What Structures Are in Plant Cells but Not Animal Cells?

Plant cells contain several structures that animal cells lack entirely, and these differences account for some of the most obvious features of plant life: rigidity, green color, and the ability to make food from sunlight. The major plant-exclusive structures are the cell wall, plastids (including chloroplasts), a large central vacuole, plasmodesmata, and the phragmoplast used during cell division. Each of these plays a role that animal cells either handle differently or do not need at all, and the details of how they work reveal why plants and animals ended up as such different kinds of organisms.

The Cell Wall

Every plant cell is surrounded by a rigid wall sitting outside the cell membrane. Animal cells have no equivalent structure. The wall is built mainly from cellulose microfibrils woven into a matrix of other complex sugars called hemicelluloses and pectins, along with proteins and sometimes phenolic compounds.¹ If you imagine a composite material like fiberglass, where stiff fibers are embedded in a softer resin, you have a rough analogy for how a plant cell wall is organized.

Many plant cells stop at this primary wall, but specialized cells add a much thicker secondary wall inside the first one. Secondary walls are reinforced with lignin, a tough polymer that waterproofs and strengthens the structure. Lignin is what makes wood hard. Without it, plants lose mechanical support, their water-conducting tissues fail, and they become more vulnerable to pests and disease.² The secondary wall is essentially what allows trees to grow tall and stand upright for centuries.

The cell wall does more than provide scaffolding. It resists the internal water pressure (turgor pressure) that pushes outward from within the cell, and that resistance is what keeps non-woody plant tissues stiff. When a houseplant wilts, what you’re seeing is turgor pressure dropping because the cells have lost water and the wall has nothing to push against. This interplay between the wall and internal pressure also drives cell growth: the cell loosens parts of its wall, water pressure stretches it, and new wall material gets deposited to fill the gap.³

Plastids and the Many Faces of the Chloroplast Family

Chloroplasts are probably the most famous plant-only organelle, but they are actually just one member of a larger family called plastids. All plastids trace back to an ancient event in which a single-celled ancestor swallowed a cyanobacterium and, instead of digesting it, kept it as an internal partner. Over deep evolutionary time, the cyanobacterium lost most of its own genome, transferred many genes to the host cell’s nucleus, and became entirely dependent on the host cell for survival.⁴ That captured cyanobacterium became the chloroplast, and a protein-import system evolved to shuttle the products of those transferred genes back into the organelle.⁵

Inside a chloroplast, photosynthesis happens on internal membrane stacks called thylakoids. The three-dimensional shape of these membranes is actively maintained by a family of proteins called CURT1, which appear to have evolved alongside thylakoids themselves.⁶ Animal cells have mitochondria, which also descended from a captured bacterium, but they never acquired plastids. That single difference is what separates organisms that can photosynthesize from those that cannot.

Beyond Green

Plastids are not always green and not always photosynthetic. The same progenitor organelle, the proplastid, can develop into several different types depending on where it is in the plant and what the plant needs.⁷ Chloroplasts handle photosynthesis in green tissues. Chromoplasts accumulate carotenoid pigments and are responsible for the red, orange, and yellow colors you see in ripe tomatoes, peppers, and flower petals.⁸ Amyloplasts store starch in roots and tubers. Leucoplasts serve various storage functions in non-pigmented tissues.

What makes this family especially interesting is that plastid types can convert into one another. When a green tomato ripens, its chloroplasts gradually transform into chromoplasts, passing through an intermediate stage that contains both chlorophyll and carotenoids.⁹ The plastid isn’t destroyed and replaced; the same organelle physically remodels itself. This interconvertibility is unique to plants and gives them remarkable flexibility in repurposing their cellular machinery as conditions change.

The Large Central Vacuole

Both plant and animal cells contain membrane-bound compartments, but mature plant cells typically have one enormous central vacuole that can occupy 80 percent or more of the cell’s volume. Animal cells may have small vacuoles or vesicles, but nothing on this scale.

