Cytoplasm is found in both plant and animal cells. It is a fundamental feature of every eukaryotic cell, and in fact every living cell on Earth, whether it belongs to a fern, a frog, or a fungus. In eukaryotic cells like those of plants and animals, the cytoplasm consists of three main components: the cytosol (the liquid portion), the organelles suspended within it, and various small particles and granules called cytoplasmic inclusions.1Journal of Clinical Research and Medicine. Cytoplasm, Cytosol and Cytoskeleton – Section: Content and Structure While the cytoplasm in a plant cell and the cytoplasm in an animal cell share the same basic identity, the way each cell type uses, shapes, and organizes that material turns out to be surprisingly different.
What Cytoplasm Actually Is
Think of cytoplasm as everything inside the cell membrane except the nucleus. The bulk of it is water, making up roughly 70–80% of the volume, with the rest being a dense soup of dissolved ions, sugars, amino acids, proteins, and lipid molecules. The watery portion alone is called the cytosol, and it acts as the solvent in which most of the cell’s chemistry takes place. Floating within the cytosol are the organelles: mitochondria, ribosomes, the endoplasmic reticulum, and in plant cells, chloroplasts and a large central vacuole. Finally, there are cytoplasmic inclusions, which are non-membrane-bound particles like glycogen granules in animal cells or starch grains in plant cells.
This three-part structure of cytosol, organelles, and inclusions is essentially the same whether you are looking at a human liver cell or a leaf cell on a maple tree. The cytoplasm is the stage on which nearly all cellular activity plays out, from energy production to protein synthesis to waste processing. Prokaryotic cells like bacteria have cytoplasm too, though they lack the membrane-bound nucleus and many of the organelles found in eukaryotes.
How Plant and Animal Cytoplasm Differs
Although cytoplasm itself is universal, the environment it exists in differs between plant and animal cells, and those differences shape how the cytoplasm behaves. The most obvious distinction is space. A mature plant cell has a large central vacuole that can occupy 80–90% of the cell’s interior volume, pushing the cytoplasm into a thin layer pressed against the cell wall. Animal cells lack this dominant vacuole, so their cytoplasm fills the entire volume between the plasma membrane and the nucleus more or less evenly.
Plant cytoplasm also contains chloroplasts, the organelles responsible for photosynthesis, which animal cells simply do not have. And because plant cells are encased in a rigid cell wall, the cytoplasm exists under turgor pressure, the force exerted by water pushing outward against that wall. Animal cells, which have no cell wall, regulate their volume through a different set of mechanisms, relying on ion pumps and water-permeable channels to keep themselves from swelling or shrinking in response to changes in their surroundings.2PubMed. Cellular volume homeostasis Both cell types face constant challenges to their volume from shifts in internal solute content or external conditions, but the tools they use to cope are adapted to their particular architecture.
Cytoplasmic Streaming in Plants
One of the most striking things the cytoplasm does in plant cells is flow. This active circulation, called cytoplasmic streaming or cyclosis, is particularly common in large plant cells and often follows remarkably organized patterns. The driving force is well understood: motor proteins coated onto organelles walk along actin filament bundles that are anchored near the cell’s periphery, and as they move, they drag the surrounding cytosol along with them.3PubMed Central. Cytoplasmic streaming in plant cells emerges naturally by microfilament self-organization The result looks, under a microscope, like a river circulating inside the cell.
Streaming solves a practical problem. Plant cells can be enormous compared to animal cells. Some algal cells are centimeters long, and even ordinary land-plant cells can be large enough that passive diffusion alone would be too slow to distribute nutrients, signaling molecules, and waste products. Cytoplasmic streaming acts as an internal transport system, ensuring that molecules and vesicles reach all parts of the cell efficiently.4PubMed. Cytoplasmic streaming enables the distribution of molecules and vesicles in large plant cells The process also appears to play a role in cell expansion during growth.
Animal cells do exhibit some intracellular movement driven by motor proteins and the cytoskeleton, but the large-scale, highly organized flow seen in plant cells is not a typical feature of animal cytoplasm. Animal cells are generally smaller, and diffusion combined with targeted vesicle transport along microtubules handles most of their internal logistics.
The Cytoskeleton and Cell Shape
Woven through the cytoplasm of both plant and animal cells is the cytoskeleton, a network of filamentous proteins and their regulators that gives the cell its shape, enables movement, and provides tracks for cargo transport.5PubMed Central. Cell mechanics and the cytoskeleton Both cell types use actin filaments and microtubules as their primary structural scaffolding. However, animal cells also rely heavily on a third class of cytoskeletal filament, intermediate filaments, which provide mechanical resilience. Most plant cells lack intermediate filaments, instead depending on their rigid cell wall for structural support.
