Plant Tissues

Tissue is a group of cells similar in structure and performing similar functions. Four types of tissues in the plants are as follows:

i. Meristematic tissues: are tissues that bring about overall growth and repair.

ii. Dermal tissues: are that form outer coverings.

iii. Ground tissues: are tissues that form the bulk of the plant body, helping in packing other tissues

iv. Vascular tissues: are tissues that help in transport of materials.

meristematic tissues are the tissues present on the tip, sides and in between layers of other tissues.

Meristematic tissues at the growing tip that bring about growth in length are called as apical meristematic tissues.

Tissues present around the edges in a lateral manner and giving rise to growth in girth of the stem are called lateral meristematic tissues.

Areas from which branching takes place or a leaf or a flower stalk grows this kind of meristematic tissue called as intercalary meristematic (also called as Cambium) tissue.

Tissues that form outer coverings are called as dermal tissues. Dermal tissue (Dermis) usually consists of a single layer of tissues having variations in the types of cell based on their functions and location.

Three different types of the epidermis (outer most layer), mesodermal (The middle layer) and endodermis (the innermost layer). In desert plants, it may be even more thick and waxy. Small pores in the epidermis of the leaf, called stomata.

Apical meristematic tissues

Explanation: Meristematic tissues at the growing tip that bring about growth in length are called as apical meristematic tissues.

Lateral meristematic tissues

Explanation : Tissues present around the edges in a lateral manner and giving rise to growth in girth of the stem are called lateral meristematic tissues.

Aerenchyma.

Explanation: The Parenchyma which contains large air cavities or spaces is called Aerenchyma.

Storage tissue.

Explanation: The Parenchyma which stores water or food or waste products is called Storage Tissue.

Stomata

Explanation: Stomata are dermal tissues that are essential for gaseous exchange and transpiration.

Xylem transports materials away from the root Xylem contains elongated tracheid cells, tubular vessels, fibers and parenchyma water to great heights in the plant body. It is up to nearly 200 ft of Eucalyptus plants and up to nearly 330 ft in the red wood trees. The xylem tracheary elements consist of cells known as tracheids and vessel members, both of which are typically narrow, hollow, and elongated. Water moves from tracheid to tracheid which serves to prevent the passage of damaging air bubbles. Vessel members are the principal water-conducting cells in angiosperms. Water flows relatively unimpeded from vessel to vessel through these perforations.

The dermal layer protects the plants from loss of water, mechanical damage and invasion by parasitic and disease-causing organisms. In big trees, the dermal tissue forms several layers above the epidermis known as bark. In desert plants, it may be even more thick and waxy.

As the stem ages and grows, changes occur that transform the surface of the stem into the bark. The epidermis is a layer of cells that cover the plant body, including the stems, leaves, flowers, and fruits, that protects the plant from the outside world. In old stems, the epidermis, cortex, and primary phloem become separated from the inner tissues by thicker formations of cork. Due to the thickening cork layer, these cells die because they do not receive water and nutrients. This dead layer is the rough corky bark that forms around tree trunks and other stems.

Cells of bark are dead and compactly arranged without intercellular spaces. They have a chemical called suberin in their walls that make them impervious to gases and water.

Bark tissues of made of woody vascular plants and consists of various biopolymers, tannins, lignin, suberin, and polysaccharides. Up to 40% of the bark tissue is made of lignin which forms an important part of a plant providing structural support by crosslinking between different polysaccharides, such as cellulose makes them impervious to gases and water.

The cells of the parenchyma are soft, thin-walled and loosely packed. All parenchyma cells differ in their function.

The Parenchyma which contains chloroplasts is called “Chlorenchyma”. The Parenchyma which contains large air cavities or spaces

is called “Aerenchyma”. The Parenchyma which stores water or food or waste products is called “Storage Tissue”.

MERISTEM: Meristematic tissues are the tissues present on the tip, sides and in between layers of other tissues. Depending on where the plant the meristem is, the meristem tissue can give rise to new leaves, flowers, or roots. The meristem is integral in plant growth—without it, plants would have no source for the production of new cells.

Apical meristem is found at the ends of roots (root apical meristem) or the tops of shoots (shoot apical meristem) of a plant responsible for the plant’s growth in length or height.

The shoot apical meristem found above ground, is composed of undifferentiated cells develop to become one of three primary meristems: the protoderm, ground meristem, or procambium. The protoderm will go on to form the epidermal tissues of the plant; the ground meristem will form the cortex and pith of the plant; and the procambium will become xylem and phloem, the vascular tissues of the plant.

The root apical meristem found below ground, is responsible for the growth and development of a plant’s roots. The root meristem produces cells in a bilateral direction, meaning that it yields two types of tissues at the same time.

Lateral meristem is responsible for lateral growth, or growth in diameter. This type of growth is known as secondary growth because it is growth around an already established stem.

Intercalary meristem or the basal meristem is located between mature, differentiated tissues. Although being relatively near an apical meristem and also composed of mostly undifferentiated cells, the intercalary meristem is distinctly different. It works independently of the apical meristem to promote the vertical growth of the plant. This allows leaves to continue growing despite being cut, in the way blades of grass continue to grow after being mowed.

Xylem consists of tracheids, vessels, xylem fibers, xylem parenchyma. Which transports water and minerals from roots to apical parts of the plant. Functions are to transport materials away from the root Xylem containing elongated tracheid cells, tubular vessels, fibers and parenchyma water to great heights in the plant body. It is up to nearly 200 ft of Eucalyptus plants and up to nearly 330 ft in the red wood trees. The xylem tracheary elements consist of cells known as tracheids and vessel members, both of which are typically narrow, hollow, and elongated. Water moves from tracheid to tracheid which serves to prevent the passage of damaging air bubbles. Vessel members are the principal water-conducting cells in angiosperms. Water flows relatively unimpeded from vessel to vessel through these perforations.

It transports food material from leaves to growing parts of plants. Pholem consists of sieve tubes, sieve cells, companion cells , phloem fibres, phloem parenchyma. Sieve tubes, sieve cells, companion cells and phloem parenchyma are living. The sap is a water-based solution, but rich in sugars made by photosynthesis. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures. During the plant's growth period, usually during the spring, storage organs such as the roots are sugar sources, and the plant's many growing areas are sugar sinks. The movement in phloem is multidirectional. After the growth period the leaves are sources, and storage organs are sinks. Developing seed-bearing organs (such as fruit) are always sinks. Because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.

Plants that we observe around us are usually multi-cellular. They perform several life processes such as growth, respiration, excretion, photosynthesis. Plants internal structure is responsible for these processes.

Few questions that arise to know more about plants tissues are as follows , Are all the cells similar, How are the cells arranged ,Are all the cells similar , Is there any difference in their arrangement, What can we infer from the above activities, How will the leaves come Which portion of the plant is responsible for this transport.

Dermal tissues of plants help them in following ways –

a) In desert plants cell walls of dermal tissues are even more thick and waxy.

b) Epidermis the dermal tissue layer has Small pores called stomata. They are enclosed by two kidney shaped cells, called guard cells.

c) Cells of the roots have long-hair like parts, called root hairs.

d) The dermal layer protects the plants from loss of water, mechanical damage and invasion by parasitic and disease-causing organisms.

e) In big trees the dermal tissue forms several layers above the epidermis. It is called bark.

f) Stomata and root hair are also dermal tissues that are essential for gaseous exchange and transpiration as well as absorption of water and minerals respectively. Photosynthesis is also carriedout by certain cells of dermal tissue.