark) –Cork reminded him of tiny rooms He named the empty boxes “cells”

Three Parts: –1) All organisms are made of cells –2) The cell is the most basic unit of life –3) Cells come from other cells What’s the big problem with this theory?

Cell Diversity Shape depends upon function Nerve Shape: Elongated branching –Function: Sends messages to and from brain Red Blood Shape: Disc-like shape prevents clogging –Function: Carries O2 throughout blood Skin Shape: Flat & broad; layers overlap –Function: Covers and protects the body

1) Prokaryote: Cells without a nucleus and other membrane-bound organelles –Oldest cells known (~4 billion years old) –Believed to have evolved first (oldest fossils) –AKA: Bacteria

2) Eukaryote: Cells with a nucleus & membrane bound organelles –More complex cells –Evolved from prokaryotes –Ex: Protists, Fungi, Plants, Animals

Endosymbiosis Theory: Chloroplast & mitochondria were free- living organisms –Both were engulfed by a larger predator cell –Both gave the larger cell an advantage (make food and energy) –Predator cell provided each protection Over time, these cells could not survive without the mitochondria & chloroplast Evidence: Mitochondria & chloroplast contain own DNA, replicate, contain own ribosomes

Quick Review Cells shape is related to its job (function) Cells are the basic units of life Cells come from other cells