Cells & The Cell Theory

Characteristics of Cells

History of the Cell

The Cell Theory All living things are composed of cells or cell fragments. All cells come from previously existing cells.

Cells Cells are organized into two groups. Prokaryotic Eukaryotic

Prokaryotic and eukaryotic cells differ in size and complexity All cells are surrounded by a plasma membrane. The semifluid substance within the membrane is the cytosol, containing the organelles. All cells contain chromosomes which have genes in the form of DNA. All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes.

A major difference between prokaryotic and eukaryotic cells is the location of chromosomes. In an eukaryotic cell, chromosomes are contained in a membrane-enclosed organelle, the nucleus. In a prokaryotic cell, the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell.

Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

Cellular Structures (Organelles)

Cell Membrane The outer covering of the cell. Regulates movement of materials into and out of the cell.

Nucleus The “brain” of the cell Controls all of the functions of the cell.

Mitochondria The chemical processes that provides energy for the cell take place within the mitochondria.

Vacuoles Storage sacks for cellular material and water.

Ribosomes Make protein that will be used by the cell.

Cell Wall Found only in plant cells the outer/protective covering of the cell. Provides support and shape for the cell.

Chloroplasts Site of photosynthesis Uses light and water to produce food molecules for the cell.

Endoplasmic Reticulum Helps movement of materials within the cell. Alters proteins made by the ribosomes.

Golgi Apparatus Changes protein molecules as needed by the cell. Stores and secretes chemicals for the cell.

Lysosomes Usually found in animal cells. Rids the cell of unwanted or defective parts. Stores digestive enzymes.

Comparing Plant Cells to Animal Cells How do plant cells differ from animal cells?

Fig. 7.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.8 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings