List of the Major Structures That Are Found in Plant & Animal Cells & Their Functions

Plasma Membrane

• Cells are held together by a semipermeable plasma membrane, also referred to as the cell membrane, which consists of two layers of proteins and fats. The plasma membrane encloses the cytoplasm -- the gelatinous substance that is the basis of the cells -- and the organelles. It functions also as a filter, regulating the influx of molecules into and out of the cell. Water and oxygen, for example, can easily traverse the membrane, while the flow of amino acids and sugars is more restricted.

Nucleus

• Plants and animal cells are eukaryotic, which means that they have defined nuclei that are encased by membranes. The nucleus holds the organism's genetic material, known as deoxyribonucleic acid or DNA. The outer membrane is porous, which allows the nucleus to interact with the cytoplasm.

Endoplasmic Reticulum

• The endoplasmic reticulum consists of a series of folded membranes in which cells produce the fats and the proteins that make up the tissues of the organism. Attached to parts of the membranes are tiny structures called ribosomes where amino acids are synthesized to make proteins. The portions of the membrane that have ribosomes are known as rough endoplasmic reticula; smooth endoplasmic reticula have no ribosomes.

Golgi Apparatus

• Proteins and fats synthesized in the endoplasmic reticulum are modified and distributed to other parts of the cell by the Golgi apparatus. Due to its function, this relatively large organelle is located near the endoplasmic reticulum and the nucleus. It consists of four to eight flattened sacs with curved ends known as cisternae.

Lysosome

• The spherical organelles known as lysosomes contain acidic enzymes that allow them to break down cellular waste materials into simple compounds, some of which are recycled by the cell. Lysosomes also break down microorganisms, such as bacteria. These organelles originate in the Golgi apparatus and break off.

Mitochondria

• In animal cells, mitochondria are organelles that convert oxygen and nutrients derived from food into a form of energy that the cell can use. The process is known as aerobic respiration; the energy produced is called adenosine triphosphate or ATP. Mitochondria are oblong-shaped and have their own DNA, which makes them unique among organelles. Mitochondria are present in plant cells but play a less important role.

Plant-Specific Structures

• Plants synthesize their own organic nutrients from nonliving components. Plant cells, therefore, contain organelles that are absent from those of animals, which get their nourishment by consuming other organisms. The organelles known as chloroplasts contain chlorophyll, the substance that makes plants green. This allows chloroplasts to convert sunlight into energy, a function that likens them to mitochondria in animal cells. Vacuoles -- large organelles that contain liquids -- store nutrients and digest waste products in plant cells, which also have stiff cell walls outside the plasma membrane.