The central vacuole is a multi-purpose organelle. It stores water, ions, sugars, pigments, and waste products. It acts as the cell’s main recycling center, containing enzymes that break down damaged proteins and other cellular debris, much like lysosomes do in animal cells.¹⁰ But the vacuole’s most distinctive role is mechanical: filled with water, it generates turgor pressure that presses outward against the cell wall. That pressure is what keeps lettuce crisp, flowers upright, and herbaceous stems rigid. It also plays an active part in growth and development, since water flowing into expanding cells is one of the main forces that drives plant morphogenesis.³

Some vacuoles also serve defense roles. Plants that taste bitter, sting, or poison herbivores often store those toxic compounds in the vacuole, kept safely away from the cell’s own metabolic machinery until the cell is damaged and the contents spill out.

Plasmodesmata

Because plant cells are encased in rigid walls, they face a communication problem that animal cells do not. Animal cells can signal each other through direct membrane contact or through gap junctions, narrow protein channels that allow small molecules to pass between neighboring cells. Plants solved this problem differently: their cells are connected by plasmodesmata, channels that punch through the cell wall and create a continuous corridor of cytoplasm from one cell to the next.¹¹

Plasmodesmata are substantially larger than animal gap junctions. Gap junctions are roughly 1.5 to 2 nanometers in diameter and only let small molecules through. Plasmodesmata range from about 20 to 200 nanometers wide and can transport complex macromolecules, including proteins and RNA, between cells.¹² The number and shape of plasmodesmata vary between cell types, which lets the plant control how freely molecules flow between different tissues. A barrier between the leaf’s internal cells and its outer skin cells, for instance, might have fewer plasmodesmata than the connections within the leaf’s photosynthetic tissue, steering molecular traffic in directions that make physiological sense.

This connectivity has a downside. Plant viruses exploit plasmodesmata to spread from cell to cell. Many viruses encode movement proteins that interact with the channel and widen it enough for viral particles to pass through, essentially hijacking the plant’s own communication network.¹³ Plants in turn can deposit callose, a sugar polymer, around plasmodesmata to narrow or close them when an infection is detected. It is an ongoing arms race played out at the scale of nanometer-wide tunnels.

How Plant Cells Divide Differently

When an animal cell divides, it pinches inward from the outside to split into two daughter cells. Plant cells cannot do this because the rigid cell wall would resist any inward pinching. Instead, plant cells build a new wall from the inside out using a structure called the phragmoplast. During the final stage of cell division, small vesicles produced by the Golgi apparatus travel along microtubule tracks and fuse together at the cell’s equator, forming a structure called the cell plate.¹⁴ The cell plate expands outward until it merges with the existing cell wall, and the two daughter cells are now separated by a new wall segment.¹⁵

The process depends on precise coordination of membrane trafficking and cytoskeletal dynamics. Disrupting the enzymes that regulate vesicle delivery to the cell plate leads to unfused vesicles and malformed wall stubs, which shows how tightly controlled the system needs to be.¹⁶ The phragmoplast has no equivalent in animal cells. It is a plant invention required by the physical constraints of dividing inside a box.

No Centrioles Needed

Animal cells organize their mitotic spindle, the apparatus that pulls chromosomes apart during division, using centrioles embedded in centrosomes. Most land plants have lost centrioles entirely. Seed plants have no discrete centrosome-like structures at all, and instead organize their spindles through a more diffuse system of microtubule-organizing centers scattered around the cell.¹⁷ Despite lacking the neat focal points that animal cells use, plant spindles work perfectly well. The underlying molecular players, including gamma-tubulin for microtubule nucleation, are conserved between plants and animals; plants just deploy them without concentrating them into a single visible structure.¹⁸

Looking at early-diverging land plants like mosses, liverworts, and hornworts reveals intermediate arrangements. Some of these species use distinct cytoplasmic organizing centers that resemble centrosomes in certain respects, suggesting that the fully diffuse spindle of flowering plants evolved gradually.¹⁹ Even so, the finished spindles at metaphase look remarkably similar across all these groups, which tells us that the end product of spindle assembly is more constrained by physics than by which molecular toolbox a cell happens to use.

