Cell Types

Cell Theory

• Every living organism is made of one or more cells

• The smallest organisms are made of single cells while multicellular organisms are made of many cells

• All cells arise from pre-existing cells

Cell Function Limits Cell Size

• most cells are small, ranging from 1 to 100 micrometers in diameter

• cells need to exchange nutrients and wastes with the environment

• no part of the cell can be far away from the external environment

• surface area to volume ratios must be kept rather large

All Cells Share Common Features

• a plasma membrane encloses all cells and regulates material flow in and out of the cell

• cytoplasm is the fluid interior where a cell’s metabolic reactions occur (cytosol)

• DNA (deoxyribonucleic acid) is the hereditary blueprint and RNA (ribonucleic acid) copies DNA for protein production (universal genetic code)

Two Basic Cell Types

Prokaryotic Cells (bacteria)

• DNA is in the form of circular loops and is free in the cytoplasm

• cells contain no internal membranes and no organelles except for ribosomes

Eukaryotic Cells (protists, fungi, animals, plants)

• DNA is linear, bound with histone proteins in structures called chromosomes and housed in a central structure called a nucleus

• cells contain complex internal membrane systems and specialized organelles

‘Naked ring of DNA’ X

Spherical (cocci)

1 µm

Rod-shaped (bacilli)

2 µm

Spiral

5 µm

Making Scientific Illustrations

• Draw only on white, unlined paper. • One drawing per page. Draw large – but not off the edge of the

page.• Draw only in pencil. • Do not shade or color your drawings. Stay focused on FORM.• Use clean, unbroken lines. No artsy sketching. • Have a title, magnification, and appropriate labeling on each

drawing.• Draw only biological structures! Do not draw air bubbles, dust,

debris, and other irrelevant objects just because you see them. • Pay attention to detail. Draw less, draw big (fill the space),

draw carefully.