Differences Between Animal Cells and Plant Cells
The biodiversity present on planet Earth is vast. There are an estimated 8.7 million species of animals and plants worldwide, of which just over 1.2 million have been discovered. In order to classify such a number of living beings, it’s necessary to establish both phylogenetic and anatomical criteria. So, do you know the differences between animal cells and plant cells?
Although both are microscopic and invisible to the human eye, it’s essential to know each of the cell types of the two most representative kingdoms on Earth. Next, we show you the most distinctive characteristics between both groups and how they condition their physiology at an organic level. Don’t miss it!
What is a cell?
Before establishing the distinctions between animal and plant cells, it’s necessary to know what they are at a general level. The National Cancer Institute defines this structure as “the minimum biological unit that can live on its own and which, in turn, is part of all living organisms on Earth.” The human body has more than 30 trillion cells, but other living things only have one.
Despite its apparent simplicity, not every microscopic structure with a circular shape and internal substances meets the requirements to be a cell. The cell theory (formulated by Matthias Schleiden and Theodor Schwann in the 19th century) states that every cell must meet the following requirements:
- It’s the basic morphological unit of all living beings. Viruses, prions, and viroids don’t have a single cell in their “body”, so they can’t be considered as living beings (they’re biological pathogens ).
- Every cell derives from a preceding cell (Omnis cellula ex cellula). As life cannot be generated from inanimate objects, it’s assumed that every cell comes from the previous division of another.
- It’s the place where the vital processes of all living beings occur. Cellular respiration, metabolism, and all basic survival reactions occur within or near the cell. Each of these structures is an open system that exchanges energy and other compounds with the environment.
- Every cell has the information necessary to replicate itself and control its cycle. By definition, a cell contains a nucleus that contains the genetic information necessary for its division (either mitosis or meiosis). Thanks to this, cell lines are able to maintain themselves over time, multiplying and replacing each other when the old ones die.
Every cell is an open system, but it differs from the environment thanks to the presence of a plasma membrane. In addition, inside it contains its own fluid (the cytosol) in which the organelles necessary to carry out its metabolism rest. Finally, it should be noted that living cells have a nucleus with DNA, which encodes the synthesis of proteins and RNA.
What are the differences between animal cells and plant cells?
With the aforementioned basic guidelines, we have shown the necessary criteria for a cell to be considered as such. However, there are clear differences between the cell types of each biological kingdom. Next, we’ll show you the most important ones among the animal and plant cell bodies.
1. The plant cell has a cell wall, while the animal cell doesn’t
The cell differs from the rest of the body and the environment thanks to the presence of a plasma membrane. As indicated by the National Human Genome Research Institute, this structure regulates the transport of materials that enter and leave the cell body. It’s made up of a bilayer of phospholipids, proteins, and other substances.
The only thing that delimits the cytoplasm of the animal cell from the external environment is the plasma membrane, but, in plants, there’s one more barrier: the cell wall. This can be defined as ‘a resistant and rigid layer that supports the growth and osmosis forces of the plant cell’. This gives the typical geometric shape to plant cells, a pattern that isn’t fulfilled in animals.
The cell wall is made up of the following layers:
- Primary cell wall: This is flexible, thin, and extensible. It’s formed when the plant cell is growing and consists of the successive accumulation of 3 to 4 layers of cellulose, a biopolymer derived from glucose.
- Secondary cell wall: This layer is synthesized once the cell has finished forming and is thicker and harder. It’s composed mainly of cellulose, although lignin, glycoproteins, and other compounds give it rigidity.
- Middle lamella: This is a layer of calcium and magnesium pectins that promotes adhesion between two contiguous plant cells.
To summarize this point, it can be stated that one of the differences between animal cells and plant cells is the presence of a cell wall in the latter. Due to the rigidity provided by the secondary stratum, the typical plant cell has a smooth, geometric shape. On the other hand, the animal cell membranous layer is more irregular and thin.
2. The plant cell contains plastids, but the animal cell doesn’t
The term plastid refers to a series of organelles characteristic of plant cells. These can’t be found in animal cells and are classified into 2 groups:
- Plastids with pigments: Chloroplasts, chromoplasts, and gerontoplasts.
- Plastids without pigments: Leucoplasts.
The most famous plastids are chloroplasts, since photosynthesis takes place in them. This process defines vegetables as a kingdom, since they all have the ability to use solar energy to form sugars from carbon dioxide thanks to the photosynthetic processes carried out by chloroplasts. In other words, plants are autotrophic living beings.
However, beyond the green chloroplasts and their chlorophyll-based pigmentation, there are other plastids. For example, chromoplasts are organelles that store the pigments that make up the yellow / orange / reddish colors of plants. On the other hand, leucoplasts are responsible for storing colorless or slightly colored substances.
The plant cell contains several types of plastids, while the animal cell doesn’t have any.
