Animal and plant cells are quite similar. Only a few differences between them alter their overall functions, and they are some of the most complex of all the cells on earth.
All organisms are made up of either prokaryotic cells or eukaryotic cells. Prokaryotes have a simple structure. They are made up of a plasma membrane and intercellular fluid called cytoplasm. Eukaryotes share both of these features with prokaryotes, but also contain more complex structures such as organelles and a nucleus. These internal features allow eukaryotic organisms to grow into complex forms such as plants, animals and fungi.
The plasma membrane of prokaryotic and eukaryotic cells acts as a barrier between the outside environment and the inside of the cell. It is composed of proteins surrounded by two layers of lipids. The free, floating movement of the protein within the lipid bilayer gives the cell an amorphous shape. The key function of the proteins is to transfer certain materials across the membrane while keeping other materials out. This regulation of material is essential for maintaining a balanced and healthful environment inside the cell.
A major similarity between prokaryotic cells and eukaryotic cells of plants and animals is the cytoplasm. Only eukaryotic cells, however, contain structures within the cytoplasm called organelles, meaning “little organs.” Each organelle performs a function in the cell. For example, the endoplasmic reticulum forms proteins from amino acids. Another organelle, called the golgi apparatus, processes the proteins. An especially important organelle, involved in metabolism, is the mitochondria. The mitochondria are responsible for converting food sources, such as carbohydrates, into energy-containing molecules for use in the cell.
The nucleus is a structure found only in eukaryotic cells. Proteins and DNA make up the majority of its contents. The DNA is arranged into strands called chromosomes. Segments of the chromosomes are called genes. The nucleus is surrounded by its own plasma membrane, called the nuclear envelope. Two organelles with the nucleus, the nucleoli, process genetic information into sub-microscopic particles, called ribosomes. These particles are passed across the nuclear envelope, delivering the genetic information to the endoplasmic reticulum.
Plant cells function in much the same way as animal cells. However, two structures are specific to plant cells: the cell wall and chloroplast. The cell wall exists outside the cell’s plasma membrane and acts as a permeable support structure. It is made up of cellulose, creating a rigid form to the cell. The cell wall allows plants to grow to great heights without loosing their shape. The other feature not found in animal cells is chloroplast. This organelle contains the proteins, pigments and enzymes necessary for photosynthesis. During this process, light energy is converted to carbohydrates, which are processed in the mitochondria.