Types of Plant Tissues

Biological tissues are organized conglomerates of cells that share a common function, nature and embryonic origin. Vascular plants have several types of differentiated cells that join together to form different tissues, whether simple or complex. This will depend on whether they have one or several cell types.

Each plant tissue has its own corresponding function. When conglomerated in conjunction with other tissues, plant tissues can create organs such as leaves, flowers, roots and stems. The different types of plant tissues can be grouped into the following two main categories:

• Meristematic tissues: these tissues are made up of undifferentiated and actively dividing cells. They are responsible for primary (lengthwise) and secondary (girthwise) growth in plants. The type of growth they carry out will depend largerly on their location in the plant.
• Permanent tissues: these tissues are composed of cells that have differentiated and specialized cells. They do not actively divide and are adapted for various stable functions such as protection, support and nutrient transport. these can be simple or complex, depending on the amount of cells from which they are structured.

Although all types of plant tissue are categorized as either meristematic or permanent, each has different functions. Before we look at the differences between animal and plant cells, we look at some of the most common plant tissue types in biology below.

We have provided a general overview of how plant tissues are structured. To fully understand the nature of plant tissues, we need to look at the different types and their functions. In addition to being simple or complex, plant tissues can be categorized as being either protective, fundamental or vascular.

Protective plant tissues

As their name suggests, protective plant tissues provide the organism with protection. These tissues form the outermost layer of the plant to make up the epidermis. This is a tissue composed of a single layer of cells that covers the roots, stem, leaves, flowers and other external parts of the plant.

The plant epidermis provides physical protection from the elements, but it also prevents water loss, regulates oxygen exchange and absorbs nutrients from the substrate. The latter occurs in the underground plant tissues, specifically in the roots.

The epidermis in the stem and leaves of plants has pores called stomata, through which carbon dioxide, water vapor and oxygen diffuse. The epidermal cells are covered by a cuticle called a cutin that mainly contains a waxy substance that protects them from water loss. Plants in deserts and other arid regions often have thick cuticles to help conserve water.

Fundamental plant tissues

Fundamental plant tissues are those which carry out a wide range of essential functions. They can be subcategorized into three groups:

• Parenchyma: forms the so-called primary cell wall of plants. Its functions include photosynthetic activity, damaged tissue repair and nutrient storage.
• Collenchyma: this is a supporting fundamental tissue as it provides strength and flexibility. It is mainly found in growing organs such as young petioles, stems, leaves, fruits and others, as well as the immature organs of herbaceous plants. It is made up of living cells with chloroplasts. Each collenchyma is classified according to the way in which its cell walls increase in thickness. Annular collenchyma have homogeneous thickening that gives a circular cell lumen, angular collenchyma have marked thickening at the angles to provide a polygonal cell lumen, lacunar collenchyma provided thickening mainly in cell walls that delimit the intercellular spaces and laminar collenchyma have thickening only in the periclinal walls, but not in the radial ones, giving the appearance of sheets of collenchyma.
• Sclerenchyma: is the supporting tissue of adult organs that have stopped growing. Its development is controlled by phytohormones. It is made up of cells that create a very thick and hard secondary wall. It does so by depositing lignin, as well as with the primary cellulose wall. This makes it even more resistant than collenchyma. Sclerenchyma is divided into two large groups of short cells (also known as sclereids or stone cells) and very elongated cells called sclerenchyma fibers.

Vascular plant tissues

Forms the phloem and xylem, vascular tissues which transport substances between different parts of the plant.

• Phloem: transports organic compounds that the plant uses as food, especially sucrose. The xylem transports water and water-soluble nutrients. These vascular tissues are long and thin, forming cylinders through which nutrients are transported. Vascular tissue is also involved with two types of meristems, the tissues containing undifferentiated cells that function during plant growth. The meristems that accompany vascular tissue are cork cambium and vascular cambium. These meristems are associated with the growth of vascular tissues.
• Xylem: a conductive tissue responsible for transporting sap (water, mineral salts and organic compounds) from the root throughout the plant. It also serves as support for the plant and provides mechanical resistance. It is a complex tissue because it is composed of different types of elements. These are conductors (tracheas and tracheids), parenchymatous, secretory (resiniferous, laticiferous) and xylar fibers (libriform, fibrotracheids, septate fibers and mucilaginous fibers).

Learn more about how the xylem and phloem support a plant's organism with our article providing the parts of plant stems.

All both plant and animal tissues are made of eukaryotic cells (i.e. cells with a clearly defined nucleus), their constituent cells have distinct differences. These differences between animal and plant tissue cells include:

• Mobility: plant cells are immobile due to their rigid cell walls, whereas some animal cells, such as immune cells, can move within the organism.
• Pigments: plant cells often contain pigments like chlorophyll for photosynthesis, while animal cells generally lack such pigments.
• Metabolism: plant cells exhibit autotrophic metabolism, meaning they produce their own food via photosynthesis, whereas animal cells rely on heterotrophic metabolism, obtaining energy from consuming organic matter.
• Growth: plant tissues have the potential for continuous growth due to meristematic cells, while animal tissues typically exhibit limited growth which determined by their developmental stage.
• Cell walls: in addition to the plasma membrane, plant cells have a rigid cell wall made of cellulose, providing structural support. Animal cells lack cell walls and have only a flexible plasma membrane.
• Vacuoles: all plant cells have vacuoles, compartments limited by the plasma membrane that contain substances such as water, enzymes and sugars. These are only present in some animal cells.
• Centrosome: animal cells have a centrosome, which plays a key role in cell division, while plant cells typically lack this organelle and rely on other mechanisms for spindle formation.
• Tissue differentiation: plants have the ability to differentiate one tissue type into another (e.g. through dedifferentiation in meristems), whereas animal cells generally lack this capacity.
• Functional specialization: plant tissues primarily serve structural, storage and photosynthetic roles. Animal tissues are specialized for functions such as locomotion, sensory perception and internal coordination.

As you can see, the tissues of these living organisms are essential for carrying out their overall functions. This is thanks to evolutionary adaptations which have created more complex organisms over time. Now you know about the types of plant tissue, you can find out what these tissues create with our article explaining the different parts of a plant and their functions.

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