In animal cells, the cytoskeleton is the main determinant of cell shape. Without a wall to lean on, the cell’s ability to resist deformation, crawl across surfaces, and divide depends almost entirely on how these filaments are arranged within the cytoplasm. White blood cells chasing bacteria, for instance, are constantly reshaping their cytoskeleton to push forward. In plant cells, the cytoskeleton still plays critical roles, particularly in organizing organelle positioning and directing the construction of the cell wall itself, but the wall provides the ultimate structural framework.
The Cytoplasm as a Metabolic Workshop
Many of the cell’s key chemical reactions happen directly in the cytoplasm, not inside any organelle. Glycolysis, the metabolic pathway that breaks glucose down into pyruvate and generates usable energy, takes place entirely in the cytosol of both plant and animal cells.6PubMed Central. Glycolysis This pathway runs whether or not oxygen is available, making it one of the most ancient and universal features of cellular metabolism. In the presence of oxygen, the pyruvate produced by glycolysis moves on to mitochondria for further energy extraction, but the initial steps are a cytoplasmic affair in every cell type.
Beyond glycolysis, the cytoplasm hosts protein synthesis on free ribosomes, fatty acid synthesis, and a host of signaling cascades. In plant cells specifically, the cytoplasm is also the site where many of the building blocks for the cell wall are assembled before being shipped outward. The cytosol’s chemical properties, its pH, its ion concentrations, its protein density, set the conditions under which all these reactions proceed. Even small changes in crowding or viscosity within the cytoplasm can influence how fast enzymes work and how efficiently molecules find each other.7PubMed Central. Correlating viscosity and molecular crowding with fluorescent nanobeads and molecular probes: in vitro and in vivo
Membraneless Compartments Within the Cytoplasm
For a long time, the textbook picture divided the cell into membrane-bound organelles (like the nucleus and mitochondria) and everything else. But research over the past couple of decades has revealed that the cytoplasm also contains structures that have no surrounding membrane at all. These membraneless organelles, which include stress granules, P-bodies, and nucleoli (the last of which sits inside the nucleus), form when certain proteins and RNA molecules concentrate together and spontaneously separate from the surrounding cytosol, much like oil droplets forming in water.8PubMed Central. The molecular language of membraneless organelles
This process, called liquid-liquid phase separation, appears to be a fundamental organizing principle in both plant and animal cells. These droplets create local microenvironments where specific reactions can be concentrated or sequestered without the need for a lipid membrane.9PubMed Central. Advances in the phase separation-organized membraneless organelles in cells: a narrative review The phenomenon is not even limited to eukaryotes; bacteria also form phase-separated droplets in their cytoplasm.10PubMed Central. Membraneless organelles formed by liquid-liquid phase separation increase bacterial fitness The discovery has reshaped how biologists think about cellular organization, because it means the cytoplasm is not just a uniform soup but a dynamically partitioned space with subregions that assemble and dissolve as the cell’s needs change.
How Cells Share Their Cytoplasm with Neighbors
Plant and animal cells have independently evolved ways to connect the cytoplasm of one cell to the cytoplasm of the next, allowing direct communication and material exchange. In plants, these connections are called plasmodesmata, tiny channels that thread through the cell wall and link adjacent cells. The cytosol flows through these channels, creating a continuous network of shared cytoplasm across entire tissues.11BioScience. Plasmodesmata and Cell-to-Cell Transport in Plants This shared space allows small molecules, signaling proteins, and even some RNA molecules to travel from cell to cell, coordinating growth and development across the organism.
Animal cells achieve something functionally similar through structures called gap junctions, which are protein channels that bridge the plasma membranes of neighboring cells. Both systems allow small molecules to pass between cells, and both have size cutoffs that regulate what can and cannot get through.12PubMed. Cell-to-cell communication in plants, animals, and fungi: a comparative review Animals also use tunneling nanotubes for longer-range cytoplasmic connections, but the general principle is the same: cells are not isolated units but share cytoplasmic material with their neighbors to coordinate tissue-level behavior.
Cytoplasmic Inheritance
Your nuclear DNA comes in a roughly equal mix from both parents, but the genomes floating in the cytoplasm follow different rules. Mitochondria (in both plant and animal cells) and chloroplasts (in plant cells) carry their own small DNA molecules, and these cytoplasmic genomes are generally passed down from only one parent, usually the mother.13Heredity. Inheritance through the cytoplasm This is because the egg cell contributes virtually all the cytoplasm to the embryo, while the sperm (or pollen) contributes almost none.
