Vacuolar apparatus of cells
The organization of vacuoles is one of the most striking distinguishing features.
In a plant cell, vacuoles are represented by large cavities. They are filled with specialized contents known as cell sap. Essentially, this is an aqueous solution where nutrient reserves or final metabolic products accumulate. Due to this structure, these large cavities act as the main osmotic reservoirs.
In an animal cell, the structure is different. Vacuoles here are typically small. They do not serve as giant storage sites, but instead perform highly targeted, dynamic tasks:
- Contractile function;
- Digestive function;
- Excretory function.
Communication between cells in tissue
To form fully functional tissues, cells need to communicate with one another.
In plants, this task is performed by plasmodesmata — specialized cytoplasmic bridges. In animal cells, the connection system is more diverse: they use several different types of junctions simultaneously to maintain attachment and exchange signals.
Differences in cytokinesis
The process of cytoplasmic division itself (cytokinesis) proceeds according to two completely different scenarios:
- Plant cell: the formation of the separating cell plate proceeds in a centrifugal direction. This means the structure begins to build from the center of the cell and gradually progresses toward its periphery.
- Animal cell: the process proceeds in a centripetal direction. A constriction forms on the membrane and deepens from the periphery to the center until the cell is divided in two.
Outer surface of the membrane
An important difference is the presence of the supramembrane complex — the glycocalyx.
This specialized layer is located directly on the outer membrane. Comparative analysis reveals the absolute polarity of this feature: the glycocalyx is completely absent in plant cells, whereas its presence is a characteristic and mandatory feature for animal cells.
Briefly: answers to topical questions
What types of intercellular junctions are characteristic of animal cells?
Animal cells feature several types of intercellular junctions:
- Tight junctions (sealant junctions that "stitch" membranes together).
- Gap junctions (channels between cells made of protein complexes called connexons).
- Desmosomes (anchoring junctions with protein plaques).
- Simple junctions (including interlocking and interdigitating finger-like membrane projections).
- Intermediate junctions (adhesive type).
Which organelles are present only in plant cells but absent in animal cells?
Plant cells contain plastids — chloroplasts, chromoplasts, and leucoplasts; animal cells lack plastids entirely.
What chemical substance forms the plant cell wall?
The plant cell wall is formed by cellulose. It is a polysaccharide located outside the plasma membrane that serves as the outer exoskeleton of the cell.
What reserve carbohydrate accumulates in animal cells?
The reserve carbohydrate that accumulates in animal cells is glycogen. It is an animal reserve polysaccharide that accumulates in the form of granules in liver cells and muscle fibers.
To avoid confusing cytokinesis: a plant "grows" from the inside out (centrifugally), while an animal cell "slims down" by pulling in its stomach (constriction proceeds from the outside in, centripetally).
Class and exam questions
What does the cell sap of plant vacuoles contain?
It is an aqueous solution containing either reserve substances necessary for cellular activity or the end products of cellular metabolism.
What functions do vacuoles perform in animals?
They are usually small in size and are responsible for digestion, excretion, or contractile activity.
What is the difference in the direction of cytoplasmic division?
In plants, the cell plate is built centrifugally (from the center to the edges), whereas in animals, a centripetal constriction forms (from the edges to the center).
What else to study on this topic
- The osmotic role of the aqueous solution of reserve substances in plant reservoirs
- Mechanisms of cell plate formation in the centrifugal direction
- Types of various junctions between animal cell membranes
- Physiology of digestive and excretory vacuoles in animal cells
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