Cell Structure: (1) Cell Membrane Proteins & carbohydrates are also associated with the cell membrane. Some proteins stick to the surface. Other proteins are free to move around within the layer.

Cell Structure: (1) Cell Membrane The free-moving proteins act as both channels and small pumps. ---channels through which molecules can pass ---small pumps which push molecules from one side of the membrane to the other side

Cell Structure: (1) Cell Membrane The carbohydrates are attached to proteins or lipids at the membrane surface. Many of these carbohydrates act like chemical identification cards, allowing cells to communicate with each other. The above description of the cell membrane is known as the Fluid-Mosaic Model.

Cell Structure: (1) Cell Membrane

Cell Structure: Cell Wall In organisms such as plants, algae, and some bacteria, the cell membrane is surrounded by a cell wall. The cell wall helps to protect the cell.

Cell Structure: Cell Wall The main component of the cell wall is cellulose. Because the cell wall is porous, water, oxygen, carbon dioxide, and other substances can pass through easily.

Cell Structure: Cell Wall

Cell Structure: (2) Nucleus Many cells contain a large dark structure called the nucleus. The nucleus is the information center of the cell because it contains DNA. The DNA in the nucleus of eukaryotic cells is attached to special proteins and forms large structures called chromosomes.

Cell Structure: (2) Nucleus Surrounding the nucleus are two membranes that form the nuclear envelope. It has dozens of nuclear pores (small openings), which allow molecules to move in and out of the nucleus.

Cell Structure: (2) Nucleus Most nuclei contain a small region called the nucleolus. It is made up of RNA and proteins. It is the structure in which ribosomes are made.

Cell Structure: (2) Nucleus

Two Basic Cell Types Prokaryotes are organisms whose cells lack any membrane bound structures. These cells do have genetic material (DNA or RNA) but not in a membrane bound nucleus. These cells have no membrane bound organelles in the cytoplasm. These are small unicellular organisms, for example, bacteria.

Two Basic Cell Types Eukaryotes are organisms whose cells contain nuclei. These organisms include both unicellular and multicellular forms. The distinction between prokaryotes and eukaryotes is a basic one that scientists consider far more important than the distinction between plant and animal cells.

Cell Structure: (3) Cytoplasm The cytoplasm is the area between the nucleus and cell membrane. The cytoplasm contains many important structures.