Eukaryotic plant and animal cells have some similarities and marked differences in structure that are key to understanding life; Every organism does occurs fundamentally because of functions at a cellular level.
If you have ever observed plant cells and animal cells under a microscope, you can plainly see that plant cells are shaped like bricks, a feature that is attributed to the cell's rigid structure. On the other hand, animal cells are typically less uniform in shape and more rounded.
At the center of plant cells is the central vacuole, which is much larger and more significant to the plant than that of animal cells. A plant's central vacuole typically occupies most of the space in a cell, while in animal cells, vacuoles are much smaller and merely used to temporarily store or transport substances. The central vacuole of a plant serves many purposes. It stores water, organic compounds, pigments, toxins, and cell wastes. The water in the central vacuole also has the added benefit of providing turgor pressure for the plant, allowing it to stay rigid and maintain structural integrity.
Another feature of plant cells vital to preserving structure is the cell wall. Composed of polysaccharides, cellulose, and proteins wound together into fibers, the cell wall of a plant cell ranges in thickness from 0.1 micrometers to several micrometers. Depending on the species of plant, cell walls can have 3 separate components: the thin flexible primary cell wall, a middle lamella made of pectins that "glue" adjacent cells together, and the secondary cell wall.
In animal cells, the extracellular matrix (ECM), composed of a complex system of proteins and carbohydrate polymers, serves a very similar function as the cell wall in plants. Integrins anchor the ECM to the cell's plasma membrane and the microfilaments inside the cell. Another type of protein called fibronectins attach the ECM to the integrins, Proteoglycans and the polysaccharide glycogen form a mesh outside the cell. Aside from providing structural support, the ECM also plays a role in regulating a cell's behavior. It reacts to signals from other cells or physiological changes in the environment and signals to the interior of the cell through the integrins.
Only plant cells contain chloroplasts, a double membraned organelle that engage in the process of photosynthesis. The structure of chloroplasts are critical to its function. Located in the palisade mesophyll area of cells in a plant's leaves and stem, chloroplasts have an outer and inner membrane, and within the inner membrane is a system of membranous sacs sitting in fluid called "stroma". Each sac is a "thylakoid", and one stack of thylakoids is a "granum", the plural being "grana". The space inside thylakoids serves as a resevoir for H+ ions during the Light Dependent Phase of photosynthesis. As H+ builds up inside the thylakoid space, the ions diffuse down their gradient and create energy for the plant in the process.
It is a popular misconception that plant cells have just chloroplasts while animal cells have just mitochondria. However, plant cells have BOTH mitochondrion and chloroplasts, as they engage in both respiration and photosynthesis.
Another feature unique to plant cells is the glyoxisome, a specialized type of peroxisome. Found usually in plant seeds, the glyoxisome contains enzymes to metabolize fatty acids.
Animal cells have centrioles, a bundle of microtubules in the 9X2 formation, which are used in mitosis. In comparison, most higher order plant cells lack centrioles.
So, in brief:
ONLY PLANT CELLS HAVE:
- More uniform brick-like shape (exceptions being young fruit cells)
- Cell walls
- Central Vacuole
ONLY ANIMAL CELLS HAVE:
- Rounded shape
- Extracellular matrix