Cells are the smallest basic unit of life. They are made up of millions of molecules and are composed of all 4 macromolecules: lipids, nucleic acids, proteins, and, yes, even carbohydrates. As a former cell biologist, my absolute, hands-down, most favorite part of being a scientist was spending hours and hours in front of the fluorescent microscope, examining the inside of the cell like a miniature spaceship navigating through the cell like a galaxy (see Isaac Asimov's Fantastic Voyage, a class sci-fi fantasy about miniature dudes who explore the human body in a miniature spaceship).
A picture of an adipocyte (a fat cell), which I took as a graduate student.
There are many different types of cells. Cells can exist as a single-celled organism (bacteria, algae, Amoebas, etc). They can exist cooperatively, making up multi-celled organisms, from snails, to birds, and of course, humans. Cells come in all different shapes and sizes. Some have cell walls, some don't. Some move around a lot; others remain motionless their whole lives. Each cell has a special function so each cell is designed a little differently. They are specialized, or physically customized according to that cell's main function. For instance, skin cells contain a lot of keratin, the structural protein that makes our skin a protective barrier and helps make our nails hard. Red blood cells are specially designed to transport oxygen and deliver it to all parts of the body. They don't even have a nuclei, which is why they are sometimes called ghosts.
Cells have always fascinated me. The intricate design of a cell is like a perfectly tuned orchestra.
Bacteria Cell (note: this is a prokaryote. The above 2 are eukaryotes).
Video About the ATP cycle:
Link to Running & ATP:
Link to Video (on my home page):
White blood cell chasing a bacterial cell (red blood cells also shown). Great for illustrating how dynamic cells are, the differences between prokaryotes and eukaryotes and cell specialization.
Link to video
Link to my Resources (Google Docs Folder):
Go here for lesson plans, ideas, and activities!
Outside links to other resources on cells:
Great ideas for a myriad of a areas related to biology from Serendip
Role-play Photosynthesis Activity
Great clip from NASA on the role of phytoplankton and the ocean