Glyoxysomes and Seed Germination

Both plant and animal cells contain peroxisomes, small organelles that carry out various oxidation reactions. But plant cells have a specialized version called the glyoxysome that animal cells lack. Glyoxysomes are found mainly in germinating seeds, where they serve a critical purpose: converting stored fats into sugars that the seedling can use for energy before it has any leaves to photosynthesize with.

Seeds often pack large reserves of oil in the form of triacylglycerol stored in oil bodies. Glyoxysomes sit physically close to these oil bodies and house the enzymes needed to break fatty acids down into four-carbon compounds, which are then converted into soluble sugars to fuel early growth.²⁰ This metabolic pathway, called the glyoxylate cycle, is essentially absent in animal cells because animals cannot convert fats into sugars in any significant way. It is one of the reasons seeds can sprout in complete darkness for days or even weeks, running entirely on stored lipid reserves until the first green leaves unfurl and photosynthesis takes over.²¹

Specialized Cell Wall Architecture in Stomata

Not all cell walls are built the same way, and some of the most dramatic examples of fine-tuned wall design show up in guard cells, the paired cells that form stomata (the pores through which leaves exchange gases). Guard cells change shape to open and close the pore, and their ability to do this depends on precisely oriented cellulose microfibrils in their walls. In most flowering plants and ferns, these microfibrils fan out radially around the kidney-shaped guard cells. In grasses, which have a differently shaped stomatal complex, the microfibrils run parallel in the narrow midsection and switch to radial in the bulbous ends.²² These patterns determine exactly how the cell wall stretches when turgor pressure changes, which in turn controls how wide the pore opens. It is an engineering feat at the microscale, and it has no parallel in animal biology because animals do not build load-bearing walls around individual cells.

Edge Cases That Blur the Lines

The neat division between plant-exclusive and animal-exclusive structures has a few surprising exceptions. Most land plants have fully abandoned centrioles and flagella, but two ancient lineages, the ginkgo tree and the cycads, still produce flagellated sperm cells. Ginkgo sperm develop from a structure called a blepharoplast, which generates roughly a thousand flagella per sperm cell, allowing it to swim short distances through a liquid medium to reach the egg.²³ These swimming sperm use proteins homologous to those found in fern sperm, bridging the gap between the motile gametes of more primitive plants and the pollen-tube delivery system of modern seed plants. Ginkgo and cycads are living fossils in this respect, retaining a cellular structure that the rest of the seed-plant world discarded long ago.

On the other side of the divide, a few organisms challenge the idea that plastids are strictly a plant feature. Some sea slugs famously steal chloroplasts from the algae they eat and temporarily maintain them in their own cells, a phenomenon called kleptoplasty. These are not true plant cells by any definition, but they do contain functioning plastids for a time. And some parasitic plants like dodder have nearly lost their chloroplasts because they no longer photosynthesize, raising the philosophical question of whether a plastid that no longer does photosynthesis still counts as a plant-defining structure. The answer, biologically, is yes: even non-photosynthetic plastids carry out essential metabolic tasks like synthesizing fatty acids and amino acids.

What Happens When You Remove the Wall

Scientists routinely strip the cell wall from plant cells using enzymes, creating naked cells called protoplasts. Protoplasts look and behave remarkably like animal cells in some ways: they are round, fragile, and capable of being fused together or loaded with foreign DNA. They retain their plastids, vacuoles, and other internal plant-specific organelles, but without the wall they cannot maintain turgor pressure or their normal shape.²⁴

Protoplasts are enormously useful in biotechnology. Because the wall is gone, genes, proteins, and gene-editing tools can be delivered directly into the cell. Researchers use protoplasts for everything from testing where a protein ends up inside the cell to performing CRISPR edits on crop species. And under the right conditions, a single protoplast can regenerate its cell wall, start dividing, and grow into an entire new plant, demonstrating the totipotency that distinguishes plant cells from most animal cells. That regenerative capacity, combined with the unique structures described above, is part of why plants are such a different branch of complex life. The cell wall, the plastid, and the vacuole are not just passive features inherited from an ancestor. They are active participants in nearly every aspect of how a plant grows, defends itself, reproduces, and responds to the world around it.