Plant Cells vs. Animal Cells, With Diagrams

Cells have often been referred to as "the building blocks of life", which indeed they are. All forms of life, from simple bacteria to human beings, are made up of cells. What is remarkable is that, despite their apparent differences, plant and animal life are made up of cells that are actually the same in most respects.

The most important structures of plant and animal cells are shown in the diagrams below, which provide a clear illustration of how much these cells have in common. The significant differences between plant and animal cells are also shown. The diagrams are followed by more in-depth information.

The structures within the cell, such as the nucleus and mitochondria, are known as organelles. The diagram above is of a "generic" animal cell. In both animals and plants, cells generally become specialized to perform certain functions. Nerve cells, bone cells and liver cells, for example, all develop in ways that enable them to better perform their specific duties. Most animal cells, however, contain the structures shown in the diagram.

Below is a "generic" plant cell diagram. The structure of plant cells can vary during the early stages of growth. This diagram depicts a mature plant cell.

Eukaryotic cells are cells that contain a well-defined nucleus, and in which the other organelles are held together by membranes. Plants and animals are both eukaryotes, and as you can see, their cells are quite similar in many ways. Organelles that can be found in both plant and animal cells include the following:

• Cell Membrane: surrounds and protects the contents of the cell. The membrane is selectively permeable, meaning that it allows certain molecules to pass through it and enter the cell, while preventing others from doing so.
• Cytoplasm: the fluid which fills the cell, in which the organelles are suspended.
• Nucleus: the cell's command center, regulating the various processes within the cell. The nucleus, which also contains most of the cell's genetic material, is usually located near the center of animal cells, and closer to the edge in plants.
• Mitochondria: converts food into energy. Active cells, which require more energy, usually contain a greater number of mitochondria. Plant cells tend to have fewer mitochondria than animal cells. Mitochondria also contain a small amount of DNA, and therefore play a role in genetics.
• Ribosomes: generate proteins from amino acids. Some ribosomes are attached to the endoplasmic reticulum, others float freely within the cytoplasm.
• Endoplasmic Reticulum: a series of sacs and tubes used to process substances such as protein and lipids, and transport them to the golgi bodies for distribution to other locations. The area where ribosomes are attached is called the rough endoplasmic reticulum. The area without ribosomes is known as the smooth endoplasmic reticulum.
• Golgi Bodies: location where substances received from the endoplasmic reticulum are processed and carried to the proper location within the cell, or out of the cell altogether.
• Vacuoles: sacs which serve as storage units. When found in animal cells, vacuoles are tiny, and are used to carry substances out of the cell, or to engulf undesirable substances such as bacteria or bits of dead tissue. In plant cells, the vacuole plays a much larger role, which is described in the section below.

Plant cells have to perform two functions not required of animal cells:

1. Produce their own food (which they do in a process called photosynthesis).
2. Support their own weight (which animals usually do by means of a skeleton).

The structures possessed by plant cells for performing these two functions create the primary differences between plant and animals cells. These structures are:

• Cell Wall: a wall on the outside of the membrane, which, in combination with the vacuole (as described below), helps the cell maintain its shape and rigidity.
• Plastids: used in photosynthesis to convert sunlight, carbon dioxide and water into food. The most well-known plastids are chloroplasts, which contain the chlorophyll that gives many plants their green hue.
• Large Vacuole: while animal cells may have many tiny vacuoles, a plant cell usually has a single large vacuole, which serves as a storage tank for food, water, waste products and other materials. The vacuole has an important structural function, as well. When filled with water, the vacuole exerts internal pressure against the cell wall, which helps keep the cell rigid. A plant that is wilting has vacuoles that are no longer filled with water.

Animal cells contain organelles known as centrioles, which are not present in plant cells. Centrioles, which help move chromosomes during cell division, are generally only visible when an animal cell is actually dividing.

It is believed that because animal cells, which are softer than plant cells, can change shape, centrioles are required to ensure that the chromosomes are in the proper location when the cell divides. Plant cells, with their more fixed shape, can safely assume that the chromosomes are correctly positioned without the use of such a mechanism.

How is it that plant and animal cells have so much in common? As hard as it may be to imagine, biologists believe that at an early point in the evolution of life on earth, plants and animals once shared a common ancestor. All life on earth, it seems, truly is related.

• Wallace, Holly. Cells And Systems. Chicago: Heinemann Library, 2006.
• Phenlan, Jay. What Is Life? A Guide to Biology. New York: W.H. Freeman and Company, 2010.
• Exams India. Differences Between Plant and Animal | Cell Procaryotic and Eucaryotic Cell 2012. http://examsindia.net/2010/01/differences-between-plant-and-animal-cell-procaryotic-and-eucaryotic-cell.html