Cells are different, yet they are made of only a single cell. have - PDF document

Cells may differ in their number. • Some organisms Cells are different, yet they are made of only a single cell. have many similarities. y • Other organisms are made of Cells function similarly in all living organisms. billions of cells. Paramecium Raccoon For example, the cells that line the Specialized Cells retina of your eye have a structure and • In multicellular function that is very different from your organisms like you, skin cells. there are many different types of specialized cells. • About 200 different types of specialized cells make up the tissues and organs of your body. Even though there are many different 1. All cells are surrounded by a cell types of cells, they all share similar membrane. characteristics. • The cell membrane is a • All cells have a barrier between the cell membrane, inside of the cell and organelles, organelles its environment. cytoplasm, and • It also controls the DNA. movement of materials into and out of the cell. 1

2. All cells contain organelles. 3. All cells contain cytoplasm. • An organelle is a • The cytoplasm is a fluid mixture that structure inside of a contains the cell that helps the organelles. cell perform its cell perform its • It also contains the functions. compounds cells • Although all cells need to survive such contain organelles, as water, salts, they don’t all contain enzymes, and other the same kinds. carbon compounds. Based on the organization of their structures, 4. All cells contain DNA. all living cells can be classified into two groups: prokaryotic and eukaryotic. • The cell theory states that all • Animals, plants, fungi, and protozoans all cells come from other cells. have eukaryotic cells. • When cells reproduce, they • Only bacteria have prokaryotic cells. y p y make copies of their DNA and make copies of their DNA and pass it on to the new cells. • DNA contains the instructions for making new cells and controls all cell functions. Scientists believe that all life on Earth Prokaryotic cells do not have a nucleus. came from prokaryotic cells. • The word prokaryotic means “before nucleus” in • The oldest fossils of Greek. bacteria are estimated to be 3.5 • Only bacteria have this b billion years old. d type of cell. • The DNA in a prokaryotic cell is bunched up in the center of the cell. • The organelles are not covered with a membrane. 2

Animals, plants, fungi, and protists all Eukaryotic cells have eukaryotic cells. • Eukaryotic cells have a nucleus and • Eukaryotic cells have a membrane-covered organelles. nucleus and membrane- covered organelles. • The word eukaryotic means “true nucleus” • There is more DNA in • There is more DNA in in Greek in Greek. these types of cells and it • The oldest fossils of eukaryotic cells are is found in the nucleus. about 2 billion years old. • They tend to be about ten times larger than prokaryotic cells. 3