3. The vacuoles of animal cells are smaller than plant cells.
Vacuoles are cellular organelles present in both animal and plant cells. These are closed compartments (or connected to the plasma membrane) that contain different fluids or solid compounds. Their general function is to store substances, although this depends a lot on the organism the cell structure belongs to.
Another difference between animal cells and plant cells lies in the size and work carried out by the vacuoles. Those of animals are small and help retain waste products, while the plant’s vacuole occupies much more and is more present in the cytoplasm. Simply put, the central vacuole of the plant cell occupies up to 30% of its volume.
Some of the functions of vacuoles are as follows:
- Isolating materials inside that may be harmful to the metabolism and functioning of the cell.
- Storing waste substances.
- Storing water (in plants). Thus, the vacuole in the plant cell acquires an essential function in the water balance.
- Maintaining the hydrostatic pressure and turgor of the plant cell.
- Allowing the support of certain tissues due to the pressure exerted by the central vacuole. This is exemplified perfectly with the petals of the flowers and the leaves.
- Allowing the germination of the seeds thanks to the use of water inside.
The term vacuole is synonymous with storage in the plant cell, but there are other vacuolar bodies that have different functions. For example, pulsatile vacuoles extract water from the cytoplasm and remove it from the cell, while digestive vacuoles metabolize certain nutrients.
Animal vacuoles are small, while every plant cell has a central vacuole that occupies up to 30% of the cell.
4. Animal cells usually have cilia, while plant cells don’t
Cilia are short “flange-like” appendages composed of microtubules and axonemes. They are about 0.25 microns in diameter and 15 microns long and are found on the surface of many animal and protozoal cells. Some of them have the task of making movement possible, while others have the purpose of displacing fluids.
All animal tissues (except blood) have hair cells of the primary type, whose main task is sensory perception. On the other hand, plant cells lack cilia in all cases, presumably due to the constrictions caused by the presence of the cell wall (rigid and thick).
5. Animal cells have more mitochondria
Mitochondria are the best-known organelles in the field of cells, since cellular respiration takes place in them. These supply most of the metabolic energy to the cell, synthesizing ATP from metabolic substrates (glucose, fatty acids, and amino acids). Another difference between animal and plant cells is that the former has more mitochondrial bodies.
As indicated by professionals, the cells of a human being can have from 2 to 2500 mitochondria, depending on the type of tissue they are part of and their immediate energy need. On the other hand, the cells of the leaves of a plant contain 300 to 450 mitochondria. Because they have plastids and a giant vacuole, there isn’t as much space in them to house the mitochondrial numbers of animals.
6. Heterotrophy vs autotrophy
As the last of the differences between plant and animal cells, it’s necessary to explore what the adaptations of each of these cell bodies translate into the organisms that they’re part of. This boils down to a couple of very simple concepts: autotrophy and heterotrophy.
Autotrophic nutrition is typical of plants and is carried out by photosynthesis already described. These are capable of synthesizing all the organic matter necessary for life from inorganic compounds (such as carbon dioxide). Put more simply, plants make their own nutrients thanks to their chloroplasts.
On the other hand, heterotrophic nutrition defines animals. Since these can’t photosynthesize, they need to obtain organic matter directly from other living tissue (be it another animal or a plant). Once the necessary nutrients enter the cell, the mitochondria are able to use them for energy.
Due to their capacity for synthesis, plants occupy the first link in the food chain and store 80% of terrestrial organic carbon. On the other hand, animals are higher in the ecosystems they inhabit and much of their energy is lost between each trophic link.
Microscopic bodies that define the entire planet
We have presented the main differences between animal cells and plant cells, but there are many more at both a physiological and anatomical level. One of the central ideas and differences is that plant cells can photosynthesize, while animal cells lack this property.
Although it seems an anecdotal difference, the ability to generate organic matter from inorganic compounds is what allows life as we know it today. Although all living beings are important for ecosystems, the maintenance of the planet rests on plants.
- Célula, Instituto Nacional del Cáncer (NIH). Recogido a 11 de septiembre en https://www.cancer.gov/espanol/publicaciones/diccionarios/diccionario-cancer/def/celula
- La teoría celular I, Museo Virtual CSIC. Recogido a 11 de septiembre en http://museovirtual.csic.es/salas/vida/vida6.htm
- Membrana plasmática, National Human Genome Research Institute (NIH). Recogido a 11 de septiembre en https://www.genome.gov/es/genetics-glossary/Membrana-plasmatica
- Mitocondrias y plastos, Morfología de plantas vasculares. Recogido a 11 de septiembre en http://www.biologia.edu.ar/botanica/tema8/8-4plastidios.htm
- How many mitochondria can be found in a healthy human sperm cell ?, Researchgate. Recogido a 11 de septiembre en https://www.researchgate.net/post/How-many-mitochondria-can-be-found-in-a-healthy-human-sperm-cell