There are exceptions. In some plant species, mitochondrial DNA can be inherited paternally. Cucumber is one well-documented case: the chloroplast genome follows the typical maternal route, but the mitochondrial genome comes from the father.14PubMed Central. Inheritance of chloroplast and mitochondrial genomes in cucumber revealed by four reciprocal F 1 hybrid combinations Certain mussels pass mitochondrial DNA through a doubly-uniparental system where males and females inherit distinct mitochondrial lineages. These exceptions are genuinely unusual, but they underscore the point that cytoplasmic inheritance is a parallel genetic system operating outside the familiar nuclear rules, and it works somewhat differently in plants versus animals.
Dividing the Cytoplasm
When a cell divides, it has to split its cytoplasm roughly in half so each daughter cell gets enough organelles and cytosol to function. This final step of cell division, called cytokinesis, works very differently between plant and animal cells.15PubMed. Cytokinesis in plant and animal cells: endosomes ‘shut the door’ In animal cells, a contractile ring made of actin and myosin assembles at the cell’s equator and pinches inward, squeezing the cytoplasm until the cell is split in two, like tightening a drawstring around a balloon.
Plant cells cannot do this because their rigid cell wall prevents pinching. Instead, they build a new wall from the inside out. Vesicles produced by the Golgi apparatus gather at the center of the dividing cell and fuse together, gradually forming a structure called the cell plate that expands outward until it reaches the existing walls, partitioning the cytoplasm into two separate compartments. Both strategies achieve the same goal, equal distribution of cytoplasmic contents, but the mechanics are essentially opposite: animal cells divide from the outside in, plant cells from the inside out.
When Cytoplasm Turns to Glass
Under extreme conditions, plant cytoplasm can do something that animal cytoplasm generally cannot: it can vitrify, transforming into a glass-like solid state. This happens in seeds and in certain desiccation-tolerant plant tissues as they dry out. As water is lost, the viscosity of the cytoplasm increases dramatically until the remaining molecules become locked in place, forming an amorphous solid rather than a crystalline one.16PubMed. Intracellular glasses and seed survival in the dry state In this glassy state, chemical reactions essentially grind to a halt, and the cell enters a kind of suspended animation that can last years or even decades.
The formation of intracellular glasses appears to be necessary for surviving severe drying. Organisms that are sensitive to desiccation tend to die at water contents where the glassy state has not yet formed, suggesting that turning to glass is not just a side effect of drying but a specific protective mechanism.17PubMed. Glass formation in plant anhydrobiotes: survival in the dry state This is one reason seeds can remain viable in soil for extraordinarily long periods. Some animal cells, like certain tardigrade cells or brine shrimp cysts, can also enter glass-like states, but the phenomenon is far more widespread and well-studied in the plant kingdom.
The Cytoplasm as Pathogen Battleground
The cytoplasm is not just a workspace for the cell’s own processes; it is also the space that many pathogens exploit. After attaching to a host cell, viruses are brought inside through the cell membrane and escape into the cytosol, where they release their genetic material. DNA viruses and some RNA viruses then shuttle their genomes into the nucleus, but most RNA viruses carry out their entire replication cycle right there in the cytoplasm.18Frontiers. How Viral and Intracellular Bacterial Pathogens Reprogram the Metabolism of Host Cells to Allow Their Intracellular Replication They commandeer the cell’s ribosomes, hijack its energy metabolism, and use the cytoplasm’s raw materials to build new copies of themselves.
Plant cells face their own cytoplasmic invasions. Many plant viruses replicate in the cytoplasm and then spread from cell to cell through plasmodesmata, the same channels that normally allow helpful molecules to pass between neighbors. Some plant pathogens even modify the size exclusion limit of plasmodesmata to move their proteins or genomes through more easily. In animal cells, intracellular bacteria like certain species of Listeria and Rickettsia escape into the cytosol from the vacuoles that initially captured them, then use the host cell’s actin cytoskeleton to propel themselves through the cytoplasm and into adjacent cells. In both kingdoms, the cytoplasm is the arena where the fight between host defenses and pathogen strategies plays out.
A Brief History of Seeing the Cytoplasm
Before the term “cytoplasm” came into common use, scientists referred to the living substance inside cells as “protoplasm,” a concept that dates to the mid-nineteenth century. For decades, two parallel frameworks coexisted: one focused on the cell as a membrane-bound structural unit, the other on protoplasm as the essential living fluid.19PubMed. Why is this journal called Protoplasma? A history of protoplasm theory and the divisions in cell biology before 1926 The unification of these ideas, and the eventual replacement of “protoplasm” with more precise terms like cytoplasm, cytosol, and nucleoplasm, happened gradually as microscopy improved and biochemistry allowed scientists to actually analyze what was in the cell’s interior. The journal Protoplasma, founded in 1926, still carries the name as a nod to that earlier era of cell biology. The shift in language reflects a deeper shift in understanding: from viewing the cell’s interior as a mysterious living jelly to recognizing it as a highly organized, compartmentalized system with specific chemical and physical properties that differ between cell types.