SECTION 3.1 WHERE LIFE HAPPENS1. Living things can be unicellular (one cell) or multicellular. A bacterium is a type of single cell.2. About 8000 of the smallest bacteria could be contained in one of the red blood cells.3. The longest cells are the thin nerve cells found in large animals and can be more than a meter long.4. The cell with the largest volume is an unfertilized ostrich egg5. The shape of a cell is linked to its function. For example, a nerve cell is long and carries messages from the spine to the toes. The contraction and relaxation of muscle tissue are responsible for movement in animals. A LITTLE NEW WORLD1. In the 1600s, people only knew about organisms they could see with the naked eye. A trio of Dutch eyeglass makers invented the microscope in the late 1500s. It consisted of a tube with lenses made from rock crystal and magnified objects up to 9 times their actual size. In 1665 the British scientist Robert Hooke published a series of drawings illustrating what he had observed under the microscope.4. In the early 1770s Anton van Leeuwenhook, a Dutch textile shop owner, began grinding lenses as a hobby. He used handheld microscopes to examine materials such as pond water and blood. BIOLOGISTS BUILD A THEORY1. By the 1830s many biologists were using the microscope as their primary investigative tool2. Mathias Schleiden was a botanist, a scientist who studies plants. He discovered that the parts of the plants he examined were made up of cells. In 1838 Schleiden generalized that all plants are made of cells.3. Theodor Schwann was studying and animals. His microscopic investigations of animal parts led him to generalize that all animals were made of cells.4. In 1858, a German doctor named Rudolf Virchow challenged the idea of ​​spontaneous generation. Virchow reasoned that new plant cells arise only from existing plant cells, and new plant animal cells arise only from existing animal cells.5. Cell theory is based on three principles:  Cells are the basic units of all life.  All organisms are made up of one or more cells.  All cells arise from existing cells. SEE SMALLER1. One of the most important tools used by biologists is the microscope.2. Until the 1950s, microscopes were optical microscopes, instruments that used sunlight or artificial light to observe objects. With the advantage of this it can magnify many microscopic objects while they are alive.